Bicycle Mechanics - New wheel is shredding tubes as fast as I can put them in.

I recently replaced my rear wheel/rim on my mountain bike, and in the last couple weeks I've gone through, like, 8 tubes. I can't seem to get one to hold air for more than a day or so.

More details: this is a pretty standard 26" rim. I've repeatedly checked the tire and the rim for anything that could be causing this, but there are no thorns, spokes, sharp edges, or anything like that. I'm very careful when putting in a new tube not to pinch it in between the tire and the rim.

When I put in a new tube, I inflate it enough that it won't get pinched, carefully get the tire back on the bead, and then inflate to max pressure, deflate to below min pressure, and then re-inflate to mid-pressure.

The tube then usually lasts me through one direction of my 8-mile commute if I'm lucky. On inspection, there is usually a gash between 1 cm and 1 inch long running lengthwise on the side of the tube that was facing the rim.

This never used to happen to me with the old rim, but unfortunately that one was banged up enough that it couldn't be properly trued anymore. I've tried every permutation of slime and tire liners, and I'm getting very frustrated. Can anybody offer any suggestions? Thanks in advance.

On inspection, there is usually a gash between 1 cm and 1 inch long running lengthwise on the side of the tube that was facing the rim.

Is the gash always in the same place on the rim? Perhaps the rim tape is askew in one spot on your new rim exposing a sharp end of a spoke or some other sharp edge on the rim.

Am I correct in inferring that the new wheel has a fairly narrow rim? If not, the following may not apply.

If so the splitting you're seeing is classic for the effects of local hyper-stretching of the section between the tire's beads.

Look at this cross section diagram of a mounted tire (http://en.wikipedia.org/wiki/Bicycle_tire). (Scroll down past photos until you find the drawing). Notice that the tube isn't round, but has a bulged area that fills the rim.

When you inflate a tire the tube first inflates round filling the tire, then the section spanning across the beads continues to inflate down (up in the diagram) into the rim. So the section at the rim side of the tube stretches much more than the rest. On narrow rims this difference can be very significant. If you look at your dead tube, you'll see the signs of that overstretching in the non-split areas as small bulges in places along the bottom.

The fix is to buy higher quality, stretchier tubes. Also buy the largest tube that is smaller than your tire, ie. if you have a 1.95" tires, you want a tube that says 1.95-2.25, rather than a 1.6-1.95. A larger tube won't stretch as far in the initial inflation stage, leaving more stretch for the rim.

Also rub the tubes with talc before installing, to allow the tube to slip within the tire and shift somewhat toward the rim. You might also try inflating to 5-10psi, and massaging the tire a bit on installation to help the tube equalize the uneven stretch. Both the talc and massage technique of of marginal benefit, but won't hurt. The real key is larger, higher quality tube.

most likely caused by a spoke, even something that doesnt feel sharp to the touch can still cause issues at high pressure, check rim tape as kencarlson said, or replace it if there is any damage to it

Rim tape properly installed? Is there something stuck in your tire that you picked up on the first ride after replacing the rim?

Is the tube the right size? Does the width match the tire?

What kind of rim and what are you using for a rim strip?

Ideally your rim strip should extend all the way across from flange to flange. Wider rims, like Rhyno Lites, work best with Velox 22mm rim tape.

And cloth tape would be preferred over vinyl rim liners.

I recently replaced my rear wheel/rim on my mountain bike, and in the last couple weeks I've gone through, like, 8 tubes. I can't seem to get one to hold air for more than a day or so.
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The tube then usually lasts me through one direction of my 8-mile commute if I'm lucky. On inspection, there is usually a gash between 1 cm and 1 inch long running lengthwise on the side of the tube that was facing the rim.


Replace the rim strip, preferably with something high-quality like Velox rim tape. I've had a couple frustrating failures due to plastic rim strips.

What kind of rim and what are you using for a rim strip?

Ideally your rim strip should extend all the way across from flange to flange. Wider rims, like Rhyno Lites, work best with Velox 22mm rim tape.

+1
Velox in the correct width to fit your rim.

I think I have this figured out. I replaced the tire, and since then have had no problem keeping air in the current tube for the last week's worth of riding. What I believe was happening is that when I was braking, there was some slippage, and the tire was spinning around the wheel. I realized this because on the most recent tube, the valve stem was damaged.

To answer everybody's questions:
@FBinNY: The new rim is more narrow than the previous one. The talc powder is good advice, and I will do that in the future. With the new tire, though, I'm still using the same cheap tubes and it seems to be working.
@KenCarlson, @hpz937, @UberGeek, etc: The rim strip is the standard vinyl strip. It appears to be in place correctly, and none of the spokes are even close to poking up underneath it. I'll get some Velox rim tape for next time, though.

Anyway, thanks all for your time and advice. It's much appreciated.

-Dan

Good deal, what PSI do you run your tires at?