Motorcycle suspension, explained simply

Preload sets how much your spring is already compressed at rest, which sets your sag — how far the suspension settles under your weight. More preload means less sag and the bike sits higher; less preload means more sag and it sits lower.

Compression damping controls how fast the suspension compresses — over a bump, under braking, or under load. More compression damping means slower to squish: firmer, with less dive and less bottoming. Less means softer, moving more freely.

Some bikes split this into low-speed compression (slow movements like braking and cornering) and high-speed compression (sharp hits like potholes and expansion joints). "Speed" here means how fast the suspension shaft is moving, not how fast you're riding.

Rebound damping controls how fast the suspension extends back after being compressed. More rebound damping means a slower, more controlled return; less means a faster, livelier one.

Packing down is worth understanding: with too much rebound damping the suspension can't fully extend between closely spaced bumps, so each one starts from a lower position than the last. The bike gradually runs out of travel and gets harsher the rougher the road gets.

The quickest way in is usually the feeling, not the theory. Start here:

Where you feel it: through the bars and your hands means front. Through the seat and pegs means rear.

When it happens: under braking or as you tip in is usually front. Under acceleration, over the rear wheel, or with a passenger or luggage aboard is usually rear.

• Whole-bike wobble or float → check tires, pressure and sag at both ends first.
• Adjust one end at a time so you can feel what each change did.

Wrong tire pressure feels a lot like a suspension problem — harsh, vague, poor grip, odd handling — so always check it before touching your suspension. It's free and takes two minutes.

Measure cold — before you ride, or after the bike has sat a few hours. Pressure climbs as tires warm up, so a hot reading looks higher than it really is.

Use your bike's recommended pressure, from the owner's manual or the sticker on the swingarm or chain guard — not the big number on the tire sidewall. That sidewall figure is the tire's maximum, not the recommended setting.

Carrying a passenger or luggage? Many bikes list a higher rear pressure for that — use the loaded figure.

Check pressures about weekly and before any long ride — tires quietly lose a pound or two a month, and cold weather drops them further. Use your own decent gauge, not the gas-station one.

Sag is how much the suspension settles under weight, and it's the foundation of a good setup — most problems, especially at the rear, trace back to it. You set it with preload, before touching damping.

Two kinds of sag

• Rider sag — with you aboard in full gear. The main setting; it sets ride height and geometry.
• Static sag — the bike under its own weight, no rider. A spring-rate check (more below).

What to aim for

Roughly 30% of your total travel at each end. Typical rear is about 30–40 mm; sport and track setups run a little less, adventure and touring a little more.

• Too much rider sag → soft, wallowy, bottoms out → add preload.
• Too little → harsh, skittish, tops out → back off preload.

How to measure rider sag with a helper (the accurate way)

Wear your full gear and set tire pressure first. At each end you compare a topped-out length to a loaded length:

• Rear: on a stand with the wheel just off the ground, measure straight up from the axle to a fixed point (a bolt on the tail or fender) — that's topped-out. Off the stand, sit on it in gear with your feet on the pegs and a helper steadying you; bounce and let it settle; measure again. Rider sag = topped-out − loaded.
• Front: same idea — lift by the bars until the forks fully extend for topped-out, then measure with you seated normally.

Measuring sag solo

• The free method: slide a zip-tie down a fork stanchion (the shiny inner tube) to the dust seal. Back up near a wall, get on in gear with a hand on the wall to steady yourself, load the suspension, then get off gently and measure how far the zip-tie moved — roughly your front sag. Approximate, but it gets you close.
• The easiest accurate way: a digital sag gauge clips to the axle and shows sag on your phone while you sit on the bike — no helper, no maths.

Static sag — is your spring rate right?

You don't set this one. You set rider sag with preload — static sag is then just whatever the spring gives you. Bike upright, no rider, measure loaded again: static sag = topped-out − this. Numbers vary, so it's a ballpark, not a target: about 10–15 mm at the rear, 25–30 mm at the front.

This one reads backwards. On its own, more sag means a softer spring — but you've already spent preload getting rider sag right, and that preload is holding the bike up now. So static sag shows how much preload it took:

• Lots of static sag — you barely needed preload → spring's probably too stiff for you.
• Little static sag, or it tops out when you dismount — you needed a lot of preload → spring's probably too soft.
• Rider sag right, static sag still way off → the spring rate is wrong for your weight, and preload won't fix it. That's a spring swap.
• Can't reach the target at all, or only reach it by flattening static sag to nothing → same verdict. Most often it means the spring is right for solo and wrong for the load you are actually carrying.

Common mistakes

• Measuring without your riding gear on.
• Not setting tire pressure first.
• Reading off-centre, or from the wrong points.
• Ignoring stiction — average two readings.

• Set sag first, then damping.
• Check tire pressure before chasing suspension — wrong pressure mimics suspension problems.
• One change at a time, small steps, and note what you did.
• Never tune around damage, leaks or worn parts — fix those first.
• Preload changes ride height, not spring rate. Damping changes speed of movement, not ride height.