Help! Inner tubes popping after tire install

[pdmtong]

I'm getting my dad's Electra Townie back into action. It had been sitting for so long the inner tubes split where they lay folded on the ground. It's a weird fun bike to go <10mph around on.

First thing was to buy two Specialized 26 x 1.9-2.3 schraeder tubes. the rim is a deep single wall. Inflated to 60psi and both popped before I could ride the bike. They split on the rim side above the first nipple next to the valve hole. Both front and rear popped in the same place.

Take to LBS to get new tubes. Mechanic says get rid of that factory rubber rim tape, use velox. Hmm, yea, that's the right move now that I have a problem that i never had when bike was new. Install two new tubes, 60psi, both pop on the spot. Install two more new tubes, same thing. Pop, same place. At least LBS gave me relief on paying for the tubes since the mechanic did the install.

The rubber base of the specialized valve is oblong. Maybe that's it. I'll find a tube with a circular valve base like the OEM tube. Bought two from REI (co-op brand made by kenda). Install to 60 psi (tire rated 40-65psi) and within 30 min POP same place.

So now I have popped SEVEN tubes (three at home, four at LBS) without even riding. So now I go to the Electra dealer. The mechanic there says he will only warranty the tubes if I pay for him to install. At this point, fine. I'll pay. I understand why that is the case.

24 hours later - POP. But a different spot. But again over a nipple. See below - the split and the nipple impression in the tube.

So I get that tube replaced. Tried installing rubber rim tape on top of the velox but its too crowded in there. Seems to me only two things left to consider: 1) another layer of velox and 2) lower pressure. IN the spirit of holding a control state for this costly experiment, decide to leave the existing velox as is and inflate 10psi less to 50psi.

these are huge cruiser 26 x 1.9 tires and the only reason to put more psi than less is so they can sit longer between inflation checks.

50psi and three hours later so far so good. what else can I do?

[pdmtong]

Pictures
https://uploads.tapatalk-cdn.com/20190906/74d5e819c91281f4d6f94f1610371614.jpg
https://uploads.tapatalk-cdn.com/20190906/bf9680ff171664472c6e53d76fc23cc3.jpg
https://uploads.tapatalk-cdn.com/20190906/58d48a74ac932b5b901d0466a8170bf2.jpg
https://uploads.tapatalk-cdn.com/20190906/a7c20f6a7e075786d97434db44dd3e4b.jpg

[cmbicycles]

That's an odd one. If there is nothing sharp exposed in the rim, and it looks like the nipples are well covered, could there be something with the tire? A rough bead or something on the inside? Other possibility could be installation if the tires are a tight fit and everyone (not too likely I think) is using tire levers to get the last section of tire to mount and pinching the tube in the process.

[rwsaunders]

Is there a shard of glass or wire in the tire casing? Hole would be in the same spot on tube if so...just guessing.

[jtakeda]

60 psi is really high for a tire that big. I think that’s the culprit

[pdmtong]

That's an odd one. If there is nothing sharp exposed in the rim, and it looks like the nipples are well covered, could there be something with the tire? A rough bead or something on the inside? Other possibility could be installation if the tires are a tight fit and everyone (not too likely I think) is using tire levers to get the last section of tire to mount and pinching the tube in the process.
not a tight fit at all. so easy to take off put on by hand
Is there a shard of glass or wire in the tire casing? Hole would be in the same spot on tube if so...just guessing.
thats the impression of the nipple into the tube.
60 psi is really high for a tire that big. I think that’s the culprit
I too am thinking that the pressure is too high given the non-buried nipple heads. I bet if it was double-walled rim with buried heads there would be no issue. What goofed me is that a similar sized mtb tire from the late 80's could handle 60psi...but then again those araya rims were probably double wall. I just dropped the psi further to 40 and will let it be...

[Rafa]

what else can I do?

A second layer of rim tape?

[charliedid]

I agree about pressure and single wall rim. 50psi is your bro.

[Black Dog]

Why not a plastic rim strip?

[Hindmost]

I agree about pressure and single wall rim. 50psi is your bro.

Yes, I think these guys have it sorted. Are there marks on the destroyed tubes that correspond to the nipple head locations? The failure looks like the tube is trying to comply with the nipple head and the rim wall and overstretching.

[pdmtong]

Yes, I think these guys have it sorted. Are there marks on the destroyed tubes that correspond to the nipple head locations? The failure looks like the tube is trying to comply with the nipple head and the rim wall and overstretching.

yes, there marks on the destroyed tubes that correspond to the nipple head locations. and yup, I bet the tube is overstretching.

my oversight here is the single wall rim aspect, as those same tubes can easily fill a narrow mtb 26" rim (albeit a double wall) and a much bigger tire without issue.

40psi and no issues today. in hindsight it seems like I should have dropped the pressure first, even before going with the velox. oh well, never dealt with this before so you learn something new everyday.

[dgauthier]

(...) 40psi and no issues today. (...)

The pressure was what stood out to me in your initial description.

Also, the valve hole in your photo looks pretty rough. If those rims were mine, I'd get out my rat-tailed file and file a nice even 45 degree bevel around the insides of the valve holes. If you decide to do this, take your time and make it as smooth, uniform, and perfect as you can. When you run your finger around the inside of the value hole it should feel silky smooth.

[dddd]

I've used countless road tubes over the years at 90psi in single-walled rims having a wide variety of internal shapes, nipple hexes and rim tapes, and have not had this problem.

So I don't think that the high pressure can be to blame.

But the problem has been identified as over-stretching local to the inside of the rim and specifically at the spoke nipples.

I believe that the reason why the tube is over-stretching is a three-way combination of deflated tube width, narrow rim with a much-wider tire, and an unusual level of contact grip between the tube and the inside of the tire near the tire beads.

During initial slight inflation, the tube rounds out and achieves enough pressure to create significant friction between the tube and the beaded areas of the tire.
This is where the tube must now slide around a corner under tension, with some of the rounded tube ending up pushed deep into the rim cavity against the rim tape.
But contact friction strongly resists the tube sliding along the inside of the tire where it juts outward just above the edges of the rim. Thus the tube is over-stretching to fill the rim cavity.

I've seen this many times with narrow rims having wider tires mounted on them. It seems that some tires are grippier than others along the inside surface, but there are other variables as well, chiefly the deflated width of the tube, as well as the configuration of the valve-area pad of rubber and in some cases whether the valve stem gets tugged outward before enough pressure has been added sufficient to pin the tube against the inside of the tire. There is also the matter of how grippy that the outside of the tube is.

I would use the largest(widest) tubes I could easily fit into the tires and apply some talc or a light wipe of silicone to the inside of the tires, which I could be confident would no longer result in split tubes.