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Arma V4 Trunnion Coil Shock

The EXT Arma V4 Trunnion Coil Shock is a gravity-focused rear shock built for riders who want coil traction with a wide tuning range for high-speed impacts, steep braking zones, and repeated hits. Its damping architecture prioritizes control deep in the travel without sacrificing small-bump sensitivity, making it a strong choice for modern downhill and park bikes using a trunnion mount.

A standout feature is HBC (Hydraulic Bottom Out Control), which ramps damping force in the final portion of the stroke to resist harsh bottom-outs. That added end-stroke support can allow a lower spring rate choice while maintaining composure on big compressions, improving compliance and traction where it matters most.

5 reasons this coil shock stands out for aggressive riding

1. HBC bottom-out circuit - Adds significant end-stroke damping support to reduce harsh bottom-outs and keep the bike stable on big hits
2. High- and low-speed compression adjustment - Separates support for impacts versus rider inputs (pumping, berm loading, braking), helping riders dial in control without over-stiffening the ride
3. PSR position-sensitive rebound and top-out control - Manages rebound behavior through the stroke while improving top-out control for a calmer feel in rough terrain
4. Large volume reservoir with bladder design - Designed to maintain consistent damping under sustained descending; reservoir pressure up to 55 psi max
5. DLC-coated steel damper shaft - Prioritizes wear resistance for long service life under high loads and frequent compression cycles
6. Spring thrust bearings - Helps keep the coil aligned and reduces spring noise during compression

Uses high viscosity index oil to support consistent damping across a wide range of riding conditions.

Note: Coil spring and mounting hardware are sold separately.