Wheel jargon explanation please
 

I have used :search: and google and can't find a simple answer so thought I'd ask you experts.

Why is it that you in the USA, that generally use imperial measurements, and countries like ours, that use metric measurements, we both record tire widths in millimeters (metric) but wheel widths in inches (imperial)?

Why no consistency between the two measurements? Would it not make more sense to have a wheel width listed as say 8.5" and a tire width listed as 8.5" rather than something like 215mm?

Or record both the wheel and tire width as 215mm?

Because racecar.

I know that doesn't make much sense

But why? Anyone know?

Ok, I'll try to be a little more serious this time. Ahem. There are numerous reasons for this:

- it's a compromise to keep both parties happy (or both equally unhappy);
- it's done to give school teachers a source of material for math problems (e.g. convert all measurements for the following tire to metric);
- it was started by an impish little elf who takes delight in watching humans scratch their heads over questions which seem simple enough but in fact have no answer;

I don't know for sure in the case of wheels and tires, but typically when some convention involves mixed units of measure or otherwise makes no sense it's because it evolved organically rather than being laid out systematically. As the automobile market started becoming more global, there was a convergence of the various systems and people started mixing and matching them based probably on whatever they could best remember. Eventually a universal convention gelled out of the turmoil.

I couldn't find anything definitive, either, but google did come up with a similar discussion from over 5 years ago (!) where they were equally unable to find real answers :bonk:

http://boards.straightdope.com/sdmb/...d.php?t=415309

I think if you used wheel width in mm's people would think that they needed to match the wheel width and tire width exactly which usually isn't the case.

Here's an example 225 width tire is roughly 8.85" and an 8" wheel is generally considered a good size for a 225 tire not a 9" wheel although it can be done it would be pretty stretched.

When i was a kid in the grade school during the early 80s I remember learning all the metric stuff... and then? It's like the US gave up on it. Metric makes SO MUCH MORE SENSE. Damn, I can't ever remember how many ounces in a gallon... but make sure you are talking about liquid ounces and not weight ounces, cause that is different.

Argh, we American's so stubborn.

Fixed it for you. :thumbsup:

Ya know, I really didn't have an opinion on the metric system till I moved to Japan. I then spent a week grumbling about it, then the next few years LOVING it! It just makes more sense.

The only bit I never got used to was temperature. I recognize it is the more logical system, but a lifetime of identifying 70 degrees as room temperature and 30 degrees as below freezing is hard to shake.