What's the legal tyre tread depth for an HGV?

The number most people remember is for a car. Heavy goods vehicles are held to a different one, and it catches drivers out at the roadside.

Where the tread actually has to be

The 1mm isn't measured on one lucky spot. The law asks for a continuous band of at least 1mm of tread across the middle three-quarters of the tyre's breadth, and around its entire circumference. The original tread pattern must still be visible across the rest of the tyre too.

In plain terms: one bald patch, or a worn shoulder that dips under 1mm around the wheel, fails the whole tyre, even if the centre still looks legal. That's why a proper walkaround means running your eye (and a depth gauge) right across and right round each tyre, not just glancing at it.

Tread isn't the only thing that fails a tyre

Plenty of tyres are pulled at the roadside with legal tread. These are instant prohibitions regardless of how much tread is left:

What it costs if you drive on it

Tyre offences are dealt with at court, not by a fixed penalty. On a goods vehicle over 3.5 tonnes the maximum fine is unlimited: it's a level 5 offence, and the £2,500 level 4 cap only applies to vehicles up to 3.5 tonnes. The court fines you per tyre. Endorsement is 3 penalty points, though a court will normally apply one set of points for several tyres found on the same occasion. An examiner will normally also issue an immediate prohibition, so the vehicle isn't going anywhere until it's put right. Four illegal tyres is a very expensive, very bad day.

The practical rule

Don't run a tyre down to the limit. 1mm is where it becomes illegal, not where it becomes worth changing. Uneven wear means part of a tyre can be under 1mm while the rest looks fine, so plan replacement with a margin, and record the check either way, because the paper trail is what protects you at audit.