Tyre measurment - where and how much new?

[cheadle hulme]

Just viewed a Z4. It had failed its MOT previously as the front tyre was below 1.6mm. This was in Novemeber when the dealer took it into stock.

It now has 4 new looking Bridgestone runflats on it, but the tread doesn't look that deep. I don't possess a tyre depth gauge (free one didn't turn up ) but using a key and a ruler it seemed there was 6mm in the middle and 4mm on the shoulders. Same front and rear.
If they were brand new Bridgestone Potenzas how much tread would they have? A

Also, dealer says all he has done is "prep" it with new tyres and refurbed alloys together with a "MOP". However the bonnet is spotless, no stone chips at all and no swirl marks that I could see. Looked brand new in fact. Front spoiler has a few dings though. Car is 7 years old, should I be wary?

[Chiswickboy]

If the tyres are worn down by 2mm on the shoulders since November then walk away.

Either the dealer is talking effluence of the male bovine about fitting "new" tyres or there is something seriously out of alignment.

[Matt UK]

If you mean 4mm on both inner and outer shoulder, I'd say it has been run too high pressures as opposed to alignment

[Jimmyarm]

How many miles has it done since the mot ?

A previous owner could have had the bonnet sprayed ?

Edited by Jimmyarm on Wednesday 12th January 21:29

[maniac0796]

I would expect a Z4 to wear quicker on the inner edges, but on both sounds like it's either been driven with the tyres flat or it has bad alignment. Or you're measuring it in the wrong place.

I would imagine from new though, they have 8 to 10mm of tread.

[Jimmyarm]

maniac0796 said:

I would imagine from new though, they have 8 to 10mm of tread.

Where do you get your tyres from ?

Most new road tyres have approx 7mm, some less.

[Cost Captain]

Matt UK said:

If you mean 4mm on both inner and outer shoulder, I'd say it has been run too high pressures as opposed to alignment

absolute opposite.

high pressure causes the tyre to "balloon" wearing the centre more heavily, giving a lower reading for the centre part of the tread compared to shoulders. low pressure causes wear on the shoulders.

new tyres start on 8mm, so you'd expect the tyres to be atleast 6mm across minimum if the car has been in a dealership for a few months.

However, depends on where you take the measurement.

Outside of the central 3/4 of the tyre, the shoulder slopes away and the tread reading will be lower. if you measure the tread on the absolute limits of the tread it will seem to be 2 or 3 mm lower than the centre but this is not a problem.

Measuring tyres correctly is a bit of an art, I would ask a friendly MOT tester to show you how to do it properly then go back and measure them again.

[Cost Captain]

Jimmyarm said:

maniac0796 said:

I would imagine from new though, they have 8 to 10mm of tread.

Where do you get your tyres from ?

Most new road tyres have approx 7mm, some less.

Last time I checked, all E marked new tyres come with 8mm, unless they are semi slick, and they start with 6.5mm

[Matt UK]

Cost Captain said:

Matt UK said:

If you mean 4mm on both inner and outer shoulder, I'd say it has been run too high pressures as opposed to alignment

absolute opposite.

high pressure causes the tyre to "balloon" wearing the centre more heavily, giving a lower reading for the centre part of the tread compared to shoulders. low pressure causes wear on the shoulders.

Yup my mistake, you are absolutely right.

[peeves]

Matt UK said:

If you mean 4mm on both inner and outer shoulder, I'd say it has been run too high pressures as opposed to alignment

If they are low on the shoulder they'd be underflated.

maniac0796 said:

I would imagine from new though, they have 8 to 10mm of tread.

10mm would be commercial tyres. 8mm would be branded tyres. 6mm are budgets.

[cheadle hulme]

Jimmyarm said:

maniac0796 said:

I would imagine from new though, they have 8 to 10mm of tread.

Where do you get your tyres from ?

Most new road tyres have approx 7mm, some less.

This is what I thought. As I said in the OP, dealer has had it in stock since November. It was MOT'd then and failed on tyre tread. Now 3 months later, at the same dealer, 5 miles further on the odo, but I can't measure more than 6mm max.

If they come with 7mm brand new then fine; thats within the tolerances of my poor measurment. I was worried that if new tyres came with 10mm, then the dealer may have fitted part worns.

10mm would seem like a tractor tread on something like a Z4 though??

[HellDiver]

Most modern tyres have less measurable tread depth on the shoulders. This is the case with Bridgestone.

A brand new ER300 will only have 3-4mm tread depth on the shoulders and 8mm in the centre, for example. On the inside shoulder there's very little tread. It's so cornering ability is enhanced, as there's more rubber on the road and less tread movement.

[cheadle hulme]

Cost Captain said:

Measuring tyres correctly is a bit of an art, I would ask a friendly MOT tester to show you how to do it properly then go back and measure them again.

You're right. I dug a key into the centre rain groove and measuresd that. looked like 6mm to me.
The retail of 4 new RTF 18" tyres is a lot, and the car is only on at £9.5k so I want to make sure its straight. Dealer seems sound.

I'll get a proper gauge I guess..

[Cost Captain]

cheadle hulme said:

Jimmyarm said:

maniac0796 said:

I would imagine from new though, they have 8 to 10mm of tread.

Where do you get your tyres from ?

Most new road tyres have approx 7mm, some less.

This is what I thought. As I said in the OP, dealer has had it in stock since November. It was MOT'd then and failed on tyre tread. Now 3 months later, at the same dealer, 5 miles further on the odo, but I can't measure more than 6mm max.

If they come with 7mm brand new then fine; thats within the tolerances of my poor measurment. I was worried that if new tyres came with 10mm, then the dealer may have fitted part worns.

10mm would seem like a tractor tread on something like a Z4 though??

10mm is 1cm... thats roughly 2 halves of fk all when considering the outside circumference of a wheel/tyre.

tyres are 8mm when new.

they just are.

[cheadle hulme]

Thanks Helldiver. Would any manufacturing blobs or lines still be visible after 5 miles?

[Kong]

Those wear pattens arent right at all. My Z4 is on it's 3rd set of rears and 2nd set of fronts.

The fronts have always worn evently and the rears considerably more on the inside edge (because of the standard camber setup).

[HellDiver]

cheadle hulme said:

Thanks Helldiver. Would any manufacturing blobs or lines still be visible after 5 miles?

The paint should be still on the tyres after 5 miles. I've been using Bridgestones for years, and typically 12-15k out of a RE050/RE050A and well over 25k from a ER300 on front wheels of a FWD. RE050 lasted 40k on the rear, and ER300 outlasted the car on the back, 65k and there was still 3mm left.

If the tyres on that Z4 are wearing at the rate you think, I would expect it to be digging a ditch on a gravel yard, and squealing like a pig on tarmac.

It's not clear from the image I posted, but the tread on the right side of the tyre (outside) is half the depth of the deep tread grooves. When you're down to 3mm across the tyre you'd be left with 4 deep grooves and little else, all the cross tread will be worn away.

I still think it's perfectly normal differential in tread depth across the tyre, and not unusual wear at all.

[Jimmyarm]

Feel its worth adding that the dealer may have put 'partworns' on which may account for your measurements.