Suspension school · Progression & Volume

Ramp Chambers: Tuning Progression with a Shock Pump

Öhlins, EXT and Manitou replace plastic tokens with a second air chamber

A growing group of high-end forks does away with plastic spacers entirely. Instead, a separate air chamber controls the ramp-up, and you tune progression by changing its pressure with an ordinary shock pump. The curve becomes a number on a gauge rather than a count of plastic parts inside a sealed leg.

Öhlins RXF38 m.2: the three-chamber design

The RXF38 m.2 runs three chambers: the main positive spring, a self-balancing negative, and a separate ramp-up chamber with its own valve. The ramp-up chamber does the job tokens would do, and there are no tokens to fit at all. Öhlins' guideline is to run the ramp chamber roughly 90psi above the main chamber. A 90kg rider might land on about 105psi in the main chamber and 195psi in the ramp chamber, then adjust from there.

The tuning logic maps directly onto what you already know. Raising ramp-chamber pressure is like adding tokens, lowering it is like removing them. The difference is resolution. A token is a fixed step, while 5psi in the ramp chamber is a fraction of a step, so you can put the curve exactly where you want it.

EXT Era: the + and ++ chambers

EXT's Era fork takes the same idea further with two auxiliary chambers, labelled + and ++, alongside the main spring. Between them they shape the middle and the end of the stroke, doing the job of tokens with far finer control, the + chamber leaning on mid-stroke support and the ++ chamber governing the final ramp. As a reference point, an 80kg rider typically runs around 65psi in the + chamber and 100psi in the ++ chamber. Because mid-stroke support and bottom-out resistance are tuned separately, you can firm up the end of the travel without making the middle of the stroke stodgy, something a bag of tokens simply cannot do.

Manitou IRT

Manitou's IRT (Infinite Rate Tune) is an independent second positive air chamber sitting above the main spring, filled through its own valve at the top of the leg. The main chamber sets sag and the initial stroke, while the IRT chamber controls support from the mid-stroke onwards. IRT pressure typically runs around one and a half to two times the main chamber, with a lower ratio giving a more linear trail feel and a higher ratio a more progressive, gravity-oriented one. Manitou publishes pressure tables for its forks, and they are the right starting point.

Why psi beats plastic

• Continuous adjustment instead of whole-token jumps, so the curve lands exactly where you want it
• Changes take a shock pump and two minutes at the trailhead, with no disassembly and no tools
• No releasing the main spring or opening the fork, so nothing can be mis-seated inside
• Three-chamber designs separate mid-stroke support from end-stroke ramp, which tokens cannot
• No parts to buy, lose, or exceed the maximum count of

The discipline it demands

The cost of all this adjustability is bookkeeping. Two or three pressures now define your spring instead of one, and the chambers interact, so follow the fill order in your fork's manual and re-check sag after any ramp-chamber change. Write every pressure down, change one chamber at a time, and re-test on the same trail. A ramp chamber also loses a few psi to the pump hose every time you check it, so use the same pump consistently and check before rides, not mid-descent.

The eMTB case for ramp chambers

These systems suit heavy bikes unusually well. An eMTB rider chasing big-hit support on a token fork can run out of maximum count, or end up with a harsh, over-stuffed end stroke. A ramp chamber adds resistance smoothly and can go further than a full stack of tokens without the spike. It also adapts quickly, so you can add 10psi of ramp for an uplift day on a 25kg bike and take it back out for Sunday's trail loop without touching a tool.