keifer

This keeps happening, on both rims: the tube develops bulges on either side of the stem along the seam where the reenforcing rubber mets the regular tube body. One of these bulges then tears.

This has been plaguing me for a while. I've installed new rim tape, given up on using valve nuts, searched the rims for burrs, verified the rim is drilled for presta, and moved a size up in tubes (tyres are 28mm, switched from 23-28mm tubes to 28-32mm tubes).

As none of that has worked, I've settled on blaming my floor pump. It is older, and it is rather difficult to install and remove it from the stem. At least, I *think* it is difficult to remove. This is my first foray with presta stems, and I'm not quite sure what the norm is.

Does this look like something a crufty, hard and/or tight fitting floor pump could cause? Money is a bit tight, and I'd rather not replace it if it is only an inconvenience for me and not the culprit.

gyozadude

I've seen tears like that for these reasons:

a) the contact area underneath the tire there is not supported properly even though you have a rim strip
b) physical delamination is occurring around the valve stem because the valve stem is being bent too much on a regular basis
c) you have a burr that is cutting the tube
d) the selection of tubes you have are bad/old/delaminated at the valve area due to age/etc.
e) too much tire bead or some burr on bead, and too narrow a rim to allow tube to seat correctly with tire mounted.

But your situation sounds like a real mystery.

DOS

Yes, floor pumps can cause that. I have two pumps, one slides on and off stems, np, the other snags on the threads of the stem and is hard to get to disengage. I have torn tubes at the stem a result. Solution, get tubes with smooth stems. The pump head won't grad the threads so will pull less on the stem. I have had just one tube fail around stem since I switched to smooth stems. That said, I also agree with gyozadude that you should explore other causes as well.

gyozadude

I'm just surprised that a pump would cause this. I have used threaded presta stems...well, forever, it seems. And if I'm busting my knuckle rocking the head to get the thing on-and-off the stem, then the grommet design is probably too tight. I know the old Silca floor pumps were some of the worst offenders. But I learned that if I ease off tightening the cap too much, it wouldn't compress the rubber grommet so much. Still tight enought to keep the air inside, but not so tight I skin my knuckles on the QR lever or pinch in in the cross between spokes trying to remove the darn thing.

I've been using now for 15+ years, an old Joe Blow floor pump. The head uses an additional lever for compression. I found by just simple, light finger tightening on the grommet, it makes it pretty easy to put the head on/take off and the lever compresses the grommet and forms the seal. The only real issue is the fast-wearing plastic middle pin at the bottom of the schrader side head with needs to be just 0.5mm longer and made of something harder than plastic. But overall, it has saved me more knuckles. And I've personally never damaged a tube rocking it because, maybe I am OCD/CDO about not damaging my tubes and would never rock the head off the presta stem as tempted and frustrated with grommets being too tight might make me.... but that's just me.:-) YMMV. BTW, I will admit, I used to splurge in get true latex ultra-light tubes. And I found that it's a great way to blow $10 if you plan to keep them in stock more than a year. Those super thin tubes seem to oxidize and fail at seams, at valves, etc.. So I now buy just regular thickness butyl tubes and keep them sealed in a ziploc until I need them. Maybe you've got old stock on thin tubes? Or the store stocked some old ones? If not... a mystery still.

ThermionicScott 

I've heard of people using washers or valve nuts inside the rim to give that area more support, but haven't tried it myself.

You should experiment with inserting the valve less far into the pump head -- it only needs to be in far enough to hold when you take your hand away, and the pressure from the pump will open the valve.

Bill Kapaun

Have you tried a different brand tube?

Just Riding

On one bike I had tubes fail in places similar to what the OP is describing.

The rim on that bike was a single wall with a deep, narrow well in the center, and was drilled for Schraeder. There was also rim tape in the well that ran along the walls of the well in addition to covering the spokes. The tape further narrowed the well, and I think this was a factor in the problem with the tubes.

What I concluded was happening was that at the valve hole, the well was so narrow that the reinforced area around the valve prevented that part of the tube from resting in the bottom of the rim. The valve sat high, and the rest of the tube stretched down resulting in the tube bulging and stretching at the edge of the reinforcement. Eventually, the bulge popped.

Its been a while, but I think I changed the rim tape around to create more width at the valve hole, and paid attention to pulling the valve stem down to seat it.

3alarmer 

If your problem is due to difficulty removing the pump valve
from the stem (and I'm not certain if it is or is not, but certainly
what you describe could be caused by constant wiggling of the
stem during removal of the pump), then you might want to work
on technique.

Always rotate the presta valve to the top position in the wheel before
you hook up your pump, and when it comes time to disengage, give
that valve a sharp downward rap at the angle where it joins the hose
to unhook it. Use the edge of your hand or loosely held fist to do this.

Best I got for you.

FBinNY 

The following theory is premised on the possibility that the OP has relatively narrow rims, and possibly fairly wide tires, but that isn't as important. If the OP doesn't have narrow rims, disregard what follows.

The distance of the leak from the base of the valve leads me to suspect that something else is at work. Specifically that the valve is being trapped fairly far from the inside of the rim by the narrow gap between the insides of the tire bead area.

This is fairly common on very narrow rims that barely allow enough space for the valve stem, never mind the wider area at the base. With the valve's base held away from the rim the tube balloons down into the gap hyper-stretching as it does so. Often you'll see stretch marks in the belly of the tube on either side of the valve

One way to sort of test the theory is to fit the valve into the rim and measure how far the valve extends from the rim on the hub side. Then mount as per normal, and if the valve is about 1/4" shorter you know that the other end in hung up. The remedy is to try to carefully nurse the valve back out as a last step after mounting the tire, but be careful because many tubes will tear from the base of the valve (right at the valve) if pulled hard.

Years ago, working on a friend's bike with a similar problem, I ended up gluing a long (2") oval feather edge patch to reinforce the belly area. I don't know if these are still available, but if so, use a standard hole punch for the valve hole and try your luck.

BTW- Don't chuck your pump. Of all possibilities, that's the least likely culprit.

FBinNY 

What's this? A straight post? Did you run out of Four Roses?

3alarmer 

Sobriety is not something to be joked about, amigo. It makes my head hurt.

keifer

I think we have it! Just checked, and the stem is about 7mm shorter when mounted.

No bueno. I'll see if I can't entice it further down in the morning.

Burton

Could also be something as simple as the threaded valve stem getting hung up on the rim tape. Tolerances can be tight sometimes. In any case its important that the valve is both well seated and straight. Whats maybe surprising is how common flats are from this kind of issue.

xenologer

+++this
I replace many inner tubes in a days work and this comes up often as described.
Typically to avoid issues, I'll inflate halfway so the tire is seated, then grab the valve with pliers and pull it till it seats against the rim (havent ripped one yet, so don't be shy about it). Then inflate to full pressure.

rfields

I had this exact problem and it turned out to be a plastic rim tape that was so old it had curled a little and the edge was cutting into the tube right where your picture shows.

ksisler

1) Buy a couple new rolls of rim tape... the heavy, stick on cloth ones (Velo brand). Make sure the width is fully wider than the individual spoke holes in the rim and fully wide enough to almost start up the sides of the rim. Pull the tape taught as you apply. Press it down all the way around with your thumb to make sure it is firmly adhered to the rim center.
2) Use your hands to install the tire on the rims... not tire irons. If you hit the rim strip with a tire lever, you can push it aside such that it exposes a spoke hole edge and the tube can expand into a spoke hole..-> leak.
3) Put the little nut back on the stem of the presta valve but don't tighten it down onto the rim...leave about a 1mm gap when the tire is deflated. Then when you push the air nozzle on, the nut will stop the stem from going into the rim. When you take the air nozzle off, first put your thumb and index finger firmly on the valve between the nut and the air nozzle. Push against the nut and pull the nozzle straight off the valve.

Those two things will solve most of the issues similar to yours.
/K

cny-bikeman

One note that does not apply to this situation but that will present somewhat similar symptoms. If one often allows the tires to be underlinflated the tire and tube will migrate on the rim. This is identifiable by the valve stem becoming crooked. Carried to an extreme it can actually cause the rim hole to cut into the valve stem. When one uses a stem nut that migration eventually stretches the tube next to the stem enough to cause a failure. Unlike the OP's problem the failure occurs mainly on one side, where you will see a distorted section of tube and (typically) a crescent shaped tear.

oldbobcat

The clue is in the quoted text. The valve section of the tube is getting pinched between the rim and the tire beads.

After seating the second tire bead in the rim, you need to push the valve stem into the tire before inflating. This will get rid of the bulge and seat the valve section of the tube inside the tire.

davidad

I have a Silca pump that is difficult to remove and does not cause that problem. I install the valve nut on the inside of the tire and that helps. Before you inflate the tube make sure that you push the valve into the rim to make sure it is not being pinched by the bead of the tire.

Continuity

Hmm - I wonder if there's any mileage in putting a valve nut on both the outside *and* the inside (making sure that it's screwed right down to the base of the stem) of the rim?

Ferrous Bueller

A dab of grease or Vaseline can make the engagement of stem into chuck much easier. May extend the life of the seal in it too.

Continuity

Can't Vaseline attack certain types of rubber, though?

Ferrous Bueller

You're right. I know you're not supposed to use it with condoms.
Oils can damage rubber, but it would be a better choice than tossing the pump.
I suppose a liquid silicone would be the best choice for a precious oil seal.

Turtle Speed

In case anyone ever reads this read in hindsight, I had the same problem on a bike last year, and made a thread about it: https://www.bikeforums.net/showthread...types-of-flats

A difference there was that the bike was using Schrader tubes on a narrow rim (kinda weird) and not Prestas. In my case, my workaround was a simple switch to Presta tubes with metal Schrader-to-Presta rim adapters. Never had any issues after that. No doubt there are other ways to fix it, but that was the path of least resistance for me.

I never had any luck merely pulling down on the valve with my hand after installing, but then I didn't think to use a pair of pliers to yank hard. But I wouldn't exactly want to be carrying extra pliers all the time in case I had a flat anyway.

Of course the OP was already using Prestas, so he couldn't slim down in valve size. But I wanted to share my experiences in case anyone comes across it in a Google search, etc.

Looigi

FWIW: If you are unhappy with the performance of the chuck on your pump, you can replace just the chuck. There are various types of chucks available. The following is good one, but there are quite a few others:

https://store.todson.com/store/topeak...it-tsl-01.html