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!

Why do they have to match?

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.

Ah! I thought it was for your proper car

Tyre Width Profile Diameter Rolling Dia
225 50 17 25.85826772

Tyre Width Profile Diameter Rolling Dia
245 45 17 25.68110236

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]

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]

225 x 49

Blxed first answer, sorry

[Edited on 21/6/09 by Macbeast]

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!