Should You Replace Tyres at 3mm or 1.6mm?
A practical guide to 3mm tread depth for UK drivers, from the CarPal mobile tyre team.
What the law says
1.6mm is the legal minimum in the UK, across the central three-quarters of the tread and around the entire circumference. Below that a tyre is illegal, full stop.
Nothing about 3mm appears in law. It is a safety recommendation, not a requirement.
Why 3mm is recommended
Tread grooves exist to channel water out from under the contact patch. Less groove volume means less water cleared per rotation, which means the tyre aquaplanes at lower speeds and takes longer to stop in the wet.
Independent testing has repeatedly shown that wet braking distances increase substantially as tread drops from 3mm toward 1.6mm. The exact numbers vary by test and tyre, but the direction is consistent and the difference is large enough to matter in an emergency stop.
The honest trade-off
Replacing at 3mm costs more over the life of the car, because you are discarding tread that is still legal. On a tyre that starts at 8mm, replacing at 3mm rather than 1.6mm uses about 78% of the usable tread instead of 100%.
What you buy with that money is shorter wet stopping distances for the last portion of the tyre’s life. Whether that is worth it depends on your mileage, how much wet-weather driving you do, and your own risk judgement.
A practical middle ground
Many drivers replace at around 2.5 to 3mm on the front axle, where most braking and steering load goes, and run the rears slightly longer.
Whatever you choose, measure rather than guess. Knowing you are at 3.5mm and wearing 1mm every 10,000 miles lets you plan. Discovering you are at 1.5mm at an MOT does not.
Frequently asked questions
Is 3mm tread legal in the UK?
Yes. The legal minimum is 1.6mm, so 3mm is comfortably legal.
Why do people say replace at 3mm?
Wet braking distances increase significantly below about 3mm because the tread cannot clear water as effectively.
Is 2mm tread safe?
It is legal, but wet grip is already noticeably reduced compared with a newer tyre.
Does tread depth affect stopping distance?
Substantially in the wet. In the dry the effect is far smaller.
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