Fork oil level calculator

The oil level (air gap) affects how much the fork firms up at the end of its travel. The calculator works out how much oil to add or remove to reach the level you want.

Result

Level does not change
Add to each leg	ml
Remove from each leg	ml
Both legs together	ml
Oil per 1 mm of level	ml
Air gap volume (one leg)	now ml → after ml

The calculation is based on the tube inner diameter. The cartridge and inner tube take up some space, so the actual air gap volume is slightly smaller.

Results are calculated estimates. Always check your vehicle manufacturer's instructions.

Matching products: Front shock oils Suspension springs

How to use

Remove the spring and push the fork fully down.
Pump the fork a few times to bleed the air, then measure the oil level from the top of the tube to the oil surface.
Enter the tube inner diameter (e.g. 41 mm) and the current and target level.
Add or remove the calculated amount with a syringe, check the level again and repeat on the other leg.

Frequently asked questions

What does the oil level change?

A higher oil level (smaller air gap) makes the end of the stroke firmer and reduces bottoming. A lower level makes it softer. The oil level does not significantly change spring rate or damping.

Can I calculate the fill volume with a formula?

No. The damper cartridge and spring take up space inside the fork, so take the fill volume from the service manual. The calculator is for changing the level, because a small change depends mainly on the tube inner diameter.

How big a change is sensible?

The level is usually changed 5–10 mm at a time. Stay within the manufacturer's range – too small an air gap can hydraulically lock the fork at the end of its travel.

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