Rim Width, is the distance between then inner surfaces of the wheel, and is where the tyre is seated against the edge of the wheel.
Rim Diameter, is the diameter of the inner surface of the wheel, and again is where the tyre is seated.
These two measurement are the most commonly quote, eg 10x5 or 10J5, which means the wheel has a 10inch rim diameter and a 5 inch rim width, the "J" allegedly refers to the shape of the wheel rim in cross section(?), and hence the type of type required, J is normal !
The other two measurements are quoted less often, but unfortunately, are more important than the first two.
PCD, Pitch Circle Diameter, is the diameter of a circle centred on the rotational axis of the wheel which passes through the CENTRE of the stud holes in the wheel. This measurement is generally quoted in millimetres and is coupled with the number of studs the wheel is designed for, so for a mini with standard hubs, the PCD is 4 x 101.6mm ( or 4 inches ).
Offset,or ET(EinpressTiefe; German!), this determines the distance between the centre of the rim surface and the face of the wheel where it is bolted to the hub. Not only does this measurement affect how much of the wheel sticks out, but also the suspension and stresses applied to bearings. It is possible to alter the offset of a wheel by the use of spacers, however, this is only useful for a wheel which has too much +ve offset.
What is the standard mini wheel size ?
There have been many standard wheels for the mini, ranging from the 3.5Bx10 rims on the early MK1/2's, through the 4.5Jx10 cooper "S" rims to the more familiar 4.5Jx12 steel and Alloy wheels, and finally the 6Jx13 Sportpack alloys.
What is the standard offset(ET)?
Due to the lack of documentation on this I've actually measured a few wheels, and the standard seems to be about 25mm +ve. Cooper 'S' Reverse rims ( not to be confused with genuine 'S' rims ) have a lower offset of about 15mm +ve. Unfortunately I don't have any Sportpack rims so don't know what they measure.
What effect will a small offset or even -ve offset have on my mini ?
Basically, apart from making the wheel stick out more from the bodywork it also adjust what is called the King Pin Offset. Without going into too much detail as I'm sure that's an FAQ all of it's own, basically what this means is the distance between the effective centre of the wheel is moved further away from the pivot of the steeping mechanism, which changes the attributes of not only the steering, but the suspension, wear and ultimately, handling of the vehicle.
Can I use Metro wheels on my Mini?
You can but you will have to use spacers aswell, this is because the Metro has a higher offset than the mini ( 35-42 +ve), and without this would probably rub on the likes of shock absorbers but would also lookvery silly.
Will 4 x 100 PCD wheels fit a Mini ( as it's only 1.6mm out )?
Absolutely not, even though it is only that small amount out, even if you could manage to push the wheel onto the hub the studs or nuts would not be able to locate properly. This would be very dangerous.
Edited by GuessWorks, 23 October 2007 - 03:08 PM.