Tyre marking

Could someone please explain how tyre marking for bicycles works. It certainly isn't like tractors :-) Tractor rims are measured in imperial units, most modern tyres have width measured in millimetres. A 540/65 R 38 tyre is nominally 540 mm wide, has an aspect ratio of 65 (tyre height is 65% of it's width) and fits a rim 38 inches in diameter.

When I look at my mountain bike, the measurements given on the side wall are reversed - 26/2.1. I guessed that would mean 26 inch rim, 2.1 inch wide.

Nah - the rim is only 22 inch diameter.

So, I was looking for a S/H hybrid / road bike with wheels something like 28/ 1 3/8ths to cope with Edinburgh's cobble stones. Now I guess that is fine, except the first bike I looked at had no sidewall sizing ! but 24" rims, looked like 1 3/8ths to me.

Obviously no sidewall markings suggests the cheapest of the cheap. Probably reflects on the bike (which was originally bought in Oz). However, I'm a curious type and I would like to understand bicycle tyre marking.

Cheers, Mike.

P.S. I notice a lot of talk in metric sizes. I can cope with metric or imperial explanations, thank you :-)

Read it all about it...

http://sheldonbrown.com/tire-sizing.html

__________________
Morphed Bianchi Camaleonte IV 2006, Ridley Damocles 2006, Garmin, Mac

Exactly what I was looking for thank you. Much easier in ISO, and I would like 35-622 or 38-622.

Cheers for this, Mike.