An interesting note on Suspension setup, summitted by Charlie Sherwood, from the Aprilla List
Unless you are 200lbs + or 140 lbs or less, the springs on the bike will probably be OK. Figuring out the right size replacement spring and supplying and installing one might be something a set-up specialist could help you with, but if you go through the bike setting up the pre-load first, then rebound, then compression, you'll probably get 80% or better of the benefit.
For regular riding on regular roads,you want less compression than racers use generally.You want to make sure the springs are strong enough for your weight. You can compensate only so much for a weak spring with pre-load settings.
You want to set the spring so it doesn't allow the suspension to bottom on the bump stops and it doesn't fully extend (top out) either. Let the spring do most of the suspension work, not the damper. You'll be more comfortable and the suspension will work better. Generally, this means the suspension should be 1/3 compressed at a standstill with full rider and gear weight on it.
Rebound damping should be set so that the bike takes about one second to rebound after being pushed down. It should simply return to static position, it shouldn't move higher and then come back down. Too much rebound damping can make the suspension "pack up" on a series of bumps. The spring eventually ends up compressed to the bump stops because rebound was too slow to recover.Too little rebound damping gives the bike a baby-buggy or pogo stick ride....springy and loose.
Compression damping is what makes a bike ride "hard" on bad (normal) roads. You want to dial in as little as possible without making the bike handle poorly. This takes a bit of experimentation. Not enough compression in front causes fork dive.You can bottom the forks on hard braking. Too much causes the bike to loose control on bumpy turns and feel too busy.
Too much compression in the rear will wreck your spine and cause the back to bounce all over bumpy corners. Too little will make it feel sloppy. A little compression goes a long way. Don't fix something with compression that you can fix with a spring pre-load change....let the springs do their job first.
On the mille rear suspension.Rebound adjustment is at the bottom of the shock. compression is on the piggy back unit on top. Spring pre-load is changed with a spanner wrench from the dealer.Everyone should have a way to adjust pre-load on their bike.....use some WD 40 on the threads and loosen the lock-ring first before adjusting.A nice dealer can show you this stuff on a slow day.
On the front, Rebound is the small middle adjustment on the top of each fork.Compression is on the bottom of each fork.Pre-load is the larger outside adjustment on top of each fork. Make sure both forks are adjusted the same.Otherwise, you will be cocking the forks with each bump.
For what it's worth, this is what I, Mr. Amature road rider do with my bikes. My Mille R, however, didn't seem to respond well to all this, so I put the settings all back to stock ("racing" on the R version) and just reduced the compression damping until the bike worked for me. I get more fork dive than before, but it doesn't bottom and it is lots more secure on bumps, of which there are plenty.