Wheel \ Tyre sizes, Metric & Imperial mixed, why?

R

RichardG

Senior member
 An Englishman Abroad.
Does any one know why when it comes to wheels &tyres we have a mix of metric and imperial measurements, for example when it comes to a rear 108 why is it 8.5J X18 and not 216J X 457 fitted with a 255mm X 18" tyre and not a 255 X 457, hope it I have made some kind of sense, it just strikes me as odd.
 
It's basically due to the US having the majority of cars in the early years and them standardising on specific tyre widths per wheel diameter. You'd get a 8x13 inch rim with a 8x13 inch tyre - if you wanted a wider/narrower tyre then you had to go to the next wheel size.

Eventually the Europeans decided there were not enough options for their needs and started adding a metric prefix to the front of the tyre size to denote that it was wider/narrower but would still fit a certain wheel. Thus you could have a 225x8x13 or a 195x8x13, and still kept within the US rule of having the width and diameter in inches.

The diameter of the wheel has remained in inches but the width has been kept in metric - and they've since added the sidewalk profile as a percentage of the width.

There used to be a history section on the Dunlop website that explained all this more clearly, but it seems to have disappeared.
 
come to think of it isn't it illegal to use imperial measurements now? don't you need to state the metric equivilant if you want to use imperial? something along those lines anyways...
 
If it were up to me we would go 100% metric and then I would only need 1 set of tools... :thumbsup:
 
peddy said:
come to think of it isn't it illegal to use imperial measurements now? don't you need to state the metric equivilant if you want to use imperial? something along those lines anyways...
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That's what got me thinking about, plus I'm currently in France and noticed the sizes were the same but somehow expected them to be in Metric.

WLH said:
If it were up to me we would go 100% metric and then I would only need 1 set of tools... :thumbsup:
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Metric Screwdrivers are a bitch to find, even harder to find Left-handed metric spanners.
 
peddy said:
come to think of it isn't it illegal to use imperial measurements now? don't you need to state the metric equivilant if you want to use imperial? something along those lines anyways...
Click to expand...

There are so many exceptions that it makes the rules itvit pointless. All supposedly to appease the EU.

I didn't see the government demanding that all our road signs were changed to kilometres.
 
mmm-five said:
I didn't see the government demanding that all our road signs were changed to kilometres.
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very true, yet i remember reading in the paper that a owner of fruit market stall was fined because he refused to displaying items in metric. hmm... shall we fine the government? bunch of hypocrites!
 
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