What the high pivot bike is compared to a DWLink6 bike (the Athertons) is like what a flex stay single pivot (XC/Stumpjumper) bike is compared to...
What the high pivot bike is compared to a DWLink6 bike (the Athertons) is like what a flex stay single pivot (XC/Stumpjumper) bike is compared to a horst link.
The normal pivot height bike is a standard DW Link and thus has a vertical brace. It needs it, it wouldn't work otherwise.
@Sonofbovril2 shows the linkage in about the samepart of the travel (and not any further) than what the video showed. And I'd really prefer a video/animation to see where it flips over (if it does of course).
@krabo83 it appears they are more or less parallel to each other and were tested back to back in NZ.
thx primoz! so they decided to go with the more complex one i guess? i admit, would be disappointed if pivot would opt for the more generic one as final version
edit: read the article, the complex one is the newest one, got it
on a sidenote, i think it's getting a bit ridiculous what's going on with bruni's bikes with all those hard covers and exaggerated secrecy, looks like they're hiding a motor there... finn's bike just has a cloth shroud which is normal IMO.
What are the chances Jordan Williams is on the Demo Prototype at the next race? Kinda crazy that he beat both his teammates (and everyone else)...
What are the chances Jordan Williams is on the Demo Prototype at the next race? Kinda crazy that he beat both his teammates (and everyone else) on the "old" Demo. It's still incredible that all 3 specialized riders were in the top 5.
The demo he’s on is a custom size for him, I can’t see him jumping on the new frame design this season, he clearly has something...
The demo he’s on is a custom size for him, I can’t see him jumping on the new frame design this season, he clearly has something that works for him. and the next race is this weekend….. so unless he has already been testing the new bike in the background, then I can’t see it happening. I also heard that even the prototype of the new frames work costly, not that would be a problem to a company like specialized. But Loic stuck to the old frame last season when Finn was already on it, to me that indicates that it must feel like a different bike to ride…. and getting to that level of speed and composure that Jordan show last weekend would have to be done on something you feel 100% confident on. (Only my opinion, could be wrong)
Makes sense, comfort on a bike can sometimes outweigh other performance upgrades to a frame/bike. To make the cliche F1 reference, lots of times when one driver gets an "upgrade package" for a race and their teammate is on the "old" package the teammate on the "old" package actually does better because they are used to the car.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
All this flex stay talk has me wishing for some actual new product spy shots
"Since this frame design combines DW6 six-bar suspension and a high-pivot, the rear triangle actually has a small amount of vertical flex built-in. Cocalis and Weagle joked about calling the system DW5, as another take on the suspension theory, and may settle on DWF6, with the "F" standing for the flex factor."
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
I remember some brand doing this (Spot? With the "living link" leaf spring maybe?) and stating the sag point as the frames resting place.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
You're either a genius or way behind the curve and they've already done it. Well done either way.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
I remember some brand doing this (Spot? With the "living link" leaf spring maybe?) and stating the sag point as the frames resting place.
Seems like...
I remember some brand doing this (Spot? With the "living link" leaf spring maybe?) and stating the sag point as the frames resting place.
Seems like a good idea in theory.
I'm not sure about Spot or any other brands, but I believe Reeb does this with the SST. I'm not sure if the resting position of the flex stays is quite at sag, but it is into the travel of the bike.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel positions? How does it change through the travel?
In any case, I think it would make sense to optimise the resting position in such a way that you have the least amount of flex in either direction to lover the overall stresses on the parts through the lifetime (thus lengthening the lifetime). It's usually the cycling of the load that does the structures in, not the absolute highest load, so optimising it for sag or zero travel might not be the most optimal part.
How stiff the frames are? Try pushing your rear end (without the wheel) together and compare that to compressing a coil spring. As for using frame parts as springs, the problem is they are undamped (composites are a bit better in this regard, but still, nothing compared to any damper used on bikes). Apparently (unverified rumors) the old, pre-shock-brace version of the Stumpjumper in carbon (not aluminium apparently) loaded up on deep travel events and had a nasty kick in the rebound caused by the bowed top tube releasing the load.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel...
Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel positions? How does it change through the travel?
In any case, I think it would make sense to optimise the resting position in such a way that you have the least amount of flex in either direction to lover the overall stresses on the parts through the lifetime (thus lengthening the lifetime). It's usually the cycling of the load that does the structures in, not the absolute highest load, so optimising it for sag or zero travel might not be the most optimal part.
How stiff the frames are? Try pushing your rear end (without the wheel) together and compare that to compressing a coil spring. As for using frame parts as springs, the problem is they are undamped (composites are a bit better in this regard, but still, nothing compared to any damper used on bikes). Apparently (unverified rumors) the old, pre-shock-brace version of the Stumpjumper in carbon (not aluminium apparently) loaded up on deep travel events and had a nasty kick in the rebound caused by the bowed top tube releasing the load.
Looks like the angle constantly increases (non linearly) throughout the travel, so that 0.3° is around the maximum I think. Its around 0.2° at half travel. Caveat all this with the fact that I dont know what the stoke is, just going by what looks about right. Much beyond this and the system starts to invert and do weird stuff.
Which part of the system starts to invert? Because the horizontal link from the bottom part should invert somewhere past the halfway point, I'm fairly sure about that one...
Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel...
Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel positions? How does it change through the travel?
In any case, I think it would make sense to optimise the resting position in such a way that you have the least amount of flex in either direction to lover the overall stresses on the parts through the lifetime (thus lengthening the lifetime). It's usually the cycling of the load that does the structures in, not the absolute highest load, so optimising it for sag or zero travel might not be the most optimal part.
How stiff the frames are? Try pushing your rear end (without the wheel) together and compare that to compressing a coil spring. As for using frame parts as springs, the problem is they are undamped (composites are a bit better in this regard, but still, nothing compared to any damper used on bikes). Apparently (unverified rumors) the old, pre-shock-brace version of the Stumpjumper in carbon (not aluminium apparently) loaded up on deep travel events and had a nasty kick in the rebound caused by the bowed top tube releasing the load.
Could it not be accounted for in the damping curve of your shock by adding some HsR ? I would make sense to consider the whole spring curve (shock spring + frame "spring") when doing you damping curve. Whether they did so or not is a different story.
No, the shock is a parallel spring and damper with the frame a separate spring in series. The damper has no effect on the frame spring. You would need to add a separate damper to the frame (mount it to who knows where) for it to have an effect.
Hopefully this works. The horizontal link is right on the brink of inverting but not sure it gets there before stroke runs out.
Hopefully this works. The horizontal link is right on the brink of inverting but not sure it gets there before stroke runs out.
As soon as the lower link goes past the midpoint of the two pivots of the upper link (looking at the lower pair), the upper link switches the direction of rotation.
No, the shock is a parallel spring and damper with the frame a separate spring in series. The damper has no effect on the frame spring...
No, the shock is a parallel spring and damper with the frame a separate spring in series. The damper has no effect on the frame spring. You would need to add a separate damper to the frame (mount it to who knows where) for it to have an effect.
If we are talking of the "spring" due to a flex pivot I beg to differ as it is a whole system and the load on the damper will still apply. Take a coil damper, remove the coil, remove IFP pressure, bottom it out in a flexstay type suspension and I would bet the thing will go back to normal and will be slowed down by the shock as it is doing so. If you are just talking about the springyness of the frame outside the suspension (like your Stumpy example) I'd agree.
I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they made this clear to Pirelli as well. Almost a worse look that they dont race on their tires. Different for Specialized running blacked out tires because they produce their own tires.
I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they...
I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they made this clear to Pirelli as well. Almost a worse look that they dont race on their tires. Different for Specialized running blacked out tires because they produce their own tires.
It’s also possible that loris hated the tyres from day 1 of trying them and struck and agreement with the team not to race on them. His results are very important to the team and he’s notoriously fussy so I’d imagine come race week he’s free to run blacked out tyres he trusts. The % of people who notice his tyre has no logo would be tiny in comparison to the people who notice the pirelli logo on his shirt
Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.
Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.
I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they...
I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they made this clear to Pirelli as well. Almost a worse look that they dont race on their tires. Different for Specialized running blacked out tires because they produce their own tires.
It’s also possible that loris hated the tyres from day 1 of trying them and struck and agreement with the team not to race on them...
It’s also possible that loris hated the tyres from day 1 of trying them and struck and agreement with the team not to race on them. His results are very important to the team and he’s notoriously fussy so I’d imagine come race week he’s free to run blacked out tyres he trusts. The % of people who notice his tyre has no logo would be tiny in comparison to the people who notice the pirelli logo on his shirt
yeah I certainly agree with you there and it makes sense. I mean kind of a win win for the team as long as Pirelli is okay with it. I imagine they are requiring a bit of testing from the team as well to help get the tires to eventually being world cup capable tires.
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the...
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
Ain't no way I'm reading all this. Give us the elevator pitch.
Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX...
Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.
Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.
Duuude i worked in a shop that sold felts with the flex stays and we would always use two people to get the shock bolts in, huge PITA.
thx primoz! so they decided to go with the more complex one i guess? i admit, would be disappointed if pivot would opt for the more generic one as final version
edit: read the article, the complex one is the newest one, got it
on a sidenote, i think it's getting a bit ridiculous what's going on with bruni's bikes with all those hard covers and exaggerated secrecy, looks like they're hiding a motor there... finn's bike just has a cloth shroud which is normal IMO.
Makes sense, comfort on a bike can sometimes outweigh other performance upgrades to a frame/bike. To make the cliche F1 reference, lots of times when one driver gets an "upgrade package" for a race and their teammate is on the "old" package the teammate on the "old" package actually does better because they are used to the car.
Going back a few pages, on the Bikes & Big Ideas podcast, Franco Fratton (EXT’s founder) hinted that a dual crown MTB fork was coming.
Is there a new sram DH drivetrain that’s coming soon? Anybody have news on that stuff that I missed?
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
All this flex stay talk has me wishing for some actual new product spy shots
doesnt the stumpjumper use a digressive damper tune to account for the spring rate of the flex stays?
On the DPS from Fox yes it does. Both comp and reb stacks
My understanding is that almost all shim stack type dampers are digressive by nature of the design?
But just because the damper is digressive does not mean that the shock itself is digressive, as the air spring is still progressive
re the pivot proto, from the other site
"Since this frame design combines DW6 six-bar suspension and a high-pivot, the rear triangle actually has a small amount of vertical flex built-in. Cocalis and Weagle joked about calling the system DW5, as another take on the suspension theory, and may settle on DWF6, with the "F" standing for the flex factor."
I remember some brand doing this (Spot? With the "living link" leaf spring maybe?) and stating the sag point as the frames resting place.
Seems like a good idea in theory.
You're either a genius or way behind the curve and they've already done it. Well done either way.
I'm not sure about Spot or any other brands, but I believe Reeb does this with the SST. I'm not sure if the resting position of the flex stays is quite at sag, but it is into the travel of the bike.
This Pivot prototype suspension design looks very similar to Polygon's "IFS", just with a flexible seat-stay rather than a seat-stay pivot?
Depending on where the rear end flexes, yes.
Based on the rough diagram @RonJon made the change in angle between the stays is 0,3°, but I think that is valid only for extreme travel positions? How does it change through the travel?
In any case, I think it would make sense to optimise the resting position in such a way that you have the least amount of flex in either direction to lover the overall stresses on the parts through the lifetime (thus lengthening the lifetime). It's usually the cycling of the load that does the structures in, not the absolute highest load, so optimising it for sag or zero travel might not be the most optimal part.
How stiff the frames are? Try pushing your rear end (without the wheel) together and compare that to compressing a coil spring. As for using frame parts as springs, the problem is they are undamped (composites are a bit better in this regard, but still, nothing compared to any damper used on bikes). Apparently (unverified rumors) the old, pre-shock-brace version of the Stumpjumper in carbon (not aluminium apparently) loaded up on deep travel events and had a nasty kick in the rebound caused by the bowed top tube releasing the load.
Looks like the angle constantly increases (non linearly) throughout the travel, so that 0.3° is around the maximum I think. Its around 0.2° at half travel. Caveat all this with the fact that I dont know what the stoke is, just going by what looks about right. Much beyond this and the system starts to invert and do weird stuff.
Which part of the system starts to invert? Because the horizontal link from the bottom part should invert somewhere past the halfway point, I'm fairly sure about that one...
Hopefully this works. The horizontal link is right on the brink of inverting but not sure it gets there before stroke runs out.
Could it not be accounted for in the damping curve of your shock by adding some HsR ? I would make sense to consider the whole spring curve (shock spring + frame "spring") when doing you damping curve. Whether they did so or not is a different story.
No, the shock is a parallel spring and damper with the frame a separate spring in series. The damper has no effect on the frame spring. You would need to add a separate damper to the frame (mount it to who knows where) for it to have an effect.
As soon as the lower link goes past the midpoint of the two pivots of the upper link (looking at the lower pair), the upper link switches the direction of rotation.
If we are talking of the "spring" due to a flex pivot I beg to differ as it is a whole system and the load on the damper will still apply. Take a coil damper, remove the coil, remove IFP pressure, bottom it out in a flexstay type suspension and I would bet the thing will go back to normal and will be slowed down by the shock as it is doing so. If you are just talking about the springyness of the frame outside the suspension (like your Stumpy example) I'd agree.
Ah, of course, I had the Stumpjumper in mind when replying before. That's what happens when you type out replies in the phone during work meetings...
I just think its so odd that they would make Pirelli a title sponsor knowing they arent going to race on their tires, im sure they made this clear to Pirelli as well. Almost a worse look that they dont race on their tires. Different for Specialized running blacked out tires because they produce their own tires.
It’s also possible that loris hated the tyres from day 1 of trying them and struck and agreement with the team not to race on them. His results are very important to the team and he’s notoriously fussy so I’d imagine come race week he’s free to run blacked out tyres he trusts. The % of people who notice his tyre has no logo would be tiny in comparison to the people who notice the pirelli logo on his shirt
Re: Loris and Pirelli, remember that the Pirelli deal is with ALL Trek factory racing riders, which includes DH, Enduro, XC, road, and maybe even CX. This is a big big team deal and, despite being the top dog on the DH team, Loris is small potatoes compared to all the other Trek athletes who have no reason to not run the tires.
Re: flex stays, some of the old Felt carbon equilink bikes had flexstays that were neutral at sag. I raced the Virtue Nine with flex stays in 2014. The bike rode fine for me so I don't know what affect that had on ride quality or stress cycles, but it sure made it a PITA to take a shock out or put it back in.
yeah I certainly agree with you there and it makes sense. I mean kind of a win win for the team as long as Pirelli is okay with it. I imagine they are requiring a bit of testing from the team as well to help get the tires to eventually being world cup capable tires.
Ain't no way I'm reading all this. Give us the elevator pitch.
Duuude i worked in a shop that sold felts with the flex stays and we would always use two people to get the shock bolts in, huge PITA.
Post a reply to: MTB Tech Rumors and Innovation