Tyre sizes

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daviemck2006
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Tyre sizes

Post by daviemck2006 »

A car in my circle of cars I help with failed the MOT on one front tyre cut on sidewall, inside edge, amongst other things. Said car has 205/40 x17 on the front and 205/45 x17 on the rear. The other side front is on 3mm tread and slightly perished. The owner is on a budget, and I have 2 near brand new 215/40 x17 tyres here. My question is, if there is any mot testers here will it pass if the 205/45 x17 were on the front, and 215/40 x17 on the rear? I make them near enough the same rolling radius so should be ok. The question will stand for myself too, when I put the 17's onto the xantia. It will have 205/50 x17 front and 215/45 x17 rear. Again is this legal?

BenC5HDi
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Re: Tyre sizes

Post by BenC5HDi »

As long as the sizes are matched on each axle - i.e. the same size on both fronts and the same size on both rear it shouldn't be an issue.

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daviemck2006
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Re: Tyre sizes

Post by daviemck2006 »

That's what I thought, as long as the wider ones on the back.

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NewcastleFalcon
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Re: Tyre sizes

Post by NewcastleFalcon »

chapter and verse is probably somewhere in this Davie.

http://www.motuk.co.uk/manual_410.htm

Regards Neil

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daviemck2006
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Re: Tyre sizes

Post by daviemck2006 »

Well all I can see is that tyres must be the same size and aspect on the same axle. Nothing about bigger/smaller on front or rear, so that's OK. All 4 wheels have to come off anyway, handbrake not holding on drivers side, and wheelbearing slack passenger side which I hope will just need a tighten up as it is not rough.

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van ordinaire
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Re: Tyre sizes

Post by van ordinaire »

I've had many cars with "big'n'littles" on: de rigour in the '70's - for RWD!

Some cars come out the factory like that: Xk8's come to mind - so mix & match to your heart's content; oh & (some) road going, FWD race cars have bigger wheels on the front: might look odd - but it's obviously OK.

dnsey
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Re: Tyre sizes

Post by dnsey »

Running different sizes can confuse ABS / ESP systems, even though the rolling radius is similar. Don't know quite why, but I do have first-hand experience of it.

elma
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Re: Tyre sizes

Post by elma »

Abs will be fine as long as axel pairs are matched. It simply detects if the wheel has locked by sensing the rotation of the toothed ring on the driveshaft and pulses the brakes to the locked wheel.

Can't comment on esp as I don't have it or know how it works.

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van ordinaire
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Re: Tyre sizes

Post by van ordinaire »

So, if you've got ABS, you can't use the spacesaver spare? That can't be right!

To put things in perspective we're probably talking about a difference in size less than between a new tire & one on the legal minimum.

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daviemck2006
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Re: RE: Re: Tyre sizes

Post by daviemck2006 »

van ordinaire wrote:So, if you've got ABS, you can't use the spacesaver spare? That can't be right!

To put things in perspective we're probably talking about a difference in size less than between a new tire & one on the legal minimum.
I think that really. I went and got 4 new tyres on to the sons skoda. It had only been a very slight scuff on the arches before but scuffing more now, and the tyres are the same size and make!

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elma
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Re: Tyre sizes

Post by elma »

van ordinaire wrote:So, if you've got ABS, you can't use the spacesaver spare? That can't be right!
You can but the brakes aren't exactly safe on a space saver. If you lock both wheels of an axle on a car with abs and non matching tyre or wheel sizes the axle will steer notchily toward the smaller wheel. One of many reasons spacesavers have a speed limit.

For the purposes of an mot and the original question. 2 tyres of the same size on an axel with different amounts of wear is fine so long as both tyres have legal tread and condition. Two different size tyres is not OK.

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Re: Tyre sizes

Post by dnsey »

I've had a similar front / rear size difference throw an ABS error. Although the difference is smaller than that between new and worn tyres of the same size, it seems that the system can't understand why the front wheels are turning faster or slower than the rear.

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Stickyfinger
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Re: Tyre sizes

Post by Stickyfinger »

it seems that the system can't understand why the front wheels are turning faster or slower than the rear
that is the point of the system after all

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van ordinaire
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Re: Tyre sizes

Post by van ordinaire »

Then XK8's (e.g.) must have exceptionally clever ABS [unlike a certain Cadillac - when I got it the front (driven) tyres were a size under but replacing them didn't alter the speedo error or make any difference to the ABS &TC lights, which stubbornly refuse to go out]