Suspension, Steering, and Wheel Alignment
This domain covers spring rates, damping, steering geometry and the measurements that prove them.
Core rules
- Set sag first: measure rear static and rider sag with the bike loaded; adjust preload to hit spec, then set rebound and compression clickers to baseline before evaluating.
- Fork oil level is measured in mm from the tube top with the spring removed and the fork fully compressed; level changes air-spring behaviour, viscosity changes damping.
- Change one click or one shim at a time and re-test the same road; record settings.
- Steering head bearings: check for notchiness with the wheel off the ground and the bars swept slowly; set preload so the assembly falls gently to a stop rather than flopping.
- Wheel alignment: string-line the rear wheel, then compare with the front; use axle marks only as a starting point. Check radial and axial runout at the rim; a loose spoke pings when tapped.
- Tyre pressures are set cold; a 1–2 psi difference changes turn-in noticeably.
Worked example
A bike feels vague and wants to stand up in corners after a rear tyre change. Reasoning: nothing in the suspension was touched, so look at what was - axle alignment and chain adjuster marks. If the rear wheel is cocked, the bike steers with the rear offset and feels like it is pushing the front. String-line the wheels, correct the adjusters and set chain slack; the geometry fix resolves it without touching damping.
Traps that cost marks
- Adjusting damping before sag and spring rate are correct.
- Measuring fork oil level with the spring installed.
- Trusting stamped swingarm marks as an alignment gauge.