The fork tubes are the polished inner tubes that slide into the outer legs. The seal runs on their surface. Gaiters (also called boots or gators) are rubber sleeves that cover the tube and keep dirt and stones off it.
What it does
A smooth tube lets the seal hold oil in and dirt out. A dent, rust pit or scratch on the tube cuts the seal lip and the fork leaks. Gaiters protect the tube from grit and from flying stones. The tubes are also clamped by the pinch bolts in the yokes, so they keep the front wheel in line.
Signs it is worn or failing
- Oil on the tube or leg: Oil leaking from a fork leg.
- Leaks again soon after fitting new seals: Fork leaks again soon after new seals.
- Dents, scratches, rust or a rough feel under a fingernail.
- Legs twisted or not parallel: Fork legs are twisted or uneven.
When to replace it
Dinged or rough tubes will wear out any new seal, so replace the tube. Do not straighten a bent tube. Fit gaiters if the tubes are clean but the bike is ridden on dusty or stony roads.
What to match when buying
- Tube diameter, length and model. Tubes for different models can look the same but differ in length.
- Gaiters: tube diameter at the top and bottom, and length.
- Buy new seals and dust seals with a new tube.
Fitting notes
- Check the tubes with a clean cloth and fingers: Inspect the front forks.
- Clean the tube and seal regularly: Clean fork seals.
- After refitting, tighten the pinch bolts evenly to the value in your bike's manual.