bike tyre stretching ????

So does Germany actually use "28" in the specification of its wheel diameter? It must be one of the few measurements in the imperial system that has survived Europe's use of the SI metric system. Are there any other cases where items are sold in imperial units (as opposed to being an integer number of inches which is translated into metric *)? If there is 1/2 inch difference in diameter of English and German 28" wheels, which one is the true diameter that you would measure? Is one the external diameter of the rim and the other the diameter of the tyre bead which is slightly smaller and has to be levered over the rin?

Incidentally, has anyone actually had to use tyre levers for fitting a bicycle tyre? I always find that I just tuck the bead in at one side, then ease it in by moving my thumbs towards the opposite side and then pull it away from the rim at the very opposite until it pops into place; and vice versa for removing. You'd think that a lever would be needed at least to make the bead pop out from the rim when removing, but I've never found one necessary. Am I unusual?

(*) For example I doubt whether 5 1/4 and 3 1/2 inch floppy and hard disks are/were advertised that way in Germany, France etc - they'd be specified in millimetres.

Reply to
NY
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You'll still see their traditional "28 x 1-5/8 x 1-3/8" marked on the side of many tyres.

Some Germans still use Fuß, Zoll and Pfund as we use foot, inch and pound.

The ISO/ETRTO measurement is the actual millimetre diameter of the bead/seat, which is the same for the tyre and the rim, although there are variations in manufacturing tolerances which lead to some tyre/rim combinations being looser or tighter than normal. The traditional tyre sizes are based on effective diameter: a fat tyre on a smaller rim has the same diameter as a skinny tyre on a larger rim, hence you get two English 26 inch tyre sizes, one with a width of 1-1/4 inch and the other of 1-3/8, with a corresponding 1/4 inch difference in rim size which seems pretty reasonable. But there is some strangeness - English

28 inch (28 x 1-1/2 as fitted to vintage "police bikes") is 635mm, a bit bigger than English 27 inch at 630mm but the German "28 inch" (commonly called 700C) is 622mm, actually smaller than 27 inch.

Wider tyres on wider rims tend to be easy to fit and remove without levers, although some cheap tyres can have very thick inflexible beads that make it harder to get them into the well of the rim, in order to get that bit of slack to pop the last bit over the edge. Conversely some wide but very light and flexible tyres (e.g. racing mountain bikes tyres with Kevlar beads) can be fiddly to fit because they're so floppy they won't stay on until they're held in shape by the partially inflated inner tube. Narrower tyre/rim combinations are more likely to be too tight to fit without levers; I have such a combination on one of my bikes, and the usual method of strapping the bead into the well of the rim just doesn't work. That one needs the application of my workshop-quality steel levers, and it's still not easy. You have to be very careful not to pinch the inner tube when you're using levers, but it shouldn't normally be necessary when fitting a tyre - when removing a tyre it may be quicker and easier to user levers, and if you're going to bin the tube you don't care about pinching it anyway.

Reply to
Rob Morley

Well I never knew that. I always thought that units such as foot, inch and pound were peculiar (*very* peculiar!!!) to Britain and countries such as US, Canada and Australia that had British ex pats. I hadn't realised that non English-speaking countries had at one time used imperial units.

Reply to
NY

In France, if you ask for une livre de beurre (a pound of butter) you will get 500g of butter - a near miss to 454g.

Reply to
Terry Casey

Don't they also use BSP pipe sizes and threads?

Reply to
Fredxx

In Germany, a pound is a half-kilo, 500g , with the definition dating to 1858.

Inch as in "Zoll" is used in plumbing: 1/2" pipe, 3/4" elbow, gasket for a 2" union. Also in the vernacular, as a "Zollstock", meaning "any yardstick" even if it's two meters, folding, and not a yard.

"Fuss" (foot) I have never heard used...

Thomas Prufer

Reply to
Thomas Prufer

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