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I haven't seen any discussion of the theory - maybe some just discovered it empirically. I would guess its because it allows the tyre to better resist the deformation caused by the lateral force during cornering, as both sidewalls are pulling the tread taught when the rim is wide. That is, its more rigid, so when the the lateral force of cornering is applied they deform less.

That will vary depending on whether you're talking about street radials or R-comp or slicks on the rim though. It's probably reasonably true for radials, less so for track tyres.

True, but track guys are always looking for any tiny increment in performance, and it was in the discussion of track rims i first saw the argument Here's the post: http://www.skylinesaustralia.com/forums/topic/156842-best-rim-and-tyre-width-for-circuit-gt-r/#entry2915649

Theory behind this?

I think the theory is 9 inch tyre, 9 inch rim...a 225 is not smaller, its the same size... though I'm not sure I agree...as a 245 or 255 is usually recomended for a 9 inch rim be it track or street....well thats what GTR come out with standard...surely Nissan cant be wrong...lol

Thanks for your help,

I made my decision and ordered 245/45/17 ..

It gives me the right look and I guess I got it 90% right with that.

I think it also comes down to person taste and what you do with your car.

As said the GTR comes with these tyres and they fit without too much drama.

Will report back when the new tyres are fitted.

For a 225/40 tyre the right rim size is 7.5 to 9.

It would look pretty stretched on a 9'' though.

http://www.carbibles.com/tyre_bible_pg4.html

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