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"If you compare a setup that gets a certain wheel force plot by using volume spacers or progressive springs and then compare it to a setup that gets the same wheel force plot but by adding progression with a linkage, you get a more consistent rebound speed across full travel with the linkage version."
This is great info, and hard to come by in the MTB world. Also a great argument for buying a link to add bottom out resistance instead of plugging in more volume reducers.
The argument of this is that, often the aftermarket links don’t only change the end stroke it will change the initial stroke as well. Volume spacers will only change the end stroke.
Definitely cool info about the rebound speeds.
This was the idea behind the dual shock bikes, you can put the “spring” on the leverage curve that you want and the “damper” for comp and rebound on a more linear leverage curve for consistent damping. (Edited below, the spring and damper are opposite of this)
I find the “consistent damping” thing interesting because I’ve never really seen a good argument for why you would want damping force to be the same for a given impact speed at any point in travel. I can see plenty of reasons you’d want damping to get stiffer deeper in travel. This is exactly why bypass shocks are a thing in motor sports. This is kind of what HBO does, so one could argue HBO is a bandaid if they wanted. Maybe for riding some chunk track where you’ll never conceivably bottom out anyway it would make sense. But the way I see it, there’s nothing less consistent than pinging off bottom out and having damping ramp through travel definitely helps with that.
"There’s nothing less consistent than pinging off bottom out"
True story. It's basically the worst feeling in the world during an "oh shit" moment.
This is just what I’ve gathered from talking with one of the designers, obviously don’t have first hand work with it, I could be inverse the damper on progressive link and spring on linear!
The bikes that have a linear damper and progressive spring on separate parts of the linkage just mimic the behavior of a rampy air spring on a linear bike. Which everyone decided was terrible years ago. I don't see the advantage of mimicking that behavior with a coil.
Linear bikes with a rampy air spring feel inconsistent as all hell with their damping IMO. I wish I could have a progressive linkage for my fork damper too.
Now that I’m looking at the photo of the Cannondale the damper is on the bottom in the stock Jykle position which is progressive and spring is in a linear position.
Would the damper in progressive link give it a feel of a position sensitive damper?
That would make a lot more sense to me. For a given wheel speed, damping force as felt at the wheel is proportional to 1/leverage^2 so any time the leverage curve is progressive you will effectively get position sensitive damping as felt at the wheel. The assumption here being that if you run over a root, for example, the wheel will generally initially be displaced at the same speed to clear it regardless of where you are in travel.
You could do it either way around depending on the track IIRC. It was so that the damper didn't "lose control." They said on progressive linkages, that the shaft speeds were too inconsistent for the damper, and the high speed circuit was handling things the low speed should be handling and vice versa depending on the position in the travel.
It mimics the use of an air spring, as the damper is speed sensitive, but the spring on the progressive link is more position sensitive. The benefit is, it doesn't have the initial stiction of an air shock, and you can get a bit crazy with the progressivity of the shock without having to change the damper tune every time.
@CascadeComponents thanks for all of the help/feedback on setup changes and reality checks for me on my nomad. I tossed the cascade link on, put the vorsprung tractiv tuned superdeluxe on and threw the smashpot in my fox 38 and the bike is unbelievable right now. I definitely feel like the added bit of progression to the suspension made it easier for me to hit the feeling I wanted in the suspension across the board. Spring rate/support, rebound speed, compression settings, etc. Also, the additional chainstay length is so, so choice and really just tied the whole room together.
Glad to hear you've got things running well! Also I really appreciate the meme.
On another note, and this is kind of unrelated to suspension but related to bike handling. I have a theory about the resurgence of steering dampers. Beside steering dampers, as of late people have been into short stems. I think one thing that gets glossed over with stem length is that the longer the stem is, the more the resultant force of an impact at your hands acts to center things. I wonder if shorter stems having less of that self centering affect has resulted in people looking to steering dampers to make up the difference.
Off the top of my head I'd say a longer stem will have less of an off-centering effect when you don't distribute forces from the two hands on either side of the bars equally. As soon as you go off centre, there will be less torque applied to the steerer as the force equilibrium will align with the steerer at a lower angle - 0 mm stem will require a 90° rotation of the bars (regardless of the width) when pushing straight forward with only one hand while a 1 metre stem with 750 mm bars will only require 20°.
Does it make sense? Obviously the stem itself is just one component, at the end of the day the horizontal (longitudional) distance of your hands vs. the steerer is what matters, so stem length and handlebar setback (or reach as BikeYoke calls it).
Definitely something to check out as I somewhat regularly switch from a 35 to a 50 mm stem. I'll be on the lookout.
@TEAMROBOT grills Fabien Barel on Canyon's FrankenMule that was used to develop the new Sender.
Hello hello hi, the flex stay discussion came and went while I didn't have access to linkage, and I won't reignite the discussion, but I have an interesting conundrum, and I was wondering if anyone familiar with linkage or kinematics could help?
Here are two identical frames, with a linkage similar to the polygon collosus, except I have both set up as a split pivot/flex stay. One is classed as a VPP with a shock linkage, the other is classed as a 6-Bar. The travel is the same, the leverage rate is the same, but the anti-rise is different between the two.
Now I'm guessing it's because the rocker link isn't being counted on the VPP version, and on the 6-Bar version, it is being counted, but could anyone tell me which version of this would be playing out in real life? Thanks in advance!
I don’t have any familiarity with linkage, but anti-rise is a product of the instant center of the member the brake caliper is mounted to. With a split pivot you have two options.
Ahhh okay! That makes sense! Would I be correct in saying, that if I mount the brake to the seat stay, the rocker is involved and if I mount it to the chainstay, it isn't?
In the first image that would be correct in a sense. Hard for me to really tell what’s going on with the second one because there seems to be some transparency turned on.
If I understand correctly the difference is just where the brake is mounted. So like mentioned, braking wise, it's a vpp 4-bar vs. A 6-bar and the same comparison would play out in real life too.
Pedalling wise both variants are 4-bars.
I had assumed that Linkage was basically the standard that most people use for calculating kinematic performance. You obviously have quite a bit of experience, so what do you use instead, rigid body dynamics equations by hand, or is there an alternative software?
Does Linkage even support calculating suspension behaviour without having a shock in the frame? As far as I played around you had to have a shock in there which limits the ability to play around as it requires you to have the layout much more defied than just trying out the main pivot locations and seeing what it does to antisquat and antirise...
To my knowledge I’m the only public alternative (https://syn.bike). Not to speak for Cascade but I believe he developed his own equation solver.
You can’t model AR/AS without the shock as shock position still has an impact. Neither software effectively models flex-pivots because it requires applying a measured angular spring rate to the effective pivot. That being said, the value is quite high so you can get a good approximation by modelling it as a conventional 4 bar with the brake and wheel attached to the chainstay (sometimes called faux-bar). Kona uses this layout for reference. You can see the impacts of the approximation as the position of the seatstay to chainstay pivot has very minimal impact on the antirise. This makes sense as the critical change is how the brake torque is translated to the frame
The reason Horst link bikes have very different (and usually considered better) antirise characteristics is because all of the brake torque tries to the rotate the seatstay member and does not get translated directly to the main pivot like it does when the wheel/brake is attached to the chainstay.
A combination of mathematica and 2D sketches in CAD. I write out all the equations using whichever variables I want to change and then use mathematica to solve them and generate plots. Conceptually all the equations are simple. I like doing it this way because it makes you really understand everything that's going on, it's quick to iterate dimensional changes, and I can come up with pretty much any metric I want if something out of the ordinary makes a comparison better. For example, those plots I posted about ramp in leverage curve vs ramp in damping force as you'd feel it at the wheel came from this:
That's pretty cool. I've thought of maybe doing something similar in MATLAB and making a GUI in the built in app designer, but always thought that the $25 to get Linkage would just be easier, also considering my Matlab license is about to run out. Is there a good website with all the AR/AS equations available for VPP/Horst/single-pivot available? Even if derive the equations from scratch, I'd prefer to have a way to validate it.
Do you have any plan to have a discounted hobbyist/ home use single time purchase license available? I have no plans to make anything commercial, and obviously $150/ month is a bit steep for tinkering around on my free time.
For those looking for free ways to solve the maths.... I've used python + sympy for solving symbolic equations then using jupyter notebook as a handy way to visualise.
It's free to use for non-commercial usage. Small businesses can get in touch for alternative pricing. Basically it's the honor system that get's audited occasionally for non-compliant usage.
If you want to write your own solver I highly recommend avoiding all of the graphical approximations used and just solve the force matrix. Once you have that the antis are trivial to calculate as they are just proportions of the vertical force to the shock force for a given input. The basic process to solve for all points in the travel is:
1. solve the loop closure equations to determine the position of each link at a given shock displacement (I found ~1mm increments is great. You don't get much out of higher resolutions
2. for each instance of a position configuration solve the force matrix to get the forces at each link for a given input force (for static leverage this is just a nominal 1 unit force vertically at the wheel).
- Leverage is the proportion of vertical force to shock force
- Anti-rise is the proportion of horizontal tire force + brake torque to shock force
- Anti-squat is the proportion of horizontal tire force + chain forces to the shock force
Validation is time consuming; partially because it's tough to understand the exact input conditions another solver might use. Linkage for example used to offer both a static and a dynamic anti value. Now they treat the frame as fixed with respect to the GCS and just move the wheel.
There are a lot of edge cases around linkage inversions, loop closure directions, and small angle trig with floating point math that make a univeral solver tricky but for basic 4 bars iterative solving isn't too complicated.
Thank you, that's great info! I'll have to try your software out.
Fun fact, leverage ratio is the derivative of Y wheel position with respect to shock position. You can save a lot of time spent doing equations for wheel force knowing that.
You can just click and drag points around to see what changes it makes - or define the x,y coordinates of each point if you want to make finer changes. You can also constrain certain dimensions, eg if you want a link or the shock to stay at a fixed length or position while the points around it are moved. Is that the kind of thing you meant? Some features are limited to the Pro version so I'm not sure if thats available in the free/basic versions
What I thought at the time would be cool was being able to define the suspension pivot points (so the single one for a single pivot or the 4 pivots for a four bar), see what the axle path, antisquat, antirise and pedal kickback is like (by limiting the travel to an arbitrary number) and THEN do the shock driving and derive the leverage ratios and the like.
This way you could have a decoupled, two step process focusing on certain things first and then off a base focusing on the final details. If I'm not mistaken you have to define everything from the start which means everything becomes a lot more complex as, oi have to fine tune the pivot points and shock placement in such a way to get the desired travel from the shock stroke. This way Linkage looks more like a fine tuning tool than a clean sheet design tool.
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