1.6, 3 or 4 mm: when should you really change your tyres?

Every autumn this argument flares up again on the car forums, with everything from “there’s still some tread” to tables full of numbers. In fact all three are right, each under their own conditions. The law allows you to drive down to 1.6 mm, physics advises at least 3 mm in the rain, and for winter a sensible limit is 4 mm.

What does the law say?

The main rule is clause 31.4.5 of Ukraine’s traffic regulations: it is forbidden to operate a car (or a lorry up to 3.5 t) with less than 1.6 mm of tread depth remaining. At the bottom of the main grooves there are tread wear indicators (TWI), small transverse ridges which, under UN Regulation No. 30, show that about 1.6 mm of groove depth is left. And the technical rules approved by Order No. 549 of the Ministry of Infrastructure say the tyre has to come off as soon as even one indicator starts to wear away.

The same order also contains a winter rule that far from everyone knows about: in the winter season the tread depth must be at least 3 mm. Some countries in Europe are stricter: in Czechia and Austria a winter tyre must have at least 4 mm of tread in winter. And Bulgaria has a different rule: from 15 November to 1 March, 4 mm of tread is required of any non-winter tyre (Article 139 of the Bulgarian Road Traffic Act), rather than of a winter one. For more detail, see the article on winter tyres and the law.

Why is 1.6 mm a limit and not a margin?

We have already covered aquaplaning: the main factor is speed, and the difference between a “rain” tread pattern and an ordinary one is a few kilometres per hour. That is true for two new tyres. A new tyre and a worn one are a different story altogether.

The tread grooves carry water away from the contact patch, and their volume melts away along with the tread depth. Picture a gutter on a roof: while the gutter is clean and deep, the water goes where it should, but half-clog it with leaves and the water spills over the edge (in our case, under the tyre). According to one of the largest tyre makers, new tyres at about 80 km/h clear up to 30 litres of water a second; until the tread is down to about 3 mm they keep a good share of that ability, and below that the risk of aquaplaning rises sharply. Add under-inflated tyres (the lower the pressure, the lower the speed at which a tyre “floats up”; NASA engineers worked that out in the 1960s while studying aircraft), and the picture is quite bleak.

In the same maker’s test the braking distance of a tyre with 1.6 mm of tread turned out to be 6.8 m longer than that of a new one (8 mm), while with 3 mm of tread it was only 2.2 m longer. Six-odd metres is a car length and a half, quite enough to end up with someone else’s bumper instead of just a scare. Below 1.6 mm a car tyre is unfit, no exceptions, and below 3 mm it clears water worse and worse. No “just till the end of the season” or “just as far as the tyre fitter round the corner”: below the limit there is no room for compromise!

A winter tyre: 4 mm and below

A winter tyre grips the road with sipes (thin cuts in the tread blocks whose edges “catch” on snow and ice) and deep grooves that pack with snow (and snow sticks to snow better than rubber does to ice). The sipes, though, as we said in the article on tread depth, are far from always cut to the full depth of the tread. Once the sipes have worn away, only rubber blocks are left, and about the only thing that makes such a tyre a winter one is the snowflake symbol on the sidewall.

So a winter tyre with less than 4 mm of tread is no longer good enough for a real winter, even though Order No. 549 formally lets you drive on it down to 3 mm. A maker specialising in winter tyres advises changing them at exactly 4 mm. Those 4 mm are the real “zero” of a winter tyre; how to take that into account when buying part-worn tyres is in the article on real tread wear.

Are we throwing tyres away too early?

Now, in fairness, the opposite view. Another big tyre maker argues that changing tyres “at 3 mm” is wasteful. By its figures, about half of all tyres are taken off while more than 3 mm of tread is left; if Europeans ran them down to the legal 1.6 mm, then, by its own calculations, this could save over a hundred million tyres a year and cut CO2 emissions by millions of tonnes.

A tyre maker campaigning for people to buy fewer tyres is an unusual picture, isn’t it? It may be that the calculation is a simple one: the winner is whoever’s worn tyre brakes better. But that does not make the argument false. And real progress here deserves to be acknowledged without grumbling: since July 2024 new models of car tyres in Europe have had to pass wet grip tests under UN Regulation No. 117 not only when new but also when artificially worn. From July 2026 that requirement has spread to practically all new car tyres being made.

So the dispute is not about who is right but about conditions. A summer tyre that you drive mostly on dry tarmac can quite legally be run down to 1.6 mm. For rain and the motorway, though, you need a margin: 3 mm, and for snow 4 mm. That makes a few more months on the old set in the dry season a matter of your wallet: that one is for you to decide. Just never below 1.6 mm: there is nothing left to decide there.

To sum up: 1.6 mm is the limit beyond which a tyre is unfit altogether, 3 mm is a sensible margin for rain, 4 mm is the real minimum for a winter tyre. Measure not by eye or with a coin but with a depth gauge, at several points (in the centre, at the edges and at different places around the circumference), and go by the smallest value (more on uneven wear). I measure my tyres like that every autumn, before the changeover. If the front tyres wear faster than the rear ones, that is a reason to think about rotating the wheels. And a tread that has “still got a bit left” only saves you until the first deep puddle.

All about tyre tread wear