The inner tube is a rubber ring inside a tube-type (TT) tyre that holds the air. Its valve pokes through a hole in the rim. Most spoked wheels need a tube, because air leaks out through the spoke holes. A rubber rim tape protects the tube from the spoke nipples.
What it does
The tube holds air pressure; the tyre gives it shape and grip. A tube loses air fast when punctured, so a flat comes on suddenly. Tubes are pinched during fitting, chafed by sharp spoke ends or a missing rim tape, and damaged if ridden flat.
Signs it is worn or failing
- Flat tyre: Flat tyre on a wheel with an inner tube.
- Slow loss: Tyre slowly loses air.
- Valve tilted or leaking: Air leaking from the tyre valve. A tilted valve means the tube has slipped on the rim; low pressure is the usual cause.
When to replace it
Replace a tube with a large cut, a split near the valve, many patches, or perished rubber. Fit a new tube with every new tyre. A small puncture can be patched, but a new tube is safer at speed.
What to match when buying
- The tube size printed on it must match the tyre size, for example 2.75/3.00-17 or 90/90-17. Many tubes cover a range; check the tyre size falls in it.
- Valve type and length: straight or bent. Match the old one so it reaches through the rim.
- Never put a tube inside a tyre on a rim made for tubeless only unless the tyre maker allows it; the rim edge can chafe and overheat the tube.
- Heavy duty tubes resist punctures better on rough roads. Avoid thin, cheap tubes with poor seams.
Fitting notes
- Inflate a little to remove folds, then fit. Use levers carefully near the valve to avoid pinching.
- Check the rim tape covers every nipple and no spoke end sticks out.
- See Repair a puncture in an inner tube and Replace a tyre.
- Fit the tube with the tyre's light balance mark beside the valve. Pump in a little air first so the tube holds a shape and is harder to pinch with the levers.
- Many dirt bikes have rim locks that stop the rim turning inside the tyre and tearing out the valve at low pressure. Work the bead round them with care.
- If no rim tape is available, a few turns of strong tape over the nipple ends is a stopgap.