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TIL that 27" tubes can work on a 29" rim. (pawb.social)

submitted 1 month ago by OwOarchist@pawb.social to c/bikewrench@lemmy.world

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When my girlfriend suggested we take the tubes off an old 27" bike to fix the flats on my 29", I thought she was being crazy and overly cheap. No way it would work. Surely I'd have to go out and buy some 29" tubes.

But fuck me sideways, it did work, and I'm currently riding just fine with 27" tubes in my 29" tires. Wasn't even that hard to get them on.

So I guess that's just a PSA for everybody ... apparently, tube sizes aren't really rules, they're more like guidelines.

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[–] Successful_Try543@feddit.org 6 points 1 month ago (3 children)

Technically, 29" tyres are just extra-fat 28" tires, the rim diametre is 622 mm for both tyres. Surprisingly, 27" tyres have a larger rim, 630 mm, than 29" tyres.
The other parameter limiting the use of the tube is the width of the tyre. As 27" tyres have a maximum size of 35-630, 29" tyres start at 50-622. Thus, the tube for 27"/28" tyres will be somewhat overly inflated (according to it's specification) in a 29" tyre.

https://www.schwalbe.com/media/29/9b/36/1711611433/faq_reifengroessen_28032024.pdf

[–] fallaciousBasis@lemmy.world 4 points 1 month ago (1 children)

What's really crazy...

27" → 630 mm (old road standard)

29" / 700c / 28" → 622 mm (mainstream)

27.5" / 650B → 584 mm (had one of these, can also fit a 26" tires in some cases, which are typically 559 mm)

Now they're doing 32" with 686mm beads.

[–] ALiteralCabbage@feddit.uk 1 points 1 month ago

This is why ETRTO matters - everyone should know 622 is 29, 28, and 700c (and honestly, using the a, b, and c, "standards" is insane anyway.

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