I read an interesting notice in the local tyre depot ,issued by Pirelli,warning of the danger of fitting mis matched tyre sizes on the same axle of volvo cars.
Basically it stated that not only should each tyre be the same size, manufacturer and tread pattern but also that the tread depth of each tyre should be within 2mm of each other.Therefore the rolling circumference of each wheel would be the same.Failure to adhere to this could lead to transmission failure.
I can see the logic that different circumferences would mean that each wheel would be rotating at a different speed thus maybe putting a strain on the transmission but what makes the transmission system in volvos that sensitive to this and do such fine tolerances apply to any other cars?
The obvious danger I can see is the use of the spare wheel after a puncture.The tread depth of the two tyres would in all probability be very different.
Regards
Paul
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On early volvo 4x4s it was imperative to have the same tyres ,
the new ones do not require this.On normal two wheel drive
I cannot see what difference it would make as the rear diff always
has the rear wheels moving at different speeds.
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Yes, I'd read this about Volvo 4 x 4's and was staggered. 2mm on the diameter equates to a circumferential difference of 0.3 / 0.4 % or thereabouts. As Andy says the front or rear diffs are constantly coping with different wheel speeds as the car negotiates bends. If the centre differential can't cope with a few mm difference in diameter, even on a continuous basis, there is something wrong somewhere in the design. I just hope owners don't get carried away and use these off road, because the slip required there will be a bit more than 0.3%!
Regards
john
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Cavalier 4x4's had the same same problem a few years ago...
I had a GSi 4x4 in 1993 and fitted new rear tyres before going on holiday. I immediately noticed a shudder when going around tight corners eg multistorey car parks. Vauxhall garage said 'have to change all 4 tyres together', lease company said 'no chance', Vauxhall Luton told lease company that if only 2 new tyres fitted they should go on front, Vauxhall garage found service bulletin that said 'no more than 2mm difference in tread depth'.
I got the new tyres swapped to the front, shudder went away, I went off on holiday with family, happy.
However, when the car was fully loaded (easy with the small 4x4's boot!), whenever I braked on the overrun, there was a small but distinct clunck in the drivetrain as what I took to be the 4x4 system disengaged to allow the abs to work. There was a corresponding clunck when I took my foot off of the brake.
Coming back through Germany the drive pinion for the drive to the rear wheels broke up... coincidence?
When I got home, my new Audi 80 TDi was waiting for me for my next 4 years of 123,000 miles of dependable and frugal, if not envigorating, motoring. Its handbook, if my memory serves me correctly, said that difference in tyre depth on quattro models was not significant...
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