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      07-02-2010, 09:09 AM   #59
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Drives: BMW 340i Touring
Join Date: Apr 2007
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Originally Posted by 335diesel View Post
Irn - as Roger says, this was a few years back when dealers didn't know what was happening.

/// =- 205/50 is quite slim/high profile. Mine are 225/45 which probably makes a noticeable difference compared to 205/50s. Cheers for the link though! Anywhere I can find weights of tyres? Seems very tricky to find any.

You are right though - 19s (255/35) are only 4mm larger than my 17s with 225/45s.

Edit - tried 255/35 again and the difference is now 27mm compared to 225/45 - over an inch. Hmmm...
This is proving quite tough to get to grips with isn't it.

255/35/19 is not the right size and is TOO BIG for a E9x. The correct rear size is 255/30/19. You can also use 265/30/19 at the rear as it is almost the same diameter. The fronts are 225/35/19. The whole point is that you choose a tyre that keeps the diameter the same.

My last car had 225/45/17s with Contis, Goodyear and Falkens, and I used to use the 205/50/17s on the same car. There was not alot of difference as the side wall is only 1.5mm deeper on the 205 over the 225 - they are pretty much the same size tyre, just a bit narrower. I chose them exactly because they are the same diameter as 225/45/17s.

Regarding weights - these are not easy to come by - but the general rule is that tyres weigh less proportionally than wheels - hence moving to bigger wheels / smaller tyres to keep the same diameter is likely to increase the unsprung mass, but it depends on which wheels etc.