Mountain Bike Reviews Forum banner
1 - 11 of 11 Posts

·
Premium Member
Joined
·
8,674 Posts
Nice one.

Keen to see float x2 shape too.

Well any air spring shape. Wish manufacturers would publish them, it's not like its really IP.
They have little incentive to. Imagine if they published them and the dampening curves and people could readily compare and match to their needs!! Prodocts don't sell based on real data usable to a small minority of users, they sell with buzz words, perceived prestige, and subjective reviews.
 

·
Registered
Joined
·
39 Posts
I have a quick question I'm running a 205x57.5 shock which in theory should have less progression at the end because the shock doesn't compress fully. But the travel limiting spacer is quite big and my question is is it enough to compensate? I haven't measure the displacement but I assume it's close to that of a normal token.
 

·
Registered
Joined
·
1,632 Posts
Interesting... I have to admit, I never really considered the impact on the hammock in the air spring and the resulting shift in the spring rate dip that changing the positive volume would have. What causes this? It seems hard to believe with how little the rate/pressure is changing in the initial part of the stroke that it's a difference in the resulting negative air spring pressure, due to the volume change impacting the pressure when the chambers are equalized. But that almost has to be it no?

Another interesting thought... I assume that the impacts are greater on shorter travel shocks because they have a larger compression ratio to begin with, no?

I don't suppose you'd be willing to do a graph overlay where you're trying to normalize the spring rate/force in the middle of the travel, and seeing what the result of initial vs bottom out spring rate is? Said another way, would you be willing to do one of these where you are using no volume reducer and a higher pressure, and graphing that against less pressure and more bottom out resistance? I ask this because I am a strong proponent of trying both approaches on each bike I own, and I suggest to other riders as well. Specifically that you try a setup that is more reliant on ramp up with softer initial rate vs less ramp up, and higher initial rate. Each frame and ride can benefit (or be impacted negatively) from either different approach. I find that sometimes, the setups can be terrain dependent as well, and there can be a compelling reason to have two baselines one with progression for big hits, and one with more initial and mid stroke support, that's willing to give up all of it's travel at the end a bit easier.
 

·
Premium Member
Joined
·
8,674 Posts
Interesting... I have to admit, I never really considered the impact on the hammock in the air spring and the resulting shift in the spring rate dip that changing the positive volume would have. What causes this? It seems hard to believe with how little the rate/pressure is changing in the initial part of the stroke that it's a difference in the resulting negative air spring pressure, due to the volume change impacting the pressure when the chambers are equalized. But that almost has to be it no?

Another interesting thought... I assume that the impacts are greater on shorter travel shocks because they have a larger compression ratio to begin with, no?

I don't suppose you'd be willing to do a graph overlay where you're trying to normalize the spring rate/force in the middle of the travel, and seeing what the result of initial vs bottom out spring rate is? Said another way, would you be willing to do one of these where you are using no volume reducer and a higher pressure, and graphing that against less pressure and more bottom out resistance? I ask this because I am a strong proponent of trying both approaches on each bike I own, and I suggest to other riders as well. Specifically that you try a setup that is more reliant on ramp up with softer initial rate vs less ramp up, and higher initial rate. Each frame and ride can benefit (or be impacted negatively) from either different approach. I find that sometimes, the setups can be terrain dependent as well, and there can be a compelling reason to have two baselines one with progression for big hits, and one with more initial and mid stroke support, that's willing to give up all of it's travel at the end a bit easier.
I can't answer all your questions, but as to the impact being greater on shorter travel shocks, that is not normally correct. Generally the travel of the shock is matched to the frame it is used with with the average leverage ratio being in the 2.4-2.8:1 range. When you get outside that range, you start needing special dampening tunes and springs (whether super light or heavy coils, or modifying the rampup for air springs).

Manitou has documents that can let you compare the changes on volume versus midstroke support (they compare at two points, equal bottoming force and equal pressure). While these are in forks, the principal is the same.

 

·
Registered
Joined
·
1,632 Posts
I can't answer all your questions, but as to the impact being greater on shorter travel shocks, that is not normally correct. Generally the travel of the shock is matched to the frame it is used with with the average leverage ratio being in the 2.4-2.8:1 range. When you get outside that range, you start needing special dampening tunes and springs (whether super light or heavy coils, or modifying the rampup for air springs).

Manitou has documents that can let you compare the changes on volume versus midstroke support (they compare at two points, equal bottoming force and equal pressure). While these are in forks, the principal is the same.

We're getting a few things mixed up here... What I'm talking about isn't the stroke of the shock or the leverage ratio, but the compression ratio of the air can. In theory, you would assume that all bikes, have a shock that is matched properly to the frame and it's corresponding leverage ratio. However, there are a large number of frames where the shock size is chosen based on other factors like packaging constraints. Fox is the only mfg that I know that actually produces and makes public, compression ratio charts to show you what the starting and max compression ratio is for each given size, and what the max/minimum volume reducer size should be. 2002-2020 Air Volume Reduction (FLOAT, FLOAT X, FLOAT DPX2 and DHX Air Rear Shocks) | Bike Help Center | FOX You can see in those charts that some of the smaller shocks have CRs that are high to begin with, and quickly get out of control even with a single volume reducer.

I can tell you from experience, that many bikes have shock sizes, and leverage ratios and air can sizes that do not play perfectly together. This absolutely influences not only the performance, but also the tunability of the suspension product. Take a look at that fox chart and think back to some of the bikes you've ridden and had... I bet it'll dig up some memories of chasing the perfect volume reduction spacer and never finding it, or struggling to ever actually bottom a particular combination, with anything near the proper sag or spring rate.

Most of this should show up in the force graph, but it does not capture how different a given shock can feel if you're on either end of it's compression ratio happy place. That's why I think it's important to find your baseline settings, and then try the other way to achieve the same thing. IE, volume spacers with less pressure, or more pressure and less volume spacers. This helps you find the crossover point where the leverage ratio, shock air can size/compression ratio and volume reducers are all in the best balance possible.
 

·
Premium Member
Joined
·
8,674 Posts
Ahhh. I see and yes, it would be nice. Bracketing the air spring is always a good idea. There have been countless times where a poster has complained of harshess, while increasing sag and decreasing volume, which pushes them further into the steep part of the ramp up of the spring, rather than moving the opposite direction, which is what is needed in that case.
 
  • Like
Reactions: TylerVernon

·
Registered
Joined
·
12,506 Posts
Discussion Starter · #11 ·
Interesting... I have to admit, I never really considered the impact on the hammock in the air spring and the resulting shift in the spring rate dip that changing the positive volume would have. What causes this? It seems hard to believe with how little the rate/pressure is changing in the initial part of the stroke that it's a difference in the resulting negative air spring pressure, due to the volume change impacting the pressure when the chambers are equalized. But that almost has to be it no?

Another interesting thought... I assume that the impacts are greater on shorter travel shocks because they have a larger compression ratio to begin with, no?

I don't suppose you'd be willing to do a graph overlay where you're trying to normalize the spring rate/force in the middle of the travel, and seeing what the result of initial vs bottom out spring rate is? Said another way, would you be willing to do one of these where you are using no volume reducer and a higher pressure, and graphing that against less pressure and more bottom out resistance? I ask this because I am a strong proponent of trying both approaches on each bike I own, and I suggest to other riders as well. Specifically that you try a setup that is more reliant on ramp up with softer initial rate vs less ramp up, and higher initial rate. Each frame and ride can benefit (or be impacted negatively) from either different approach. I find that sometimes, the setups can be terrain dependent as well, and there can be a compelling reason to have two baselines one with progression for big hits, and one with more initial and mid stroke support, that's willing to give up all of it's travel at the end a bit easier.
That's the really interesting thing with negative volume. It's the same regardless of shock stroke. Whether you want that or not.
Equalisation depth is set by the ratio of diameters and the volume of negative. Once this has been sorted it doesn't change for different stroke shocks.

Sure you can setup an air-can with reduced negative volume and equalisation closer to topout for shorter shocks. But does it ever happen?
 
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top