Suspension Basics: Part 1

By Sean Coker

Suspension, in a perfect world, would not be needed. Anyway you slice it, suspension robs power, alters geometry and draws attention away from riding. But the fact remains that we need suspension to deal with the irregularities all around us: potholes, ripples in pavement, overlapping sections of asphalt, etc. So what do all those knobs on our bike do and how can they help make me a better rider?

A properly set up suspension allows a motorcycle to better deal with the inconsistencies of real world riding. With the help of a couple of friends, a few minutes and some note taking skills, you too can properly set up a bike for free. Modern bikes are frequently equipped with adjustable preload, dampening, and compression settings. These three settings are often found on the front and rear of the bike and help determine the nature of the bike's handling.

Getting started, Setting Sag

There are two types of sag: static and free. Static sag involves how much the suspension compresses under the weight of the rider and free sag involves how much compression occurs under the weight of the bike alone. Measuring static sag is easier with the help of a few extra hands. Start by measuring the total amount of suspension travel by lifting the front end completely off the ground. For traditional forks, measure from the top of the dust cover to the bottom of the triple tree and for upside down/inverted forks measure from the dust cover to the top of the axel mount. Record this measurement as L1.

Mount the bike and have someone depress the forks, letting them rise until they stop, this measurement is known as L2. Get off the bike and measure how much the suspension sags from its own weight (free sag), this is known as L3. Static sag is= L1- (L2+L3)/2. Street riders should aim for anywhere from 1.25-1.5 inches of static sag for the front end. Now the rear wheel.

The procedure for measuring the rear suspension is nearly the same. Pick a spot directly above the rear axel and use this point for measuring. Using a center stand or some buddies to lift the sub frame until the rear wheel is off the ground (race stands will not work because they are still loading the suspension) and measure from the axel to our point of reference. Record this measurement as L1. Mount the bike and have a friend stabilize it from the front. Have a second friend depress the rear about an inch (do not bounce!) and let the suspension ride to a resting place. Record this measurement as L2. Now have your friend lift up the rear of the bike an inch and let the suspension drop to its resting place. Record this measurement as L3. Spring sag is actually in between L2 and L3, the difference is the frictional drag of the linkage. Again use the formula static sag= L1- (L2+L3)/2. If there is too little or too much sag then an adjustment is needed, which is done via preload.

Preload is the initial compression of a spring and is accomplished generally by a slotted screw that depresses a spacer on the front forks and a ramped collar (or collars) on the rear. By screwing in the preload adjuster, or tightening the rear spring collar, we are adding more preload. If there is too much sag add preload, and conversely too little sag is remedied by removing preload. Remember, preload is a minor adjustment and if no amount of preload will set proper static sag, different springs are needed. Note: some bikes are equipped with a dampening adjustment to the inside of the preload adjuster. Adjusting preload will not change dampening settings.

If your bike does not come equipped with a preload adjustment on the front, fear not. Raise the front of the bike and remove the fork caps. Identify any stock spacer located inside the fork and measure its length. Find the biggest piece of PVC pipe that fits inside of your fork, and, using a miter box to ensure proper perpendicular cuts, cut sections of PVC pipe in varying º inch lengths. Make sure to deburr the edges before placing inside your forks. Write the length of the spacers on the spacer in a back marker and reinstall the fork caps. Go about measuring static sag again and adjust spacer length based on need.

Next month, we dive deeper into suspension settings.