I am mostly into Vintage road bikes so don't feel qualified to have an opinion. A friend is having a problem with his mtn bike getting flats. I am quoting him here hoping that someone might have an idea what is happening to his bike. He says this is happening with new tubes that he has just installed.

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It's an 80 PSI tire (well worn to be sure and no doubt overdue for replacement) and I had the first tube inflated pretty firm. Thinking *that* might be the problem, I didn't inflate the 2nd one as much but I've never had tube problems like this before. Every tube is failing right where the schrader valve goes through the little hole in the rim -- a chronic issue with these thicker/beefier tubes as they tend to 'walk around' inside the tire . . . making it nearly impossible to keep the valve straight as it should be. By gluing in a thorn-proof liner, I may have made it even harder for the tube to hold a fixed position. And yet the back tire has the same upgrade (IIRC) with no issues . . . can't remember the last time I had to fix a flat on the back . . . and that tire is in comparably (read: crappy) condition "

Any idea what might be happening to him?

Tubes are lazy and don't walk on their own. Since your friend reports walking, evidenced by valves tilting, we can deduce that the tire is walking and dragging the tube along.

Tires do walk, but it's pretty rare. It's caused by torque from hard climbing or hard braking, but rare because there's normally plenty of friction between the tire and rim. Therein lies the solution. Remove the tire and thoroughly clean the rim, likewise for the bead area of the tire, and remount dry.

If that doesn't solve the problem, then he'll need to use something to increase the friction, but I don't think it'll come to that.

BTW- a bike forum isn't like a medical one, where one might feel the need to invent a fictional friend to avoid embarrassment.You're safe here discussing your innermost mechanical secrets.

I've had that a couple of times. Usually when I've been a bit lazy with the small hand pump after a trail side flat repair. But once on a pair of folding tires with a slicker-than-average bead.
With the folders I eventually coated one of the beads with Liqui-Sole, which solved the problem.
Before they went to tubeless, a few of my riding buddies(who really liked using low pressures) would glue one bead to the rim using glue for tubular tires. Glueing one bead leaves one side "open" for replacing a tube.

Although it doesn't sound like the cause this time, it can't hurt to check that the edge of the valve hole is smooth and free from burrs.

"I had the first tube inflated pretty firm. Thinking *that* might be the problem, I didn't inflate the 2nd one as much . . . "

"Pretty firm" = "I didn't use a pressure gauge." The problem was underinflation.

Thinking *that* might be the problem, I didn't inflate the 2nd one as much . . . " Ironic.

Tell your friend to get a pressure gauge and use it. If he keeps the pressure above around 35 psi, the problem will magically go away.

Depending on what is "firm" or "pretty firm" this may be the issue, especially with fat tires.

Air pressure presses the bead against the rim, and provides the necessary friction. Large tires have higher "creeping" forces owing to the rim being farther from the ground, and combined with lower friction because of underinflation, may creep.

So, before taking my advice to clean and dry the rim and tire, the "friend" might try inflating closer to rated pressure and see if that's all that's necessary.

Thanks guys -- maybe this will work this time?

Thanks Guys. I'm capnjonny's friend at the top of this thread. What FBinNY is saying makes perfect sense. I'll clean the inside faces of the wheel *and* the tire beads with lacquer thinner -- let 'em dry, reassemble and see what happens. It is a 2" tire on a 26" wheel -- 35 to 80 PSI inflation range and I'm quite certain I'm near the top of that range. I rode 20 miles a day (same bike; same tires) back & forth year 'round to work for years -- retired since Oct 2015 -- but never had issues like this before. I've always used the beefy "thorn proof" tubes as goatheads were the bane of cycling existence in those days in the Boise, ID area. I wonder, too, if the thin, powdery sand around here might work like graphite powder?

As a former motorcycle racer, I tend to rely HEAVILY on the front brake and at least once a year, I get a front flat due to the tube leaking from the valve stem, This is true for all my road and Mtb's... a definite PITA!

I ride tubulars and once when riding in the mountains during a hot spell, had a double creeping issue. The rear crept back from climbing, and the front crept forward from braking. Fortunately for me, the front issue was worse, and I could manage it by flipping the wheel every day or two, but the rear had to be remounted a few times until I was out of the hill country.

It is easier to ride out a rear flat. Now, I replace my tubes annually and use the old one as a spare. The stem is literally ripped out of the tube but lately, I no longer use the locking nut, just a loose stem and that seems to help.

I am going to try going tubeless on the Mtb's this year. Wish me luck!