You've found a bike that looks perfect. The price is right. The photos look good. Before you hand over any money, run through these five checks. They take five minutes and could save you hundreds, or keep you safe.
1. Check the Frame Number
This is non-negotiable. Every bike has a serial number, usually stamped under the bottom bracket shell.
Why it matters: It's the only reliable way to check if a bike is stolen. Cross-reference it with BikeRegister and your local police database.
Red flag: The seller can't find the serial number, or the area where it should be stamped looks filed or altered.
2. Inspect the Frame for Damage
Run your hands over the frame, especially around:
- Head tube, where the fork meets the frame. This takes the most crash force.
- Down tube / seat tube junction, common stress point.
- Chainstays, look for cracks near the dropout.
- Underneath the bottom bracket, stone chips are fine; cracks are not.
For carbon frames: Tap gently with a coin. A dull thud (instead of a clear ring) can indicate delamination. Be especially thorough around any areas with paint touch-ups, they may be hiding damage.
For aluminium frames: Look for wrinkles, dents, or bulges. Aluminium doesn't give warning before it fails.
3. Check the Drivetrain
The drivetrain (chain, cassette, chainrings) is the most expensive wear item on a bike.
Quick chain check: If you don't have a chain checker, pull the chain away from the front chainring at the 3 o'clock position. If you can see daylight between the chain and the ring, the chain is worn.
Cassette check: Look at the teeth. They should be symmetrical. Shark-finned teeth (hooked to one side) mean the cassette needs replacing.
Cost implication: A full drivetrain replacement (chain + cassette + chainrings) costs £100-300 depending on the groupset. Factor this into your offer price.
4. Spin the Wheels
Lift each wheel off the ground and spin it. Watch the gap between the rim and the brake pad (or fork, if disc brakes):