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      09-05-2011, 06:16 PM   #30
Lotus7
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Quote:
Originally Posted by clarka@csolve.net View Post
We just bought a set of used aftermarket BMW rims with 245/50/R18 Yokahama W Drive tires on them. The rims and tires are like new! Unfortunately, we did our homework on tire size but not on rim compatibility. They are off of a 7 series. We will check with our tire guy this week to see if they will work. We are keeping our fingers and toes crossed!

Worst case scenario, we bought them for a good price so hopefully we can flip them if we need to.
The Spec. for X3 (F25) wheels in the 18 inch diameter are:
wheel width = 8 inches
Bolt circle = 5 X120 mm
Hubcentric bore = 72.5 mm
Offset = 45 mm (acceptable range 43 to 47)

For the 7 Series (depending on year/chassis):
wheel width = 8 or 8.5 inches (OK)
Bolt circle = 5X120 mm (OK)
Hubcentric bore = 72.5 mm or 74.1 mm (depending on model)
(will fit if 72.5, but if 74.1 reducing rings can be installed) (qualified OK)
Offset = 18 mm (acceptable range 15 to 20mm) (NOT OK)

If the wheels are from a late model 7 Series, they might actually mount on the X3 because they have the correct center bore. However the centerline of the tires will be 25 mm further out on each side. That may cause the outer sidewall to rub on the fender, but more importantly the wheel bearing loading will be way off center leading to almost certain wheel bearing damage. Unfortunately, the lack of enough positive offset can’t be compensated. (spacers reduce the effective offset for positively offset wheels, so won’t help.

The other issue is the that the TPMS transmitters in the 7 Series wheel won’t work with a F25 chassis X3, so would all have to be replaced if you want the TPMS system to function.

Since they're aftermarket rims, you may be lucky and find the person who purchased them for the 7 didn't bother to get the correct offset for that chassis. It's easy to measure the offset (again it should be around 45 mm for the X3).
Sorry for the bad news.
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