Nightstick29
New Member
- Feb 14, 2026
- 2
- 0
is there a way to calculate how much air you were need in a air rear shock that is 205X65 if you know you need a 800lb spring if were to do a coil shock 205X65 ?
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Air vs coil spring conversion: 205x65 shock 800lb equivalent
- Thread starter Nightstick29
- Start date
There isn't a clean formula that converts lb/in spring rate into PSI directly, and it's not because nobody's bothered - it's because the two springs behave differently through the stroke. A coil is linear (constant rate all the way through), while an air spring ramps up progressively as it compresses, so a single "PSI equivalent" only really holds true at one point in the travel, not the whole curve.
The rough method people do use: force = pressure × effective piston area. If you know the air shock's piston bore area, multiply it by PSI to get the force at that instant, and you can compare that to what an 800lb/in coil would be exerting at the same amount of compression. But most shock makers don't publish that bore figure, and even mtbr's old spring-rate threads land on the same conclusion - you can't just convert PSI to coil spring rates, and it's not something you can turn into a simple formula.
The practical fix nearly everyone actually uses instead: forget matching numbers between the two systems entirely, and just set the air shock by sag percentage for your weight. Cane Creek's own guidance is to add air until sag is roughly 25%-35% of the shock's stroke - that gets you to the same functional setup point the 800lb coil would be aiming for, without needing a conversion at all.
One thing I'd flag though - on a 205x65mm shock, that 800lb figure you've worked out for the coil version should already be tied to your rider weight and the bike's leverage ratio. If you tell me those two things I can sanity-check whether 800lb is even in the right ballpark, since that's more useful than chasing a PSI number that doesn't really exist.
