Suspension school · Brand-Specific Technology

Manitou: IRT Dual Air and the Reverse Arch

Mezzer, Mattoc and Dorado, and how IRT pressures work

Manitou forks are instantly recognisable by the reverse arch behind the stanchions. The engineering under the surface is equally distinctive, led by the IRT dual air system that gives you two pressures to set instead of one.

IRT: Infinite Rate Tune

IRT uses two positive chambers. The main lower chamber sets sag and governs the initial stroke. A separate IRT chamber above it runs at higher pressure and progressively takes over as the fork compresses, controlling mid-stroke and end-stroke support independently of how the fork feels off the top.

• Always inflate the IRT chamber first, then the main chamber
• IRT runs well above the main pressure: Manitou's chart puts a 73kg rider on a 160mm Mezzer at around 52psi main and 84psi IRT
• Maximums are 120psi in the main chamber and 200psi in IRT
• More IRT pressure adds mid and late-stroke support without hurting small-bump feel; more main pressure changes sag and the whole curve

Mezzer Pro

• Manitou's enduro fork, also marketed for eMTB use, with the longer-travel Mezzer LT alongside
• MC2 damper: 10 clicks of low-speed rebound, 4 clicks of high-speed compression and 10 of low-speed compression
• A hydraulic bottom-out circuit is built into the damper but is not externally adjustable
• Recent Mezzer Pro and LT models list an updated MC2-Pro-X damper

Mattoc (2023 Onwards)

The revived Mattoc is a 34mm trail fork covering 110 to 150mm of travel. The Pro version is essentially a scaled-down Mezzer, with the MC2 damper and IRT air spring, which makes it one of the most tunable forks in its weight class.

Dorado

The Dorado is Manitou's inverted dual-crown downhill fork. The current generation launched in July 2021: a 37mm carbon chassis on the Pro, Dorado Air with IRT, and the TPC+ damper with hydraulic bottom-out acting over the final 30mm of travel, in 180 to 203mm options for 27.5 and 29 inch wheels.

Setup Notes

• Follow Manitou's setup chart for both pressures before improvising, and keep the IRT-first filling order
• Tune support in 5psi IRT steps, treating it like an infinitely variable volume spacer
• Tune sag in 2 to 3psi main chamber steps
• Re-check sag after large IRT changes, since the chambers interact slightly