Inner tube size

Hello there unicycle world,

I have a 19" Nimbus Equinox, need a new inner tube and can’t find the right size.

I looked up the tube size here:

That says I need:
Tube size: 20" x 1.95 - 2.125"

So I ordered it. But it’s the wrong size. Way too big. Which makes sense given that then rim is 19" and the tire is 20", but I’m not seeing any 19" tubes on

Ideas welcome. The uni is just dead until I solve this…

Did you contact I emailed them a question not long ago and they answered the same day and it was during the weekend.

Are you sure it’s too big? The first time I changed an inner tube I thought it would never fit - I was expecting it to fit neatly round the rim but it was quite loose.

20" tubes will fit your trials wheel. Just pump it up, and you will see. Or get a 19" inner tube for a motorcycle, but they are heavy and expensive. I always just use whatever the widest 20" tube the bike store carries is, never been an issue.

A tube meant for a standard 20" wheel should actually be kind of small for a trials wheel. Not in diameter, but in width. If it’s significantly to big you probably got something meant for a 24 or 26" wheel. There should be a marking on the box and tube itself stating the size.

A standard 20" tube will be somewhat stretched out and therefore be a bit more susceptible to pinch flatting, won’t hold air quite as well (need a top-up every week or two), and might not have the same feel at lower pressures. Some people think the weight difference is worth it.

If you go for a motorcycle tube DO NOT GET A 19" TUBE!, motorcycles measure their wheels by rim size (much more sensible) rather than total diameter. You would want a 2.5/2.75-15 motorcycle tube.

Well, whatever is going wrong is probably some kind of newbie problem. I’m totally missing some basic thing. But the distance between tube and rim is 4-6" - maybe well beyond what you were seeing.

Album of additional photos of the issue:

I tried putting putting on the tire and riding it anyway, but the tube pushes the tire off the rim.

but well played.

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Wait, what’s the troll? You mean the fact that the tube is comically huge compared to the rim?

That’s the thing I can’t figure out myself!

OK, being a newbie myself I’ll assume you are serious. You’ve blown the tube up to that size. A tube is like a balloon. You can blow it up to whatever size it will reach until it bursts, just like you can blow up a condom until it’s a lot bigger than the item it is meant to fit. No-one can see what size the tube actually is in that photo. Put one edge of the tyre in the rim. Then put the tube into the tyre with just a tiny bit of air in it to stop it getting pinched. Then push the other edge of the tyre onto the rim. Then blow up the tube in the tyre to the pressure suggested on the tyre wall.

The other day I bought two 20" tubes from the LBS (Local Bike Shop). The guy behind the counter brought me 20" x 1.8" - 2.3" tubes from the back room. I told him I had previously bought the wider variety from the same shop. They came in a bigger box, they were thicker, heavier. He completely dismissed me, telling me the narrower tubes would work just fine. He didn’t say whether or not the larger ones were in stock, and he didn’t offer to check for them. SOB (Shop Of Bikes).

You can probably guess how the story ends. Two rides later, I got a flat. Of course, it could have happened on the wider, thicker tube. There are a lot of thorns in my nearby park. I’m still mad at the bike shop. I want to tell them to stop being jerks to their customers.

While a thorn is just bad luck, I also prefer wider tubes, if I can find them. They are more resistant to pinch flats. However the biggest issue with thin tubes in wide tires is that you can’t really patch them as well once you get a flat. The patches can’t expand in the same way that the tube does, so usually the glue joint just fails.

i always use the cheapest 20" tube from walmart for both 20" wheels and 19" wheels and have never had a problem with them. the one time I bought more expensive “bmx specific” tubes, I got a flat within the first couple of rides ¯\(ツ)

I doubt the tube had anything yo do with you getting a puncture, unfortunate as it is. Coincidental possibly but bad luck too.
There are some big thorns around where I am and I know not even the puncture resistant Schwalbe Marathon plus tyres can fend those of.

The dude on the bike shop may have only had the tube he gave you as there are shorteges World wide for certain cycle related items.
Punctures ruin a ride for sure.

If you want a thick heavy tube for a trials wheel you could try a 15" motorcycle tube. Add some sealant to that and it really might be flat-proof.