Static Sag or "Race" Sag is the amount the bike compresses from fully extended, with the rider on board.
Here's how to measure it the Race Tech way. It is a little different but much more consistent and accurate.
- First extend the forks or shock completely and measure from the wiper to the bottom of the triple clamp on forks or from the axle to a vertical reference point on the chassis. This is L1.
- Take the bike off the stand, put the rider on board in riding position. Get an assistant to balance the bike or have the rider hold onto something, comress the suspension about 25 mm (1") and let it extend very slowly (slowly is the critical term). Where it stops, measure the distance between the wiper and the bottom of the triple clamp or the axle and the reference point on the chassis again. Do not bounce. This is L2. (If there were no friction in the seals the bike would come up a little further.)
- Next lift up on the suspension and let it drop very slowly. Where it stops measure again. Do not bounce. This is L3. The reason L2 and L3 are different is due to stiction or drag in the seals and bushings. (If there were no friction in the seals or the linkage the bike would drop a little further.)
- Half way between L1 and L2 is where it would come to rest with no friction. Therefore L2 and L3 must be averaged and subtracted from L1 to calculate true Static Sag.
Static Sag = L1 - (L3 L2)/2
- To adjust Static Sag make longer or shorter preload spacers or use the preload adjusters, if available.
It is important to note that there are no magic Sag numbers. However here are some guidelines to use as starting points. Please refer to the DVS Valving Search for specific guidelines.
|Bike Type ||Front % ||Front (mm) ||Rear % ||Rear (mm) ||Rear Free Sag (mm) |
|Dirt Bikes (>300mm travel) ||22-25% ||65-75 ||30-35% ||95-110 ||25-50 |
|Dirt 80cc Minis ||22-25% ||55-65 ||30-35% ||85-105 ||20-40 |
|Street Bikes ||28-33% ||30-35 ||28-35% ||30-40 ||2-17 |
|Road Race Bikes ||23-27% ||25-35 ||23-30% ||25-35 ||2-17 |
Free Sag is the amount the bike compresses from fully extended without the rider on board. It is used a a guideline to see if the spring rate is in the right ballpark. If the Static Sag is correct and the Free Sag is too small the spring rate is TOO SOFT. If there is too much Free Sag the spring rate is TOO STIFF.