Bicycle Mechanics - ok newb suspension fork question.

What exactly is rebound and preload, and how do you gague what the right settings for each are?

Just wondering since my Manitou fork has these settings and I was playing around with them a bit.

Mountain bike suspensions aren't my greatest strength, but I'll try. Everybody refers to them as "shock" forks, but that's really a misnomer. A better word would be "suspension" fork. Your car's suspension has springs and shock absorbers. The better bicycle suspension forks also have both. The cheapies only have springs.

Preload is a screw adjustment on the suspension spring. Increasing the preload stiffens the spring and makes it react less to small bumps. In a way, that might sound like a bad thing, but it also means that the fork is bobbing less. In general, the smoother the trail, the less preload you'll want. You'd like for the fork to just bottom out on the biggest single hit of the trail.

If you ride off a foot high dropoff, your fork is obviously going to initially compress. The next thing that is going to happen is the spring is going to rebound and push the fork back to it's extended position. If you allow the fork to spring back with too much force, the momentum of this movement will actually cause the front wheel to lift off of the trail momentarily. Rebound dampening smooths out this movement and keeps the front wheel on the ground where it belongs.

Everybody likes to talk about travel because that's an objective number that they can brag about. I think that QUALITY of travel, how smoothly it operates through it's cycle, has a much greater impact on your bike's handling. When you get your dampening dialed in you will find yourself riding the downhills much, much faster, but at the same time, more securely because you'll have much better control over your bike. With no dampening or with poor dampening you'll have to brake to keep from sliding off of the outside of the curves. With good dampening you'll stick to the inside of the same curve at a significantly higher speed.

Preload first. This is the amount of spring tension on the fork. you set it by sag (How much the fork droops when your static weight is on it, you can check this with a handy ziptie on the fork stanchion) You want around 15% of travel as your base. Can be more or less, depends on your riding style and what you like the feel of. Most forks have a chart that will give you a start point.

Rebound. this is the amount of damping your fork has on return. (As it uncompresses from a hit) The ideal for this is that it will allow the fork to cycle out from the roughest series of impacts you will hit on a given course. That is, if you run over a series of stutter bumps, you want the fork to return from each to be ready for the next. If you have to much rebound, the fork will not have enough time to spring back and will compress a little more over each bump til the point it is fully compressed and is doing nothing. As most people don't really set up for a course, pick the roughest place you ride and play with the damping, only making small changes(The key to any setup) until it feels like you like it.