20p Tyre Tread Test

ChumLee

Stub_Mandrel wrote: »

Interesting to go back to the Government's summary of that research:

For the car and tyre combinations considered, the stopping distance performance at differing tread depths has been measured. The results illustrate that, generally statistically significant increases in stopping distance begin to manifest themselves at tread depths below approximately 3mm, although the magnitude of the increase is not consistent across all the car and tyre configurations.

The stopping distances and the yaw stability of a vehicle fitted, firstly, with an incorrectly oriented directional tyre and, secondly, with a deflated run-flat tyre, were measured. In both cases no significant reductions in either braking performance or yaw stability were evident.

The effects of tyre pressure reductions of 10% and 20% on the stopping distance and yaw stability of a vehicle have been measured. The results demonstrate that, whilst the yaw stability was unaffected, the stopping distance increased by between 5% and 11%.

Seems that keeping your tyres well pumped up is almost as important to stopping distance (it also saves you fuel and makes your tyres last longer, moneysavers... )

100 psi in mine and saving a fortune. 👍

Paradigm

I run my tyres to around 2mm, they're still legal & I only change them then to make sure I stay legal.
I can't remember the last time I had to make an "emergency" stop where braking distances would be a factor...

Joe_Horner

Got to agree with Arcon5 that the OP has a point. There's a world of difference between advisable to change and illegal.

That test is generally promoted as a way to check your tyres are "legal" and the MSE article gives the same impression if you don't know any better - and if you do know better then you don't need the article in the first place.

WellKnownSid

arcon5 wrote: »

Tyres with a 3mm tread have an increased stopping distance also. Get them changed at 6mm to avoid this.

If you lived in Germany you probably would.

TBH all cars I've ever driven have had noticeable grip issues once they hit 3mm or near offer.

Iceweasel

Of course all this needing tread nonsense only applies when the roads are wet.

In the dry you're far better off with no tread at all - especially if you have no rear brakes or drive an M3 - even more so if you hear voices in your head telling you to post the first thing that you think off, just to get a reaction on this forum.

Quite dark matter-ish.

But as others have said it would have been better if the message had been that if your tyres fail the 20p test they are nearing the point where they would be illegal.

The tread wear indicators or a pukka depth-gauge are preferable to some random coin of course.

almillar

i would not run a tyre down to 1.6mm the legal minimum, when a tyre reaches that low a tread depth the stopping distance is increased and the overall performance of the tyre is greatly reduced

what price safety?

... in the wet.

Tyres with a 3mm tread have an increased stopping distance also. Get them changed at 6mm to avoid this.

... in the wet.

Slick tyres are far better in the dry, the grooves are only there to get rid of water and keep the tyres touching the road. The less groove, the less water it can clear, and the higher chance of aquaplaning.

All MSE need for clarity is - the legal limit is 1.6mm across 75% of the tyre (isn't that right?). Many people recommend changing at 3mm, roughly equivalent to that 20p test.

Isn't Germany's minimum 3mm and that's where we get a lot of our retreads from?

Joe_Horner

almillar wrote: »

All MSE need for clarity is - the legal limit is 1.6mm across 75% of the tyre (isn't that right?). Many people recommend changing at 3mm, roughly equivalent to that 20p test.

Broadly right but the 75% must be "central" - so you can't have the outside or inside 25% scrubbed clean even if the rest of it is good.

Except that on most modern tyres (with 3 or 4 deep lateral grooves) the shoulders - as far in as the first deep groove - aren't counted as tread because they're initially significantly shallower than the main grooves (with the wear indicators in them). So the shoulders can both be scrubbed as smooth as Kylie's bum and the 75% rule only applies to 75% of what's left in between them.

That's certainly not suggesting running round on tyres like that is a good idea, but it does illustrate that the rules for legality are nowhere near the 20p test!

ChumLee

Joe_Horner wrote: »

Broadly right but the 75% must be "central" - so you can't have the outside or inside 25% scrubbed clean even if the rest of it is good.

Except that on most modern tyres (with 3 or 4 deep lateral grooves) the shoulders - as far in as the first deep groove - aren't counted as tread because they're initially significantly shallower than the main grooves (with the wear indicators in them). So the shoulders can both be scrubbed as smooth as Kylie's bum and the 75% rule only applies to 75% of what's left in between them.

That's certainly not suggesting running round on tyres like that is a good idea, but it does illustrate that the rules for legality are nowhere near the 20p test!

And all that is of course for vehicles up to 3500kg. Anything above that or a motorcycle it's 1mm or for mopeds you just need to see the tread pattern.

Joe_Horner

ChumLee wrote: »

And all that is of course for vehicles up to 3500kg. Anything above that or a motorcycle it's 1mm or for mopeds you just need to see the tread pattern.

Exellent point, which does raise the question of why a car with less than 3mm (nearly double the legal minimum) is an accident waiting to happen being driven by Freddy Kruger's less social twin but 40 tonnes of artic on the same is fine

ChumLee

Joe_Horner wrote: »

Exellent point, which does raise the question of why a car with less than 3mm (nearly double the legal minimum) is an accident waiting to happen being driven by Freddy Kruger's less social twin but 40 tonnes of artic on the same is fine

Or Tommy Asbo on his moped with 0.5mm of tread and a provisional licence pishing down with rain on the way back from his CBT.