What exactly is Sag?

HUSK,
Sag is how far the rear suspension compresses when you sit on the bike. It can be measured from the rear seat mount bolt to the rear axle.
To take the measurement, first unload the rear susp., let the bike settle slowly, then take a measurement. Next, either sit on the bike (in full riding gear) or stand on the pegs, and have someone else measure between the same points as before.
The difference, or sag, should be between 90 and 100mm to the best of my knowledge. This probably differs from bike to bike. Your owners manual should tell.
To increase the sag, simply decrease the tension on the rear spring by loosening, or raising, the nuts(or whatever they're called) on top of the spring. This can be done with a spanner wrench or, as I did mine today, with a large round punch and a hammer(careful). To decrease the sag, just tighten the nuts to compress the spring.
Obtaining the proper sag adjusts the rear spring tension specifically to your weight.
I'm no expert here so, if any of this is wrong, someone please correct me.
Hope this helps.
Alyn.

I believe "free sag" is how far the weight of the bike compresses the suspension. "Race sag" should be how far your weight compresses it past the "free sag" point.
Yes, you should adjust the sag before all other settings.
It does make a difference in the way your bike handles, mainly because the suspension is set up properly.

Free sag = bike under it's own weight only
Race sag= bike and rider
Boh measurements are the difference from fully extended.

I know this post is a bit old but I just want somebody to elaborate on it a bit. Firstly my bike is a 2000 CR125. I assume moving the two nuts up and down on the shock is the way I adjust the Race Sag on my bike aswell but how is the static sag adjusted? Also how do I know when I have reached the limits of the current spring(with regards to the sag) and should change it?


Thanks very much,

You are right, you adjust it by turning the collars or nuts on the shock down or up to preload, or unload the spring. Your static sag, or free sag is dependant on the spring and amount of preload on it. First set your sag or race sag to 100mm or thereabout. After that is set, measure the static sag. If static is less than about 15mm, then you need to get a stiffer spring. If it is more than 25mm, you will need a softer spring.

Great, thanks!