You will need at least 1 person to help you measure your bike’s sag. It is easiest if you have 2 people to help you throughout the process. You can also flip over a sturdy 5 gallon (18. 9 L) (18. 92 L) plastic bucket or a milk crate to use as a makeshift stand.
Make sure that this fixed point is on the arc that the rear axle moves in when the shocks compress. If it is not, pick another spot on the side panel or fender that is and mark it so you can take all the measurements using the same reference point. This measurement is called the unloaded sag because there is no weight on the shock springs.
Don’t ever measure the sag of your bike on a slope or you will not get accurate numbers.
Make sure the bike has proper fluid levels and at least half a tank of gas as well. The idea is to mimic your normal riding conditions as closely as possible so the sag you measure is accurate and you can adjust it properly.
The sag measurement with a rider is called the rider sag or race sag.
The sag measurement without a rider is known as the static sag or free sag.
For example, let’s say the unloaded measurement was 605 mm, the measurement with you on the bike was 500 mm, and the measurement with the bike sitting by itself was 565 mm. Your rider sag would be 105 mm and your static sag would be 40 mm.
You might have to hit the punch more than once to loosen the lock nut. Hit it as many times as necessary to start turning the lock nut counterclockwise.
Don’t worry too much about how far you loosen the lock nut right now. The idea is just to give yourself some room to work with the bottom lock nut so you can adjust the sag. If the top lock nut is still hard to turn, you can spray some WD-40 on the shock spring’s threads to lubricate them.
For example, a 50cc-65cc dirt bike should have a rider sag of 70 mm and a static sag between 25-35 mm. A dirt bike with a 125cc-450cc engine should have a rider sag of 102-105 mm and a static sag from 30-40mm.
Keep in mind that 1 full rotation usually equates to a 2-3 mm adjustment to the sag. You can check your bike’s owner’s manual or search online to find the exact recommended ranges for your specific dirt bike.
For example, if you want your bike’s rider sag to be 102-105 mm and it is currently at 107 mm, tightening the bottom lock nut 1 full rotation will decrease the sag to about 104-105 mm.
This will hold the bottom adjuster ring in place so the stag stays set.
You don’t need to measure the unloaded sag with the bike on a stand again. You can use the same number you got before to calculate the new rider sag and static sag. You can repeat the adjustment process, tightening or loosening the shock spring’s adjustment nut as required, until you set the sag exactly where you want it. Turn the adjustment nut less than 1 full turn if you want to make very minor adjustments of less than 2 mm.
