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Purchased new inner tube for front wheel of Huffy Green Machine. Old tube measurement stated, 20x1.95-2.125. I took that measurement to bike shop. Was given a new tube with its box reading 20”x1.90”-2.125” I placed a squirt of air into the new tube to sit it in the rim. Put tube valve through wheel valve-hole. Began fitting tube around wheel, and under the tyre. It quickly became obvious the tube was too long.enter image description here I took tube out and put about 10psi into it, thinking the tube with more air would squeeze onto the rim. Instead, it was clear that the tube was way too big for the wheel. See photo. Further, the tube looked like it was distorted (I tried to add more photos as seen in other posts, but I could only add one after resizing down to 40KB - APOLOGIES) I have read Q+As on here regarding the bulging issue – some answers saying it was a defect, while others saying it is normal.

So, 3 questions, please: A – Is the tube too big, or will it adjust once constricted by the tyre and wheel? B – Is that bulge normal? C - The tyre recommends 40psi, yet the tube is bulging at 10psi. Should I pump another 30psi into it when it is placed back on the wheel? Thank you.enter image description here

Billybob
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Tl;dr: 10 psi is 10× too much (at least)

It sounds to me like you've got too much air in it. Remember that the tube seals in the air, but the tyre resists pressure.

Until fully constrained by a tyre, I wouldn't put in enough to register on the gauge on my pump, at most enough to give it some shape. Call it 0.5-1 psi based on feel. Sometimes it's easier with a floppy tube and I put in none at all.

Your tube may have been sized for a few different rim sizes as there's more than one standard for 20". Some tubes are sold for 26" and 27.5" - they're clearly a bit long for the former.

I risked (maybe sacrificed, but it should patch) a spare 20" tube to demonstrate:

20" tube, almost no air This is let down, but without the air squeezed out, resting on a 20" wheel for comparison. It's about the same size as the tyre.

One stroke of the pump more After one stroke of the pump, the gauge hasn't moved but the tube is already bigger.

5 strokes of the pump 5 strokes of the pump - gauge still reading zero, noticeably bigger

10 strokes By 10 strokes, the inside is as big as the outside should be, but the gauge is still on the peg

15 strokes, now big enough for a 24" wheel at 15 strokes, the needle has budged, but I've fetched a 24" wheel for comparison because the 20" fits through the tube.

a hole 20 strokes, still under 7.5 psi (the first line on my gauge is 0.5 bar). It looked too big for the 24" and this happened.

under 10 psi, as big as a 26" wheel I taped it up and pumped while holding the tape on with my other hand, which only slowed the leak. I still didn't get to 10 psi, but the tube was as big as a 26" wheel - though taking the photo was hard and it lost some air as I did so.

All the tyres are 1.75" to 1.95" width BTW.

The important thing is to not catch the tube in the bead, which I suspect is why you're pumping it up, but that doesn't necessarily make it easier. Pumping it up a bit much outside a tyre can stretch it permanently, though it's still usable if that happens, and you may not have gone that far.

I suggest you get the tube in the tyre, start putting the tyre on the rim, then let some air out.

Chris H
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    Chris H, you are a gem. Thank you for answering so promptly. I also appreciate your tip re: photos. Finally landed a shot in the OP. Hope that it helps to show the size and the bulge. – Billybob Jul 23 '23 at 09:03
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    Ok, that's pretty impressive. It still could be stretch from inflation. 10psi is a lot for an uncontained tube. But if it was that sort of size before it had ever been inflated, I'd be looking for size markings on the tube itself (some have them, some don't) in case it had been boxed wrong – Chris H Jul 23 '23 at 09:26
  • ... More air will always make it bigger in all dimensions, unless there's something in the way (like a tyre) – Chris H Jul 23 '23 at 09:27
  • Is that shot normal? Only 10psi added to see if tube would fit. Clearly it will not, unless it will be confined when in the tyre. Is that a proper size tyre for that wheel? Is that bulge expected at 10psi? Thanks once more. – Billybob Jul 23 '23 at 09:14
  • Thank you kindly, once more. The old tube without air looked to be a suitable fit for the wheel. The new tube with only a puff of air, looked way too big. Ther was too much over hang when i was not even half way around putting it undwr the tyre. That is why I took it off the rim and put 10psi in it to have an idea of its actual size. I will deflate it, let is return to its natural size, then put back on and pump to 40psi as the tyre recommends. – Billybob Jul 23 '23 at 11:15
  • I don't know if you repair your tubes - I do. But even if you don't, if the old one only had a small leak you can pump it up, maybe putting some tape over the leak, and see what happens. I might even do a demo if I've got a spare 20" tube – Chris H Jul 23 '23 at 11:29
  • I've done the demo. That tube has been in my possession for about 5 years, and it was on a bike my daughter got 2nd hand. So it's pretty old. Your new one could survive a little more, but you're lucky to still have it. – Chris H Jul 23 '23 at 12:45
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    Chris. Your Unicycle photos are a clever way of demonstrating your point. Thank you for that effort in having me "see" the matter. – Billybob Jul 23 '23 at 23:05
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That's a 20 inch wheel, so its either 406mm or 451mm.

That tube has been inflated so much it has stretched in two directions and looks like a 26" tube.

Let ALL the air out, and let it rest overnight. This will allow the rubber a chance to collect itself and shrink down.

The butyl rubber has stretched far beyond what it would do on your wheel, because there's no tyre around it to hold it together. The tube is close to rupturing because its inflated in the air not in a tyre.

When installing the tube into the tyre, it can sometimes help to add at-most one single pump of air, which is almost nothing. 10 PSI is far too much - it is almost a second atmosphere!

You want just enough air for the tube to become managable as a tube, not a flat ribbon, so 0.5 PSI at most

Good luck !

Criggie
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  • I wondered if "a squirt of air" meant using a compressor. Sometimes to find leaks I have to pump tubes up this hard, and then they never fully recover, but they can still be used. – Chris H Jul 23 '23 at 10:54
  • The the difference between the circumference for smaller and larger 20" is 14 cm. If the wheel is the smaller one and tube for larger, no wonder it doesn't fit. – ojs Jul 23 '23 at 11:59
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    @ojs, it will be fine for both. I ran a tyre for a year before finding out that the tube in it was 24", in a 26" tyre, and I've used 29" MTB tubes in 26" wheels when I ran out of 26" spares. It doesn't matter if it gets a bit folded inside the tyre, so long as it's not caught in the bead. – Chris H Jul 23 '23 at 12:43
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    "Looks like 26" seems about right from my testing - I was still under 10psi when I stretched a 20" tube to about 26". – Chris H Jul 23 '23 at 12:44
  • @ChrisH one squirt normally means one push of the handle on a pump, and for some pumps then half or even less may be all that's needed. – Criggie Jul 23 '23 at 19:34
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    @Criggie that's what I'd mean, because I use a manual pump. But for people who commonly use CO2, or have a compressor, it's more likely to mean 1 squeeze of the trigger. Half a stroke max on my floor pump, touring tyres, but up to 3 strokes of my Road Morph on a 29er MTB. But then I might let a bit out before seating the 2nd bead. – Chris H Jul 23 '23 at 20:16
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    Yes Chris H and Criggie, the squirt of air was from a small electric pump - about a second's worth. When the tube looked way too big, I took it off and put in the 10psi. It then definitely looked the wrong size. Thanks OJS for the info on the big and small wheels. The 20 is on the old and new tube. I thought the 20" was for the diameter, and therefore would be uniform. I am learning something. Why should there be a difference? I will contact the shop for their advice and get back to you with results. Thank you all again for your help. – Billybob Jul 23 '23 at 23:02
  • @Billybob deflate the tube, and leave it overnight to contract. That will help. – Criggie Jul 23 '23 at 23:59
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    @Billybob the inch "diameter" has very little to do with the actual size of the tire – ojs Jul 24 '23 at 12:33
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    @ChrisH I appreciate the "if it doesn't fit you need a bigger hammer" attitude but generally tubes should fit without folding them – ojs Jul 24 '23 at 12:34
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    @ojs yes, I should perhaps have said "even if" it gets a bit folded - because a 451mm tube shouldn't be folded, just squashed in a bit in a 406mm tyre. Some of the stretch in this one will be permanent, and might lead to having to fold it. Schwalbe seem to sell different tubes for 406 and 451 anyway, but Conti's fit both along with some even rarer intermediate sizes – Chris H Jul 24 '23 at 12:39
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    Thanks ojs. I had no idea of that, thinking 20" referred to the wheel diameter. Anyway, I took all the advice: let air out of tube and waited for 2 days so it could settle after any stretching. Rang the shop and they said to just whack it on and see how it turns out. The tube was bigger than the old tube and there was slack when placed on the rim and inside the tire, necessitating some scrunch. It’s on with 40psi and I wait for my daughter to return from school to test pilot the gear. Thank you all for your kindness in helping me out of this simple process that was stressful for me. – Billybob Jul 26 '23 at 01:55