bike wrench

1134 readers

1 users here now

A place to ask bicycle repair questions, and for bike shop monkeys to share advanced non commercial wrenching resources (no YouTube self promotion). This is only for repair related topics.

!bicycles@lemmy.ca

!micromobility@lemmy.world

founded 2 years ago

MODERATORS

j4k3@lemmy.world

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

submitted 2 weeks ago by OwOarchist@pawb.social to c/bikewrench@lemmy.world

10 comments fedilink hide all child comments

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.

top 10 comments

sorted by: hot top controversial new old

[–] hemko@lemmy.dbzer0.com 9 points 2 weeks ago

Yeah so it's perfectly fine to stretch up 1 wheel size, though the tube won't be quite as durable for example when you hit a curb and the tube is pinched between tire and rim, but it's pretty minimal

You could also use larger tube in a smaller wheel by folding the tube a little bit. I've heard fitting a 29" tube on 24" kid's mountain bike just to finish a day.

TPU tubes you probably don't want to stretch on bigger wheel, but folding down to a smaller is perfectly fine

Aaaaaaanyways whenever you use "wrong" size tube, only do so if you just need to fix quick to keep on going. Grab a right size from a shop when you can and replace it.

[–] BigTwerp@feddit.uk 6 points 2 weeks ago

Does that mean I can carry a smaller spare tube and save 3.2 grams? Bonus!

[–] Successful_Try543@feddit.org 6 points 2 weeks ago (2 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 3 points 2 weeks 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 week 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.

[–] Alcoholicorn@mander.xyz 1 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

Wtf how did that happen?

Is it like 5.56, 5.7, .22, and .223, all being 5.7mm diameter?

[–] pr06lefs@lemmy.ml 4 points 2 weeks ago* (last edited 2 weeks ago)

I think this bit of insanity is due to 27 referring to the outer diameter of the tire rather than the rim diameter. "27" appears to be a road bike standard as tire sizes are around 1 inch on that Schwalbe chart. If you have a 630mm rim and a 1.1 inch tire, 630 / 25.4 + (1.1 * 2) = 27.0 for the outer diameter.

On the other hand, "29 inch" is a mountain bike standard with a tire size ranging from 2 to 2.4 inches or so. For a 622mm rim and 2.2 inch tire you get 622 / 25.4 + (2.2 * 2) = 28.8 outer diameter.

If the OP has a "29" inch tire, that's a mountain bike. And I suspect their "27" inch tire bike is also a mountain bike, which is actually a "27.5" size which is a mountain bike standard, with a 584mm rim diameter. If that's the case they would have had to stretch the tube a bit to get it on the 622mm rim of the 29er, but at least that tube would be intended for a mountain bike sized tire, say 2.4 inches.

[–] theskyisfalling@lemmy.dbzer0.com 3 points 2 weeks ago (1 children)

You can also cut up old tubes and use them as patches on other tubes if you only have glue left :)

[–] nocturne@slrpnk.net 1 points 2 weeks ago

Back before there were puncture protector readily available, we would use old tubes to cover our new tubes to give another layer of goathead protection.

[–] fallaciousBasis@lemmy.world 0 points 2 weeks ago

29" refers to the tire size.

The rims are both 622, probably.