Öhlins RXF 36 m.2 Spring Swap
Coil sprung forks used to be the best performance option available. Since that time air springs have improved by leaps and bounds and major brands like RockShox and Fox stopped producing top of the line coil forks. More recently aftermarket options have begun popping up allowing you to retrofit your air fork into a sweet spring. This makes them a great update for riders interested in a coil-sprung fork. Many of these options have a downside, though; they typically weigh more than the original air-sprung fork and often more than a stock coil-sprung option.
But perhaps the biggest disadvantage is that most, if not all retrofits, are stuck as a coil once the change is done. It’s not impossible to switch back to an air spring but in most situations, a minimum requirement involves the costly process of replacing the CSU to do so successfully.
Öhlins opted for a self-contained air spring for the new RXF36 m.2, making it possible to switch from coil to air and back again. I recently posted my review of the Öhlins RXF36 m.2 coil fork and have now been on the air spring for awhile. I thought it would be worthwhile sharing the process of the change. I visited Vorsprung Suspension in Whistler, a local authorized Öhlins Service Centre, to get the change done professionally.
While it can be as simple as a straight forward spring swap, Öhlins sells forks with different compression tunes in the damper. The coil-sprung m.2 comes with Öhlins' C60 damper tune but the air-sprung fork comes with a lighter C50 tune. Öhlins feels the different characteristics between an air and coil spring necessitate adjusting the compression to provide a comparable ride quality, regardless of an individual's spring choice. For each spring the rebound tune remains the same at R40.
The parts for the air spring were mostly contained within the air spring cartridge assembly, the exception being a replacement end cap for the spring system. For the coil setup, the end cap has a smaller relief for the piston rod but because the air spring piston rod is larger, it requires a different part to secure it in the stanchion. Apart from this and the required special "Coil kit tool,” anyone capable of a lower leg service shouldn't have any problem changing the springs in either direction. Öhlins has also started releasing service manuals and video to help capable at-home and shop mechanics access the information needed to successfully perform these services.
Where things get tricky is changing the shim stack to match Öhlins’ specifications. Removing the damper cartridge is no more difficult than the spring swap but digging into its internals is more complicated. Öhlins appears to do a good job of applying Loctite to their threads and each step required a little heat to loosen things up. Once inside, the inner workings of the TTX damper are visible. Steve at Vorsprung informed me that the damper uses a variable diameter clamp system. A downside is it can be finicky to put together to specifications thanks to the assembly requiring a very precise torque. Get it wrong and oil won't be able to adequately flow through the valves, degrading performance.
The variable diameter clamp system basically stiffens or softens the shim stack, and when it reaches the firmest position it also closes off the LSC circuit. It's a very good system in the sense that it allows for you to "revalve" the compression damping in a very similar way to a softer or stiffer shim stack. – Steve Matthews, Vorsprung
It is possible to perform the spring swap without changing the compression tune in the fork. Doing a straight swap makes the process much faster but to properly review the air-sprung fork, I had to change it to reflect what Öhlins sells to consumers. So far everything feels great and with the lighter damper tune my settings are very close to the coil with heavier compression valving. Before completing the review I will swap out the air spring for the coil but test the current C50 tune with that to see how it affects things. Look for that review soon.