George Mann

Hi. I have an issue which I believe was caused by the use of the rubber rim strips that I was using on top of the factory liner.

These strips may have caused my tubes to move excessively on the rim when I was riding, and the rear tube was damaged at the stem causing a blowout.

I see no other reason for the tube shifting this much. Do you?

alcjphil

What size tire? What air pressure were you running?
Sometimes tires can creep on the rim if run at too low a pressure when you brake for extended periods

George Mann

26" x 2.0 at 50psi.

Andrew R Stewart 

The number one cause of a tube moving about within the tire/rim is too little air pressure. As the wheel turns there's a force acting on the tire, trying to rotate it around the rim. The tire could do this with no issue but for the valve being trapped in place by being in the valve hole. The outward appearance is of the valve becoming tilted as it exits the valve hole. Inside the tube is being pulled away from the valve, stretching the tube, and on the other side of the valve the tube is being pushed against the valve. If allowed to continue long enough the tube can become stretched that the wall give out and/or the tube becomes bunch up on its self on the other side of that valve.

Another, less common, reason to have a base of valve blow out is from the valve not being fully seated against the rim and between the tire's two beads. The tube does its balloon thing and fills the gap, causing the tube wall to get thin right at the valve's base.

A third reason is the opposite happening. The tube is trapped under the tire bead. The bead can't fit down on the rim's bead seat and thetire isn't overlapping the rim fully. As the tire/tube is filled w/ air the bit of the tube trapped under the tire bead acts as a pneumatic jack and it lifts the tire up and further out of the rim. If allowed to continue this can cause a gap between the rim and the tire bead and the tube goes all balloon like and expands out this gap. Andy

pdlamb

#1 sounds like a pretty good argument to go tubeless.

Wouldn't #3 blow the tire off before it let the tube rotate on the rim?

Andrew R Stewart 

Tubeless- Not in my book. Simply inflating the tire to a working pressure solves this. No need to get messy or hard to mount stuff.

Agreed and this is why #3 didn't mention any tire creeping about the rim. Andy

Moe Zhoost

A tube is not going to move much in a properly inflated tire.

IPassGas

I have always added talc powder to the tube when installing. I thought this helped the tube shift into place and out from under the tire bead. Is powder still (or was it ever) considered to be useful in this regard? Alternatively, I suppose the talc could also be detrimental (thinking of this thread), facilitating tube slippage if the tire is somewhat under inflated.

Andrew R Stewart 

Talc has been regarded as a once installed method of reducing tube/tire friction. As in reducing the rubbing between them which can slowly abrade the tube and decrease rolling resistance (albeit for a very slight advantage, very slight).

Now good tube install technique will go a long ways at reducing the possibility of tire blow off at the valve. Once the tire is fully mounted one pushes the valve stem up and into the rim. This helps insure the fat wall thickness at the valve base is above and between the tire beads and not down tight against the rim's bead seat shelf. A very simple few moments. As with any initial tube inflation a slow and periodic tire seating check will confirm all is well, tire seating wise. Andy

Moe Zhoost

Jobst Brandt's opinions rate high with me. See: https://sheldonbrown.com/brandt/talcum.html

IPassGas

agreed, and if I might add, those of Mr. Stewart's

George Mann

The tube, being a thick puncture resistant Ultracycle, is too large to fit into the bead of the rim (measured and tested), causing the tube to float above it.

Yet the person selling the tube claims it is compatible.

Dave Mayer

I once got stuck deep in the wilderness with a rear wheel in which the valve stem had been torn off. No repair possible. Cause was obviously the tire rotating relative to the rim. The rim strip has too little mass to have caused this.

On these types of rides (no cell service, and nothing but bears for miles around), I carried two spare tubes, a patch kit, and a bunch of tools. After suffering the same fate with both spare tubes, I had to walk 7 miles out. Turns out my pathetic mini-pump was only capable of generating 25 psi, even if I pumped with all my might. Should have known there was a reason that I found this pump on a trailhead a few months earlier.

Got a better pump, and have never had this problem since (20 years).

pdlamb

This is one area I disagree with Jobst. Back in the usenet days, he also argued that the tube sticking to the tire will slow a leak caused by an oblique Michelin wire puncture. I've never seen this alleged benefit -- all my punctures seem to be close to normal to the tire/tube interface. But I've had to wrestle an un-powdered tube out of a punctured tire enough times that powdering is now part of my at-home puncture routine.

George Mann

So what would you'all say is the minimum and maximum amount of air that a 26" 65lb tire should be filled to?

Andrew R Stewart 

It all depends on the tire's fit to the rim. And this is why this type of question has no answer that is correct for all the possible tire/rim combos, the tens of thousands of the combos... This is why we write about the need to pay attention to what you are doing, visually checking the tire's seating as the pressure goes up. If a shop did less and the rider suffered a blow out we would all turn our gaze to the shop... So when the rider is doing the inflation the same standard should be followed. Or the uninformed will suffer. Andy

George Mann

So how the heck does one know when a tube is properly inflated?

Tubes shouldn't be this complicated!

George Mann

I just measured my rims, and found that they are unusually thin. They measure 14.2875mm (9/16).

The tubes are 31.75mm (1.25) when inflated. The fit between the tube and tire when on the rim is tight enough that the stem gets caught in the bead, abraiding against it, making it impossible for the tube to sit in the bead.

Furthermore, the edges of the rims stemhole is so rough that it easily cuts into the stem!

So it looks like I will need a new set of rims (I may go tubeless). Or perhaps this pairing can be converted to tubeless?

Moe Zhoost

If your inner rim width is indeed 14mm, then I doubt that you will have much success with a 2.0 tire. What make/model are these rims? I've never seen 26" rims that narrow.

George Mann

Neither have I. The rims are LOBO Matrix, and Trek specs them between 2.1 and 2.35

Crankycrank

If memory serves the hot ticket for mountain bikes years ago was to use very narrow rims and 2"+ tires of that era were designed to work on those rims. Just guessing but maybe newer tires have a different design and don't work so well with the narrow rims.

cyccommute 

Brandt’s opinion here is somewhat contradictory. He says that the tube can’t move when it is inflated…something I agree with…but then says that the tube being welded to the tire will make it take longer for a tire to deflate. Which is it? Tire can’t be stuck to the tube or a stuck tube is harder to deflate. Never mind that th rate of deflation of a tire has little to do the state of the tire and tube. He also says that the tube can’t vulcanize to the inside of the tire but then says that the tube has talc in it to keep it from sticking to itself.

I’ve run across tons of tires and tubes that can’t be separated. Granted they are almost always old tires but talc in the tires helps keep that from happening and makes pulling a tube out of a tire easier.

Andrew R Stewart 

Tubes are not complicated. But not all tire/tube/rim combos work as wished or as assumed they should.

I'll bet a virtual beer that the valves are Schreader, not Presta. One of the reasons why Presta valves are liked by many is that the stem is narrower, providing less interference with the tire beads when in narrow rims.

I also will suggest a thick walled "puncture resistant" tube is a poor choice when running a narrow rim just for the reasons you are finding. I assume (there's that word again) you have flat issues, true? Can you describe the flats? Poke throughs or pinches? Have you tried tires with casing plys of cut resistant materials (Kevlar as example)? IME PR tubes are partial solution with many drawbacks.

BTW the PR tube's inability to fit down in between the tire beads on this narrow a rim is exactly what I was referring to in my first post.

Back in the late 1980s really narrow ATB rims (in the 559 ISO) were the shiz. Campy made some that were around that 14mm internal width. The problem we sometimes saw with these was the tire's wanting to come unseated when running low pressures and doing aggressive maneuvers which had significant side forces. The angle the tire casing left the rim was so severe the bead wouldn't interlock with the rim's hook edge well. Andy

George Mann

Schrader valves. The tube failed when it shifted, damaging the base of the valve. My tires are CST Sensamo Controls (puncture resistant liner).

cyccommute 

50 psi in a 2” tire shouldn’t shift. If you had a slow leaker flat, you could drop pressure enough to get some tube creep which might cause your problem. Additionally if the valve stem weren’t at 90° to the rim when you pumped up the tire, that can stress the valve stem as well. It’s very common to cut an angled valve stem, even with proper inflation.