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Help! I have a wheelchair with an 18 x 13/8 tire. The new tire is exactly the same make and spec as the old one and the tube is the correct size too. As soon as the tube is inflated it pushes the tire off the rim. I and several experienced others have spent hours trying to make the tire fit. We have tried three new tires and several tubes. Its an old wheelchair that fits a house too small to use a new chair in. Any ideas?

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cat1commuter [1421 posts] 4 years ago
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Sounds like the tyre is the wrong size. (The size of the inner tube will not be critical.) Do you have the old tyre still? It may have ETRTO numbers on it. If you want to know what ETRTO numbers are, then Sheldon Brown can explains better than I can. The long and short of it is that there should be some funny numbers on the tyre guarantee that you can order the correct size. Inches and fractions of inches are notoriously confusing describing tyres sizes in the bicycle world, and that probably extends to wheelchair tyres too.

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phototext [8 posts] 4 years ago
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Thanks Cat1commuter.
I agree thats the obvious solution but the new tyre is exactly the same make, tread, marking even colour!

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A V Lowe [582 posts] 4 years ago
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Don't always rely on the ETRTO numbers. I bought a 633 (BCD) tyre for my bike and despite having same numbers as the tyre removed it would not quite fit the rim, and it was a Michelin World Tour tyre. Turned out the the US mm is possibly different from the European one as the manufacturer eventually admitted to producing 2 different sizes with the same ETRTO numbers on the carcase, and some US products had escaped into the UK market.

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cat1commuter [1421 posts] 4 years ago
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A V Lowe wrote:

Turned out the the US mm is possibly different from the European one as the manufacturer eventually admitted to producing 2 different sizes with the same ETRTO numbers on the carcase, and some US products had escaped into the UK market.

That would be insane. I can't believe it.

What I could believe is that manufacturing tolerances are out.

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cat1commuter [1421 posts] 4 years ago
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phototext wrote:

Thanks Cat1commuter.
I agree thats the obvious solution but the new tyre is exactly the same make, tread, marking even colour!

I would try to measure the actual bead seat diameter of your rim, in that case. If it matches the quoted ETRTO number for your tyres, then I would return your tyres as defective. What make are they? Try a quality manufacturer like Schwalbe.