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How to choose wheel size for a set of tyres ??

Discussion in 'Z3 Roadster & Coupé' started by PeterJ, Aug 18, 2013.

  1. PeterJ

    PeterJ Zorg Legend
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    Hi all,
    I have been trying to get what I thought would be a simple question answered, but I am having difficulty ... can anyone kindly advise?
    I have a set of R18 M3 wheels on my Z3 which I find boring (sorry M3 owners!) and am in the process of buying a new set of wheels direct from the factory in China (seems most wheels on sale are from China, just that many people don't realize it & pay a small fortune for the wheels thinking they re made in US/EU etc!) at about 20% of the cost you pay in US/EU for the same wheel from the same factory. I have a new set of Toyo Proxes Front: 225/40 R18 & Rear 255/35 R18 and would like to know what size wheels I should buy to suit this size of tyre (I like the tyre size and the tyres are almost new & more expensive than the wheels (!) so I want to keep the existing tyres) ... I have no idea what size the my current M3 tyres are (or maybe they are M5?.. I don't know) as they were fitted by the previous owner.
    My question is that when I order my new wheels from the factory, apart from R18, what other dimensions shall I quote to make sure I get the right tyre? & should all four wheels (not tyres) have the same dimensions??

    Any help appreciated!

    Peter J
     
  2. Daz3

    Daz3 Zorg Legend

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    When I had those size tyres on my zed I had my 18" inovit dtms that were 8j up front with an et 45 and 9j at the rear with an et of 45.
    Or you could try this site. If you put in your standard wheel and tyre size you can match the rolling radius' up by trying different wheel sizes hth.
     
  3. Daz3

    Daz3 Zorg Legend

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    The et or offset depends on what model zed you have as they vary ;)
     
  4. PeterJ

    PeterJ Zorg Legend
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    I have a preface lift 1998 2.8 and I would like to keep the R18 and the tyre size I mention. I just don't seem to be able to find out what R18 wheels to get in terms of size other than the '18' part... sorry for being a dummy !
     
  5. PeterJ

    PeterJ Zorg Legend
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    I have chosen BBS Chromes, but don't know what size wheels I need other than R18
     
  6. Daz3

    Daz3 Zorg Legend

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    As above you'll need 8j (8") front which is the width and 9j (9") for the rear those size wheels with the tyres you have will give you the correct radius. Stud pattern is 5x120 and the offset wants to be about et45 depends what's available in that wheel. If you ring the company your buying from they'll say wether they'll fit or not.
     
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  7. Daz3

    Daz3 Zorg Legend

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  8. zedonist

    zedonist Guest

    If you can acces the site try rimstyle.com, you will find your wheels and get the width and offset required for your car
     
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  9. Jonttt

    Jonttt Zorg Addict

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    Just to clarify I take it you mean most CHEAP ( usually copy) wheels are made in china. Did you not see the test trading standards had carried out by British standards on the cheap Chinese imports recently ? They don't just crack on impact but totally disintegrate !

    You gets what you pays for but personally anything that puts 325HP between me and the Tarmac I don't do cheap Chinese imports. I've got a cheap iPhone charger if you want it though, like new apart from some slight scorch marks on the edge lol
     
  10. PeterJ

    PeterJ Zorg Legend
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    I think I also need to measure the 'off set' which seems to be the distance between the hub and the wheel
    Hi John, yes, you have a point, but you may be suprized at the number of wheels you think are made in UK/EU/US etc, but if you can get to the truth, they are often made in China but they do not tell you that. There are plenty of companys around selling wheels in Western Countries at Western prices, that are from China and you can bu for a fraction of the price because most of the costs you pay are traders profit margins. I am sure there are exceptions and I hope the wheels you have are where you think they are from.
    By the way, apart from iPhone chargers, as far as I know, all iPhones are made in China by Foxxcon, a Taiwanese company.
     

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  11. Jonttt

    Jonttt Zorg Addict

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    The ones under licence are made to certain standards, the cheap copies are not.
     
  12. zedonist

    zedonist Guest

    Don't Foxconn make electronics?
     
  13. PeterJ

    PeterJ Zorg Legend
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    we seem to have strayed off topic here which was about how to choose the size of a wheel for a Z3 for a given set of tyres which is probably my fault for mentioning the word 'China':nailbiting: ! ... just assume the wheel is purchased in UK, coz the question is the same :thankyou:
     
  14. zedonist

    zedonist Guest

    I think you have the answers above Pete, just need to do a bit more reading and measuring to get your perfect fit on the actual make of wheels, Lewy on this site has current thread going where he has the same size tyres fitted, but on 8.5J wheels all round, so there a number of permutations you can have, speak to BBS for the optimum
     
  15. PeterJ

    PeterJ Zorg Legend
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    Yes, thanks. Daz also gave me some good info. So in conclusion, when choosing a wheel,I should take into account the following measurements:

    1. Diameter (18' in my case)

    2. Width: Choices eg. 8" front 9" rear or 8.5" all round (for my tyre sizes)

    3. Stud Pattern 5 x 120

    4. Off Set of et45 (which I think is the distance between the hub and part of the wheel closest to it).

    Kindly let me know if I have missed anything

    I will search to find out a bit more about 'off Set' & tomorrow, hopefully get my existing wheels measured ... the problem is that I am not allowed by law to drive my car from Hong Kong to the wheel factory in China (about 1.5 hours away) so will need to go there by chauffer from the boarder ). ie, I will not have my existing wheels with me when I purchase the new ones for size comparison purposes ... and don't want to bring them all the way home to Hong Kong only to find they are the wrong size:bashhead:

    Thanks for your help:)

    Peter
     
  16. PeterJ

    PeterJ Zorg Legend
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  17. g8jka

    g8jka Zorg Guru (III)
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    I have BBS LM reps, in 18 inch.

    Fronts are 8J and rears are 9J, both with an offset of 35. The fronts sit perfect and the rears have 5mm spacers but sit pretty good even without them. Tyres are 225/40/18 on the front and 255/35/18 on the rear.

    I would go for 8J upfront and 9J rear so they are staggered and get an offset as close to 35 as possible. If you go higher on the offset it wouldn't be a problem but it would look better with spacers to push them out a little.

    Hope that helps.
     
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  18. PeterJ

    PeterJ Zorg Legend
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    Thanks Dave. That is good to know
     
  19. PeterJ

    PeterJ Zorg Legend
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    Hi Dave, do you have the same 35 off set all round or just the rear? Thanks
     
  20. g8jka

    g8jka Zorg Guru (III)
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    Same all round Peter, mine is a facelift model and it sits flush with the arches. The wide arch pre facelift should have a similar gap but I would try and measure this. Measure how much space you have between your current wheels and the edge of the arch. If its a 45 offset with a 10 - 15 mm gap then you could go to 35 offset etc.
     

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