To set motorcycle suspension sag, measure the suspension fully extended, measure it again with you sitting on the bike in riding position, and subtract the second number from the first. That difference is rider sag. If it's outside the target range for your bike, adjust spring preload and measure again. Do the rear first, then the front, and you'll have a bike that sits at the height and balance its designers intended.
What sag is and why it matters
Sag is how far the suspension compresses under load before you hit a bump. Getting it right does three things:
- Leaves travel in both directions. The wheel can drop into dips as well as rise over bumps.
- Sets the bike's attitude. Front and rear sag together change steering geometry, which affects how quickly the bike turns and how stable it feels.
- Shows if the springs suit you. If you can't reach the target sag with the preload adjuster, the spring rate is probably wrong for your weight.
Key terms
| Term | Meaning |
|---|---|
| Free sag (static sag) | How far the bike settles under its own weight, no rider |
| Rider sag (race sag) | How far it settles with you aboard in full gear |
| Preload | How much the spring is compressed before any load, set by the adjuster |
| Stiction | Friction in seals and linkages that stops the suspension settling exactly |
Penske Shocks puts the preload rule simply: tightening the preload adjuster adds preload and reduces sag; loosening it does the opposite.
What you need
- A helper (two is better)
- A metric tape measure or a sag measuring tool
- A pencil or tape to mark reference points
- Rear stand or a way to lift the rear wheel off the ground
- Preload adjustment tools: a spanner wrench, hex key or the bike's preload knob
- Your riding gear
- Owner's or service manual for sag targets and adjuster details
How to set motorcycle suspension sag: rear
1. Pick reference points
Choose a fixed point on the rear axle (the center of the axle bolt) and a point directly above it on the frame, fender or side panel. Mark it with tape. Measure in a straight vertical line.
2. Measure fully extended (L1)
Lift the bike so the rear wheel is off the ground and the suspension hangs fully extended. Measure from the axle to your mark. Race Tech calls this measurement L1.
3. Measure with the rider aboard, accounting for friction
Get on in full gear and sit in your normal riding position with feet on the pegs (on a dirt bike, Race Tech has the rider stand on the pegs). A helper holds the bike upright. Don't grip the bike with your knees, and stay still.
Seals and linkages create friction, so the suspension can stop in slightly different places. Race Tech's method handles this with two readings:
- L2: Have a helper push the rear down about 15 mm and let it rise slowly. Measure.
- L3: Have the helper lift the rear about 15 mm and let it settle slowly. Measure.
4. Do the math
Race Tech's formula is: sag = L1 − ((L2 + L3) ÷ 2). In plain words, average the two loaded readings and subtract that from the fully extended reading.
Race Tech also points out that if L2 and L3 differ by more than about 4 or 5 mm, the linkage probably needs attention, since too much friction makes the suspension work poorly no matter what you set.
5. Measure free sag the same way
Repeat with no rider on the bike. Free sag helps you judge whether the spring rate is right.
How to set front sag
The front follows the same idea, measured along the fork tube:
- Fully extended (A). Lift the front until the fork is fully extended (on a front stand, or by lifting the bars with the bike secured). Measure from the bottom of the fork's top clamp or the fork seal to the axle or the lower fork leg.
- Rider aboard (B1). In riding position, have a helper push the bars down and release. Measure.
- Rider aboard (B2). Have the helper lift the bars slightly and release. Measure.
- Calculate. Average B1 and B2 and subtract from A, as Penske Shocks describes.
Typical sag targets
Your bike's manufacturer or suspension maker may give exact numbers. As a starting point:
| Use | Front rider sag | Rear rider sag |
|---|---|---|
| Street riding | Around 35–45 mm | Often around 30–35 mm |
| Track riding | Around 30–35 mm | Often around 25–30 mm |
| Off-road (long-travel dirt bikes) | Varies; check the manual | Often around 95–105 mm |
The front street and track ranges come from Penske Shocks. Other figures are common starting points, not rules. Long-travel suspensions use much larger numbers, and many riders and tuners work in percentages of total travel instead. Always use your bike's spec when one exists.
Adjusting preload
- Rear threaded collar: Loosen the lock ring with a spanner, turn the adjusting ring to compress (more preload) or relax (less preload) the spring, then lock it.
- Rear ramp collar: Rotate to the next step with a spanner. Coarse but quick.
- Remote or hydraulic knob: Turn the knob, common on touring and adventure bikes.
- Front: Many forks have a nut or hex on the fork cap. Turn both legs the same amount. Forks without adjusters may need spacer changes.
Make small changes, then measure again. Record the settings.
Reading the results
| What you find | Likely meaning |
|---|---|
| Rider sag too high, even with lots of preload | Spring too soft for your weight |
| Rider sag OK but almost no free sag | Spring too soft, preloaded heavily to compensate |
| Rider sag too low, even with minimum preload | Spring too stiff |
| Large difference between L2 and L3 | Too much friction in seals or linkage |
If the springs are wrong, a different rate is the fix. See progressive vs linear fork springs and how to choose a motorcycle rear shock.
Common mistakes
- Measuring at an angle instead of straight up and down
- Skipping the friction check (one reading instead of two)
- Setting the rear and forgetting the front, or the reverse
- Setting sag without gear and luggage you normally carry
- Turning fork preload adjusters by different amounts
- Expecting preload to fix a worn-out shock
When to see a mechanic
Get professional help if:
- You can't reach a reasonable sag with the adjuster range
- A shock leaks oil, or the fork seals are leaking
- The suspension tops out, bottoms out or pogoes even with correct sag
- The bike weaves or wobbles at speed (stop riding and have it checked)
- You need new springs, a revalve or a shock rebuild
A motorcycle suspension repair shop can set sag, fit springs and rebuild dampers. Our shock replacement cost guide covers typical prices, which vary by bike, region and shop. To find a local shop, see the motorcycle repair directory.
Frequently asked questions
What is the difference between free sag and rider sag?
Free sag (also called static sag) is how much the bike settles under its own weight. Rider sag (race sag) is how much it settles with you aboard in riding position and gear.
Does adding preload make the suspension stiffer?
Not exactly. Preload changes ride height and sag, not the spring rate. A spring that is too soft for you stays too soft even with more preload, which is why a new spring is sometimes the real fix.
Do I need to reset sag when carrying a passenger or luggage?
Usually yes, at least at the rear. Many touring bikes have a quick preload adjuster for exactly this. Check your owner's manual for recommended settings.
How often should I check sag?
Check it when you get a bike, after any suspension work or spring change, when your riding gear or load changes a lot, and if handling starts to feel off.
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References
- Race Tech: Setting Sag the Race Tech Way (racetech.com)
- Penske Shocks: How to Properly Set Your Motorcycle Front Suspension Sag (penskeshocks.com)