Signs You Need New Tyres: Tread Depth, Cracks and Bulges
Tyres are the only part of your car that touches the road, so their condition affects how well you steer, brake and grip in the rain. The good news is that you can check most warning signs yourself in five minutes, with no tools.
Short version: replace a tyre if the tread is worn to the wear indicators, if there is a bulge or deep cut in the sidewall, or if it is very old. Do not wait until the tread is completely smooth.
1. Check the tread depth
New car tyres usually have around 7 to 8 mm of tread. The legal minimum in many countries is 1.6 mm, but braking distances in the wet get noticeably longer well before that point. Many tyre experts suggest replacing at about 3 mm.
Wear indicators
Look in the main grooves of the tread for small raised bars, sometimes marked with the letters TWI on the sidewall. When the tread wears down level with these bars, the tyre has reached its legal limit and must be replaced.
The coin test
If you do not have a depth gauge, push a coin into the groove. If you can see the whole rim of the coin, the tread is very shallow. A cheap tread depth gauge is more accurate and costs very little.
2. Look for uneven wear
How a tyre wears tells you about your car as well as the tyre.
- Worn on both outer edges: the tyre has often been run under-inflated.
- Worn in the centre: it has often been over-inflated.
- Worn on one edge only: the wheel alignment is probably out. See our guide to tyre rotation and wheel alignment.
- Patchy or scalloped wear: worn suspension parts or wheels that are out of balance.
3. Check the sidewalls
Run your hand carefully around the sidewall and look for:
- Bulges or bubbles. These mean the internal cords are broken. The tyre can burst without warning, so stop using it and replace it.
- Deep cuts or cracks that expose the fabric or cord.
- Cracking in the rubber on old tyres, which is a sign of ageing. See how to check how old a tyre is.
4. Look for objects and damage in the tread
Nails, screws and stones can lodge in the tread. If a tyre keeps losing air, do not just keep pumping it up. Have it inspected. A repair from the inside by a professional is possible for many punctures in the central tread area. Damage in the shoulder or sidewall generally cannot be repaired safely.
5. Pay attention to how the car feels
- Vibration in the steering wheel or seat that gets worse with speed.
- The car pulling to one side.
- Noticeably longer stopping distances or slipping in the rain.
- A humming or roaring noise that is new.
These can have causes other than the tyres, but tyres are the first place to look.
Replace in pairs or sets
When you replace only two tyres, fit the new ones on the rear axle if you can. This helps keep the car stable if you brake hard on a wet road. Ideally, replace all four together with the same size and type, and check the load index and speed rating. Our guide on reading the tyre sidewall explains what to look for.