How to set sag on a motocross bike

Sag is how far the bike settles under its own weight and under yours. It sets the ride height of the rear, which changes the steering geometry and how the bike balances front to rear. If sag is wrong, no amount of clicker changes will make the bike feel right, so it is always the first thing to check.

What you need

• A stand that lifts the rear wheel off the ground
• A tape measure (a metal one is easiest)
• A friend to read the measurements
• A C-spanner or punch and hammer to turn the shock's preload rings
• Your full riding gear: boots, helmet and body armour add several kilos

Step 1: Measure the unloaded length (L1)

Put the bike on the stand so the rear wheel hangs free. Measure straight up from the centre of the rear axle to a fixed point on the rear fender or side panel. Mark that point with tape so you use exactly the same spot every time. Write the number down. This is L1.

Step 2: Measure race sag (L2)

Take the bike off the stand. In full gear, stand on the pegs in your normal attack position, with your weight centred and your feet on the pegs, not dabbing the ground. Bounce lightly a couple of times and settle. Your friend measures the same two points again. This is L2.

Suspension has some friction, so for a more accurate number take two readings: one after pushing the rear down a little and letting it come up, one after lifting it a little and letting it settle. Use the average.

Race sag = L1 − L2

Step 3: Compare with the target

Always check your owner's manual first, because the right number depends on the shock linkage. As a starting point:

• Most full-size motocross bikes with a linkage: around 100–105 mm
• KTM, Husqvarna and GasGas models with the PDS (no-linkage) shock: around 105–110 mm

Step 4: Adjust the preload

Loosen the lock ring on top of the shock spring, then turn the adjusting ring:

• Too much sag? Tighten the ring (more preload) to lift the rear.
• Too little sag? Loosen the ring (less preload) to lower the rear.

Go in small steps, one turn at a time, tighten the lock ring and measure again. One turn usually changes race sag by a few millimetres, but it varies between bikes, so always re-measure instead of counting.

Step 5: Check static sag

Static (or free) sag is how far the bike settles under its own weight, without you on it. Put the bike on the ground, let it settle, and measure the same two points. Static sag = L1 − that number.

With race sag set correctly, static sag is usually around 30–40 mm. It tells you whether the spring suits your weight:

• Static sag well under 30 mm: you needed a lot of preload to hold the bike up, so the spring is probably too soft for you.
• Static sag well over 40 mm: you needed very little preload, so the spring is probably too stiff for you.

If either happens, a different spring rate will help more than any clicker change.

Write it down

Sag changes as the shock spring settles and when you change tyres, links or your own weight, so check it every few rides and after any change. Save your sag, preload and clicker settings in MX Rider Pro for each bike, and you can always go back to the setup that gave you your best lap times.