For manual testing and adjustment of a motorcycle’s suspension sag, Racetech’s method is the most accurate. The geometry in their formula eliminates any marginal grey area by averaging results against one-another from both directions. Basically, what goes up wants to come down (springs), so we take note of both the ceiling and floor before predictively calculating the horizon.
Physically, this is a two or three person job. These instructions assume that you have friends on hand to help out. With that in mind, pizza and soda are a wise investment.
You’ll need to measure and write down three figures per axle (front/back). We’ll call them F1, F2 and F3. For accuracy, you should only collect one axle’s figures at a time.
F1: Place the bike on it’s center stand. For the front, in line with your forks, measure (in millimeters) from the axle to the base of your fairing or it’s nearest neighbor. For the rear, measure (in millimeters) from the axle straight up to nearest part of frame.
F2: Remove the bike from it’s center stand and have the rider get on board (seated in riding position while holding still to maintain a consistent center of gravity). While one person keeps the bike vertical, another must push down on the target spring(s) by 25mm (about an inch). Slowly release pressure. Measure the stopping point using the same locations from F1.
F3: Repeat the procedure used to obtain F2, this time lifting upward instead of pushing down. Now, enter your resulting figures and hit “Calculate”.
The formulas for calculating static sag and stiction are as follows:
Static Sag = F1 – ( ( F2 + F3 ) / 2 )
Stiction = F3 – F2
For street, sport-touring and standard bikes, the ideal sag is 1/4 to 1/3 of the suspension’s total travel. That’s between 30 and 35 millimeters for sport, sport-touring and standard bikes or 25-35 millimeters for road race bikes. The FREE sag, which applies only to the rear suspension and uses the same system of measurement, should be between 2 and 8 millimeters. The stiction should be between 2 and 5 millimeters.
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