Fork oil controls damping inside the front forks and has a major effect on handling, comfort and bottoming resistance. Correct oil quantity, oil height and viscosity will vary between motorcycle models and fork designs.
Always check the specification for your exact year and model before filling the forks.
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Fork oil quantity is normally listed as a volume for each fork leg, usually in millilitres or cubic centimetres.
This method is commonly used when the forks have been completely drained and rebuilt.
Small amounts of old oil can remain trapped inside the fork, so measuring oil height is often more accurate after servicing.
Fork oil level is normally measured from the top of the fork tube down to the oil surface.
The fork spring is usually removed and the fork fully compressed before taking the measurement.
A smaller air gap means more oil and greater resistance to bottoming near the end of the fork stroke.
| Oil Grade | Typical Use | Effect |
|---|---|---|
| 5W | Light damping or modern cartridge-style forks | Faster fork movement and softer damping |
| 7.5W | General-purpose intermediate setting | Between 5W and 10W damping |
| 10W | Common starting point for many conventional forks | Moderate compression and rebound damping |
| 15W | Heavier riders or worn conventional forks | Slower and firmer fork movement |
| 20W | Older damper-rod forks requiring heavy oil | Significantly firmer damping |
Important: Fork oil viscosity numbers are not always identical between manufacturers. One brand of 10W oil may flow differently from another brand.
Leaking fork seals allow oil to escape and can contaminate the front brake. Inspect the fork tubes for rust, scratches or pitting before fitting new seals.
A normal fork service may require fork seals, dust seals, retaining clips, guide bushes, slide bushes, copper washers and fresh fork oil.
| Oil around the fork tube | Damaged seal, dirt trapped under the seal lip or scratched fork tube. |
| Fork feels too soft | Low oil level, light oil, worn springs or internal wear. |
| Fork feels harsh | Too much oil, heavy oil, excessive spring preload or binding. |
| Forks bottom easily | Low oil height, weak springs or insufficient compression damping. |
| Uneven fork action | Different oil quantities, bent components or incorrect wheel and axle alignment. |
Confirm the motorcycle year, model and fork type. Where possible, measure the fork tube diameter and check the numbers printed on the original seal.
Note: Model specifications can vary between countries and production periods. Always confirm oil quantity, oil height and replacement-part fitment before assembly.