Set your Race Sag!
The single most important thing to make your dirt bike work is setting
your race sag. Adjustments as small as 1/4 inch have a dramatic, obvious
effect on the bikes handling. Don't get your shock rebuilt, don't get a new
tire, SET your RACE SAG!! Then you can check into other stuff...
To set up your sag you will need to take some measurements; You can
set your sag with only R1 and R2, but the others will be helpful in suspension
setup as well. If you don't do anything else, just do R1 and R2, and get them
The first is with the suspension extended, bike on stand with wheels off the ground.
The second is with the rider IN FULL GEAR on the bike. I usually stand on the foot pegs for this measurement.
You'll have to lean on a wall or have an assistant hold the bike upright. Make sure you are balanced, using only
slight fingertip pressure to keep the bike upright.
And the last is the bike supporting it's own weight. Again, it must be balanced as in measurement 2.
These will require an assistant, obviously. The rear measurements can be from anything around the
rear axle to some point on the rear fender, more or less straight up from the axel. It's important to use
the same points each time.
Setting your 'Race Sag'
so your bike has a chance to work right
When you subtract measurement 2 from measurement 1, that is your 'race sag'. Most modern bikes have
12 inches of rear wheel travel, and require 3.75 to 4 inches of race sag. Your owners manual should list
your particular bikes requirements. My bike lists it as 100mm +/- 5mm. If no data is available,
use 1/3 to 30% of the total wheel travel. If it's a full size MX bike (125 through 500), you can set
it to 4 inches and you'll be good to go. There are two spanner type nuts on your shock holding
the spring at the top end. First loosen the upper one (the lock nut) and then adjust by turning the
lower one. You can check as you go make the adjustment without tightening the locknut back down,
just jump on and get the new R2 measurement. R1 won't change.
Front wheel travel is also usually 12 inches. My bike lists the race sag at 80mm +/- 5mm. Check your manual.
When you subtract measurement 3 from measurement 1, that is the 'static sag'. This isn't something you set.
Your static sag should be within the limits given in your owners manual. If it is not, you need to change the
spring, set the race sag, and measure again. My manual lists front and rear static sag at 30mm, +/- 5mm.
If your static sag is too little, it means that you have had to set too much preload to get the race sag in spec.
This means that your spring is too weak. If there is too much static sag, the spring is too strong. A good
suspension shop should be able to tell you what spring rate you will need, based on your bike make and
model, and on your weight. When you get all this right, your bike will perform the way it was designed;
And that means you'll ROCK!!
No helper? Check out the Solo method!