Estuche

Hey, does anyone know how much the chainstays length is reduced when, say, a Brompton, Moulton, or Birdy's rear shock is compressed? What percent or how much smaller does a rear shock of the kind used in folding bikes get when compressed? 10% of its original size? What is that, 3mm?

grayrest

As near as I can measure with my calipers (the positioning is hard), the spring on my Birdy compresses 3.4mm and is 42.5mm uncompressed.

I measure the chainstay at 427mm so at most it would be 0.8% of the distance but the shock itself is off-axis and forms a triangle between the BB, rear axle, and contact point on the stem so it's a bit shorter than that.

Falconista

The current Moultons have an fixed triangle between the crank and cassette, so the chainstay or chain length doesn't change at all when the suspension is compressed.

Looking at it the other way, pedalling hard doesn't compress the suspension, which was an energy loss on some mountain bikes.

Schwinnsta

It is front suspension where most of the losses occur.

Jipe

What kind of losses ?

Schwinnsta

Pogo losses from up and down motion. Losses from shocks are acceptable to me if they allow for faster speeds overall. So they may allow faster speeds on real bad roads but generally substract from speed on smoother roads.

Geepig

I would imagine that if speed is the aim, then having the front forks steal a portion of each and every power stroke must be annoying, plus the extra weight that has to be continually re-accelerated.

Still, I will take the hit on my larger bikes, because it makes it easier on my old wrists.

Schwinnsta

Actually its more about efficiency than speed..

Geepig

Yes, very true, and energy conversion rates etc., I just wanted to keep to your subject of speed.