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  • Anti Squat and shock progression
  • lovewookie
    Full Member

    Is there, or can someone explain in plain-ish english, the graphical representations of anti squat and rear shock progression?

    It seems to be talked about a bit more than it used to, and although I know what anti squat is, I’m not always following what it means on a graph. I’m a bit better with progression, but it’s where that is in relation to travel and the shock.

    so.
    1. anti squat, stops the bike compressing the shock when pedaling. useful for the first bit of shock stroke to keep the bike stable when pedaling and reducing bob. however, I’ve seen graphs that wiggle, graphs that go down, graphs that go up, with little extra other than ours is betterer…what does it all mean.?

    2. suspension progression – adds a bit of stiffening where they want it. be that mid stroke, or end of stroke. I’d assume that this does vary depending on the shock setup? or is the shock setup more fine tuning and you can’t change what the bike is supposed to do that much? again, lots of wiggly graphs seen, but what does what? what makes for that ‘bottomless’ feel, or make the bike feel more ‘poppy’

    3. shock progression – moar tokens…..simplistically ramps the shock up toward the end of stroke, less tokens = more linear. yeah?

    anyone care to explain, with graphs..;-)

    thanks in advance.

    (btw, I’ve no specific bike in mind, just curious)

    the00
    Free Member

    Yes, you understand progression.
    A standard linear coil spring will have a linear spring rate. You can get progressive coil springs, although they are hard to make accurately.
    All air springs will show some degree of progression, but it will be different for each model. The volume of the air spring can be tuned with tokens. Again each model will respond differently to tuning, and how much it effects mid-stroke or bottom end. The trouble is that no manufacturers publish meaning numbers for you to make a comparison, and I haven’t seen any independent test published. For example we may be told that a spacer or MegNeg make x% difference, but without raw numbers that make comparison impossible.

    My understanding is that bottomless would be ramping up sharply (progression) deep in to the travel, and ‘poppy’ might be a ramp more in the mid range. Bit subjective though, and depends on more than just spring rate.

    Bike suspension progression will add to the shock progression.
    A linear bike with a liner spring will have a linear rate overall.
    So the more sharply progressive the design of the suspension, the more likely that will need to be balanced out with a linear shock.

    Anti-squat is broadly as you describe. Because it relates to effective pivot point, chainring ‘drive point’ and rear wheel position, it will change as the suspension moves. For different designs it moves in different ways. It is a feature of a bike, but not really something that can alone be chosen to be better or worse. It is the anti-squat around sag point that is most obviously felt.

    thisisnotaspoon
    Full Member

    Anti squat used to be called chainstay growth (or at least they’re a way of explaining the same thing), if the chain wants to get longer as the suspension compresses then pedaling wants to shorten it. So pedaling is pulling the rear wheel down. Which counteracts the tendency of the suspension to want to bob when you put weight into pedaling the bike.

    Progression is just he change in leverage ratio. If it starts off 3:1 then the rear wheel moves 3″ and the shock moves 1″, this will feel easy for the wheel. If it ends at 1:1 then it’s much harder. This is what gives suspension it’s bottomless feel on some bikes. Whereas others with a linear rate tend to bottom out more as the last bit is as easy as the first.

    Progression in the shock spring is a fudge for progression in the frame/linkage. You can add spring rate towards the end of the stroke by reducing the volume. But you cant (in any shock I’m aware of at the moment) increase the compression at the end of the stroke (it can be done, it’s just not really something bikes would use).

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