Definitive Guide to Setting Your Bike's Compression and Rebound Damping
Ok so some basics first.
What is damping?
Most dirt bikes have a suspension system that has forks up front and a rear shock absorber connected to a complex array of linkages and lever arms. The fork and the shock absorber have a spring in them that resists the force from bumps, and oil that is sqeezed through variable hole sizes to "dampen" the spring effect. That is, without the oil to dampen the spring action, the spring would oscillate back and forth like a pogo stick until its energy is released - in the form of heat and through the friction in your suspension system.
Why is damping important?
Damping is used to control bottoming but more importantly, it is used to optimise traction. Changes made to the front and rear damping can affect the way a bike corners, accelerates and absorb bumps - including large ones and hard landings off jumps. Optimising you damping can help you to get that power to the ground sooner, smoother and more confidently!
You want enough compression damping to ensure that you don’t smash though the shock absorber's full stroke when you hit bumps, and enough rebound damping that the bike isn’t bouncing like an excited puppy, but not so slow that the shock hasn’t returned for the next bump.
Here is a guide to help you determine what adjustments need to be made. It should be noted however that every track, surface and riding condition will be different and so you may need to adjust your settings for each situation.
|Bike feels too soft or plush.
|Increase rebound damping front and rear.
|Bike feels too hard, stiff or harsh.
|Reduce rebound damping front and rear.
|Rear of bike kicks around and wont stay in line.
|Increase rear rebound damping.
|Bike dives excessively in corners or under braking.
|Increase fork rebound damping and/or compression.
|Bike squats under acceleration.
|Increase rear compression damping.
|Bike feels dull and lifeless and the front wants to "knife" in corners or is twitchy and hard to balance. You will know this if it happens - the bike will want to stick it's handlebars into your stomach.
|Increase front rebound damping.
|Bike chatters in corners, or under-steers, feels "bouncy" and lively. Rider's will have less confidence in this condition.
|Reduce front rebound damping.
|Jumps and large bumps
|Increase compression damping.
|Suspension rebounds too quickly, bouncing the bike back up.
|Increase rebound damping.
Pro Tip: Start off with the manufacturers recommended settings and make small changes from there. Adjust only rebound or compression at any one time. This way you will know the cause and effect of each setting.
The simplest way to go about this that we have found over the years is to follow this general sequence to setting your rebound and compression damping:
1) Set your front and rear compression to suit the largest bump of jump landing. This way, you will make use of the full available stroke in your bike's suspension. If there are no jumps or big bumps like in flat-track, back the compression damping right off and then progressively increase it until the bike stops diving excessively in corners or under hard braking and the rear does not pack under acceleration.
Pic: Compression Adjuster. The screw is for low speed adjustment and the flat, outer "Nut" is for high speed adjustment
High Speed vs Slow Speed Compression Adjustment
Most modern bikes have low speed and high speed compression damping adjustments. The high speed controls the big bumps and the slow speed controls the smaller stuff. Setting the compression damping is often a compromise - if the suspension is optimised for the big bumps then often the suspension will be too stiff for the small stuff which is why having a high and low speed adjusters is cool - you can increase the optimisation window to take in more of the track conditions. Once you have set the high speed for the largest bumps, work on the low speed setting for the rest of the track.
2) Accelerate through some sharp bumps, stutters or similar. Increase the rebound damping in the rear shock absorber until the bike stops kicking around and tracks straight.
Pic: Rebound adjuster screw at base of shock absorber
3) Ok so now you have pretty much got the rear end sorted. Now all that is left is to fine-tune the front rebound damping for optimal cornering. Feel the balance of the bike in corners - if it feels like the bike is hard to balance around the corner (i.e. the bike wants to knife in the corner and put the handle bars into your stomach), then increase the rebound damping. Conversely, if the bike tends to want to understeer through a corner or slide out and run wide, then decrease the rebound damping.
Consult your bike's user manual on how to adjust the rebound and compression damping for your forks - every bike is different - most have compression adjustment on the top of each fork and rebound underneath (hard to get too especially when you're out in the paddock and the base of the forks are covered in mud!). Some, like with KTM's forks, one fork may handle compression while the other handles rebound and the adjusters are both on top of each fork. We like this design! The adjusters will typically have a screw for low speed and a nut for high speed adjustment, just like the shock absorber. KTM's forks have clickers that you can adjust with your fingers!