What sag actually measures
Sag is how much the suspension compresses under the bike's own weight (static sag) and under your weight in riding gear (rider sag). Correct sag keeps the suspension working through its intended travel range instead of topping out over small bumps or bottoming out under load.
Target sag numbers
| Bike type | Static sag (no rider) | Rider sag (with gear) |
|---|---|---|
| Sportbike | 5–10mm (front & rear) | 25–35mm rear, 30–35mm front |
| Standard/naked | 5–10mm | 30–35mm rear |
| Adventure/touring | 10–15mm | 30–40mm rear |
| Cruiser | 5–10mm | 25–30mm rear |
How to measure rear sag
- Measure distance A from the rear axle to a fixed point on the tail with the bike on a stand, wheel fully extended.
- Remove the stand and let the bike settle under its own weight (have a helper hold it upright); measure distance B.
- Sit on the bike in full gear, feet on the pegs, and bounce gently to settle the suspension; measure distance C with a helper holding balance.
- Static sag = A − B. Rider sag = A − C.
- Adjust preload (not damping) to bring rider sag into the target range, then recheck static sag falls within spec.
Preload vs damping — don't confuse them
Preload sets the spring's starting point and controls sag — it doesn't change spring stiffness. If you need more than the preload adjuster's full range to hit target sag, the spring rate itself is wrong for your weight and no amount of adjustment will fix it.
Damping (compression and rebound) controls the speed of suspension movement, not the amount of sag. Set sag first, always, before touching damping clickers.
Setting damping after sag is correct
- Compression damping: too soft feels vague and wallowy under braking; too stiff transmits harsh bumps directly to the chassis.
- Rebound damping: too fast makes the bike feel like it's pogoing after bumps; too slow causes the suspension to 'pack down' and get progressively harsher over successive bumps.
- Adjust one click at a time and ride the same stretch of road to compare — changing multiple settings at once makes it impossible to tell what helped.
Signs the spring rate is wrong
If you're maxed out on preload and still can't hit rider sag targets, or the bike sits far outside the range with preload backed off entirely, the stock spring doesn't match your weight. This is common for riders well above or below the OEM's assumed 150–170 lb baseline, and the only real fix is a correctly rated aftermarket spring.
Frequently asked questions
- Can I set sag by myself without a helper?
- It's possible using a strap or zip-tie around one fork leg or shock body as a marker, but readings are more accurate with a second person supporting the bike while you sit on it in riding position.
- Do I need to reset sag if I add luggage or a passenger?
- Yes — sag is meant to be adjusted for the load you're actually carrying. Many adventure and touring bikes have quick preload adjusters for exactly this reason.
- How often should suspension be serviced?
- Fork oil and seals are typically serviced every 15,000–20,000 miles, and shocks should be inspected for leaks or fade every service interval. Track use shortens both intervals significantly.
Related guides
Some links on this page are affiliate links. See our affiliate disclosure.