Tyre wear calculation

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Discussion

pincher

Original Poster:

9,403 posts

232 months

Thursday 25th August 2022
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If you had tyres that were notionally 7mm from new and that across 2/3 of the tyre, there was still 7mm of tread left and the inside was down to 6mm, what would you say was the percentage of wear?

Would the calculation be across the whole tyre of only across the worn section?


Hopefully, the above makes sense!

Scrump

23,420 posts

173 months

Thursday 25th August 2022
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6.17%
HTH

samoht

6,586 posts

161 months

Thursday 25th August 2022
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If you're thinking about the legality of a tyre, the minimum is 1.6mm across the central three-quarters of the tyre. So if the 'inside' band that was down to 6mm is more than one-eighth of the width of the tyre, then the tyre has 6mm of tread remaining. If it's still min 7mm across the central 3/4s then it's still 7mm legally.

If you're thinking from a safety point of view I would generally take a model that the total volume of inter-tread gap will be available to dispel the water. So from that angle I'd take an average across the whole width. So if it was 6mm on the inside edge graduating to 7mm by one-third of the way in, and then maintaining that 7mm to the outside edge, the average tread depth would be 6.83mm (6 and 5/6ths mm). This probably best predicts aquaplaning performance.


pincher

Original Poster:

9,403 posts

232 months

Thursday 25th August 2022
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My reason for asking is that one of my cars had a service the other day and they do one of those health check videos - they told me that the rear tyres, which were new two weeks and (max) 250 miles previously, were 7mm, 7mm, 6mm (outer to inner) and 31% worn laugh

Scrump

23,420 posts

173 months

Thursday 25th August 2022
quotequote all
pincher said:
My reason for asking is that one of my cars had a service the other day and they do one of those health check videos - they told me that the rear tyres, which were new two weeks and (max) 250 miles previously, were 7mm, 7mm, 6mm (outer to inner) and 31% worn laugh
If they assume the tyres came with 8mm tread and the legal minimum is 1.6mm then that gives 6.4mm of useable tread.
As your lowest reading of tread depth was 6mm this gives 2mm of wear out of 6.4mm = 31%
bowtie

Smint

2,357 posts

50 months

Thursday 25th August 2022
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This does highlight how difficult it is for tyre buyers to learn how much tread a specific new tyre comes with, as above i suspect the garage assumed the tyres came with 8 or 9mm of tread when new.
On tyre makers websites and on tyre sales sites it should be a requirement to display the tread depth, some sites have this info on some but not all tyres, if i had this info no way would i buy a set with only 7mm when new.

Nokian tyres have a useful feature, tread depth remaining in mm is in the tread moulding, as the tread wears down the new depth is revealed, simple.

GreenV8S

30,857 posts

299 months

Thursday 25th August 2022
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pincher said:
what would you say was the percentage of wear?
I'd say it was the percentage of the tyre's useful life that had been consumed. That would be determined by whatever would cause the tyre to need replacing first.

Pica-Pica

15,201 posts

99 months

Thursday 25th August 2022
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Scrump said:
pincher said:
My reason for asking is that one of my cars had a service the other day and they do one of those health check videos - they told me that the rear tyres, which were new two weeks and (max) 250 miles previously, were 7mm, 7mm, 6mm (outer to inner) and 31% worn laugh
If they assume the tyres came with 8mm tread and the legal minimum is 1.6mm then that gives 6.4mm of useable tread.
As your lowest reading of tread depth was 6mm this gives 2mm of wear out of 6.4mm = 31%
bowtie
This. However, I have never known a percentage quoted, only a remaining depth. For the stated reason that not all tyres come with 8mm tread when new. Best to buy your own tread gauge and keep an eye on the depths. Get a depth and pressure gauge set, such as TireTek.

brillomaster

1,504 posts

185 months

Friday 26th August 2022
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id say your tyres were slightly over inflated if they're wearing quicker on the inside than on the edges.

neenoy

48 posts

110 months

Friday 26th August 2022
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pincher said:
My reason for asking is that one of my cars had a service the other day and they do one of those health check videos - they told me that the rear tyres, which were new two weeks and (max) 250 miles previously, were 7mm, 7mm, 6mm (outer to inner) and 31% worn laugh
Have the new tyres really lost 1mm of tread in just 250 miles? If it really is wear, I would get the alignment checked/adjusted asap.

pincher

Original Poster:

9,403 posts

232 months

Friday 26th August 2022
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Pica-Pica said:
Scrump said:
pincher said:
My reason for asking is that one of my cars had a service the other day and they do one of those health check videos - they told me that the rear tyres, which were new two weeks and (max) 250 miles previously, were 7mm, 7mm, 6mm (outer to inner) and 31% worn laugh
If they assume the tyres came with 8mm tread and the legal minimum is 1.6mm then that gives 6.4mm of useable tread.
As your lowest reading of tread depth was 6mm this gives 2mm of wear out of 6.4mm = 31%
bowtie
This. However, I have never known a percentage quoted, only a remaining depth. For the stated reason that not all tyres come with 8mm tread when new. Best to buy your own tread gauge and keep an eye on the depths. Get a depth and pressure gauge set, such as TireTek.
I agree - but the point I will make to the dealer is that the percentage figure is what most people would take notice of and if they can't be sure of their calculation then they shouldn't include it on the report (or write it on the tyre as part of the video).

It's no big deal in the scheme of things, just everso slightly irritating.

E-bmw

11,050 posts

167 months

Friday 26th August 2022
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brillomaster said:
id say your tyres were slightly over inflated if they're wearing quicker on the inside than on the edges.
No, he said they have worn more at the inner edge, not the centre of the tyre.

Cold

16,011 posts

105 months

Saturday 27th August 2022
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Did you take your car to the same place I took my Vantage back in July? laugh

They reported that my PS4S tyres were wearing unevenly with only 6-7mm remaining on the tread when I took it in for a service. They were under 100 miles old.

pincher

Original Poster:

9,403 posts

232 months

Saturday 27th August 2022
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That’s the thing - if they hadn’t been so new, I probably wouldn’t have taken anywhere near as much notice. As I said, they were put on two weeks earlier and other than a bit of town driving, I drove from Essex to Pangboirne to Marlow and back to Essex - just think it was a bit of a nonsense that they were almost a third worn.

I emailed the (main) dealer back with a suggestion that they could just report the depths as they find them, rather than trying to make a %age calculation based on assumptions - probably won’t hear back but it made me feel all superior laugh

Edit - oddly enough, mine were PS4S as well biggrin

Edited by pincher on Saturday 27th August 06:00

Sheepshanks

37,129 posts

134 months

Saturday 27th August 2022
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A few years ago I felt I had to have a go at a dealer (part of a very large dealer group) who called and told me in their best serious voice that the tyres, which were 4mm front and 5mm rear needed to be changed immediately “as they were close to the 3mm European legal limit”.

pincher

Original Poster:

9,403 posts

232 months

Saturday 27th August 2022
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That’s just downright dishonest - what did they say when you pulled them up on it?

Sheepshanks

37,129 posts

134 months

Saturday 27th August 2022
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pincher said:
That’s just downright dishonest - what did they say when you pulled them up on it?
They backtracked and said it’s an advised limit.

pincher

Original Poster:

9,403 posts

232 months

Saturday 27th August 2022
quotequote all
mad