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Discussion Starter · #1 · (Edited)
Hi all,
I have an older long-travel fork that I am interested in turning into a short travel fork for my DJ (saving the price of a new Argyle toward some better project).

Published maximum pressures for air springs are for the uncompressed spring at its stock length (not reduced by "travel spacers"). This is the state in which a user is actually standing there with his or her shock pump, and so makes sense. But I expect that the critical value (for seal integrity) is air spring pressure at bottom-out. Pressure which will change proportionally to the change in spring volume as the piston moves through its stroke. See Boyle's Law. Pressure will be highest where spring volume is lowest, at bottom-out.

The folks who make the forks know the initial and ending volumes and the ending pressure the seals can take, and work backwards to the maximum (leaving some margin for safety) for the uncompressed spring.

My question is, if I am filling an air spring that has been shortened by travel-reducing spacers (and so it's total, uncompressed volume is less), can I go above the published maximum, knowing that upon bottom-out the ending pressure won't be as high as with the full-length (full volume), nonreduced spring at published max? Does this reasoning hold up?

Note: this is different from spring-curve tuning with volume spacers (e.g. Float shocks, Pike forks) because those spacers reduce both the initial and ending volumes, and they affect the ending volumes more because they take up proportionally more space in the ending volume. There you have to worry about compression ratio going too high. I feel like this may be the opposite, with inital volume lower but ending volume unchanged.
 
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