The difference between a traditional front fork (left) and the new KYB PSF (right) is immediately obvious: no springs. Shifting both spring duties to compressed air allows a radical simplification of the fork mechanism, reducing parts count and, as a result weight. It also allows an unprecedented level of adjustability; altering the “spring rate” is as simple as breaking out your foot pump.
These air forks, a production first, are fitted to the 2013 Honda CRF450R. There, they reduce unsprung weight by nearly two pounds, meaning suspension movements will be burdened by that much less inertia, allowing the tire to better maintain contact with the ground. Ride quality and steering response will also benefit from the reduced weight.
Exclusive to the CRF, the compression adjuster screw now sits on a raised mount, angled back towards the rider. The air valve, the same design used on tires, is also mounted up top. To check pressures, you just use your tire gauge. To adjust them, you either let some air out or pump some in. Stock, pressure is set at 33psi, a range that shouldn’t necessitate excessive amounts of pumping to reach.
In this video, created by VitalMX, KYB’s Dan Worley talks about the new forks.
The key to the concept’s successful execution lies in the significantly increased piston size, increased from 21 to 32mm. The oil movement is then spread across a larger surface area, enabling more precise control. This is the resolution Dan talks about above. Basically, thanks to technology like that, we’re now able to realize a concept first attempted with the 1976 YZ125.
I’m warned that I shouldn’t push variable “spring” rates as the big deal here. While it is adjustable, that’s only within a fairly limited range. Think of dropping or upping pressures as more akin to adjusting preload. Just now, you can do that with a bicycle pump. The big deal here is reduced weight.
“Adjusting preload on an mx fork is a bitch and the new fork makes that as easy as setting your tire pressure,” says former MX race bike builder Sean. “Ditching the steel springs may mean you don’t have quite as many setup options, but you also don’t have the weight of those springs or the hassle of changing them out. And, you’ll definitely know if you blow a fork seal.”