Thanks for the detailed reply.
Originally Posted by
FBinNY
When I see a long gash as you describe on the inside of the tube, I suspect one of two things, both user error (sort of).
1- if it goes with a low bang and the tire ends up off the rim for a length, then it's usually that the tube was trapped under the bead, and eventually jacked the tire over the side of the rim, or the tire was simply seated badly and didn't hold. The key elements are the bang, and the tire ending up OFF the rim.
2- it blows quietly, with a muted bang, or the psssst you describe, and the tire is found on the rim all the way around, and the slit is long vs a small puncture, then I immediately look at the width and interior profile of the rim.
There was no bang, more like a loud hiss, and the tire did not blow off the rim. So it wasn't option 1.
See if mt theory matches your situation based on these points.
1- narrow rim
2- long slit
3- tire NOT blown off
4- no or muted bang
5- evidence of over stretching, on either side of the slit, or elsewhere along the rim side of the tire (not always present, but if so is solid confirmation).
All true except for number 1. I have 20 x 1.50" tires, so the rim isn't particularly narrow. I had another look at the tube, here's a photo:
I hope you can see the dimple above the gash, where the tube was stretched. It looks like the tear started sideways, and then turned to follow the grain of the rubber. So now I'm guessing that the tube got caught on something on the rim side, stretched as it inflated, and eventually tore, causing the gash. The thing is, I don't know what that something on the rim is. The nipples are recessed, and there's rim tape. I'd have to take the wheel apart yet again to see, but for now the tire seems OK, so I'd rather leave well enough alone. I rode to work today, and so far so good. The mystery is partially solved, so thank you. I'll have something to look for next time.
BTW @
FBinNY, Chain-L is my go-to lube.
We met very briefly once at the Philly bike show.