Continous flats on one MTB wheel

[FlandersZA]

Hi,

 

This has been driving me nuts! My friend has a 26er and for a while now, without fail she will get a flat on her back tyre every ride, and sometimes multiple flats. She isn't running a tubeless setup (yet) and the tubes always bomb out in the same way. The tube tears at the base of the valve stem (is that what it's called?) every time. I have checked numerous times and there are no sharp edges or anything. Once I even created a buffer with duct tape and a rubber patch so that there could be zero chance that the rubber part of the tube could make contact with the hole in the rim. The problem persisted. Sent to LBS and the guy said that it was likely old/loose/worn rim tape that was shifting under braking, causing stress on the tube and so he replaced it. Miraculously, the next ride went off without a hitch but then the problem came back. 

 

Here's what it looks like now with new rim tape:

 

 

We've been pondering whether it could actually be the tyre itself causing this to happen. She is running what was meant to be a cheapie interim tyre before moving to a tubeless setup. It's a R200 Arisun something or other and it has very soft, thin sidewalls. Could it be that the tyre is not offering enough support, thus making the tube shift under load and causing it to tear?

 

Really want to get this resolved because although she's now an expert tyre changer, she is at maximum gatvol level and so am I.

 

Cheers.

 

 

[johanpre44]

I suspect that the torn tube at the valve stem may be because of movement of the tire after it was already fairly flat.

 

Some silly things I always check:

1. Check the tire itself for thorns etc. before putting the tube back, may be worth checking the tire bead for any rough/sharp edges. I literally rub my hard on the inside of the tire to try and find any thorns.

2. Check the rim, rim-strip, spokes if they can cause any punctures (had sand and a spoke catching me out in the past) - I guess you already did this

3. Pressure... I found that a higher pressure on tubes sometimes help a lot for stopping punctures to happen (I used to run 3 to 3.5 bar on my MTB tubes in a 2.125" wide tire which helped a lot).

 

Hope you get it sorted out, but I must say that I have not had any issues since switching to tubesless.

 

You may be able to pick up some very good 26" Tubless ready tires at Solomons in Woodmead (chances are that it will be cheaper than all the tubes you are replacing at the moment). Stans works well, but for the price I prefer Tire Juice (R70 for 4 wheels).

[JXV]

Was the rim drilled to take Schrader valves. If using Presta valves in such setup the hole in the rim will be too big and the tube may burst through.

 

I think there is a rough edge somewhere or a crack that opens under load or a spoke poking through.

If it always tears near the valve then how tightening the Presta retaining ring...it should not be winched tight with a pair of pliers....hand tight is ok

[Wyatt Earp]

Tell her not to tighten the valve down before she puts the tyre on.

Valve loose, put the tyre on the rim, inflate the tube and then tighten the valve down.

[MTBc]

1 word solution: tubeless.

[FlandersZA]

Hey everyone, thanks or the replies.

 

We have tried harder pressures to no avail. She's using presta and I'm sure the rim's valve hole is presta sized. It seems to fit snugly and they're the same size as the ones on my bike. Also, she has made sure that tightening the valve only comes after the tyre is fully pumped. Still, the tubes always rip right at the base of the stem - sometimes 1-2km into a ride on a brand new tube. It's a really frustrating mystery.

[Boerklong]

Can it be that the tyre is loose? On acceleration or braking the tyre moves the tube?

[FlandersZA]

Can it be that the tyre is loose? On acceleration or braking the tyre moves the tube?

 

That's what we've been wondering. I mean the tyre doesn't physically feel loose although it isn't the hardest tyre I've ever changed in terms of getting it on/off the rim. But we've scratched our heads over this one to the point where it seems like the only logical answer here. I wonder if anyone has experienced similar?

[Boerklong]

That's all I can think of. Buy a good quality tyre. Tubes are going to cost a fortune at this rate. At least when you put a better tyre on you can tick that box. Worth a try...

[Boerklong]

I know on our mx bikes if you don't tighten or have a rimlock in, the tubes valve gets ripped of every time. Though the force is much greater the principle stays the same. You wont be able to feel it by hand.

[ballisticz4]

 

Though the force is much greater the principle stays the same. You wont be able to feel it by hand.

 I agree, I had a bike back in the day that use to rip valves when braking hard. Tyre was a smidgen to big for the rim, that caused the tube to move around more, even though it was pumped quite hard. After we changed the tube and pumped it up, it all felt good, by hand, but a few hard breaking sessions and it was all over. What id id notice then was after a few rides, the valve would be skew, with the tip facing the rear, and that was what lead us to this conclusion. Hope you come right with this one.

[nolipoli]

Flanders, where are you based? I think I have a slightly used 26" tubeless ready tire that she can have. If I remember correctly, its a Bontrager something or other, and well suited to rear application.

[Eugene]

I haven't read though the replies, so I hope this wasn't mentioned.

 

Apply talcum powder quite liberally to the valve area. It reduces friction and will help the valve and tyre to move around without it tearing off the tube.

[FlandersZA]

Nolipoli, you're a legend. Will give it a bash this weekend. Thanks again!

[lefthecountry]

Sounds indeed like the tyre is rotating a bit on the rim when accelerating or braking. Since the tube is stuck at the valve, all the pressure of the rotation will go into the part near the valve, since that's what's stopping the rotation. This will cause many flat tyres on / next to your valve.

 

I have this problem on my mtb when I run less than 2 bars of pressure. When I have more pressure the tube pushes the tyre hard enough to the rim for it to stay in place.

 

I also had this problem on my fixed gear bike. After having many flats I found the problem: I switched to a 32mm wide tyre, while my tube was only ment for tyres up to 25mm wide. This ment that the tube was to small to apply enough pressure to the tyre for it to stick well into the rim. When I bought wider tubes, appropriate to the size of the tyre, this problem got solved immediatly.

 

 

 

Long story short: for me this seems like her tyre is rotating on her rim. It can be caused by lack of air pressure and/or too skinny tubes for the tyre.