Tyre Profiles... Let Me Know If This Sounds Stupid.

[Dobz]

I'm on the hunt for Federal 595 RSR tyres in 255/45/17. I called up a tyre dealer and he informed me that he could only get 255/40/17 but he explained the tyre profile would be the same as 45. Clearly 40 and 45 are different numbers but seeing I'm not tyre guru I don't know what to believe. Is this guy talking crap?

[StreetR32]

If your talking about affecting your speedo then its based on a rolling diameter - most tyre shops should be able to match tyres to suit your car.. Just ask the question when you talk to them.

Edited October 28, 2012 by StreetR32

[GTSBoy]

The height difference between the tyres is 5% of 255mm, which is of course, 12.75mm per sidewall. Total is double that, being 25.5mm, out of a total of 661mm. Rolling circumference will therefore be 4% less with the lower sidewall height. Speedo will read 4% faster when running the smaller tyre, at the same real speed.

[KiwiRS4T]

If you have an awd attessa car you would not want to mix 40 and 45 profiles.