Tyre Safety Guide: Tread Depth, Pressure, and MOT Requirements

Tyres consistently rank among the top three causes of MOT failures in the UK, yet the checks involved are simple enough for any driver to carry out at home. Understanding the minimum tyre tread depth MOT UK requirements, how to check tyre pressure, and what else the tester examines can save you the cost and inconvenience of a retest.

Minimum Legal Tyre Tread Depth in the UK

The legal minimum tread depth for cars and light vans in the UK is 1.6mm, measured across the central three quarters of the tyre's width and around the full circumference. At the MOT, any tyre measuring below 1.6mm in the required area results in an immediate failure — categorised as a "dangerous" defect.

The tyre tread depth MOT UK minimum is a legal floor, not a recommended maintenance threshold. Most tyre safety organisations recommend replacing tyres at 3mm, as braking distances in wet conditions increase significantly between 3mm and 1.6mm. At 1.6mm on a wet road at 70mph, stopping distances can be up to 44% longer than at 3mm.

To check tread depth at home, use a tread depth gauge (available for around £3–£5) or use the 20p test: insert a 20p coin into the main tread grooves. If the outer band of the coin is visible, your tread is likely below 3mm and the tyre should be inspected professionally.

What the MOT Tester Checks on Tyres

At the MOT, the tester inspects each tyre (including the spare on older vehicles where applicable) for the following:

• Tread depth: measured at multiple points across the tread width to confirm it meets the 1.6mm minimum across the central three quarters.
• Tyre condition: the tester looks for cuts, bulges, lumps, or exposure of the ply or cord structure. A single cut more than 25mm long or deeper than 10% of the tyre's section width is a dangerous failure.
• Correct fitment: mismatched tyre sizes on the same axle, or a tyre fitted inside out, will fail the MOT.
• Type compatibility: mixing radial and cross-ply tyres on the same axle is an automatic failure.
• Valve condition: damaged or leaking valve stems are noted as advisories or minor defects.

Tyre pressure is not directly measured at the MOT, but severely under-inflated tyres that show visible structural distortion may be flagged.

How to Check and Set Tyre Pressure

Correct tyre pressure is critical for safety, fuel economy, and tyre longevity. Your vehicle's recommended pressures are found on a sticker inside the driver's door jamb or in the owner's handbook. Pressures are usually given in PSI (pounds per square inch) or BAR, and often differ between front and rear axles and between lightly loaded and fully laden conditions.

Check pressures when the tyres are cold (before driving more than two miles). Most petrol station forecourt compressors are accurate enough for this purpose. Digital tyre pressure gauges provide a more convenient home check and cost around £10–£15.

Common signs of incorrect tyre pressure to watch for before your MOT:

• Under-inflation: excessive wear on the outer edges of the tread, the tyre appearing "flat" when viewed from the side, poor fuel economy, and sluggish steering response.
• Over-inflation: accelerated wear in the centre of the tread, a harsher ride, and reduced grip in corners.

Uneven Tyre Wear and What It Means

Uneven tyre wear is often a sign of an underlying mechanical problem that will itself be checked at the MOT. Examples include:

• Feathering or sawtooth wear: typically caused by wheel misalignment (tracking out of specification). A wheel alignment check costs around £30–£60 at most tyre fitters.
• One-sided shoulder wear: often indicates excessive camber angle, which may be caused by worn suspension components such as control arm bushes.
• Diagonal wear patterns: can indicate worn shock absorbers that cause the wheel to bounce and scrub unevenly.

Replacing tyres without addressing the underlying alignment or suspension fault will result in rapid wear on the new tyres — and another MOT failure.

Preparing Your Tyres Before the MOT

In the week before your MOT, carry out a thorough tyre check using this simple routine:

• Check tread depth at the centre and both shoulder edges of each tyre.
• Inspect the full circumference of each sidewall for cuts, bulges, or cracking.
• Check and adjust tyre pressures to the manufacturer's specification.
• Ensure all four tyres are the same size and type on each axle.

If any tyre is borderline on tread depth (below 2mm), it is worth replacing it before the test rather than risking a failure. A part-worn tyre at a budget fitting centre is often cheaper than the cost of a retest and the time involved.

See what failures were recorded on your car's last test by running a quick MOT check or browse the full common MOT failures guide to understand what else to check before your test.