I know I'm simplifying a complex subject but I was told by a suspension expert that for a smother ride the compression should be backed off (obvious) and the rebound should be increased. If that's true why do they tend to get set in a similar way together e.g 5 clicks in for rebound and 4 clicks in for compression for a soft ride and 17 clicks in for rebound and 16 clicks in for compression for a sportier ride? I'm talking from a manual setting of Ohlins on a MTS Pikes Peak but it's the principle I'm asking about really. Any sensible comments welcome.
The relationship of compression and rebound is crucial to the compliance of the ride. If you increase the rebound as suggested, the bike will pogo stick and be totally unrideable. My preference is for a soft suspension but my rebound setting is always less than the compression by 2 or 3 clicks. I suggest you find a suspension expert who understands and works with adventure bikes which are very different to short travel sports and sports touring bikes. Andy
Oh here's a right can of worms. Let me try to peel the lid off without getting sprayed in worm juice. Let's take a look at the rear shock. If you screwed both adjusters full in (closed) and dyno'd it. You'd find the rebound curve much stiffer than the compression this is by design in the shim stack. (assuming it's a sport bike and you have a 2way adjustable shock?) So the rebound forces will always be Higher than compression. (Why?) Well there's a bloody big spring holding the bike up so compression is trying to tune the rate the spring reacts after the wheel has moved up via a bump or cornering force. But when the spring is released (and it could in theory be totally unloaded) the rebound works hard to keep this motion in check to preventive rear wheel becoming unloaded. (Or you out of the seat) But here's the thing. If you back the compression off and over increased the rebound. Then you can create what's known as pump down. Which happens when the suspension is too slow to recover its norminal ride height before the next vertical input (bump or corner force) which will have a diverse affect on the handling/ ride. So it's a fine tune. But generally I set my Trackday bike to be as supple on compression without bottoming the fork or keeping off the bump stop at the rear. Rebound to control how quick it suspension recovers back to static ride height. Tricky! Let the argument begin!
They are not really related - compression damping controls how quickly a wheel travels upwards and rebound damping controls how quickly a wheel travels downwards. If you have insufficient compression damping you will have a very harsh ride, same as if you have way too much. This also applies to spring preload. As has been said above - take it to someone who knows what they're doing to get baseline settings, then keep notes on any changes you make, preferably testing any changes on the same piece of road. If you want to learn more about it watch the Dave Moss youtube videos and read some of the good books on the subject. When it comes to suspension, as in most things, it's very easy to get lost and make a right mess if you don't know what you're doing and don't keep notes on changes you make. Basically the two types of damping are not related other than that they control the same wheel i.e. there is no 'set rebound damping to x-percent or x-clicks more/less than compression damping' regardless of what a manual or expert seems to suggest.
Always try to have a balance so that it compresses and returns at roughly the same rate. To exaggerate the point: it takes two seconds to compress it should take two seconds to spring back. If it's a really bumpy road then probably want it returning a bit compressing and returning a bit slower (?) without allowing it to chunk down, as described by air duck. I.e. Softer
I'm not sure that standard suspension units on consumer bikes allow enough adjustment to trigger pump-down - I suspect that it would not get manufacturing approval. Race units are a different story, of course.
Given some of the mega bumpy B roads about, they are Imagine it being really soft, on a long fast straight, first bump collapses and can't recover before the next and so on...feels like a pogo stick and wallowy all at once. My old monster used to do it until I changed it all, both on road and track
