Modern sporting motorcycles can come with a near dizzying array of suspension adjustment. Pre-load, compression damping, rebound, high-speed damping, low-speed damping, etc. Where to start?
Before you start looking over your bike to see what we're talking about, please note this article is primarily intended for the sportbike rider. Most cruisers have little or no suspension adjustment. You either live with what the factoryave you, you have your suspension components upgraded with after market units, or have the internal bits replaced by a professional.
The easiest and most important adjustment you can make is to set the static sag. Sag is just what it sounds like – how much the bike sags when you're on it.
Ideally your sag should be from 25 to 30 mm, or 1 to 1 in inches, on most bikes. To find out where your sag is, you'll need a helper. Dress up in all your usual riding apparel, including helmet, leathers, boots, etc. You want to set your sag using the same weight as when you ride. While standing next to the bike, push down on the tail once or twice to make sure the suspension is at its normal resting position.
Using a dowel rod, yard stick, or similar device, measure the distance from the ground to a particular point on the motorcycle. Turn signals or a point on the seat or frame will work fine. Just make sure the point you measure from is not covered up when you're on the bike. OK, got the measurement? Either write down the measurement (in inches or millimeters) or simply mark the spot on your rod / stick.
Now get on the motorcycle, in full gear. This is where your helper is needed. For the most accurate measurement, try to hold the bike fully vertical with both your feet on the pegs. In this position, take another measurement. See the difference? That is your sag. If it's smaller than 1 inch or greater than 1 in inches, you'll need to adjust the pre-load on your forks and / or shock to get the desired results. Increase pre-load (typically a clockwise turn of the adjusting screw or collar) a little at a time to reduce your sag. Decreasing pre-load will increase the amount your bike sags.
Adjusting rebound and compression damping is probably more complicated, and requires riding your bike and trying different settings over time. More compression damping in front reduces the amount your bike will dive under braking. More in the back will reduce how much the rear end squats under power. Too much compression damping can cause the bike to ride rough, transmitting every bump in the road to you without absorbing much. If you're only riding on a smooth racetrack, more compression damping might be a good thing. If you ride on gnarly back roads, you'll probably want to soften up your settings.
Rebound damping affects how much your wheels "bounce" off the brakes and wallow under power. Too much rebound damping and your suspension will not react fast enough to properly follow bumps in the road. Your forks or shock can get "packed down" by repeated bumps, which reduces your suspension travel and can lead to a very poor ride, or worse. Too little rebound damping in the front or rear and your bike will be walling around like a '68 Cadillac, making it very unpleasant and hard to control.
Your mission is to find the right balance for you and your riding style. Usually it's best to start out with the settings your bike came with from the factory. There's a reason why they're set where they are. From there, spend a little time on the bike. Is it too stiff? Does it wallow? Pay attention to how the different ends of the bike feel. Adjust accordingly, but not too much. We suggest adjusting in increments of one click at a time, until you find the sweet spot you're looking for.
Once you get your favorite settings dialed in, you can start playing around with them a little at different times. For example, you might want to tighten things up a bit for a fast track day at California Speedway. Or you might want to loosen them up a notch or 2 if you're planning to ride Carmel Valley Road (ask me how I know!). Whether or not you choose to leave the settings alone or make occasional adjustments, making your motorcycle handle better for you and your riding style lower lap times, and will definitely enhance your riding enjoyment.