Rear travel

Red.Devil.Ghost

I was just wondering, how is rear travel calculated? I mean, if you look at the rear shocks, there is no way that they can move 120mm?

Cheers

benpinnick

Its the distance that the axle of the wheel moves - not the shock.

Red.Devil.Ghost

OK - but for the wheel to move up, the shock has to compress so surely it can only go so far?

I'm just trying to understand it all a bit better. Thanks for the quick answer.

oodboo

It's just leverage rates. For example some bike have a leverage rate of 2:1 so for every 2" the wheel moves through the travel the shock compresses 1".

oodboo

See my crude drawing:

The travel at the end is the same but the shock ok the left is much smaller and move less than the shock on the right.

bails87

It's exactly what's already been said.

But think about a pair of scissors. The tips of the blades move further than your fingers when you open and close them.

Red.Devil.Ghost

Cheers guys.

oodboo

Yeah but then with different linkages things are moved around but the same principle applies.

Red.Devil.Ghost

oodboo - I think that reply was to my post before I edited it).

So on some shocks they have extra air chambers and things like that. What's the purpose of that?

cooldad

Adjustability.

benpinnick

Extra air chambers are to compensate for the fact that an air spring is both non linear (DRCV/boost valve type shocks) and that an air spring isn't in a neutral state when unloaded (thats the purpose of a negative spring). Both these are designed to make air springs behave more like coil springs.

T

mrmonkfinger

benpinnick wrote:

an air spring isn't in a neutral state when unloaded

what's a 'neutral state'?

switzerland?

nicklouse

Red.Devil.Ghost wrote:

oodboo - I think that reply was to my post before I edited it).

So on some shocks they have extra air chambers and things like that. What's the purpose of that?

sometimes nothing. some times lots it all depends on the maker and which shock you are looking at. also the same shock sold with a fram may not be the same as one bought after market due to bike makers requirements.
also consider different sus designs have different ratios. see the image above. move the shock to the right and you need more shock stroke for the same travel. move it to the left and you need less. BUT as the shock has less movement on the left it has to do more work so will get hotter faster.... and visa versa.

again it comes down to specifics. just because one shoch has a piggyback does not mean is it better or worse than another infact one shock might be great for XC but crap for DH or FR. a shock for AM and FR might just be OK for DH and work for XC but might be to heavy............


back to the rear travel here there is some fun as some bike makers use the total vertical movement and other use the travel of the axel which will be more than the vertical travel in most cases.

aint it all fun.