Originally published November 17, 2013. This article documents the FOX shock upgrade program offered for the original Polaris RZR XP 900. Similar RZR XP 900 shock service and upgrade options are currently available through Shock Therapy.
Rebuildable shocks require periodic maintenance. As shock oil ages, heat and repeated use can reduce its damping performance. Worn seals, contaminated oil and reduced nitrogen pressure can also make the suspension feel harsh, inconsistent or less controlled.
Servicing the original FOX shocks on a Polaris RZR XP 900 can restore performance without replacing the complete suspension. At the time this article was published, FOX also offered several upgrades that added external adjustments and higher-performance internal components to the stock shocks.
FOX Upgrade Options for RZR XP 900 Shocks
The original FOX shocks fitted to many Polaris RZR S, RZR 4 and RZR XP models included low-speed compression adjustment. FOX offered three upgrade levels for owners who wanted additional tuning capability without purchasing a complete replacement shock package.
Stage 1: Dual-Speed Compression
The dual-speed compression adjuster provides separate high- and low-speed compression settings. This gives the driver a broader tuning range for different terrain and driving styles.
Low-speed compression can be adjusted to improve body control, while high-speed compression can be tuned to handle sharp impacts, aggressive whoops and hard landings.
Stage 2: Rebound Adjustment and Racing Components
The Stage 2 package added rebound adjustment, a FOX high-flow racing piston and revised valving. Rebound adjustment controls how quickly the suspension extends after the shock has been compressed.
Stage 3: Complete Compression and Rebound Upgrade
The complete Stage 3 package combined the dual-speed compression adjuster, rebound adjustment, FOX high-flow racing piston and revised valving. It brought the original shocks closer to the tuning capability of FOX’s 2.0 Piggyback RC2 coil-over shocks of that era.
Polaris RZR XP 900 Shock Upgrade Process
Understanding the Shock Adjustments
Low-Speed Compression
Low-speed compression refers to the speed of the shock shaft—not necessarily the vehicle’s ground speed. It primarily affects slower suspension movements such as body roll in corners, front-end dive under braking, rear squat under acceleration and compression through rolling terrain or g-outs.
The goal is to use enough low-speed compression damping to maintain good body control without creating excessive harshness or reducing traction.
High-Speed Compression
High-speed compression affects faster shock-shaft movements caused by square-edged bumps, abrupt jump faces, harsh landings and aggressive whoops.
For recreational riding, the usual goal is to run only enough high-speed compression to resist bottoming while maintaining compliance over rocks, chop and small bumps.
Rebound Adjustment
Rebound damping controls how quickly the shock extends after being compressed. Too little rebound damping can make the vehicle feel springy or cause it to kick after an impact. Too much rebound damping can prevent the suspension from extending quickly enough between bumps, causing the shocks to pack down through consecutive whoops or rough terrain.
Make adjustment changes in small increments and record the original settings before experimenting.
RZR XP 900 Shock Upgrades Are Still Available
Although this article originally covered the factory FOX upgrade program, Polaris RZR XP 900 owners can still have their shocks serviced and upgraded through Shock Therapy.
Shock Therapy offers suspension tuning and shock-service options for the RZR XP 900, along with a model-specific dual-rate spring kit. Contact Shock Therapy with your exact model, vehicle weight, accessories, typical terrain and driving style to determine the appropriate service or upgrade package.
