The 1999 Passat TDI Sport runs 205/60/R15 tyres, which seems to be a funny old size - not especially common and a bit pricey.
My question is this: is the '60' measurement fixed based on the wheel being used? I.e. could I conceivably use tyres of a different 'profile' measurement?
205/55/R15s seem to be a hell of a lot cheaper and more readily available at knock down prices on E-bay.
As far as I can hypothesize, using a lower profile tyre would reduce the overall diameter of the wheel & tyre unit. Would this mean a slower road speed for a given engine speed in a given gear? Would lower profile tyres even fit the alloys? I don't want lower profiles to look cooler, I want a cheaper size of tyre!
If anyone has any thoughts, recommendations, or experience of this sort of thing, it'd be much appreciated. Also, info on the cheapest place to get tyres would be helpful...
Cheers.
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Looking at Johnsons Tyres website (which I use as a guide for good prices to find matches for locally)
Premium tyres are about £45-£50 for a tyre.
For a Passat sizzed car, I would think this to be good, are you being given bad prices?
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There would be no problem in fitting 55 profile tyres in place of the 60's - but the gearing and speedometer will read slightly differently - a small price to pay IMO.
The only difference would be the wheelarches will look slightly less 'full' with the skinnier tyres and perhaps road noise and ride quality might suffer.
Shop around is my advice...
--
groups.msn.com/honestjohn - Pictures say a thousand words.....
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"Standard" profile radial tyres are 82% give or take (cross plies are 100% as far as I know).
205/60/R15 tyres will have a rolling diameter contribution from the tyres of 2 times 205mm times 60/82=300mm. The suggested replacements are 2 times 205 times 55/82=275.
The bit from the wheels is 15x25.4=381mm
So the amount the speedo would under read by as a percentage is:
1-(275+381)/(300+381)x100=3.67%
(No need to convert to circumference as pi will be divided out).
I?ll not claim supreme accuracy as there will be small amounts of variation between different makes of tyres, but this is near enough for you to decide if the difference is acceptable to you.
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Slidding,
What % error occurs then if the specified tyre is fitted with full depth tread i.e 8mm and then is changed at the legal limit i.e 1.6 mm ?
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Depends how big it is!
Some tyre makers have given the actual rolling diameter of their tyres as this will be less that the caluculated owing to load.
However it is fair to assume the differnce will be a bit more than calculated.
So in the example, if the 681 mm is new, then 1-(681-12.8)/681 as a percentage is not a bit less than the change. Near enough 1% calculated, but I guess the true figure is still less than 1.5%
And that is why we don't worry about MPG and speedos when our tyres wear.
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Useful website for calculating overall diameter of wheel and tyre.
www.tyresave.co.uk/tyresize.html
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Hi Sliding,
Your calculations are all very clear though I think the 82% might be a misnomer. As far as I have always been able to work out a, for instance, "50" aspect ratio tyre has a profile 50% of the width of the tyre, not 50% of 82% of the width.
Your point about load is a good one, the effective diameter of a wheel/tyre is reduced considerably when the tyre is under inflated relative to the load.
Regards.
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205/60V15s are common - had 10 or 12 on a 1.8T over the last 4 years - ATS mobile always came the following day to fit them - company car so I didn't pay. Dunlop (mainly) and a pair of Avons.
If you want a really odd size try 185/50R16!!!
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Ian
I'd agree - 205/60V 15 is a common size used by many E36 BMWs.
JS
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