wheel question.. why is width and diameter in inches but

[Louis-Alain Richard]

Maybe the explanation lies in these facts:

1- Offset exists only on wheels that are NOT zero-offset (where the bolting
flange is in the center of the tread)
2- All RWDs (American cars until 1980) usually use zero-offset wheels 
3- FWD cars are an European invention (since the 30s with Citroen)
4- FWD cars need positive offset wheels so the load on the wheel bearings is
in the center of the tire tread and the CV joint is not too far inboard.

So, my guess is that European manufacturer needed the offset for their FWD
cars (and measured it in mm) but the tire standards were already cast in
stone (in inches, more precisely). 
Hence the dual standards of the automotive wheels.

FWIW,

Louis-Alain
In Quebec where dual standards are everywhere. 
I am 6'3", but my car fuel economy is around 12 liters/100km.


> >
> >When Michelin invented radials (mid 60?s?) they, being
> >French, sized them in mm but had to keep the inch
> >wheel part to allow radials to be fitted to all the
> >existing wheels.
> >
> >A few car companies have done metric wheels (Rover in
> >this country) but they have never caught on, largely
> >because of limited tyre choice and at the risk of
> >copyright problems ?if it ain?t broke......?
> >
> >Mike
> >
> >--- Alex Kowalski <akowalsk at comcast.net> wrote:
> >> It's not a stupid question.  The simple answer is
> >> that Jimmy Carter tried to convert the United States
> >> to the metric system.  The only people who used the
> >> metric system at that time were engineers and
> >> scientists who were looking for something
> >> complicated like a universal, base-ten measurement
> >> system with which they could communicate with their