Affect of elevation on bicycle suspension

[ruadhrigh]

Last night I had a trailside discussion about how (or if) elevation differences could affect the performance of a bicycle shock. The idea was that air shocks should not be affected because the air spring is in a sealed vessel. Though one rider claimed his suspension acted differently at higher elevations.

We all agreed that temperature had a great affect on suspension, but disagreed on elevation.

What could be some of the ways that elevation would cause suspension to behave differently?

 

[voko]

Elevation SHOULD have effects on a pneumatic suspension. First consider a spring suspension. It is not air tight, so the air pressure inside equals the air pressure outside, there is no pressure difference, so it is not affected by air pressure (short of smaller effect of air pressure on lubricants, but let's ignore those).

A pneumatic suspension, however, is air tight. So the pressure inside is independent of the pressure outside, and there is a pressure difference. That difference changes with elevation (unless there is a contraption to modify the internal pressure in accordance with the external pressure, which I don't think a bicycle suspension would have).