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Author: Subject: help me work out my tyre sizes...
aerosam

posted on 21/6/09 at 12:59 PM Reply With Quote
help me work out my tyre sizes...

I have fitted 245/45/R17 tyres to the rear, I want to fit 225 wide tyres to the front, so what profile should they be to match the rears?

The wheels are 8.5J x 17inch.

Thanks!





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Mark Allanson

posted on 21/6/09 at 01:06 PM Reply With Quote
Why do they have to match?





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aerosam

posted on 21/6/09 at 01:15 PM Reply With Quote
because if they are a different diameter they will rotate at a different rate to the rears and confuse the ABS.

Should have mentioned this is for my tintop BMW.





Had enough of this dictatorship known as LCB. Gone elsewhere, not coming back. Kiss my ass ChrisW.

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Mark Allanson

posted on 21/6/09 at 01:24 PM Reply With Quote
Ah! I thought it was for your proper car





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Mark Allanson

posted on 21/6/09 at 01:29 PM Reply With Quote
Tyre Width Profile Diameter Rolling Dia
225 50 17 25.85826772

Tyre Width Profile Diameter Rolling Dia
245 45 17 25.68110236





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Humbug

posted on 21/6/09 at 01:32 PM Reply With Quote
245/45/17 has a theoretical diameter of 65.23cm

225/50/17 has a diameter of 65.68cm, i.e. just under half a cm different depends how sensitive the ABS is

(I calculate a 225/41.3/17 to have a diameter of 61.77cm, quite a lot different...)

[Edited on 21.06.2009 by Humbug]

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tul214

posted on 21/6/09 at 01:35 PM Reply With Quote
225/50/17 would give a +5mm difference
225/45/17 would give a -18mm difference

Ha Ha...eta..must type faster!!

[Edited on 21/6/09 by tul214]





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Macbeast

posted on 21/6/09 at 01:37 PM Reply With Quote
225 x 49

Blxed first answer, sorry

[Edited on 21/6/09 by Macbeast]

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aerosam

posted on 21/6/09 at 05:32 PM Reply With Quote
So the 245 wide tyres have a rolling circumference of 102.463cm and the 225 tyres have 103.169cm.

So the front tyres will turn 0.706cm less for every rotation of the rears.

I doubt it's that sensitive - thanks guys!





Had enough of this dictatorship known as LCB. Gone elsewhere, not coming back. Kiss my ass ChrisW.

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