Monday, October 19, 2009
Today I would like to talk about setting the sag on your motorcycle. This is probably one of the most misunderstood, yet simple things to set up. First, you’re going to need a helper, a tape measure and a pad of paper to scribble on. You will also need to get your total suspension travel from your owner’s manual or some other reference material.
We need to take three measurements. R1; unloaded sag, R2; static sag, and R3; rider sag. What you do is measure from your axle straight up to some point fixed on your bike. See the photo. The first measurement, R1 is taken with the suspension fully extended. All weight is removed from the bike by either putting it on a center stand, work stand, or by pulling it over on the side stand while your friend measures.
Then measure for R2, which is the “Static Sag” is with the bike only carrying it’s own weight, off the stand, balanced upright. The third is R3, which is taken with you on the bike, at least a half of a tank of fuel, all your gear and what load you normally carry. I find that I can balance near a wall using my elbow to keep me right at that balance point while my friend measures.
Now that we have those numbers, you will need your total travel from your owners manual. I am going to use 10” of suspension travel as an example. Your bike should squat (R3) 30% of your total travel. In our example’s case, that should be 3”. If you squat more than 3”, you need more preload into your rear spring. If you squat less than 3”, remove some preload.
Ok, so where does R2, the static sag come in? Good question. You bike should squat from .5” to 1” depending on the bike you have under it’s own weight. If you have to put in so much preload on the spring to get your R3 number correct that you have less than .5” of static sag, your spring is too soft and you need a stiffer spring.
If your rider sag is correct, but you have more than an inch of static sag, your spring is too soft. And obviously, if you can not get your rider sag correct with your stock spring no matter how much preload you put in or take out, you need to go stiffer or softer with your spring.
Getting your spring settings correct can totally transform how your bike handles and should be done immediately after getting a new bike. It is one of the cheapest modifications you can do to your bike that gain the most in return.
In my next article I will talk about setting the sag in your forks.