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As you are looking at LLTek”s “wheels for BMW” page - we can assume you’re interested in outfitting your car with a new set to provide a tougher, faster, or cleaner look. The table below lists information that is key to your successful purchase. This is as far as the assumption goes and as far as looks go - there are a number of issues worth being informed about before you jump all over your credit card. The issues are technical and will determine not only suitability can also affect a vehicle’s safety. Mounting rims on your car based on appearance alone might be ok for display competition car shows (yes! buy the 20” wheels) but probably will have serious effects on the car’s handling not to mention placing undue loads on bushings and ball joints and your car’s suspension in general.
If your purchase here is for driving (and you do not have a personal mechanic) then the manufacturer’s original offset should be maintained. Most likely your wheels will have the offset stamped i.e. “ET42” and that will be your guide ( ET is an abbreviation from the German word “Einpresstiefe” literally translating as “insertion depth. If your wheel is not stamped here is how to make the calculation - (Warning! - if in doubt - have this checked by an expert.)
Calculating Offset
Calculating the offset of your wheel is best managed on a level surface with the tire off.
1) Measure the overall width of your wheel (just because you have an 18”x7.5” wheel does not necessarily mean the overall is 7.5” - what it does mean is that the measured distance between the outboard flange and inboard flange will be 7.5”.
2) Divide the measured overall width by 2 and this will yield your centerline (a zero/ neutral offset point).
3) Determine the amount of backspacking designed into your wheel by placing the wheel face up on the ground. Measure the distance from the ground to the hub-mounting plane. This measured distance is known as your backspacing.
4) Subtract the measurement of backspacing from your measurement of centerline and the result is Offset but measured in inches.
5) Final step: multiply your offset measurement inches by 2.54 and this will yield your offset in millimeters.
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