UK tyre depth

Joe_Horner

Yet Michelin, who really should know, say to keep them all the way to the 1.6mm limit because changing before that is wasteful, unnecessary, and means you're getting rid of them at the point they're just reaching their best:

https://www.honestjohn.co.uk/news/miscellaneous/2016-10/qa-replacing-tyres-at-3mm-tread-an-absolute-waste-says-michelin-director/

https://fleetworld.co.uk/changing-tyres-at-3mm-unnecessary-says-michelin/

Given that they would stand to sell a LOT more product if there was a change in the law, it seems likely that they can be trusted on this.

Jackmydad

Joe_Horner wrote: »

Yet Michelin, who really should know, say to keep them all the way to the 1.6mm limit because changing before that is wasteful, unnecessary, and means you're getting rid of them at the point they're just reaching their best:

https://www.honestjohn.co.uk/news/miscellaneous/2016-10/qa-replacing-tyres-at-3mm-tread-an-absolute-waste-says-michelin-director/

https://fleetworld.co.uk/changing-tyres-at-3mm-unnecessary-says-michelin/

Given that they would stand to sell a LOT more product if there was a change in the law, it seems likely that they can be trusted on this.

Interesting articles. Thanks.
As said in the comments on the Honest john site though. you have to be careful of uneven tyre wear. Particularly with modern wide tyres, and snug wheel arches / low sills making them tricky to measure.
The other thing is how do you measure?
I use either a dial caliper which has a "stick" for depth measurement, or I've got a proper tyre depth gauge with a vernier for tenths.
At the end of the day as long as you stay legal, it seems you can choose for yourself.
For the present time at least.

BeenThroughItAll

Jackmydad wrote: »

Interesting articles. Thanks.
As said in the comments on the Honest john site though. you have to be careful of uneven tyre wear. Particularly with modern wide tyres, and snug wheel arches / low sills making them tricky to measure.
The other thing is how do you measure?
I use either a dial caliper which has a "stick" for depth measurement, or I've got a proper tyre depth gauge with a vernier for tenths.
At the end of the day as long as you stay legal, it seems you can choose for yourself.
For the present time at least.

I use the TWI bars on the tread. If they're sitting below the tread surface, all is good. If they get near the tread surface (2-2.2mm I'd guess) replace.

Joe_Horner

Jackmydad wrote: »

Interesting articles. Thanks.

You're welcome.

One part I thought was particularly interesting was the direct reference to Kwikfit - everyone's favourite "would you like new shock with that?" chain - as backing tyre changes at 3mm. That on its own should be enough to raise doubts in any sane motorist!

seatbeltnoob

replace your tyres after 1.6mm. keep your !!!!!!!g distance and drive at a safe speed.

changing the tyre at 3mm is completely unnecessary. always get my moneys worth and change the tyres after the tread falls just below 2mm and never came close to a collision

that's because i use my brain, dont tailgate and dont do 50mph on a narrow (single lane) wet country road just because the speed limit says I can

jase1

BeenThroughItAll wrote: »

The result is that many German drivers change any tyres, summer or winter, once they reach 3-4mm tread; which is only realistically about half their lifespan.

That isn't true. At 3mm a tyre only has 1.4mm of a total of at least 6mm of usable tread left, which is less than 25% -- and this assumes an original depth of 7.5mm which is usually a bit conservative.

Joe_Horner

jase1 wrote: »

That isn't true. At 3mm a tyre only has 1.4mm of a total of at least 6mm of usable tread left, which is less than 25% -- and this assumes an original depth of 7.5mm which is usually a bit conservative.

But tyres wear more slowly as the tread gets lower because the shallower tread is more rigid - part of what makes them more efficient and grippier in the dry (see Michelin comments above). More rigid tread = less scrubbing movement = less wear.

So 3mm left is somewhere between 1/4 and 1/2 of the useful life. Which is a significant waste of money and resources and a significant environmental impact as well.

BeenThroughItAll

jase1 wrote: »

That isn't true. At 3mm a tyre only has 1.4mm of a total of at least 6mm of usable tread left, which is less than 25% -- and this assumes an original depth of 7.5mm which is usually a bit conservative.

It's not as simple as that, because tyre wear isn't linear. I won't claim to know all the reasons why, but I can tell you from experience over many hundreds of thousands of miles that tyres wear quicker at first and the wear speed declines considerably as the tyre reaches the 5-4-3mm wear range. I assume it's something to do with the fact that there is more movement in the tread blocks when they're 'taller' when new.


The tyres I had changed on my wife's Audi last week were 21,000 miles old, but when I swapped them from the rear to the front nine months (10Kmi) ago, the tread depth was just over 3.6mm on both - so the next 10K miles used approximately 2mm of the tyre, whilst the first 11K used about 4-4.5mm.

Iceweasel

Tread block movement under acceleration, braking, or steering is referred to as 'squirm' by tyre designers - apparently.

Less tread depth obviously means less squirm.

I used to think that the word could only be applied to politicians being interviewed by the likes of Jeremy Paxman.

almillar

I won't claim to know all the reasons why, but I can tell you from experience over many hundreds of thousands of miles that tyres wear quicker at first and the wear speed declines considerably as the tyre reaches the 5-4-3mm wear range.

Yep, as Iceweasel says, when you corner, accelerate or brake, the blocks on the tyre (the bits between gaps!) stick out more, get moved around more, and are more prone to friction, and therefore wear. When they wear down a bit, the move around less, and keep a more uniform shape.

To state categorically that 1.6mm isn't enough, you need to know how much water a tyre (yes, they'll all vary!) can disperse. That will tell you how fast you can drive through standing water, before the tread fills up, and you aquaplane.