Setting your rear sag is the one of the most important parts of insuring your suspension is set up correctly. The spring must be the correct rate, this is checked by measurements which is described below. The spring on your bike is only holding you in the correct part of the stroke for the valving to work correctly. If the spring is to soft, you will be sitting to far into the stroke and out of the "Meat" of the valving. Causing it to feel very harsh. Take a few minutes to measure the sag. If you cannot get the sag correct you will need a different rate. This should be the very first thing you check and get correct for your suspension. If the springs are correct, the valving cannot work properly.
Motocross Dirt Bike ”SAG” = Measurement A minus Measurement B
Place the bike on a stand, wheels un-weighted… and measure from the left inside fender bolt, or a easy access point to where the back fender comes in contact with the side panel, to a point on the rear axle in MM. You should use a metric tape measurer or a sag measuring tool to guarantee accuracy.
Now take the bike off of the stand, place the rider on the bike in a normal riding position over the middle of the foot pegs. Be sure all riding gear is worn in order to use the most accurate weight on the springs for the SAG measurement. Have a friend measure the exact same two points as measured above when attaining measurement A (measure from the left inside fender bolt to a point on the rear axle). Measure the number of MM for B.
SAG = A minus B (NOTE: 1” = 25.4mm)
As a rule of thumb, SAG should range from 95mm to 110mm (Big bikes with a linkage), 100mm to 105mm near optimal. This optimal number changes depending on the model of your bike and type of riding you plan on doing, so check your manual. However, for us, 105mm is a good starting point to adjust the SAG.
Too much rider sag indicates you must increase pre-load to the spring by turning the Spring / Pre-load Adjuster clockwise (decreases rider sag measurement). Too little rider sag indicates you must decrease pre-load to the spring by turning the Spring / Pre-load Adjuster counter clockwise. (increases rider sag measurement).
Next you will need to check the Static SAG, typically called Free SAG. To adjust your FREE SAG, you will use the exact measurement you obtained in measurement A….and will subtract measurement C from it.
Static Sag (Free Sag): = Measurement A minus Measurement C
With the bike off the stand and the rider off the bike; push down on the back end and let the bike come up by itself. Measure between the exact same two points you used to get A and B. Measurement A minus Measurement C is your FREE SAG.
As a rule of thumb, Free SAG is generally 25 – 45mm.
If you set your rider sag and your free sag does not fall within the recommended range; a spring change may be needed. Spring change meaning that your spring is either too much or not enough for your weight. Less than 25mm generally indicates a stiffer spring is needed and more than 45mm indicates a softer spring is needed.
Call 813-714-2038 if you need us to run our spring calculator for you and get the correct springs.
SAG SETTINGS BY BIKE
Yamaha 125/250cc 2 Strokes 102mm 250f/450f 104mm 85cc 90mm
Suzuki 125/250cc 2 Stroke 100mm 250f/450f 105mm
Kawasaki 125/250cc 2 Stroke 103mm 250f/450f 104mm 85/100cc 90mm 65cc 70mm
Honda 125/250cc 2 Stroke 102mm 250f/450f 105mm 85/150f 90mm
KTM Big Bikes W/Link 108mm W/Out Link 125mm 85cc 100mm 65cc 75mm 50cc 60mm
Cobra 50cc 60mm 65cc 75mm