My wife's bike (old Trek 970) got a rear flat on the road the other day. No big deal, I found a medium size hole and patched the tube. Rim seemed fine and tire felt smooth inside. I noticed the tire was pretty much shot in the sidewalls, though it had good tread still.

The next day we rode about two miles and parked it outside the store, in the sun. When we came out it was flat. Much larger hole in the same spot.

I put an old, patched tube in a brand new Michelin tire. Pumped it up to 55 pounds or so and it blew out.

Put a brand new tube in the new Michelin. Pumped it up to 45 pounds. Rode about four miles, parked it outside in the sun. Now she just told me it is flat.

Any idea what's going on?

Thanks.

I had something similar happen to my hybrid last season... tire kept going flat (total of 7 times!) after patching or replacing the tube. Everything seemed to be OK, nothing stuck in the tire - I checked 7 times.
Turns out that the rim tape was worn out (stretched?) and would "creep" when the tube was being re-inflated, exposing the tube to the spoke holes in the rim below. Replaced the rim tape and everything was fine after that.

Thanks KLiNCK. I did notice the rim tape was pretty worn, but nothing seemed exposed and I had no spare. I'll try replacing it and see what happens.

Open to any other suggestions.

Agree with above. A "big hole" is usually not from a poke through or pinch but from a lack of containment. A cut or slit in the tire casing, a spoke access hole in the rim that's not well covered by a good rim strip are the common causes.

There are many bikes that come from the factory with box section/double wall rims that have poor and stretchable rim strips. these strips can and do get pushed into the rim holes and/or get a slit or hole themselves. Then the tube expands into the gap and blows out like a balloon being over inflated. Think of a hernia.

If you have a box section rim and rubber rim strips replace the strip with a plastic or cloth one. Andy.

If the puncture is located on the inside of the tube, then it's likely a rim tape issue, if on the outside well.... need more info. Where is the puncture ?

The blowout was in the side of the tube. The holes were in the side too.

I pumped it back up this afternoon and it seems to be holding. So maybe it was a valve or something this time, just coincidence? I'm going out tomorrow and will pick up a rim strip, just to be sure.

Thanks for all the advice; I'll be back if it goes flat again.

First you must analyze were the hole is on the tube. Inner dia. Outer dia. Or sides?
Outer side would most likely be something still in the tire.
Inside would be spoke nipples and or bad rim liner.
Sides pinch flats.
This I would assume because you say it’s in the same place all the time.

you ever think that maybe your wife likes to watch you change her rear wheel? that's not all bad...

well you did say the sidewalls were shot, holes and tears in sidewall lead to blowout when the pressurized tube pushes thru then ruptures from the force of it's own internal pressure. doesn't matter if theres still tread left if other parts of tire are fail, change the tire

Not nearly enough detail to be certain, but here are some ideas:

You are the common element in the second, third and fourth flats (and maybe the first also).

Flat # 2: The single most important step in flat repair is correcting the cause -- failing that wastes everything else.
Flat # 3: Most likely caused by mounting technique.

What a great forum - thanks all.

You would have thought, after about 45 years of experience at it, that I'd know how to fix a flat tire by now. Apparently not, LOL.