Bicycle Mechanics - Multiple flats with leak at same place: where the stem joins the tube.

Hi:

I'm getting multiple flats on my rear tire. They leak is where the stem meets the inner tube.
I suspect that the stem is being forced against the hole in the rim for the stem. This happens after about 10 - 20 miles of use, which is about a week's worth of riding for me.
The repair folks are coming up with a number of interesting reasons why this might be occurring; for example, that I have a thorn-resistant (and slimed) tube (something about its weight versus a regular tube), my weight, the fact that I have a milk crate that I carry stuff in, and that I don't fill my tires daily. I could believe any of these if I hadn't been riding for years with this bike with no problems until now. They recently replaced the tire, and that's when the problems started, so naturally, I suspect that it's the tire.

As I mentioned, the current working theory is that it's the heaviness of a thorn-resistant tube, so they put a regular tube on, and I'm trying that.

My question is this:
Has anybody had this experience, or are there experts out there who might know why a brand new tire would be the problem?

Any advice is appreciated!

Thanks!

Doesn't sound like tube problem, if leak is in same spot, more likely rim issue. There might be a chip or indentation on the rim that is "cutting" the tire. Feel around the rim, see if there are any rough spots (which you can sometimes just sand down, depending on the rim material.
Also, are there any dents in the rim?

might help if you tell what type of bike, size of tires, air pressure you have in them and the type of riding you do.

eg. if you have 26"x2" mtb tires with schrader valves that you're running at 45 psi mainly on streets, you wouldn't expect to fill them as often as a high pressure (>110 psi) 700c tire, so who knows if that suggestion about not filling the up often enough is even valid.

Thanks for the reply.

I did take a look at the rim; it's brand new, and I didn't feel any sort of burr, chip, or other deformity. No dents in the rim.

Thanks for the reply -- and please see my reply to himespau for more details and an update.



Doesn't sound like tube problem, if leak is in same spot, more likely rim issue. There might be a chip or indentation on the rim that is "cutting" the tire. Feel around the rim, see if there are any rough spots (which you can sometimes just sand down, depending on the rim material.
Also, are there any dents in the rim?

Howdy:

Right -- details would be helpful. Thanks for asking! I had to go out and take a look and I noticed something that might be a problem.

It's a Giant Sedona. It looks like a mountain bike, but it's not really designed for true mountain biking.

I ride a little less than 4 miles a day on streets. I don't go off curbs or anything like that, nor do I go much over 10 mph.

I like keeping my tires pretty full, around 60lbs, but it varies.

It looks like I'm using Schrader valves. They look like the valves that are on car tires -- I didn't know they had a name. Heh.

The rims are 26".
The front is stamped with 26x1.95. I'm pretty sure that it's the tire that came with the bike originally.
The rear tire is stamped with 26x2.0, though. Assuming that the original tire on the rear was 1.95", would that be enough of a difference to cause the problem that I'm having? Or to put another way, are 1.95" and 2.0" tires interchangeable?











might help if you tell what type of bike, size of tires, air pressure you have in them and the type of riding you do.

eg. if you have 26"x2" mtb tires with schrader valves that you're running at 45 psi mainly on streets, you wouldn't expect to fill them as often as a high pressure (>110 psi) 700c tire, so who knows if that suggestion about not filling the up often enough is even valid.

there might be a rough spot at or near the hole in the rim for the stem , try filing or sanding the area and also make sure your rim strip is covering the area too . use a better rim strip if possible . yes keep tire up to pressure does help . your wight and the wight of your cargo have nothing to do with this. when below pressure the tube can move around and that what causing this.

Are they using tubes that are one size too small for your tires? If they are using tubes for 1.75" tires, that could cause the tubes to stretch and cause the flat. It could also be the quality of the tubes themselves.

there might be a rough spot at or near the hole in the rim for the stem , try filing or sanding the area and also make sure your rim strip is covering the area too . use a better rim strip if possible . yes keep tire up to pressure does help . your wight and the wight of your cargo have nothing to do with this. when below pressure the tube can move around and that what causing this.

+1
I would check you rim strip and then check the valve hole - I will always run some sand paper over the valve hole when mounting a new wheel to smooth out the drilled spots with sharp edges.

60 psi sounds too high for a mountain bike tire. I usually run 30 to 35.

+1
I would check you rim strip and then check the valve hole - I will always run some sand paper over the valve hole when mounting a new wheel to smooth out the drilled spots with sharp edges.

60 psi sounds too high for a mountain bike tire. I usually run 30 to 35.

Thanks for the advice. I've been keeping the pressure on this bike between 50 and 60 for many years with no problems -- until now. I will check the valve hole when I get a chance.

Thanks!

Are they using tubes that are one size too small for your tires? If they are using tubes for 1.75" tires, that could cause the tubes to stretch and cause the flat. It could also be the quality of the tubes themselves.

Good question. I'm going to take it to another mechanic and see what they say. I'm willing to accept that the tubes themselves have some problem, I find it hard to believe that the same exact flaw would appear in the exact same place on two tubes. But, anything's possible -- I'll keep it in mind.

Thanks!

Tube damage around the valve stem is often caused by rough handling when pumping or connecting/disconnecting the pump head. I went through a series of tubes the same way years ago and I was sure it was faulty tubes, but the problem stopped soon after I learned to support the mini pump from the rear while pumping.

What kind of pump do you have?

Also, 60psi is 100% acceptable in most 26X2 or 26X1.9 tires if you are riding on the road.

Remove the tyre and inner tube.
Check for rough edges around the valve hole of the rim and smooth with emery paper.
Check that your rim tape is in place. If not, replace wit Velox brand.
Check that the spoke heads to not poke into the inner tube.
Fit a new tube with a metal valve.
When you put the inner tube back in, ensure that it points naturally to the hub, not at an angle. Threaded metal valves have a nut to secure the valve in position.

This is a fairly easy one to do yourself and good practice for puncture repairs.

Tube damage around the valve stem is often caused by rough handling when pumping or connecting/disconnecting the pump head. I went through a series of tubes the same way years ago and I was sure it was faulty tubes, but the problem stopped soon after I learned to support the mini pump from the rear while pumping.

What kind of pump do you have?

Also, 60psi is 100% acceptable in most 26X2 or 26X1.9 tires if you are riding on the road.

Thanks for the reply. I don't think that's the problem, though. I'm getting about 10 - 20 miles of use before the tube fails, so I haven't had a chance to fill the tube at all, yet.

Thanks!

I've had this very same problem on a road bike with 28mm tires. The torn valve stem is always the rear tire. I do not know the cause but a torn stem cannot be repaired. For this reason I now carry two spare tubes. One possible solution is to cut a small hole in a patch and glue it in place over the stem as a preventative.

Arg, I just remembered one other thing:
The problem has spanned two rims.
So, the chronology goes like this:
I noticed a bulge in the tire and had it replaced.
About a week later (20 miles or so) I got a flat, as described above.
I had the flat repaired, and while working on it, the mechanic noticed that the axle was broken, so we replaced the entire rim.
About a week later (20 miles or so) I got another flat, exactly like the first.

So that's where I'm at now.

It seems inescapable to me that the tire is the problem. I just don't know enough about bikes to guess why that might be.

Thanks!!

Do you use the little round nut that threads down on the stem? If so, this might be pulling the stem through and pressing the edge of the rim into the stem/tube junction, cutting the tube prematurely

Do you use the little round nut that threads down on the stem? If so, this might be pulling the stem through and pressing the edge of the rim into the stem/tube junction, cutting the tube prematurely

Nope, nothing like that. Even if that were the case, would failure be practically instant? I mean 20 miles isn't far on a bike.

Does your bike come with single wall or double wall rims?

Single wall rims sometimes have a deep narrow center channel, and this forces the tube to expand and deform to fill that channel. Thicker rim tape can help reduce the deformation required, but near the valve, it may force the base of the value to fit into the channel and that can delaminate the valve stem base from the tube and cause leakage. The stresses could be stronger on thorn-resistant tubes. But I've only encountered this maybe twice in 30 years. The other potential problems as others have suggested seem much more likely.

If the problem persists, make a donut out of a piece of canvas or Cordura and put it over the valve stem before putting it back in. Learn to fix these yourself. Some double walled rims have a larger hold on the inside surface allowing the tube to pucker into the space when it is inflated. The donut will help keep the tube from pressing against this edge. In the bike shop, the most frequent cause of TR tubes failing was running them under inflated, but it sounds like you have that covered.

Here's an update.
If the same pattern holds true, my tire should have failed today. But it didn't. I've been checking the stem daily and it seems to be perpendicular to the rim, so that's good. It was down about 20psi, though, which is a little alarming. So maybe the solution was to go to a thorn resistant tube. I'll post back here in about a month or if I get another flat whichever happens first.
Thanks, everybody, for your input! I appreciate it!!

You need to put air in your tires more frequently. THey should not be allowed to get down to 20psi. THis was likely the cause of the original problem. Adding air every 2 or three days is not unusual.

You need to put air in your tires more frequently. THey should not be allowed to get down to 20psi. THis was likely the cause of the original problem. Adding air every 2 or three days is not unusual.

I agree that it's important to keep air in my tires. However, I would say that loosing 30 - 40 psi over a period of 20 miles indicates some other problem. How do folks that take long rides handle it? I mean do folks really get off every hour (assuming 20 mph) because they're down to 20 psi? That seems unlikely to me, although I don't really ride long distances, so it might be that's the way that it is. However, prior to what I mentioned in my OP, I rarely had any problems with low pressure. I would go for months without having to fill up. So far, not having a thorn-resistant tube seems to be the answer, strange as it seems to me.

Thanks!

THe distance you ride is not why the air is leaking out, it is the total time - riding and not riding - that allows the air to escape.
Although you should be able to ride for a week or more with lower pressure (less than 100psi) tires before you really need to add air. If your tires have 50psi (nice and firm) on Monday and 15 PSI (so soft that the valve is moving around) on Friday then I would call that a 'very slow leak,' which is usually caused by a tiny pinhole somewhere in the tube, or possibly a leaky valve.

I agree that it's important to keep air in my tires. However, I would say that loosing 30 - 40 psi over a period of 20 miles indicates some other problem. How do folks that take long rides handle it? I mean do folks really get off every hour (assuming 20 mph) because they're down to 20 psi? ...Thanks!

As with the last reply by DCB0, I pump up every few days on 28/32C tires. Maybe once a week on my 2 inch wide street tires. It's not a function of mileage, but time. Air slowly diffuses through rubber tubes. About twice as fast with latex than with rubber. So yeah, you might need to re-inflate with latex every other day. But normal butyl rubber (the lower cost tubes) hold air pretty well. And I'm talking about losing about 10 - 15% pressure over 3 days (e.g. 90 psi down to 80 psi).

It definitely sounds like you have a slow leak.

You need to do the tube dunk test. Remove your wheel and dismount the tire and extract the tube. Note the orientation of the valve and the tire on the rim. Pump the tube up so it's quite bloated. Put the tube in water. Find the leak. If it's on a place that is NOT the valve, then note the location, and then feel the inside wall of the tire for tiny slivers of sharp metal or glass or thorns. Often, if you have a very thin metal wire (e.g. a strand of brake cable wire) it will not put a big hole into the tube and partially plugs the hole when the tube is pressed up against it, and so the leak will be very slow.

If it's the valve, then you should see it as well. You can take some spit or soapy water and cover the valve and see if bubbles start to rise. that means you need to tighten the valve stem inside (they make a cheap tool to do that).

Hello, everybody:

Thanks for all the responses. This is my +1 month update. So far, no more flats. So, going with the regular tubes (as opposed to thorn-resistant) seems to have done the trick. I still drop a few psi's during the week, but I can accept what folks have said about that being normal. I just checked both tires, and they're both still full (I check them every Friday). So, again, thanks to everybody!

I'll post again in a few months with an update.