Rear shock
Rear shock
The spring and damper that control the rear wheel of a full-suspension bike. Its tune and setup decide whether the back of the bike grips, pedals and lands well.
Also known as: shock, rear suspension, shock absorber
Key facts
- Standard
- metric and trunnion mounts
- Service interval
- air can every 50 h, damper every 200 h
Air or coil
- Air shocks are light and easy to tune with a pump — the choice of most trail and cross-country bikes.
- Coil shocks use a steel spring: more sensitive and consistent on long descents, heavier, and the spring rate is changed by swapping the spring.
Sizes
A shock is described by two numbers: eye-to-eye length and stroke, for example 210 × 55 mm. The frame multiplies the stroke into wheel travel through its linkage, so a shock only fits the frames made for its size and mount.
Setup
Set sag first — usually 25–30 % of the stroke — then rebound. A climb switch or lockout firms the shock for long smooth climbs; open it again before the descent.
Care
An air can wants new seals and grease about every 50 hours, the damper a full service around every 200. A shock that feels sticky, loses pressure or makes new noises is asking for it sooner.
Related articles
- RockShox — An American suspension brand founded in 1989 by Paul Turner. Its first fork, the RS-1, brought front suspension to mountain biking; since 2002 the brand has been part of SRAM.
- Full-suspension bike — A mountain bike with suspension at both ends. The rear shock keeps the back wheel on the ground over roots and rocks, which means more grip, more control and less fatigue.
- FOX — An American suspension maker founded in 1974 by Bob Fox. Its forks and shocks — recognisable by the gold Kashima Coat — are fitted to mountain bikes of every discipline.
- Suspension fork — The telescopic front fork that lets the front wheel move up over bumps instead of throwing them into your hands. It is what steers the bike through rough ground.
- Suspension setup — Half an hour with a shock pump makes a bigger difference than most upgrades. Set the air pressure by sag, then rebound, then compression — one change at a time.
- Sag — How far the suspension compresses under the rider's own weight, standing in the riding position — given as a percentage of travel. The first number to set on any suspension.
- Suspension travel — How far a wheel can move on its suspension, in millimetres — the first number in any mountain bike's description. More travel absorbs bigger hits; less travel pedals and weighs less.