The one thing to keep in mind about stack is as the headset bearings are spaced further apart the fore/aft "stiffness" of the SC fork is...
The one thing to keep in mind about stack is as the headset bearings are spaced further apart the fore/aft "stiffness" of the SC fork is reduced. Obviously, there are a lot of factors as to if or how this actually effects ride feel but, yes, technically stack can change the feel of the fork. I'm not a bike designer but possibly this could explain the non-linear growth of stack vs reach.
I work a lot on this stuff with students who are getting bombarded with a data is everything kind of messaging. Here's a quick visualization of how I think of this. No numbers, no units, no data points and all the misleading stuff (false precision, red herrings, non-generalizeability) that can sometimes accompany them. These are hypothetical relationships and they're sometimes more useful.
That green curve isn't real, but we have a lot of evidence that it represents something real closely enough. The curve has one peak that represents the highest performance* (a weird composite of a lot of different factors we could measure which makes this pretty squishy right out of the gate) of all the different rebound damping settings available for a given suspension, bike, trail, rider, conditions.
With fit, there just isn't a good reason to assume, even for a single measure of of a single component (e.g. bar width), that the green curve looks anything like that beautiful, simple, suspension damper rainbow of excellence.
Maybe it looks like this:
Because what is the reach? what is the stem length? What is the terrain? How's your lower back?
The reason I'm comfortable taking all that for given in the first example with damping is because IRL, every other choice has already been made, from bike frame to spring rate, and the rider is at the trailhead setting a clicker. With fit, many of the choices are simultaneous and in flux, and they interact. Maybe the client already committed to a frame and doesn't want to change that one $$$ handlebar. But everything else can move.
Shown in both figures are a starting point (purple), and two alternate settings to test the ride/fit quality against. Faint is wider brackets and bold is narrower brackets (which might violate some people's idea of how bracketing is supposed to work, if you want to always start wide and narrow in). Either way can work; choose the better option (red or purple, purple or blue, red or blue, techniques vary) and it's supposed to move you in the direction of the optimum to begin a second iteration of the process a little closer to that peak. Except round one for this curve can send you in both directions!
The one thing to keep in mind about stack is as the headset bearings are spaced further apart the fore/aft "stiffness" of the SC fork is...
The one thing to keep in mind about stack is as the headset bearings are spaced further apart the fore/aft "stiffness" of the SC fork is reduced. Obviously, there are a lot of factors as to if or how this actually effects ride feel but, yes, technically stack can change the feel of the fork. I'm not a bike designer but possibly this could explain the non-linear growth of stack vs reach.
To put it simply, your steerer is not indefinitely stiff and thus it will bow like a banana between the two bearings. Again, this is dependent on leverage, rider, etc. so a light rider on a 100mm fork, probably not much flex. However, a heavier rider on a 180mm fork with virtually the same steerer as the 100mm fork, yes, there will be a difference in flex. Plus, I believe the angular contact of headset bearings do not help the situation and can act more like a ball socket than a rigid linear connection.
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and handle the downs with whatever you get'. This would apply to anything up to an enduro bike & co. I have since tried higher bars and have noticed a bit change in the way I ride down and have fully gone into the hat eating mode.
So my 'rule' would be find what makes the person riding the bike comfortable in the situation where they want to have the most fun (or need to be the fastest). The higher bars suck for (technical) climbing, but it makes descending SO much more fun.
BTW, hip angle was mentioned on the previous page. Speaking with a roadie friend hip angle is a non-issue with mountain bikes because of the overall upright position compared to roadies. So shorter cranks won't do that much. They will raise seat heights and make cockpits even lower if anything.
Waiting for PVD to chime in on this conversation...
But here's my thought on the original proposed idea: Most customers don't even know exactly how tall...
Waiting for PVD to chime in on this conversation...
But here's my thought on the original proposed idea: Most customers don't even know exactly how tall they are, let alone their inseam, wingspan, or other potentially relevant measurements. (Men, especially, tend to overestimate their height and ask for a larger frame size than they realistically need. Source: working in shops.) If this theoretical mountain bike fitting law is going to be based on or related to physical proportions, it'll only be as useful/accurate as the customer's measurements are. If those measurements are self-reported, they're probably going to be wrong or inaccurate much of the time.
Please no on the PVD part. Not sure how many people have interacted with him, but seeing his comments in the framebuilders group on Facebook and the garbage and and hate he manages to type up make @bizutch seem like a teddy bear... He is utterly incapable of holding a conversation, can only handle confirmation of his views.
Waiting for PVD to chime in on this conversation...
But here's my thought on the original proposed idea: Most customers don't even know exactly how tall...
Waiting for PVD to chime in on this conversation...
But here's my thought on the original proposed idea: Most customers don't even know exactly how tall they are, let alone their inseam, wingspan, or other potentially relevant measurements. (Men, especially, tend to overestimate their height and ask for a larger frame size than they realistically need. Source: working in shops.) If this theoretical mountain bike fitting law is going to be based on or related to physical proportions, it'll only be as useful/accurate as the customer's measurements are. If those measurements are self-reported, they're probably going to be wrong or inaccurate much of the time.
Please no on the PVD part. Not sure how many people have interacted with him, but seeing his comments in the framebuilders group on Facebook and...
Please no on the PVD part. Not sure how many people have interacted with him, but seeing his comments in the framebuilders group on Facebook and the garbage and and hate he manages to type up make @bizutch seem like a teddy bear... He is utterly incapable of holding a conversation, can only handle confirmation of his views.
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and...
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and handle the downs with whatever you get'. This would apply to anything up to an enduro bike & co. I have since tried higher bars and have noticed a bit change in the way I ride down and have fully gone into the hat eating mode.
So my 'rule' would be find what makes the person riding the bike comfortable in the situation where they want to have the most fun (or need to be the fastest). The higher bars suck for (technical) climbing, but it makes descending SO much more fun.
BTW, hip angle was mentioned on the previous page. Speaking with a roadie friend hip angle is a non-issue with mountain bikes because of the overall upright position compared to roadies. So shorter cranks won't do that much. They will raise seat heights and make cockpits even lower if anything.
Disagree about hip angle not mattering in MTB. I agree that for most riders who aren't on an extreme XC bike with a flipped 90mm stem, bar height isn't affected much by hip mobility, but hip mobility absolutely affects a rider's optimal bar reach distance, because hip angle determines a rider's "effective torso length" and thus bike fit. I have poor back and hip mobility and I can feel that limitations in a seated position on an MTB. Specifically, it's shocking how short of an effective top tube I need to feel comfortable for a 6'3" person, on a road bike or MTB. When I ride a bike that's too long, it kills my wrists, shoulders, and neck, because I'm reaching too far and can't have a neutral posture, so I have to support the weight of my torso with my muscles. If my back was flatter (which is a function of hip and back mobility) I'd be more stretched forward naturally and would be happy to have my bars further forward.
Waiting for PVD to chime in on this conversation...
But here's my thought on the original proposed idea: Most customers don't even know exactly how tall...
Waiting for PVD to chime in on this conversation...
But here's my thought on the original proposed idea: Most customers don't even know exactly how tall they are, let alone their inseam, wingspan, or other potentially relevant measurements. (Men, especially, tend to overestimate their height and ask for a larger frame size than they realistically need. Source: working in shops.) If this theoretical mountain bike fitting law is going to be based on or related to physical proportions, it'll only be as useful/accurate as the customer's measurements are. If those measurements are self-reported, they're probably going to be wrong or inaccurate much of the time.
I think it shows how problematic it is to choose a size for a customer without putting him on the bike on a fitting station.
Any size choice should be made with proper measurement with the customer on the bike (because the geometry chart doesn't always correlate with the actual bike).
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and...
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and handle the downs with whatever you get'. This would apply to anything up to an enduro bike & co. I have since tried higher bars and have noticed a bit change in the way I ride down and have fully gone into the hat eating mode.
So my 'rule' would be find what makes the person riding the bike comfortable in the situation where they want to have the most fun (or need to be the fastest). The higher bars suck for (technical) climbing, but it makes descending SO much more fun.
BTW, hip angle was mentioned on the previous page. Speaking with a roadie friend hip angle is a non-issue with mountain bikes because of the overall upright position compared to roadies. So shorter cranks won't do that much. They will raise seat heights and make cockpits even lower if anything.
Always best to prioritize your bike for your intended use case. I recently switched from 170mm to 152mm cranks (I'm 6'0"). While my seated position is a little higher, I feel more comfortable on the descents. I have greater flexibility with my feet closer together.
To demonstrate the difference, try standing with one foot in front of your hips and the other behind (as you would be standing on your pedals) and try turning your hips. Bring your feet closer together (just an inch or two) and try turning you hips again. It's much easier to turn with your feet closer together.
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and...
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and handle the downs with whatever you get'. This would apply to anything up to an enduro bike & co. I have since tried higher bars and have noticed a bit change in the way I ride down and have fully gone into the hat eating mode.
So my 'rule' would be find what makes the person riding the bike comfortable in the situation where they want to have the most fun (or need to be the fastest). The higher bars suck for (technical) climbing, but it makes descending SO much more fun.
BTW, hip angle was mentioned on the previous page. Speaking with a roadie friend hip angle is a non-issue with mountain bikes because of the overall upright position compared to roadies. So shorter cranks won't do that much. They will raise seat heights and make cockpits even lower if anything.
Disagree about hip angle not mattering in MTB. I agree that for most riders who aren't on an extreme XC bike with a flipped 90mm stem...
Disagree about hip angle not mattering in MTB. I agree that for most riders who aren't on an extreme XC bike with a flipped 90mm stem, bar height isn't affected much by hip mobility, but hip mobility absolutely affects a rider's optimal bar reach distance, because hip angle determines a rider's "effective torso length" and thus bike fit. I have poor back and hip mobility and I can feel that limitations in a seated position on an MTB. Specifically, it's shocking how short of an effective top tube I need to feel comfortable for a 6'3" person, on a road bike or MTB. When I ride a bike that's too long, it kills my wrists, shoulders, and neck, because I'm reaching too far and can't have a neutral posture, so I have to support the weight of my torso with my muscles. If my back was flatter (which is a function of hip and back mobility) I'd be more stretched forward naturally and would be happy to have my bars further forward.
What do you do on a road bike then? I see hip mobility very much being influenced by how far hunched forwards you are riding a bike and that was the discussion I was mentioning - you're a lot more hunched over on a road bike so you potentially hit your upper hip joint limit sooner than on a MTB.
What happens if you mitigate hip/back issues with bar height instead of a shorter top tube?
I guess it really goes to show how a few cases from this thread throw any hard truths out the window and only keep the 'it depends' as THE hard truth...
@haen which cranks at 152 mm? I've ran 175s a few years ago until I bent one last year, switched to 170 and am getting a set of SX cranks at 165 for testing purposes today. Might make sense to try out an even shorter one too... Ideally it would fit a DUB BB and a Sram 3 bolt chainring :D
What do you do on a road bike then? I see hip mobility very much being influenced by how far hunched forwards you are riding a...
What do you do on a road bike then? I see hip mobility very much being influenced by how far hunched forwards you are riding a bike and that was the discussion I was mentioning - you're a lot more hunched over on a road bike so you potentially hit your upper hip joint limit sooner than on a MTB.
What happens if you mitigate hip/back issues with bar height instead of a shorter top tube?
I guess it really goes to show how a few cases from this thread throw any hard truths out the window and only keep the 'it depends' as THE hard truth...
@haen which cranks at 152 mm? I've ran 175s a few years ago until I bent one last year, switched to 170 and am getting a set of SX cranks at 165 for testing purposes today. Might make sense to try out an even shorter one too... Ideally it would fit a DUB BB and a Sram 3 bolt chainring :D
You're right, it's waaaaay more pronounced on the road bike than my mountain bike, but if I were racing XC it would probably be more of a big deal. I run short cranks on my road bike to open up my hips and I size down to a 58 to get a shorter reach value, and I typically run a shorter than average stem (somewhere in the 90-110mm range). Shorter cranks were a revelation for me on the road bike.
But I don't think my case makes it hopeless to size someone (or get a close guestimate). One of the easy questions is "can you touch your toes?" If the answer is no, that tells you a lot. You could even refine it more, like "I can barely touch my toes," "not even close," and "I can almost put my hands flat on the ground." That tells you a lot about back and hip mobility and I have a pretty solid guess whether they'll have a longer or shorter "effective torso length" than their height or inseam measurements would otherwise indicate.
I didn't mean hopeless, I just meant that with the amount of edge cases it's really hard to define a set of 'do this and this' instructions. You have to look at each case on its own.
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and...
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and handle the downs with whatever you get'. This would apply to anything up to an enduro bike & co. I have since tried higher bars and have noticed a bit change in the way I ride down and have fully gone into the hat eating mode.
So my 'rule' would be find what makes the person riding the bike comfortable in the situation where they want to have the most fun (or need to be the fastest). The higher bars suck for (technical) climbing, but it makes descending SO much more fun.
BTW, hip angle was mentioned on the previous page. Speaking with a roadie friend hip angle is a non-issue with mountain bikes because of the overall upright position compared to roadies. So shorter cranks won't do that much. They will raise seat heights and make cockpits even lower if anything.
I think it’s so interesting that you’re the first person to mention and prioritize fun.
I think you all should meet up at like an airport hotel conference room and measure each other for a weekend and please post the days in this thread so I can go ride without the possibility of running into any you. You goddamn nerds.
I think you all should meet up at like an airport hotel conference room and measure each other for a weekend and please post the days...
I think you all should meet up at like an airport hotel conference room and measure each other for a weekend and please post the days in this thread so I can go ride without the possibility of running into any you. You goddamn nerds.
How's this for starters:
-We size a frame based on reach.
-We prioritize grip in the pursuit of fun.
-Bar height and width...
How's this for starters:
-We size a frame based on reach.
-We prioritize grip in the pursuit of fun.
-Bar height and width must be adapted to rider size (shoutout C*ckpit thread).
-Saddle height can be determined as with road fitting, but not saddle tilt.
I put everything in bold, so it must be true.
OK, but...
"based on reach": Reach relative to what? Height? Wingspan? And in what relationship? Linear proportion? Something else?
"prioritize grip": How? And to what degree? How much of grip is actually a function of fit vs. stance, technique, tire pressure, etc?
"adapted to rider size": Again, what part of a rider's size? Arm length? Shoulder width? Torso height? Hand span? And what should that relationship be?
Not saying any of these are bad ideas--in fact, I think they're probably good general principles--but for them to be provably better (or worse) than any other system out there, they'd need to be a lot more specific. Otherwise we're just in the nebulous realm of maybes.
How's this for starters:
-We size a frame based on reach.
-We prioritize grip in the pursuit of fun.
-Bar height and width...
How's this for starters:
-We size a frame based on reach.
-We prioritize grip in the pursuit of fun.
-Bar height and width must be adapted to rider size (shoutout C*ckpit thread).
-Saddle height can be determined as with road fitting, but not saddle tilt.
I put everything in bold, so it must be true.
1 - What about saddle horizontal position (determine the position of the center of mass when seated) ?
2 - What about the distance between the saddle and the cockpit when seated (determine muscle engagement in the leg and an upright position increases back pain: you need to engage back muscle to absorb impact/vibration).
3 - What about the upright handlebar height (determine the max slope angle you can push against the front wheel to maintain traction).
You cannot choose a size without being properly measured on the bike, and most of the time you need to make a compromise of some sort.
Lastly, the fun factor of a bike is largely affected by suspension setup: to be specific, you can make any bike lively (having back the energy you put in to pick and put the bike somewhere else) with proper rebond speed and spring progression. You can also adapt a bike that feels bike by shortening and rising the handlebar.
This makes no sense.
I work a lot on this stuff with students who are getting bombarded with a data is everything kind of messaging. Here's a quick visualization of how I think of this. No numbers, no units, no data points and all the misleading stuff (false precision, red herrings, non-generalizeability) that can sometimes accompany them. These are hypothetical relationships and they're sometimes more useful.
With fit, there just isn't a good reason to assume, even for a single measure of of a single component (e.g. bar width), that the green curve looks anything like that beautiful, simple, suspension damper rainbow of excellence.
Maybe it looks like this:
Shown in both figures are a starting point (purple), and two alternate settings to test the ride/fit quality against. Faint is wider brackets and bold is narrower brackets (which might violate some people's idea of how bracketing is supposed to work, if you want to always start wide and narrow in). Either way can work; choose the better option (red or purple, purple or blue, red or blue, techniques vary) and it's supposed to move you in the direction of the optimum to begin a second iteration of the process a little closer to that peak. Except round one for this curve can send you in both directions!
To put it simply, your steerer is not indefinitely stiff and thus it will bow like a banana between the two bearings. Again, this is dependent on leverage, rider, etc. so a light rider on a 100mm fork, probably not much flex. However, a heavier rider on a 180mm fork with virtually the same steerer as the 100mm fork, yes, there will be a difference in flex. Plus, I believe the angular contact of headset bearings do not help the situation and can act more like a ball socket than a rigid linear connection.
Up to the end of last year I was fully in the camp 'make the bike fit for pedalling if it's meant to be pedalled and handle the downs with whatever you get'. This would apply to anything up to an enduro bike & co. I have since tried higher bars and have noticed a bit change in the way I ride down and have fully gone into the hat eating mode.
So my 'rule' would be find what makes the person riding the bike comfortable in the situation where they want to have the most fun (or need to be the fastest). The higher bars suck for (technical) climbing, but it makes descending SO much more fun.
BTW, hip angle was mentioned on the previous page. Speaking with a roadie friend hip angle is a non-issue with mountain bikes because of the overall upright position compared to roadies. So shorter cranks won't do that much. They will raise seat heights and make cockpits even lower if anything.
Please no on the PVD part. Not sure how many people have interacted with him, but seeing his comments in the framebuilders group on Facebook and the garbage and and hate he manages to type up make @bizutch seem like a teddy bear... He is utterly incapable of holding a conversation, can only handle confirmation of his views.
Disagree about hip angle not mattering in MTB. I agree that for most riders who aren't on an extreme XC bike with a flipped 90mm stem, bar height isn't affected much by hip mobility, but hip mobility absolutely affects a rider's optimal bar reach distance, because hip angle determines a rider's "effective torso length" and thus bike fit. I have poor back and hip mobility and I can feel that limitations in a seated position on an MTB. Specifically, it's shocking how short of an effective top tube I need to feel comfortable for a 6'3" person, on a road bike or MTB. When I ride a bike that's too long, it kills my wrists, shoulders, and neck, because I'm reaching too far and can't have a neutral posture, so I have to support the weight of my torso with my muscles. If my back was flatter (which is a function of hip and back mobility) I'd be more stretched forward naturally and would be happy to have my bars further forward.
I think it shows how problematic it is to choose a size for a customer without putting him on the bike on a fitting station.
Any size choice should be made with proper measurement with the customer on the bike (because the geometry chart doesn't always correlate with the actual bike).
Always best to prioritize your bike for your intended use case. I recently switched from 170mm to 152mm cranks (I'm 6'0"). While my seated position is a little higher, I feel more comfortable on the descents. I have greater flexibility with my feet closer together.
To demonstrate the difference, try standing with one foot in front of your hips and the other behind (as you would be standing on your pedals) and try turning your hips. Bring your feet closer together (just an inch or two) and try turning you hips again. It's much easier to turn with your feet closer together.
What do you do on a road bike then? I see hip mobility very much being influenced by how far hunched forwards you are riding a bike and that was the discussion I was mentioning - you're a lot more hunched over on a road bike so you potentially hit your upper hip joint limit sooner than on a MTB.
What happens if you mitigate hip/back issues with bar height instead of a shorter top tube?
I guess it really goes to show how a few cases from this thread throw any hard truths out the window and only keep the 'it depends' as THE hard truth...
@haen which cranks at 152 mm? I've ran 175s a few years ago until I bent one last year, switched to 170 and am getting a set of SX cranks at 165 for testing purposes today. Might make sense to try out an even shorter one too... Ideally it would fit a DUB BB and a Sram 3 bolt chainring :D
You're right, it's waaaaay more pronounced on the road bike than my mountain bike, but if I were racing XC it would probably be more of a big deal. I run short cranks on my road bike to open up my hips and I size down to a 58 to get a shorter reach value, and I typically run a shorter than average stem (somewhere in the 90-110mm range). Shorter cranks were a revelation for me on the road bike.
But I don't think my case makes it hopeless to size someone (or get a close guestimate). One of the easy questions is "can you touch your toes?" If the answer is no, that tells you a lot. You could even refine it more, like "I can barely touch my toes," "not even close," and "I can almost put my hands flat on the ground." That tells you a lot about back and hip mobility and I have a pretty solid guess whether they'll have a longer or shorter "effective torso length" than their height or inseam measurements would otherwise indicate.
I didn't mean hopeless, I just meant that with the amount of edge cases it's really hard to define a set of 'do this and this' instructions. You have to look at each case on its own.
I think it’s so interesting that you’re the first person to mention and prioritize fun.
Because it was such a big difference in how I ride my bike and has made me eat the hat I loved to wear before.
Just goes to show, nothing is for sure.
I'm....a Teddy 🧸 Bear??? Fffffffuhhh....
I think you all should meet up at like an airport hotel conference room and measure each other for a weekend and please post the days in this thread so I can go ride without the possibility of running into any you. You goddamn nerds.
Closing the page will have a very similar effect. And it's even easier to do. The wonders of internet!
I think my keyboard is the wrong size, running a stand up desk size XL
Guilty as charged.
How's this for starters:
-We size a frame based on reach.
-We prioritize grip in the pursuit of fun.
-Bar height and width must be adapted to rider size (shoutout C*ckpit thread).
-Saddle height can be determined as with road fitting, but not saddle tilt.
I put everything in bold, so it must be true.
OK, but...
"based on reach": Reach relative to what? Height? Wingspan? And in what relationship? Linear proportion? Something else?
"prioritize grip": How? And to what degree? How much of grip is actually a function of fit vs. stance, technique, tire pressure, etc?
"adapted to rider size": Again, what part of a rider's size? Arm length? Shoulder width? Torso height? Hand span? And what should that relationship be?
Not saying any of these are bad ideas--in fact, I think they're probably good general principles--but for them to be provably better (or worse) than any other system out there, they'd need to be a lot more specific. Otherwise we're just in the nebulous realm of maybes.
1 - What about saddle horizontal position (determine the position of the center of mass when seated) ?
2 - What about the distance between the saddle and the cockpit when seated (determine muscle engagement in the leg and an upright position increases back pain: you need to engage back muscle to absorb impact/vibration).
3 - What about the upright handlebar height (determine the max slope angle you can push against the front wheel to maintain traction).
You cannot choose a size without being properly measured on the bike, and most of the time you need to make a compromise of some sort.
Lastly, the fun factor of a bike is largely affected by suspension setup: to be specific, you can make any bike lively (having back the energy you put in to pick and put the bike somewhere else) with proper rebond speed and spring progression. You can also adapt a bike that feels bike by shortening and rising the handlebar.
Post a reply to: What are the hard truths of mountain bike fitting?