Tyre sizes

[Panic Button]

Why do tyre sizes mix imperial with metric?

Tyre width in Millimetres

Diameter of inner rim in inches.

[chas2008]

its easy to alter tyre widths to metric, but imagine the logistics of the diameter !! wheels have always been measured in inches, if the manufacturers suddenly decided to go metric( unless they used the metric equivelant of inches which would cause even more confusion) it would mean all tyre manufactures would have to come up with a complete set of new measurements for every tyre !!! would cost 10s of millions.
As a point of interest the plumbing trade mixes metric/imperial

[R1Geezer]

Because it has the benefit of annoying both the EU and the US all at once!

There are metric tyres in existance but they are generally shunned by the motor industry and cars with them are very much devalued.

Chas is correct that if they went metric they'd have to replace every jig in every factory, lots of wonga!

[Panic Button]

... but other manufacturers are having to change machinery or jigs every week for new car models etc.

There would be no problem supplying the correct wheel sizes to metric or imperial wheels - are there not loads of different shapes and sizes already?

It just seems odd to me that on wheel diameter alone everyone stays imperial, while so much else is constantly changing.

We even decimalised our currency for Pete's sake!

[chas2008]

i dont think the wheels would be an issue, it would cause havoc with the tyre manufactures.....

[ChuckFickens]

As R1 said, there are metric tyres about, the old BMW 901's 525TD used to be fitted with TD230/55ZR390 tyres, so the rim size was 390mm!

All that happened is all the owners found out when they went to get the first set of tyres that it worked out cheaper to buy 4 new 16inch rims and a set of tyres to match rather than 4 390mm tyres.

(I think some of the early Austin metros came with metric wheels too, and everyone changed them too)