How to Check Tyre Tread Depth, and What the Tyre Is Telling You

You are stood on the drive and something about a tyre has caught your eye. Maybe it looks flatter on one side, maybe the grooves look shallow, maybe you just have not looked in a while.

Here is how to check tyre tread depth properly, and more usefully, how to read what the tyre is telling you. Depth is one number. The pattern of wear is a diagnosis, and it is free.

The two minute version

You need no tools. A coin will do, and every tyre already has a built-in gauge you may not know about.

1. Park somewhere flat and turn the wheels to full lock so you can see the front tyres properly.
2. Look for the wear bars: small raised ridges of rubber sitting in the bottom of the main grooves, spaced around the tyre.
3. Run a fingertip across one. If the bar is flush with the surrounding tread, that tyre is at the legal minimum and needs replacing now.
4. Check the outer edge, the middle and the inner edge separately. They wear differently and the inner edge is the one nobody looks at.
5. Repeat across all four, and do not skip the spare if you have one.

The wear bars are not a rough guide. They are moulded in at the legal minimum depth deliberately, so a bar level with the tread means the tyre is finished, not nearly finished.

The coin test, and why depth alone is not the whole story

If you want a number rather than a yes or no, a coin gives you a usable approximation. Insert one into the main groove and see how much of the outer band disappears. If the band is visible, the tread is getting low and you are into replacement territory.

Do it in at least three places around the tyre and across the width, not once. A tyre can be perfectly legal at the point you happen to test and worn out three inches away, which is exactly the situation the single-check habit misses.

Worth knowing what the legal minimum actually buys you: it is a floor, not a recommendation. Wet braking and resistance to aquaplaning fall away well before a tyre reaches it, so a tyre that is legal in December can be a genuinely poor tyre by February. Many people replace before the limit for that reason rather than out of caution.

Reading the wear pattern, which is the useful part

Even wear across the tread means the tyre is doing its job and the car is set up correctly. Anything else is a symptom, and the shape of it usually names the cause.

• Both edges worn, middle fine: chronic underinflation. The tyre is running on its shoulders.
• Middle worn, edges fine: chronic overinflation. The centre is carrying the load on its own.
• One edge only, usually the inner: an alignment or suspension issue. This is the one people find far too late because the inner edge faces away from you.
• Patchy or scalloped dips around the tyre: worn suspension components letting the wheel bounce.
• A saw-tooth feel when you run a hand along the tread in one direction: feathering, again alignment.
• One tyre far worse than its pair: something specific to that corner, not a driving-style issue.

The useful habit is to run a flat hand across the tread rather than only looking. Feathering and cupping are much easier to feel than to see, and both are telling you about something other than the tyre.

Do not stop at the tread: read the sidewall

Plenty of tyres are taken off the road for something on the sidewall while the tread still has years in it. The sidewall carries the load and has no steel belt behind it, so damage there matters more than the same damage in the tread.

• A bulge or egg-shaped lump: the internal casing has failed and the air is pushing out through the remaining rubber. This one is not a wait-and-see. Stop using the tyre.
• A cut deep enough to show fabric or cord: finished, regardless of tread depth.
• Fine surface cracking across the sidewall: age and ultraviolet exposure. Worth watching, and worth taking seriously on an older tyre.
• A scuff from a kerb that has only removed surface rubber: usually cosmetic, but worth a proper look at the inside face too.
• Any distortion or flat spot in the profile when the tyre is correctly inflated: get it looked at.

Sidewall damage is also why run-flat and low-profile tyres are less forgiving of a hard kerb strike than a tall soft-sidewalled tyre. There is simply less rubber between the rim and the kerb.

How old is too old?

Rubber ages whether you drive on it or not. A tyre that has spent six years on a car doing two thousand miles a year can be more of a problem than one that has covered thirty thousand in two.

Every tyre carries a four-digit date code on the sidewall: the week and the year it was made. It is worth knowing where yours is, particularly on a caravan, a trailer, a classic or a second car that sits still for months at a time.

There is no single expiry date, and anyone who gives you one confidently is oversimplifying. What is fair to say is that an older tyre with surface cracking, on a vehicle that sits outside and rarely moves, deserves a proper inspection rather than a glance.

When to just get someone to look

Checking tread is genuinely a two-minute job you can do yourself. There are a few findings where the sensible next step is somebody with the car on a ramp.

• Wear concentrated on one edge, which usually means alignment and will eat the replacement tyre too if it is not corrected first.
• Any cupping or scalloping, which points at suspension rather than tyres.
• A bulge, a cord-deep cut, or anything you are unsure about on a sidewall.
• One tyre wearing far faster than the other on the same axle.
• A vibration or a pull that has appeared alongside the wear.

The point is not to worry you. It is that fitting new tyres to a car with an alignment fault is buying the same problem twice, and a check costs a fraction of a set.

A sensible routine

Once a month, with the pressures, is plenty for most people. Walk round, look at all four, feel the tread with a flat hand, glance at the sidewalls.

Do it before a long trip and before winter, because those are the two moments when marginal tread stops being marginal. And do it in daylight, because a torch flatters a tyre and a low sun shows up every irregularity in the tread.