Nope, if youre changing the progression, be ready to adjust settings for it....
Sorry but that is not right, if you make leverage curve more progressive with the same starting point and lower end of travel rate,it effectively increases both spring rate and damping (because rear triangle has less leverage over the spring and at the same time it compresses the shock faster which means it will produce more damping force with the same settings).
No. This has been discussed in the past (not sure if here or not), but bike brakes are mounted with a lot more support than radial...
No. This has been discussed in the past (not sure if here or not), but bike brakes are mounted with a lot more support than radial mount brakes on motorbikes. The caliper being offset means the caliper isn't only pulled perpendicularly to the bolts, but is actually pushed onto the fork/frame/adapter axially as well. This takes a lot of the load off the bolts and the mounting interface and we can thus run smaller bolts than what would be needed with radial mounting. Plus changing rotor sizes might become a lot more limited (running a 200 or a 220 mm rotor on a 160 mm radial mount would make for some LOOOOOOOOOONG bolts) as you don't want the bolts to be too long.
There is some logic to the madness that is the current post mount standard. What does need to die a painful, but quick death is the 203 mm rotor standard. In a world of 200 mm direct mount interfaces, standardised 20 mm jumps between rotor sizes, 220 mm rotors becoming the norm, etc. how in the hell can we still have 203 mm rotors that are so widespread (is there anyone else besides Sram making 200 mm rotors at all?)?? And then you have 220 and 223 mm rotors, there are some proto 246 mm rotors out there (Neko), etc. It's a clear 'fuck logic, that's why' situation. If 185 mm rotors were able to be done away with, why is the 203 option so persistent?
Damn you with the long post where I want to reply to the last paragraph but have to quote the whole thing lol. You know who came up with the 200mm rotor size right? The same brand that now sells forks with 200mm PM mounts on boxxer and zeb. Guess who is using 203mm direct mount on their forks for a longer? Yep that's right, the other biggest player fox. If you expect those two to deal with that in a manner normal adult would, you are delusional 🙂 203 was and still is legacy standard for dh bikes and even though I'm all for metric system, I never saw any problem with classic 160-180-203. Now add 223mm for wagon wheels and call it a day , because you can run that with standard M6 washers under caliper no problem on RS forks, putting 220mm on fox 40 not so much. On frames it's a moot point since most enduro/dh frames still come with 180mm PM mounts and we have the right adapters for all those sizes already.
Regarding the Norco tidbit, my first reaction (after looking at the Pit Bits 2 days ago) is that they have multiple dogbone and swing links to...
Regarding the Norco tidbit, my first reaction (after looking at the Pit Bits 2 days ago) is that they have multiple dogbone and swing links to drive the shock and can play around with that to alter the shape of the leverage ratio. The reaction came as I was looking at it the other day and wondering how high the forces in those small links must be and then instantly thinking this must be it for the patent. There could be something else, but as far as I saw, they are running an inverted horst link with an additional linkage to drive the shock. So kiiiiiinda what Specialized are doing with the Demo conceptually-wise.
Forgive my terrible illustration, but more or less this. I’m guessing in making that lower link much smaller than on the Range they had to get...
Forgive my terrible illustration, but more or less this. I’m guessing in making that lower link much smaller than on the Range they had to get creative to make leverage curve work out and ended up with the linkage driven solution that then had the benefit of more miscellaneous adjustments to play with.
I could be misunderstanding, you're an expert, I'm not. But from the article showing a flip chip at the fwd shock mount: "This adjustment at the forward shock mount is not a geometry adjustment but a kinematic position that goes hand in hand with an secondary dog bone link that is specific to the type of shock - air or coil."
I know they say it's for air or coil, but maybe it's more? By altering dogbone and fwd shock mount position they could make a more progressive curve and thus have more sag (with same pressure/spring rate), but by altering the starting point of travel (i.e. raising the unsagged bb height) the geo at sag would be the same. In the quote robot started this with, "method of leverage curve progression adjustment... without needing to alter shock tune, damper settings, spring rate or shock pressure." They don't say that overall travel is kept the same Nor recommended sag. I've no idea if damper settings should stay the same in that situation though. Just a thought.
Or it's just marketing. It does have a slight whiff of "zero compromises" type of marketing speak.
I could be misunderstanding, you're an expert, I'm not. But from the article showing a flip chip at the fwd shock mount: "This adjustment at the...
I could be misunderstanding, you're an expert, I'm not. But from the article showing a flip chip at the fwd shock mount: "This adjustment at the forward shock mount is not a geometry adjustment but a kinematic position that goes hand in hand with an secondary dog bone link that is specific to the type of shock - air or coil."
I know they say it's for air or coil, but maybe it's more? By altering dogbone and fwd shock mount position they could make a more progressive curve and thus have more sag (with same pressure/spring rate), but by altering the starting point of travel (i.e. raising the unsagged bb height) the geo at sag would be the same. In the quote robot started this with, "method of leverage curve progression adjustment... without needing to alter shock tune, damper settings, spring rate or shock pressure." They don't say that overall travel is kept the same Nor recommended sag. I've no idea if damper settings should stay the same in that situation though. Just a thought.
Or it's just marketing. It does have a slight whiff of "zero compromises" type of marketing speak.
I mean yeah as soon as you get into changing other variables like travel or geo then it’s possible, but those are some very significant variables when it comes to how a bike handles and I’m not sure it would be wise to do that. The other possibility is they are tweaking the leverage curve in. Way where the middle stays the same and only the beginning and end change. This would get you start of stroke sensitivity and end of stroke support while mid-travel stays identical.
I would also guess the lack of a need for a dropper post on a dedicated DH frame allowed them to use more of the seat...
I would also guess the lack of a need for a dropper post on a dedicated DH frame allowed them to use more of the seat tube for the additional linkage. I'm seconding @Primoz's concern about the high forces going into those dogbone pivots - the upper one in particular has a lot of leverage over the shock link, and I hope they have any potential durability problems sorted if it ever carries over to a production model.
Also, I can't say how accurate this is (to my eyes it seems close, even using a photo for reference, but it's hard to tell), but the linkage could theoretically result in some pretty interesting leverage curves with two inflection points (the only thing similar is the newer Focus JAM/Thron). I highlighted the different 'phases' you could distinguish in the wheel force gradient:
Yellow = soft small-bump, Green = consistent mid-stroke support at/after sag point, Blue = slight reduction for medium/large hit absorption, Magenta = end-stroke/bottom-out support. Overall they might be too subtle to really notice in this implementation (it could just feel pretty linear until the end), but this sort of 'quad-phase' design accounting for medium/large compressions could be pretty interesting compared to the usual 'triple-phase' stuff you hear all the time (small-bump compliance/mid-stroke support/bottom-out prevention) from Canyon, Marin and others.
One thing I’d like to point out is that there isn’t a single region of travel that controls bottom out resistance. Bottom out resistance includes all the work your shock does to slow you down between its initial starting point when you impact and bottom of travel. In the case of a drop to flat it’s the area under that force curve plus whatever amount of damping you’ve chosen to add. So the blue curve has significantly more bottom out resistance than the one that sits below it. I feel like the bike industry perpetuates the idea that just the end of travel region controls bottom out in isolation and it just doesn’t work that way. The best extreme example of the why this is is if you were to make force near zero for all of travel and then spike up to max force at the very end. Mean force an adult male can apply when jumping and stomping with both feet is between 17000 N and 18000 N so easily enough to overwhelm 2300 N at end of travel if early travel provides no resistance. At the end of the day an impact really should be quantified as an energy input though.
*I understand one curve is for wheel force and one is for wheel rate. Just figured I'd use the more linear curve as a comparison since they both end in the same spot.
Sorry but that is not right, if you make leverage curve more progressive with the same starting point and lower end of travel rate,it effectively increases...
Sorry but that is not right, if you make leverage curve more progressive with the same starting point and lower end of travel rate,it effectively increases both spring rate and damping (because rear triangle has less leverage over the spring and at the same time it compresses the shock faster which means it will produce more damping force with the same settings).
But then youre just making adjustments at the other end, or bottom out.
Obviously its a "window" that all settings work in, if the progression is a bump of 3%, you might not be changing anything, but is anyone noticing a progression change of 3%?
something like 10% is going to require some changes to your shock settings. You can choose not to touch anything, but youre likely leaving some performance on the table.
Leverage curve for Dissent, to get the three different progressions, youre increasing both the top, and bottom end of the curve, its going to require a different shock setup to get the most out of whats available.
I could be misunderstanding, you're an expert, I'm not. But from the article showing a flip chip at the fwd shock mount: "This adjustment at the...
I could be misunderstanding, you're an expert, I'm not. But from the article showing a flip chip at the fwd shock mount: "This adjustment at the forward shock mount is not a geometry adjustment but a kinematic position that goes hand in hand with an secondary dog bone link that is specific to the type of shock - air or coil."
I know they say it's for air or coil, but maybe it's more? By altering dogbone and fwd shock mount position they could make a more progressive curve and thus have more sag (with same pressure/spring rate), but by altering the starting point of travel (i.e. raising the unsagged bb height) the geo at sag would be the same. In the quote robot started this with, "method of leverage curve progression adjustment... without needing to alter shock tune, damper settings, spring rate or shock pressure." They don't say that overall travel is kept the same Nor recommended sag. I've no idea if damper settings should stay the same in that situation though. Just a thought.
Or it's just marketing. It does have a slight whiff of "zero compromises" type of marketing speak.
I mean yeah as soon as you get into changing other variables like travel or geo then it’s possible, but those are some very significant variables...
I mean yeah as soon as you get into changing other variables like travel or geo then it’s possible, but those are some very significant variables when it comes to how a bike handles and I’m not sure it would be wise to do that. The other possibility is they are tweaking the leverage curve in. Way where the middle stays the same and only the beginning and end change. This would get you start of stroke sensitivity and end of stroke support while mid-travel stays identical.
Hum. Possible, but probably less than ideal. And what's the point? Wanting to keep the same base tune is advantageous for spares reduction for pro teams and way simpler if it goes to market. But keeping the same clicks and pressure seems like it'd force changes and overall have more cons than pros. Doesn't make sense. Norco might just be playing mind games?
Considering that Darrell seems to be all in on coils, I would imagine they're bleed ports and/or oil fittings. *shrug*
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used that same tech. That said, I'd agree those look like bleed ports.
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used...
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used that same tech. That said, I'd agree those look like bleed ports.
Good point about the pneumatic bottom out, but wouldn't that be a spring-side only thing? I've honestly only worked with rear shock stuff from them.
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used...
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used that same tech. That said, I'd agree those look like bleed ports.
I would hope the fork is more advanced than their acs3, something like the Smashpot with a tunable hydraulic bottom out ( or like the 11.6 if you will )
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used...
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used that same tech. That said, I'd agree those look like bleed ports.
Good point about the pneumatic bottom out, but wouldn't that be a spring-side only thing? I've honestly only worked with rear shock stuff from them.
It's not a pneumatic bottom out per-se, there's a shorter piston inside the coil spring that is tunable and is there to add ramp up over the last... 30 % of travel? Or even more?
Nope, if youre changing the progression, be ready to adjust settings for it....
Yeah thats kinda my point. You can idenpendatly change progression via flip chip, which they state is their patent.
But obviously with a differerent leverage curve you would setup your shock slightly differently, but their patent doesnt claim that, just independent adjustment.
Yeah thats kinda my point. You can idenpendatly change progression via flip chip, which they state is their patent.
But obviously with a differerent leverage curve...
Yeah thats kinda my point. You can idenpendatly change progression via flip chip, which they state is their patent.
But obviously with a differerent leverage curve you would setup your shock slightly differently, but their patent doesnt claim that, just independent adjustment.
IDK, it just sounds like marketing bullshit to me
We know from that article that the new bike uses both the flip-chip at the shock mount and a different dogbone link to change the leverage curve, so I think it's very plausible they can keep it similar before the sag point while changing the behavior after it. That would be unique compared to every other progression-adjustment system I can think of right now, and could be patented.
The fun thing with patent law, at least in the US, is you can patent anything if you are specific enough. For example DW link and Horst link are conceptually identical. DW link is pretty much a Horst link set up where the lower link is super short instead of being the entire chainstay. If the Horst link patent had been written in a more broad manner it’s likely DW would never have been patentable. So it will be interesting to see how this Norco one plays out. It would be easy to do a Santa Cruz link set where a flip chip on the lower link combined with different upper links gives control over progression without altering leverage ratio at the sag point. I’m guessing the Norco patent won’t be broad enough to prohibit that even though both are flip chip plus a linkage member.
I was reading the PB Norco article and came to the quote we were discussing before:
"The second patent applies to the method of leverage curve progression adjustment we’ve designed into the bike which allows us to alter the level of support from the rear suspension in isolation without needing to alter shock tune, damper settings, spring rate or shock pressure."
This time I read it as the patent covering altering the level of rear suspension support through altering the leverage curve progression, not through tuning the shock (through pressure/spring rate, damper setting or damper tune). So not that it's there to alter it without changing the shock tune, but that it's there to alter the behaviour of the suspension BESIDES tuning the shock as well. On most bikes you're left to tuning the shock and that's it.
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you reduce the positive air volume and increase the ramp up.
Now with the new Boxxer they are saying that with the change from 35mm to 38mm and the extra travel, that the fork was ramping up too quick (which we saw with the Zebb as well), but surely the larger legs and increased travel equals larger positive chamber which equals less ramp up?
So now they have gone to a smaller self contained positive chamber (requiring higher pressure) in the Boxxer (and probably soon to be seen in the Zebb as well) which supposedly has less ramp up? Doesn’t that seem contradictory, or am I confusing more/less ramp up with more/less controlled ramp up?
ps. This also correlates to their recommendations that longer travel versions of the same fork require fewer volume spacers.
I was reading the PB Norco article and came to the quote we were discussing before:
"The second patent applies to the method of leverage curve...
I was reading the PB Norco article and came to the quote we were discussing before:
"The second patent applies to the method of leverage curve progression adjustment we’ve designed into the bike which allows us to alter the level of support from the rear suspension in isolation without needing to alter shock tune, damper settings, spring rate or shock pressure."
This time I read it as the patent covering altering the level of rear suspension support through altering the leverage curve progression, not through tuning the shock (through pressure/spring rate, damper setting or damper tune). So not that it's there to alter it without changing the shock tune, but that it's there to alter the behaviour of the suspension BESIDES tuning the shock as well. On most bikes you're left to tuning the shock and that's it.
It could have just been poorly worded, but lots of bikes have flip chips to alter progression. I doubt that could be patented.
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you...
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you reduce the positive air volume and increase the ramp up.
Now with the new Boxxer they are saying that with the change from 35mm to 38mm and the extra travel, that the fork was ramping up too quick (which we saw with the Zebb as well), but surely the larger legs and increased travel equals larger positive chamber which equals less ramp up?
So now they have gone to a smaller self contained positive chamber (requiring higher pressure) in the Boxxer (and probably soon to be seen in the Zebb as well) which supposedly has less ramp up? Doesn’t that seem contradictory, or am I confusing more/less ramp up with more/less controlled ramp up?
ps. This also correlates to their recommendations that longer travel versions of the same fork require fewer volume spacers.
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is out of either and exists in the physical). In order to think it through, you need to start by considering the volume. The formula for the volume of the air chamber is V=pi*(radius ^2)*height
For our usage, that is volume = pi * piston area squared * air spring travel distance. This formula is quadratic, meaning that small increases in the radius of the piston surface area, have significant impact to the overall volume.
In our case:
For a 38mm piston surface area the volume is 3.14 * (19 ^ 2) * 200mm = 226 cc's
For a 34mm piston surface area the volume is 3.14 * (17 ^ 2) * 200mm = 181 cc's
So, for an 11% chance in piston surface area, the volume is impacted by 20%.
Now that we've grasped how impactful slight changes in piston area have to the overall volume, you can move into compression ratio. Simplified, compression ratio is the following: CR = (Displaced volume + Compressed volume) / Compressed Volume. Said another way: CR = (volume compressed or displaced by the air spring + volume compressed above the air spring) / Volume compressed above the spring. As you can see, we now have 3 variables, all leveraging the above and first mentioned volume formula, which is again, quadratic with regards to piston radius.
In the simplest of terms, the quadratic nature of the volume calculation, shows up multiple times in the path of calculating the compression ratio. Said another way, since the swept area of the fork/cylinder is going to remain constant for this discussion, the fastest and most impactful way to impact the compression ratio is through the piston surface area. Adding a small amount more, gets magnified significantly as you walk the dog through the formula's.
This isn't even taking into account some of the other, not intuitive things that add up like this same quadratic equation showing up again when compressing the air in the lowers. If you want your eyes to really roll back in your head, you can throw adiabatic expansion into the mix.
So... to simplify. The piston surface area is the biggest and most impactful thing from a design perspective.
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is...
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is out of either and exists in the physical). In order to think it through, you need to start by considering the volume. The formula for the volume of the air chamber is V=pi*(radius ^2)*height
For our usage, that is volume = pi * piston area squared * air spring travel distance. This formula is quadratic, meaning that small increases in the radius of the piston surface area, have significant impact to the overall volume.
In our case:
For a 38mm piston surface area the volume is 3.14 * (19 ^ 2) * 200mm = 226 cc's
For a 34mm piston surface area the volume is 3.14 * (17 ^ 2) * 200mm = 181 cc's
So, for an 11% chance in piston surface area, the volume is impacted by 20%.
Now that we've grasped how impactful slight changes in piston area have to the overall volume, you can move into compression ratio. Simplified, compression ratio is the following: CR = (Displaced volume + Compressed volume) / Compressed Volume. Said another way: CR = (volume compressed or displaced by the air spring + volume compressed above the air spring) / Volume compressed above the spring. As you can see, we now have 3 variables, all leveraging the above and first mentioned volume formula, which is again, quadratic with regards to piston radius.
In the simplest of terms, the quadratic nature of the volume calculation, shows up multiple times in the path of calculating the compression ratio. Said another way, since the swept area of the fork/cylinder is going to remain constant for this discussion, the fastest and most impactful way to impact the compression ratio is through the piston surface area. Adding a small amount more, gets magnified significantly as you walk the dog through the formula's.
This isn't even taking into account some of the other, not intuitive things that add up like this same quadratic equation showing up again when compressing the air in the lowers. If you want your eyes to really roll back in your head, you can throw adiabatic expansion into the mix.
So... to simplify. The piston surface area is the biggest and most impactful thing from a design perspective.
@ebruner thank you for the explanation/science lesson! 🙂
That both explains and significantly complicates the whole thing at the same time 🙈
Basically it’s not as straightforward as I initially thought…
But for sure very interesting news. Current version is a beast. Their suspension is so good, it makes you wonder why such a small company can create something that works so fine and the big names often don't nail their kinematics.
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you...
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you reduce the positive air volume and increase the ramp up.
Now with the new Boxxer they are saying that with the change from 35mm to 38mm and the extra travel, that the fork was ramping up too quick (which we saw with the Zebb as well), but surely the larger legs and increased travel equals larger positive chamber which equals less ramp up?
So now they have gone to a smaller self contained positive chamber (requiring higher pressure) in the Boxxer (and probably soon to be seen in the Zebb as well) which supposedly has less ramp up? Doesn’t that seem contradictory, or am I confusing more/less ramp up with more/less controlled ramp up?
ps. This also correlates to their recommendations that longer travel versions of the same fork require fewer volume spacers.
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is...
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is out of either and exists in the physical). In order to think it through, you need to start by considering the volume. The formula for the volume of the air chamber is V=pi*(radius ^2)*height
For our usage, that is volume = pi * piston area squared * air spring travel distance. This formula is quadratic, meaning that small increases in the radius of the piston surface area, have significant impact to the overall volume.
In our case:
For a 38mm piston surface area the volume is 3.14 * (19 ^ 2) * 200mm = 226 cc's
For a 34mm piston surface area the volume is 3.14 * (17 ^ 2) * 200mm = 181 cc's
So, for an 11% chance in piston surface area, the volume is impacted by 20%.
Now that we've grasped how impactful slight changes in piston area have to the overall volume, you can move into compression ratio. Simplified, compression ratio is the following: CR = (Displaced volume + Compressed volume) / Compressed Volume. Said another way: CR = (volume compressed or displaced by the air spring + volume compressed above the air spring) / Volume compressed above the spring. As you can see, we now have 3 variables, all leveraging the above and first mentioned volume formula, which is again, quadratic with regards to piston radius.
In the simplest of terms, the quadratic nature of the volume calculation, shows up multiple times in the path of calculating the compression ratio. Said another way, since the swept area of the fork/cylinder is going to remain constant for this discussion, the fastest and most impactful way to impact the compression ratio is through the piston surface area. Adding a small amount more, gets magnified significantly as you walk the dog through the formula's.
This isn't even taking into account some of the other, not intuitive things that add up like this same quadratic equation showing up again when compressing the air in the lowers. If you want your eyes to really roll back in your head, you can throw adiabatic expansion into the mix.
So... to simplify. The piston surface area is the biggest and most impactful thing from a design perspective.
Uuuuum... Pretty sure the compression ratio (V_start:V_end) defines the ramp up. What the larger diameter of the piston does is provide the same force at a lower pressure or a higher force at the same pressure (through the surface area). Technically the ramp up should be the same. That's why the shocks started getting more cavernous eyelets and additional sleeves to increaser the ending volume and reduce the compression ratio. And that's why triple chamber solutions also work as they effectively lower the compression ratio, but linearly through the travel. And that's why Intend made the 1,5-crown fork, to increase the air spring volume.
Didn't look into the new Boxxer, but with a spring cartridge you could lower the piston diameter and increase the positive chamber size by wrapping it around the smaller piston - if you have a 32 mm piston and the accompanying sleeve for it to run in, you can use the 32 to 38 mm space of the stanchion as the positive spring, greatly increasing the positive volume and thus the ramp-up. For example.
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is...
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is out of either and exists in the physical). In order to think it through, you need to start by considering the volume. The formula for the volume of the air chamber is V=pi*(radius ^2)*height
For our usage, that is volume = pi * piston area squared * air spring travel distance. This formula is quadratic, meaning that small increases in the radius of the piston surface area, have significant impact to the overall volume.
In our case:
For a 38mm piston surface area the volume is 3.14 * (19 ^ 2) * 200mm = 226 cc's
For a 34mm piston surface area the volume is 3.14 * (17 ^ 2) * 200mm = 181 cc's
So, for an 11% chance in piston surface area, the volume is impacted by 20%.
Now that we've grasped how impactful slight changes in piston area have to the overall volume, you can move into compression ratio. Simplified, compression ratio is the following: CR = (Displaced volume + Compressed volume) / Compressed Volume. Said another way: CR = (volume compressed or displaced by the air spring + volume compressed above the air spring) / Volume compressed above the spring. As you can see, we now have 3 variables, all leveraging the above and first mentioned volume formula, which is again, quadratic with regards to piston radius.
In the simplest of terms, the quadratic nature of the volume calculation, shows up multiple times in the path of calculating the compression ratio. Said another way, since the swept area of the fork/cylinder is going to remain constant for this discussion, the fastest and most impactful way to impact the compression ratio is through the piston surface area. Adding a small amount more, gets magnified significantly as you walk the dog through the formula's.
This isn't even taking into account some of the other, not intuitive things that add up like this same quadratic equation showing up again when compressing the air in the lowers. If you want your eyes to really roll back in your head, you can throw adiabatic expansion into the mix.
So... to simplify. The piston surface area is the biggest and most impactful thing from a design perspective.
I'm quite glad I just skipped to the last line on that one.
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you...
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you reduce the positive air volume and increase the ramp up.
Now with the new Boxxer they are saying that with the change from 35mm to 38mm and the extra travel, that the fork was ramping up too quick (which we saw with the Zebb as well), but surely the larger legs and increased travel equals larger positive chamber which equals less ramp up?
So now they have gone to a smaller self contained positive chamber (requiring higher pressure) in the Boxxer (and probably soon to be seen in the Zebb as well) which supposedly has less ramp up? Doesn’t that seem contradictory, or am I confusing more/less ramp up with more/less controlled ramp up?
ps. This also correlates to their recommendations that longer travel versions of the same fork require fewer volume spacers.
I think what RS is talking about is the ramp up in the lowers. The trapped ambient pressure in the lowers adds to the overall spring rate when the fork is compressed. I'm guessing they kept the ID of the lowers relatively similar to the old forks and just used thinner bushings for the 38, thus there's less volume in the lowers.
If you only use a spring cartridge with a smaller diameter, the spring-side ramp-up from the lowers will also be reduced as the volume is increased with the stanchion being opened up.
Apparently connecting the bleedports of the Zeb reduces the ramp-up. If true, I'd say it's because the damper side is experiencing exactly this - a much larger lowers volume overall with less ramp-up. Bleeding the spring-side air to the damper side will offset some of that issue and bring it to somewhere in the middle of it all ramp-up-wise.
Sorry but that is not right, if you make leverage curve more progressive with the same starting point and lower end of travel rate,it effectively increases both spring rate and damping (because rear triangle has less leverage over the spring and at the same time it compresses the shock faster which means it will produce more damping force with the same settings).
Damn you with the long post where I want to reply to the last paragraph but have to quote the whole thing lol. You know who came up with the 200mm rotor size right? The same brand that now sells forks with 200mm PM mounts on boxxer and zeb. Guess who is using 203mm direct mount on their forks for a longer? Yep that's right, the other biggest player fox. If you expect those two to deal with that in a manner normal adult would, you are delusional 🙂 203 was and still is legacy standard for dh bikes and even though I'm all for metric system, I never saw any problem with classic 160-180-203. Now add 223mm for wagon wheels and call it a day , because you can run that with standard M6 washers under caliper no problem on RS forks, putting 220mm on fox 40 not so much. On frames it's a moot point since most enduro/dh frames still come with 180mm PM mounts and we have the right adapters for all those sizes already.
I could be misunderstanding, you're an expert, I'm not. But from the article showing a flip chip at the fwd shock mount: "This adjustment at the forward shock mount is not a geometry adjustment but a kinematic position that goes hand in hand with an secondary dog bone link that is specific to the type of shock - air or coil."
I know they say it's for air or coil, but maybe it's more? By altering dogbone and fwd shock mount position they could make a more progressive curve and thus have more sag (with same pressure/spring rate), but by altering the starting point of travel (i.e. raising the unsagged bb height) the geo at sag would be the same. In the quote robot started this with, "method of leverage curve progression adjustment... without needing to alter shock tune, damper settings, spring rate or shock pressure." They don't say that overall travel is kept the same Nor recommended sag. I've no idea if damper settings should stay the same in that situation though. Just a thought.
Or it's just marketing. It does have a slight whiff of "zero compromises" type of marketing speak.
I mean yeah as soon as you get into changing other variables like travel or geo then it’s possible, but those are some very significant variables when it comes to how a bike handles and I’m not sure it would be wise to do that. The other possibility is they are tweaking the leverage curve in. Way where the middle stays the same and only the beginning and end change. This would get you start of stroke sensitivity and end of stroke support while mid-travel stays identical.
Yes,
more than likely youll need to adjust spring rate, which will then in turn affect both rebound, and compression
One thing I’d like to point out is that there isn’t a single region of travel that controls bottom out resistance. Bottom out resistance includes all the work your shock does to slow you down between its initial starting point when you impact and bottom of travel. In the case of a drop to flat it’s the area under that force curve plus whatever amount of damping you’ve chosen to add. So the blue curve has significantly more bottom out resistance than the one that sits below it. I feel like the bike industry perpetuates the idea that just the end of travel region controls bottom out in isolation and it just doesn’t work that way. The best extreme example of the why this is is if you were to make force near zero for all of travel and then spike up to max force at the very end. Mean force an adult male can apply when jumping and stomping with both feet is between 17000 N and 18000 N so easily enough to overwhelm 2300 N at end of travel if early travel provides no resistance. At the end of the day an impact really should be quantified as an energy input though.
*I understand one curve is for wheel force and one is for wheel rate. Just figured I'd use the more linear curve as a comparison since they both end in the same spot.
But then youre just making adjustments at the other end, or bottom out.
Obviously its a "window" that all settings work in, if the progression is a bump of 3%, you might not be changing anything, but is anyone noticing a progression change of 3%?
something like 10% is going to require some changes to your shock settings. You can choose not to touch anything, but youre likely leaving some performance on the table.
Leverage curve for Dissent, to get the three different progressions, youre increasing both the top, and bottom end of the curve, its going to require a different shock setup to get the most out of whats available.
Hum. Possible, but probably less than ideal. And what's the point? Wanting to keep the same base tune is advantageous for spares reduction for pro teams and way simpler if it goes to market. But keeping the same clicks and pressure seems like it'd force changes and overall have more cons than pros. Doesn't make sense. Norco might just be playing mind games?
Newly-posted pic of the Push fork, are those bleed ports?
https://www.instagram.com/p/CvtQCfjuMkI/
Considering that Darrell seems to be all in on coils, I would imagine they're bleed ports and/or oil fittings. *shrug*
Push has used a pneumatic bump stop in their coil fork conversion kit for while, so I wouldn't be at all surprised it this fork used that same tech. That said, I'd agree those look like bleed ports.
Good point about the pneumatic bottom out, but wouldn't that be a spring-side only thing? I've honestly only worked with rear shock stuff from them.
I would hope the fork is more advanced than their acs3, something like the Smashpot with a tunable hydraulic bottom out ( or like the 11.6 if you will )
It's not a pneumatic bottom out per-se, there's a shorter piston inside the coil spring that is tunable and is there to add ramp up over the last... 30 % of travel? Or even more?
https://www.pushindustries.com/products/acs3-fork-coil-conversion-kit?v…
he all but confirmed it will be coil on MTBR suspension forums, when someone asked what spring type it will be using, Darren said
"Not really known for our air springs 😜"
Yeah thats kinda my point. You can idenpendatly change progression via flip chip, which they state is their patent.
But obviously with a differerent leverage curve you would setup your shock slightly differently, but their patent doesnt claim that, just independent adjustment.
IDK, it just sounds like marketing bullshit to me
We know from that article that the new bike uses both the flip-chip at the shock mount and a different dogbone link to change the leverage curve, so I think it's very plausible they can keep it similar before the sag point while changing the behavior after it. That would be unique compared to every other progression-adjustment system I can think of right now, and could be patented.
The fun thing with patent law, at least in the US, is you can patent anything if you are specific enough. For example DW link and Horst link are conceptually identical. DW link is pretty much a Horst link set up where the lower link is super short instead of being the entire chainstay. If the Horst link patent had been written in a more broad manner it’s likely DW would never have been patentable. So it will be interesting to see how this Norco one plays out. It would be easy to do a Santa Cruz link set where a flip chip on the lower link combined with different upper links gives control over progression without altering leverage ratio at the sag point. I’m guessing the Norco patent won’t be broad enough to prohibit that even though both are flip chip plus a linkage member.
Latest bikerumour podcast with Chris Canfield is pretty interesting. Particularly the discussion towards the end which centres on his new layouts: https://bikerumor.com/podcast-086-chris-canfield-explains-multi-link-suspension-designs/
I *think* this is the related CF3 pending patent with the x3 selectable axle paths: https://patents.google.com/patent/US20210380195A1/en?inventor=Christopher+Canfield&page=1
I was reading the PB Norco article and came to the quote we were discussing before:
"The second patent applies to the method of leverage curve progression adjustment we’ve designed into the bike which allows us to alter the level of support from the rear suspension in isolation without needing to alter shock tune, damper settings, spring rate or shock pressure."
This time I read it as the patent covering altering the level of rear suspension support through altering the leverage curve progression, not through tuning the shock (through pressure/spring rate, damper setting or damper tune). So not that it's there to alter it without changing the shock tune, but that it's there to alter the behaviour of the suspension BESIDES tuning the shock as well. On most bikes you're left to tuning the shock and that's it.
Can someone please explain to me where the hole in my logic is: if you have a Lyrik or Pike and you add volume spacers, you reduce the positive air volume and increase the ramp up.
Now with the new Boxxer they are saying that with the change from 35mm to 38mm and the extra travel, that the fork was ramping up too quick (which we saw with the Zebb as well), but surely the larger legs and increased travel equals larger positive chamber which equals less ramp up?
So now they have gone to a smaller self contained positive chamber (requiring higher pressure) in the Boxxer (and probably soon to be seen in the Zebb as well) which supposedly has less ramp up? Doesn’t that seem contradictory, or am I confusing more/less ramp up with more/less controlled ramp up?
ps. This also correlates to their recommendations that longer travel versions of the same fork require fewer volume spacers.
It could have just been poorly worded, but lots of bikes have flip chips to alter progression. I doubt that could be patented.
new trek supercaliber gen 2
https://www.vitalmtb.com/features/lighter-weight-more-travel-trek-super…
It doesn't quite work like that. The compression ratio of the positive chamber is based on a few things that are fixed (once teh fork is out of either and exists in the physical). In order to think it through, you need to start by considering the volume. The formula for the volume of the air chamber is V=pi*(radius ^2)*height
For our usage, that is volume = pi * piston area squared * air spring travel distance. This formula is quadratic, meaning that small increases in the radius of the piston surface area, have significant impact to the overall volume.
In our case:
For a 38mm piston surface area the volume is 3.14 * (19 ^ 2) * 200mm = 226 cc's
For a 34mm piston surface area the volume is 3.14 * (17 ^ 2) * 200mm = 181 cc's
So, for an 11% chance in piston surface area, the volume is impacted by 20%.
Now that we've grasped how impactful slight changes in piston area have to the overall volume, you can move into compression ratio. Simplified, compression ratio is the following: CR = (Displaced volume + Compressed volume) / Compressed Volume. Said another way: CR = (volume compressed or displaced by the air spring + volume compressed above the air spring) / Volume compressed above the spring. As you can see, we now have 3 variables, all leveraging the above and first mentioned volume formula, which is again, quadratic with regards to piston radius.
In the simplest of terms, the quadratic nature of the volume calculation, shows up multiple times in the path of calculating the compression ratio. Said another way, since the swept area of the fork/cylinder is going to remain constant for this discussion, the fastest and most impactful way to impact the compression ratio is through the piston surface area. Adding a small amount more, gets magnified significantly as you walk the dog through the formula's.
This isn't even taking into account some of the other, not intuitive things that add up like this same quadratic equation showing up again when compressing the air in the lowers. If you want your eyes to really roll back in your head, you can throw adiabatic expansion into the mix.
So... to simplify. The piston surface area is the biggest and most impactful thing from a design perspective.
@ebruner thank you for the explanation/science lesson! 🙂
That both explains and significantly complicates the whole thing at the same time 🙈
Basically it’s not as straightforward as I initially thought…
But for sure very interesting news. Current version is a beast. Their suspension is so good, it makes you wonder why such a small company can create something that works so fine and the big names often don't nail their kinematics.
Uuuuum... Pretty sure the compression ratio (V_start:V_end) defines the ramp up. What the larger diameter of the piston does is provide the same force at a lower pressure or a higher force at the same pressure (through the surface area). Technically the ramp up should be the same. That's why the shocks started getting more cavernous eyelets and additional sleeves to increaser the ending volume and reduce the compression ratio. And that's why triple chamber solutions also work as they effectively lower the compression ratio, but linearly through the travel. And that's why Intend made the 1,5-crown fork, to increase the air spring volume.
Didn't look into the new Boxxer, but with a spring cartridge you could lower the piston diameter and increase the positive chamber size by wrapping it around the smaller piston - if you have a 32 mm piston and the accompanying sleeve for it to run in, you can use the 32 to 38 mm space of the stanchion as the positive spring, greatly increasing the positive volume and thus the ramp-up. For example.
I'm quite glad I just skipped to the last line on that one.
I think what RS is talking about is the ramp up in the lowers. The trapped ambient pressure in the lowers adds to the overall spring rate when the fork is compressed. I'm guessing they kept the ID of the lowers relatively similar to the old forks and just used thinner bushings for the 38, thus there's less volume in the lowers.
If you only use a spring cartridge with a smaller diameter, the spring-side ramp-up from the lowers will also be reduced as the volume is increased with the stanchion being opened up.
Apparently connecting the bleedports of the Zeb reduces the ramp-up. If true, I'd say it's because the damper side is experiencing exactly this - a much larger lowers volume overall with less ramp-up. Bleeding the spring-side air to the damper side will offset some of that issue and bring it to somewhere in the middle of it all ramp-up-wise.
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