Heading away from my house, I noticed my bike was bouncing up and down, and discovered a big bulge in my rear tire. So I put it back in the garage, and took the other bike.

Upon un-mounting the tire, I discovered that the cords on the inside of the tire were badly frayed, over roughly an inch. On the outside, plenty of rubber left, but two large punctures on either end of where it was frayed. The punctures look like a vampire bite from an old horror movie. The tire was still holding pressure -- it has a MrTuffy liner.

The tire is a Cheng Shin C637, and fortunately I had a new one to install right away. It's a cheap tire, but I've gotten good lifetime out of them with the liner -- this one is probably four or five years old, ridden for daily commuting, about 8 miles round trip.

I'm curious as to what caused this. Maybe something went through the tire but not the liner, wandered around inside while fraying the cords, and then bored its way back out, like some little stone.

The picture is of the inside of the tire, splayed open with a spring clamp in my workshop.

The most likely is that whatever made the two punctures cut a number of cords as glass does, rather than sliding between strands the way a nail might. When you cut a number of adjacent strands it weakens the tire, and it begins to tear much the way any fabric is easier to tear once you get it started.

This might not have happened all at once. The cuts may have happened, and as you suspect, the liner may have saved the flat. Then over time, the fabric started fraying and tearing. That second stage might have taken minutes, hours days or even weeks, but the stage was set when those initial cuts were made. The lumps and bumps were the result of the tire tearing and getting fatter locally, and acted as a telltale, telling you something was wrong, ad sparing you the high speed blowout people feet.

You said it , cheap tire. Better tires are constructed better with usually some better mileage.

Someone else posted and then apparently deleted a reference to the possibility that the edge of the liner caused this.

It's a valid point and needs to be considered. As you ride and the tire flexes (especially if ridden at comparatively lower pressure), the end of the liner slides forward and back. Over time this can chafe and abrade the inside of the tire, eventually cutting into the cords which then fray and tear apart like a weighted rope would if cut part way through.

So whether the cords were cut by an outside source, as evidenced by the cuts in the tread, or abraded by the liner, the effect is the same, they'd fray apart and the tire would blow.

This isn't a reflection of tire quality, the same can and does happen to any tire regardless of price or quality. As a long term tubular rider, I can attest that even the most expensive silk tires can go this way.

My first thought.

Odds are very good that spot was where the ends of the liner overlapped...

@FBinNY and @rmfnla, that's an excellent thought, and I had similar concerns myself since I've read about pinch flats caused by tire liners. So I removed the tire carefully to preserve the arrangement of the tube and the liner. The ends of the liner were elsewhere around the tire, and the liner didn't look any different around where the tire was damaged. These things are somewhat of a pain to get centered all the way around when installing for the first time.

So I'm going with the external puncture theory.

That's what I originally suspected, but like to have all options before me before settling on a single theory.

That says it all. Even though your pic is small, I think the problem is one related to quality and NOT something you did or ran over.

-SP

You might have read the text before deciding that a tire magically had two punctures simply by virtue of being below your elitist threshold for tire quality.

There were two plausible explanations for likely cause, and we didn't have to indict the tire by brand. Cheng Shin tires aren't the lightest out there, but have a very long history of holding up fine until worn out or damaged by a road hazard.

I've had the dreaded S-bulge happen on some major name brand tires. One was on a Vittoria that I'd only had about 1 month, and it developed at mile 80 of a century.

I'll admit that I don't like to spend big bucks on tires, but tire quality is a bit of a gamble these days. I've never had S-bulges develop until the last 5 years or so and I've been road riding since the '80s.

It's all useful information. Who knows, maybe cheap tires are more failure prone, but in this particular instance, I'm inclined to believe that the punctures caused the resulting failure. The wheel had been a bit lumpy for a few weeks, but I had been thinking more in terms of the truth of the wheel, and inspected the spokes but not the tire.

A new tire of the same type, that I already had on hand, is on the bike, with the old liner. Going forward, I could just keep re-using the liner in an endless succession of cheap tires, or ditch the liner and get a puncture resistant tire for a better ride (so I imagine). I'll probably have 4 - 5 years to figure that out, meanwhile, other projects beckon.

Sorry FB. I DID read the post and I am FAR from being "elitist."

Tires get punctures all the time but still dont fail in the way the OP described and pictured.

I have been familiar with Cheng Shin product since the 80's. I havent seen any difference in their quality over the years.

While many use their product without trouble, others have failures. If that happened with a different brand I would be surprised, but if I saw the failure and was asked what brand the tire was I would have guessed right.

-SP