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

[PeterJ]

so I had the existing wheels off today which are copy M3 wheels from Taiwan with no off set written on them. I measured them both and found:

Front: R18, Width 8inch (203mm), Wheel backspace 6.25(160mm); Offset 160 - (203/2) = 58
Rear: R18, Width 9inch (228mm), Wheel backspace 6.25 (160mm); Offset 160 - (228/2) = 46

I measured the back space by placing a flat metal meter rule across the wheel & it was just about touching the inner rim even though the tyre was still on. I then measured the distance between the point where the wheel hub contacts the wheel when bolted on out to the metal rule (as described in in the web linked I posted above. I was surprised to find the back space the same on both wheels despite the difference in width as I knew that would mean a different offset between front & rear. the offset on the front seems too big???? The front wheels used to rub the inside of the wheel arches on full steering lock when I first purchased the car with 255/35's all round on the same wheels, but the rubbing stopped when I changed the front tyres to 225/40's on the front (& kept 255/35 on the rear). Attached is the rear wheels picture for your reference ... I will post a couple more views (excuse the dog pooh on the left tyre!)

 

[PeterJ]

Here are some more views of my Z3 to show how the wheels/tyres fit into the arches (existing) ... do the offset values I mention seem reasonable given the way the wheels look on the car?? The tyres on some of the pictures are Dunlop Z1's but also front 225 & rear 255 on the same wheels

 

[Aceman]

Your offset calculations are slightly out as I have just worked them out to;

Front: 57.25
Rear: 44.45

Seems you are slightly high on the imperial to metric conversion of the backspace readings
going on a 25.4 conversion figure. But this doesn't account for the high front figure which would show with your front wheels looking too inboard. Are you sure they are 8" and not 8.5" ?

Pictures from directly behind/front and inline with the body work would make it clearer to see how far the wheels poke out and give an idea what they are like if you could Peter.

I am also astonished that you had 255 width tyres originally on the front as I would have thought they would be way to wide for 8" rims and look noticeably so and that they fit with such a high offset.

 

[zedonist]

The front offset calculation cannot be right, i think all wheels must be 9". At 57 i think it would rub no matter what tyre, re-check before ordering wheels, are there no markings on the wheel on the inside, they should at least have the rim width on them, can you take a photo of the inside Pete? Looking on this web site, it does not look like the M3 had an offset that high http://www.gruppeb.com/BMWwheels/

Also don't forget the offset is specific to the wheel style as well, so those BBS Chromes may be different to what you have, drop BBS a mail, i am sure they will give you the specification required

 

[Aceman]

Must admit I thought the same that's why I suggested they might be bigger as those figures don't really tally.

 

[PeterJ]

Thanks. I would agree that my measurements seem not to make sense. So difficult to measure without proper equipment... also in this part of the world, it is so difficult to find people who know what they are doing. The local guy I went to runs a large wheel store in Hong Kong, yet he said he never measured off set & does not know how to ... he measured the width using callipers, but I would not be surprised if it was not correct as he was very 'rushed' & would not focus... I tried to measure the rims with a rule, but that was not possible to do accurately. I will post a picture of the front.

On the 'other paw', I am looking into the possibility of a set of wire wheels from India as on the attached photo which I cannot quite tell if a 2.8 like mine of a 1.9

If you look at the wire wheels on this picture, what wheel diameter, width & off set should I consider for my 1998 2.8? I would be using higher profile tyres if I choose the wire wheels like on the picture, so perhaps 17 inch rims rather than my existing 18inch? or even 16 inch? I would like them to be reasonably wide, but perhaps not quite as wide as my existing. Hope you can kindly offer some advice (but not on whether wire wheels are right for the Z3 or India is like China etc! ) on the best wheels for my Z3 that would make the car look more like a 'Beefy Classic'! Thanks again!

 

[PeterJ]

 

[PeterJ]

above are pictures of my existing front wheels. They are made in Taiwan & not genuine M3 whels, but are OK, part from I find the M3 wheels unsuitable for my style of Z3. Any comments about the offset welcome

 

[PeterJ]

more views of my existing wheels (Toyo Tyres)

 

[PeterJ]

sorry, but 'Donkey brain' here could not work out how to rote the first three photos! ... never mind, you can still see the wheel relative to the body

 

[Brian H]

Front: R18, Width 8inch (203mm), Wheel backspace 6.25(160mm); Offset 160 - (203/2) = 58
Rear: R18, Width 9inch (228mm), Wheel backspace 6.25 (160mm); Offset 160 - (228/2) = 46

A question, sorry if I missed it earlier in the thread, how did you measure the wheel width? from what point to what point?

 

[zedonist]

Thanks. I would agree that my measurements seem not to make sense. So difficult to measure without proper equipment... also in this part of the world, it is so difficult to find people who know what they are doing. The local guy I went to runs a large wheel store in Hong Kong, yet he said he never measured off set & does not know how to ... he measured the width using callipers, but I would not be surprised if it was not correct as he was very 'rushed' & would not focus... I tried to measure the rims with a rule, but that was not possible to do accurately. I will post a picture of the front.

On the 'other paw', I am looking into the possibility of a set of wire wheels from India as on the attached photo which I cannot quite tell if a 2.8 like mine of a 1.9

If you look at the wire wheels on this picture, what wheel diameter, width & off set should I consider for my 1998 2.8? I would be using higher profile tyres if I choose the wire wheels like on the picture, so perhaps 17 inch rims rather than my existing 18inch? or even 16 inch? I would like them to be reasonably wide, but perhaps not quite as wide as my existing. Hope you can kindly offer some advice (but not on whether wire wheels are right for the Z3 or India is like China etc! ) on the best wheels for my Z3 that would make the car look more like a 'Beefy Classic'! Thanks again!

Its a 1.9 in the picture, the 1.9 is narrow body with shorter trailing arms and drive shafts to the 2.8, so wheel offsets tend to be the same, but you cannot go as wide as a 2.8 on the rear due to inner clearance. again i would approach the company and ask them what offset they have that would suit a Z3

 

[PeterJ]

the guy at the garage measured them with calipers, but was so rushed, I don't think he did it properly ... I tried to measure with a rule, but not practical... I would not be surprised if the measurements are wrong... maybe I will try to measure again with someone else

 

[Lewy]

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

Yes you can run staggered tyres on non staggered rims, my fronts are 225/40/18 and my rears are 255/30/18 iirc. All running in 8.5j rims.

Buying wheels out of China might get you a bargain but do check those weights as I made the mistake of buying replica cheap wheels and whilst they look good, the handling is all over the place compared with the forged style 24s that I had on before. Our Zs are not that heavy compared with the E30 / E36 where our cars get most of their parts and so whilst E36 wheels are a definite fit, I would keep to under 11kg (max) per wheel but lower if you can.

 

[Jonttt]

You need the correct central bore. To big and you will need spigot rings, too small and it won't fit ;-)