BY MARK JOHNSON

Properly setup suspension not only helps you ride faster, it also allows you to have more fun and ride safer. Understanding the fundamentals of your dirt bike’s geometry and suspension will help! 

REAR SHOCK

The rear shock sag sets the ride height of your bike, which directly defines the steering-head angle and swingarm geometry. A typical baseline of 100–105mm of race sag positions the chassis for neutral balance, but deviations alter handling dramatically. Excessive sag will make the rear end ride lower, which will lengthen the wheelbase and relax the fork rake. Stability will improve, but corner initiation will suffer. Insufficient sag or a taller rear height will steepen the head angle. This makes the bike turn sharply, but it will lose straight-line stability, often developing head-shake under braking.

Static sag should typically be between 30mm and 40mm, and this will indicate if the rear spring rate is correct. If static sag is outside this range, the spring rate, not the clickers, is the first adjustment to investigate. Too low, say 20mm, shows there is too much preload on the spring to achieve sag, and a stiffer spring is needed to increase the static sag.

DAMPING

Suspension damping is governed by the hydraulic resistance of oil flowing through valving circuits. External adjusters alter bleed pathways, increasing or decreasing damping. 

Low-speed compression: The low-speed compression adjuster controls chassis pitch from rider input, throttle, braking and body movement. Too little low-speed control allows excessive dive or squat, while too much creates harshness and traction loss. Low speed often gives the feel of the setup for the rider.

High-speed compression: The high-speed compression responds to impacts like braking bumps and jump landings. Insufficient high-speed compression can allow the bike to ride deep in the stroke and create deflection and harshness. This adjustment also controls how much overall support you have, particularly in the mid-stroke. It is a great way to control positioning and to help prevent it from moving too quickly through the stroke.

Rebound: The rebound damping controls recovery speed. Overly slow rebound packs the suspension, reducing travel and traction. Overly fast rebound destabilizes the chassis, producing kicking issues or a loose sensation. 

When making changes to the low-speed, high-speed or rebound settings, the changes should be made in two-click increments or 1/8 turn for some high-speed adjusters, with testing isolated to a single change for clarity.

TERRAIN DIFFERENCES

Different terrain demands different damping balances. For hard-pack tracks, reduced low-speed compression improves mechanical grip, while slightly slowing or speeding up rebound keeps the tires planted on chatter bumps. On sand tracks, you can increase the low-speed damping to maintain strong wheel pressure to the ground, while slowing rebound helps to keep control of excessive movement. On tracks with deep ruts, a well-balanced bike helps the bike track with the rut rather than climbing out. Fork-height changes are advised in these circumstances for adjusting the balance of the bike. 

COMMON ISSUES

If your front end tucks in corners, that means you have insufficient compression support in the fork or too much weight on the front end. If the rear end is kicking side to side on braking bumps, the shock rebound is too slow, preventing recovery before the next impact. If the rear end is kicking vertically, the shock rebound is too quick or the shock spring is over-preloaded. If you experience head-shake while on the throttle, the sag is too low. If you feel harshness on square-edge bumps, you could have excessive high-speed compression.

Clicker tuning is ineffective if the internal system is compromised. Suspension oil degrades, bushings wear, and nitrogen charge pressure drops, all of which alter damping characteristics. Service intervals of 20–30 hours are typically sufficient for the average rider to maintain consistency. For faster riders, servicing as frequently as every 10 hours is commonly required to maintain a consistent feel.

Mark Johnson was an in-house WP suspension technician at Red Bull KTM for 10 years. He has won championships in Supercross, motocross and off-road racing. Now, Mark’s shop, Research Engineering Performance, or “REP,” is based in Temecula, California. They offer factory-level experience to everyday riders.