How to Check Tyre Tread Depth (and Why 3mm Beats 1.6mm in Winter)

• A car tyre needs at least 1.6mm of tread across the central three-quarters of its width and all the way round, and the MOT files anything below that under Dangerous.
• National Highways recommends changing a tyre at 2mm in summer and 3mm in winter, well before the legal line.
• An illegal tyre can bring a £2,500 fine ($3,350) and 3 penalty points per tyre, while a mid-range replacement costs £75 to £120 ($101 to $161).

The 1.6mm Rule Measures Less of Your Tyre Than You Think

The legal minimum for a car is 1.6mm of tread, and it applies to the central three-quarters of the tread breadth and around the entire circumference of the tyre. The Highway Code sets the same figure for light vans and light trailers. Motorcycles, large vehicles and passenger-carrying vehicles need 1mm.

The measurement is narrower than most drivers assume. The DVSA MOT inspection manual counts only the primary grooves, the deep channels that hold the tread wear indicators or are cut as deep as the ones that do. Shallower grooves and the fine slits called sipes are secondary grooves, and testers ignore them. The strips of tread either side of that central three-quarters can be bald without breaking the rule.

So the reading that counts comes from a primary groove, somewhere in the middle three-quarters of the tyre. A gauge dropped into a shallow side groove will show a number that means nothing at the MOT, and a reading at the shoulder of the tyre falls outside the measured band. The tyre has to pass at every point in that central band, so one good reading on one patch of rubber proves little.

Where and How to Measure Tread

Start with the tyre itself. Look inside the main grooves for the tread wear indicators, the features the MOT manual uses to identify primary grooves. A groove that holds one, or is cut as deep as one that does, is a primary groove and the one to measure. Any shallower groove can be skipped.

A tread depth gauge gives you the actual figure, and the method follows from the rule. Take a reading in a primary groove on the inner side of the central band, one in the middle and one on the outer side. Then roll the car forward and repeat at several points round the circumference, as the law covers the whole tyre and wear is rarely even. Do all four tyres, and do the spare too if you carry one: the MOT inspects only the tyres fitted to the road wheels, but National Highways advises checking the spare.

Run a hand over the tread and sidewall as you go. National Highways adds that cuts and wear can sit anywhere across the tyre, so the sidewall gets a look too. The MOT manual sets out what testers do with cuts. Cord showing on its own is a fail. Cord that appears when a tester gently opens a cut with a blunt tool is a fail. Cord that can be felt but not seen fails when the cut runs past 25mm or 10 percent of the section width, whichever is the greater. Swellings or splits that point to a failing tyre structure sit in the Dangerous category, the one the manual also uses for tread below the limit.

Why 3mm Beats 1.6mm in Winter

The legal limit and the sensible limit are different numbers. National Highways traffic officer Dave Harford, whose patch includes the M5, M42 and M50, gave this advice in August 2021:

“Although the legal limit for tyre tread depth is 1.6mm, we recommend you don’t let the tread get that low. Changing the tyre at 2mm in summer and 3 mm in winter is good practice and maintains overall good tyre performance in all conditions. To check your tyre pressure, visit most fuel and service station forecourts, which have an air machine for checking and inflating your tyre pressure.”

The gap between the two figures gives you a margin. A tyre at 3mm in November still has 1.4mm to lose before it reaches the legal line (3mm minus 1.6mm). Bumper’s cost guide ties braking distance and grip to the tyres, with wet roads as the case where a cheap or tired set shows its limits, so a 1.4mm cushion is worth having in November. National Highways gives the recommendation as 2mm in summer and 3mm in winter, so a tyre between 2mm and 3mm passes the summer advice and misses the winter one.

Harford also made a wider request about checking the whole tyre before a long drive:

“This is the last bank holiday of the summer, so we expect the roads to be busy with people looking to make the most of a long weekend. But the last thing anybody wants on the way to their destination is to have a vehicle breakdown. It’s really important people spend a few minutes checking the condition of their tyres before setting off.”

The numbers behind that request came from National Highways research reported in 2021. The survey found one driver in six checking tyres before a long trip. Worn or wrongly inflated tyres sat behind one in five motorway breakdowns, and nearly a third of drivers admitted they lacked confidence in checking pressure. The research dates from August 2021, so treat the percentages as a five-year-old snapshot. The checks themselves are the ones in any set of winter checks in 10 minutes.

What Uneven Wear Tells You

A tyre that wears fast on one edge is telling you something about the car. The Highway Code links heavy or lopsided wear to three culprits: a fault in the brakes, a fault in the suspension, or wheels out of alignment. It wants each one fixed as soon as possible. The same page says under-inflated or over-inflated tyres adversely affect both brakes and steering.

Pressure is the cheapest fault to rule out. The Highway Code tells drivers to check pressures weekly, before you drive and with the tyres cold, as warm or hot tyres can give a misleading reading. The right figure comes from the car maker and depends on how heavily the car is loaded. The handbook lists it. Cold weather pulls the number down overnight, a pattern explained in why tyre pressure drops overnight in winter.

A car that pulls to one side under braking is a separate warning. The Highway Code says the most likely causes are a brake fault or incorrectly inflated tyres, and it advises consulting a garage or mechanic immediately.

The MOT manual draws its own lines around pressure and mixed tyres. A tyre that is obviously under-inflated is a Minor defect. Tyres of different sizes on the same axle, or of different structure such as radial-ply and cross-ply, are Major defects. Cars first used on or after 1 January 2012 also have a tyre pressure monitoring system, and a malfunction in it is a Major defect. A warning lamp that stays lit does not automatically mean the system has failed, as the lamp can also be showing an earlier pressure loss.

A car that wears one pair of tyres faster than the other is worth raising with the garage, and the routine for how often to rotate tyres shows what skipping it adds to the replacement bill.

What a Replacement Costs

A 2026 cost guide from the car repair finance firm Bumper puts a new tyre at £45 to £250 or more, and the spread follows the brand and the car. A budget tyre costs £45 to £70 ($60 to $94). A mid-range tyre costs £75 to £120 ($101 to $161). A premium tyre costs £120 to £250 or more ($161 to $335 or more).

The car changes the bill as much as the tyre does. A small city car costs £45 to £80 per tyre ($60 to $107), a hatchback or saloon £70 to £120 ($94 to $161), and an SUV or crossover £100 to £180 ($134 to $241). Performance and luxury cars start at £150 and run to £300 or more ($201 to $402 or more).

A full set of four costs £180 to £280 ($241 to $375) in budget tyres, £300 to £480 ($402 to $643) in mid-range and £500 to £1,000 or more ($670 to $1,340 or more) in premium. For most drivers the guide puts a mid-range tyre at £75 to £120 as the balance of price and performance, and suggests setting aside £80 to £120 ($107 to $161) per tyre for a reputable mid-range brand.

Garages often advise fitting tyres two at a time across one axle, the front pair or the rear pair, so handling and braking stay level. Fitting a single new tyre beside a badly worn partner can reduce grip. A pair of mid-range tyres on one axle costs £150 to £240 ($201 to $322), so a driver who spots wear at 3mm on both fronts can budget the bill before the tyres reach the limit. Some fitters include wheel balancing in the price and others charge for it separately, so ask before you book.

A puncture is the exception. A repair costs £20 to £40 ($27 to $54) and the guide calls it worthwhile when the puncture sits in the middle of the tread on a tyre that is otherwise sound. Sidewall damage, or a tyre that has been driven flat, means a new tyre.

The Fine, the Points and the MOT

The penalty for getting it wrong is steep. National Highways advises that a driver stopped by the police with illegal tyres could receive a £2,500 fine ($3,350) and 3 penalty points per tyre. The Highway Code gives no figure and names penalty points for some vehicle defects without a figure.

The MOT is firm on one point and relaxed on another. The manual lists tread below the required depth as a Dangerous defect, the same category as a split tyre structure or a valve likely to cause sudden deflation. It relaxes on the outer strips of the tread, which can be bald, and on tyre age for a car. The Highway Code bans tyres over 10 years old only on the front axles of goods vehicles over 3.5 tonnes and passenger vehicles with more than 8 seats, so the rule does not cover a family car, yet National Highways still lists tyre age among the checks before a long trip.

The routine is short. Check pressure weekly with the tyres cold. Read the tread in the primary grooves at several points on each tyre. Book a replacement when any tyre reaches 3mm in winter, or 2mm in summer, and do not wait for 1.6mm. A tyre at the legal limit has no margin left, and a tyre at 3mm still does.

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Sources

• GOV.UK: The Highway Code, Annex 6. Vehicle maintenance, safety and security
• GOV.UK (DVSA): MOT inspection manual, 5. Axles, wheels, tyres and suspension
• GOV.UK (National Highways): Motorists urged to check tyres before setting off this bank holiday
• Bumper: Tyre Replacement Cost Guide

Reviewed by Preetam Gadekar