View Full Version : Tyres and rims

19th Aug 2005, 14:54
Just a quick question.... why are wheel rims measured in metric while tyres are mainly in inches?..... I know it's not an aviation related topic but PProoners are good on cars as well.

Biggles Flies Undone
19th Aug 2005, 15:20
Is that right? I thought that it was the other way around - wheels in inches and tyre sizes in mm..... :confused:

19th Aug 2005, 15:32
Why are heroin and cocaine traded in grams while cannabis is traded in ounces?

19th Aug 2005, 15:41
Biggles......you're right.... it is the other way around!!! typed in a hurry without engaging brain. And the answer is.......?

Biggles Flies Undone
19th Aug 2005, 15:46
Wheels are made in the UK in proper sizes. Tyres made by furriners who don't understand Imperial? Anyway, the tyres sound a lot sexier as 265x35 than the equivalent in inches ;)

19th Aug 2005, 17:00
sound a lot sexier as 265x35 than the equivalent in inches

Dunno about this - 10" is on the high side of modest - even up norf

19th Aug 2005, 17:25
It's even worse than that though isn't it? Aren't tyres measured in a combination of inches and millimeters?
Mine say 215 x 17 on them meaning they're either far too tall or far too narrow if the units aren't mixed. :confused:

19th Aug 2005, 17:31
I suspect Cheerio is right - IIRC it all came in with these new-fangled radials. Before them we had tyre sizes like 5.60 x 13 - i.e. both measurements were in inches. Then the Michelin X appeared - and these were 145 x 13. So blame Michelin (b**** frogs!!)

Conan the Librarian
19th Aug 2005, 17:33
SG that sounds like 4X4 territory to me. My own rubbery bits on the Volvo are 195/60R15V

195 is section width of casing in mm

60 is the aspect ratio of the tyre. Only 60% as high as wide

R is for Radial

15 is the wheel size in inches.

V is the speed rating

There are some oddball metric wheel sizes about though... I think they were introduced with the incredible (still laughing...) Dunlop Denovo run flat tyre, which would put us in the late 70s and early 80s

As for 560X13 and similar, where the measurements were all imperial, they were almost all of crossply construction.


19th Aug 2005, 17:49
Nope, not a 4x4, which would have been clear if I'd said they're 55% aspect ratio, but I didn't as it would have diluted my point about the stupidity of the sizing system. ;)

By the way of another useless piece of information, some slicks (often still of cross ply construction if that has any bearing) are maked either all in metric or all in imperial depending on their origin.
Which ever units are used it seem far more logical to stick to one or the other.... not that you could easily get it wrong I suppose... 215" wide tyres may be a little excessive and 17mm diameter ones would make cattle grids interesting. :ouch:

Onan the Clumsy
19th Aug 2005, 18:04
Aren't tyres measured in a combination of inches and millimeters? that's because the tyre size containes the rim size :8

Here's everything you could possibly want to know about tyre sizing (http://www.discounttire.com/dtcs/infoSidewall.dos) courtesy of Discount Tire [sic]

19th Aug 2005, 18:07
How many North Americans are seeing the title of the thread and wondering what a "tyre" is :E :E

19th Aug 2005, 18:11

It's still stupid. You don't go into a timber merchants and ask for a length of 4"x100mm, measure your cars fuel consumption in litres per mile, say you're 6' 25mm tall or... or.. :(

Romeo Charlie
19th Aug 2005, 18:22
You don't go into a timber merchants and ask for a length of 4"x100mm

Ah, but you do ask for 2m of 4x2.

19th Aug 2005, 18:48
Yeah, but you'd of wanted a 2 metre length of 4"x4" so they'd still have got it wrong. ;)

Ok, ok, that was spurious and yes I did mean to say 'a length of 4"x50mm' previously because I did have 4x2 in mind and I don't want to play any more and, umm, where's me bat and ball I'm going home.... I'm still not 6' 25mm though.... :{

19th Aug 2005, 19:12

Pretty sure it was Dunlop, a Belfast man who invented the pnuematic tyre. He's a blue plaque and everything.


Gotta stick up for the old country like.


19th Aug 2005, 23:45
I suspect that if you wanted 2 m of 4x4 you would be offered 1.8 or 2.2 metres.
I think sheet goods are still basically 8' x 4' but labelled in millimetres. It's all a mess.

Don't forget that metric is too complicated for the cousins though and they are still imperial.

Mike W

20th Aug 2005, 02:25
How many North Americans are seeing the title of the thread and wondering what a "tyre" is
Jerricho...that's why I opened this thread. :8

20th Aug 2005, 02:48
That's as maybe Skylark but I didn't want 4x4 whatever length it comes in. I wanted 4x2, I ba££sed up due to the mixed units. :rolleyes:

Actually, hang on, going back to tyres... explain me this one then Onan. You said that's because the tyre size contains the rim size Which means the inches match up in one direction but I still have a 215mm wide tyre on a 7" wide rim. Same axis, mixed units.
See, it is daft... and I'm not as stupid as I thought I was. :hmm:

20th Aug 2005, 10:46
It just doesn' sound the same -
"bugger off, or I'll wrap this bit of 100mm by 50mm round yer 'ead"

20th Aug 2005, 10:58
If Americans are confused about tyres, they would be equally baffled by a length of 4x2.
It would be 2x4 over there.

Incedentally I am always impressed that they stick to the imperial system, europeans are so snobish about the metric system but the space shuttle seems to make it into space and back on pints, gallons, feet, inches, 1/8ths 1/16ths etc

20th Aug 2005, 11:35
Only just .. . ;)

20th Aug 2005, 16:11
Judes, your honesty stands above all others ;)