1. The problem with air spring is that unlike coil, it does not return to Zero energy state.
If you initially pumped 130 psi in the positive chamber of the fork (the valve is at the top facing
the rider) you will still have these 130 psi when the fork or shock fully returns. Coild spring will
have zero pressure as it fully returns. Therefore with air spring the return will be harsh and abrupt
2. Therefore we need a cushion that will make the return softer, something has to slow down this
return, some counteracting force must be introduced for the gentle full return to happen.
3. Enter the cushion or negative chamber (the valve is at the bottom of the left leg of the fork. As the
spring returns it "hits" an "obstacle", a cushion, like your face hitting an airbag, making the impact
(extension) less violent.
4. More pressure in the negative chamber makes this "cushion" bigger shortening the legs reducing
fork available travel. Big fat cushion make riding "softer" for some.
5. For big guys it seems that it is better to have a little bit more pressure (10 psi or so) in the positive
chamber compared to the negative one.
6. Some say that such DUAL AIR fork will work better if in general the difference in pressure in
positive and negative chambers is small (10 psi or so).
7. My numbers so far: rider weight 240. Positive chamber pressure 130 psi, negative chamber
pressure 110 psi. I will tweak it from there.
8. To set the rebound, dial the knob so that the ride is a POGO STICK. After that little by little turn it
so it becomes comfortably soft but not too soft. For rear shock ride off the curb and the suspension
should bounce only once!
Now the diagram:
