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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > Regional Forums > UK > UK Technical Forum > tyre Size going from 17 to 18



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      06-02-2009, 08:21 PM   #1
BMW_NP
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tyre Size going from 17 to 18

Hi
basicly i manged to punture my RFT twice now i got it repaired the first time and i had a punture on the same tyre i got repaird a few months ago,

And i was thinking of getting a new set of rims for my car just was waiting for the tyres to wear out (2-3months) but i though might as well get new rims now, what i wanted to ask i check the current tyres on my car and both front and back are 225/45/R17 i have a 325i , but reading a lot of other threads and looking in the bmw accessories book the set up should be 225/45/R17 front and 255/40/R17 on the back, could it be that the prevois owner changed them , because from what i can see the alloys the OEM

and if i was to upgrade to lets say 18's what tyre size would i need?

thanks
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      06-03-2009, 01:56 AM   #2
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17's on a 325 are 225/45 all round as standard and as an option are available with 225/45 on the front and 255/40 on the rear.
18's as standard come with 225/40 at the front and 255/35 at the rear
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      06-03-2009, 02:20 AM   #3
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tire width depends on rim width. you can get a 19" rim and still put 225 on it if the width is max 8.5

OEM e90 18" bmw rims are staggered meaning that the front will have a width of 8 and the rear will have a width of 8.5 corresponding to 225 and 255

you could also get a non OEM rim that has the same width on all corners and go with 225 all around
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      06-03-2009, 05:14 AM   #4
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Thanks, or clearing that up for me kend and neo,
1 more question, is there really any diffrence in handing/safety if i was to get repica alloys,
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      06-03-2009, 05:40 AM   #5
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and would 225/40/18 fit all around because i dont see why the back has to be 35, wouldnt that make the back tyres a little bit small then the front if they were 40
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      06-03-2009, 05:46 AM   #6
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The 35 and 40 figures refer to a percentage of the width, this figure is the sidewall height.
So a 225/40 -17, a 225/40 -18 and 255/35 -18 all have the same overall height and rolling radius.
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      06-03-2009, 05:49 AM   #7
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oh i see i forgot the sidewall was done as a percentage
so if i was to get 18" on 225 all round, will 225/40/18 tyres all round would be fine?
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      06-03-2009, 06:19 AM   #8
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yes, 225/40/18 all around would be fine IF your new rim width does not exceed 8-8.5 (even on 8.5 it will look a little stretched, best is to go for 18x8)
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