WP Fork Spring Rate Calculator
Recommended Rate: — N/mm
Note: Most WP forks (XACT, XPLOR) use standard spring increments of 0.2 N/mm. If your result is between sizes, choose based on whether you prefer more bottoming resistance or more initial plushness.
Understanding WP Fork Spring Rates
Correct spring rates are the foundation of a well-performing suspension system. For WP suspension, commonly found on KTM, Husqvarna, and GasGas motorcycles, the fork spring rate (measured in Newtons per millimeter, or N/mm) determines how the bike holds its "ride height" under the weight of the rider and bike.
Why Your Weight Matters
WP components are generally valved and sprung for a "target rider" weighing approximately 75kg to 85kg (165-187 lbs) without gear. If you fall outside this range, your forks will sit too high or too low in the stroke, forcing the internal valving to work in a zone it wasn't designed for. This often results in a harsh feel, even if the springs feel too soft.
Discipline-Specific Springing
- Motocross: Requires higher rates to handle high-speed jump landings and deep G-outs.
- Enduro/Woods: Requires slightly softer rates to deflect off rocks and roots while maintaining traction.
- Cross-Country: A balance between the two, focusing on stability at speed without being as rigid as a pure MX setup.
Practical Example
If an Intermediate rider weighs 95kg (with gear) and rides a KTM 450 SX-F (4-stroke), the calculator will factor in the increased weight (+0.4 N/mm over baseline) and the heavier engine torque (+0.2 N/mm). A typical recommendation might be 4.8 N/mm or 5.0 N/mm, whereas the stock spring is often 4.4 or 4.6 N/mm.
How to Verify Your Rates
Once you install the recommended springs, you should check your Static Sag and Rider Sag. For most WP AER or XPLOR forks, you are looking for roughly 30mm to 40mm of static sag (bike weight only) and 75mm to 85mm of rider sag (total weight). If you cannot achieve these numbers by adjusting the preload, you may need to move up or down one spring rate increment.