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Hi,

I'm a newbie so please be patient as this is my first post.

Car: E46 Sport 2003, M Sport wheels, 6 speed box etc.

My current tires, as supplied from new by BMW are:
224-40-18 and 255-35-18 Michelins.

I have read the forums and understand that the M3 has:
225-45-18 and 255-40-18 tires.

Can I fit the M3 size tires, since I understand they are cheaper, and if so what effect will this have?

One of my rear tires needs replacing whilst the other one has 3mm of tread. I realise that if I changed the size I would have to fit a pair on the rear. Can I just change the rears since the fronts are in good condition, assuming that I can fit the different M3 size?

Finally, irrespective of the above, could I just change one of the rears, assuming I kept the standard tires?

I normally change tires in pairs but had a bill of £1.200.00 yesterday for new disks, pads and service etc. so money is tight at the moment.

Many thanks in advance.

Regards

John
 

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12,959 Posts
Hi John,

If you changed the sizes to M3 then the difference in rolling circumference would show on your speedo as follows. (showing fronts just to display size/speed differences)

225/40 18 - 225/45 18 would mean that your speedo would be displaying 70mph but actually travelling at 72.47mph

255/35 18 - 255/40 18 @ 70mph you would actually be travelling at 72.81mph

Tyre sizing is supposed to be kept within +/- 2.5% of the original tyre size.

Fronts = 3.53%

Rears = 4.01%
 
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