After the seventh pinch flat in a year, I began to wonder! One night, as I was in the garage repairing a pile of tubes, I started thinking. After thinking about what might cause pinch flats, I realized they were not caused by under inflation. I have rubbed talcum powder into the tire casing and on the tubes so the tube would slide around when it was inflated, and continued to have pinch flats. I came to the realization that they are caused by the tube getting caught between the tire’s bead and the rim. The actual flat could occur any time afterward, but it usually happens when you hit a bump thus putting a sharp stress on the tire and tube.

I let the air out of the tire I had just mounted. I checked it by pushing my thumbs against the near rim, and pulling the tire away from the opposite rim. After checking around the tire I found a small section of tube caught between the bead and the rim. There was my next pinch flat. I moved the tube out of the way of the bead and checked the rest of the tire and pumped it up. Since then I pump up each tire a little, let the air out, and inspect it. I haven't had another pinch flat in over fifteen years.

This has always been the accepted way to inflate any tube/tire combination. You always want a small amount of air in the tube ( new or repaired ) to make it take the shape of the tire. This makes it less likely that you will catch the tube with the pry bar ( if one or two are used to remount the tire to the rim ). I've always used talc on the tube when inserting it into the tire. Always get the air nozzle side installed first and carefully tuck the tube inside the tire and make sure no part of the tube is outside the rim. Seat the tire carefully on one side of the rim and then the other side, using a pry bar only if necessary to prevent damage to the tube or the tire. Inflate a few pounds, check the tire sidewalls, deflate, the inflate to the desired pressure. Don't forget to use some "spit" on the valve tube to make sure the valve core isn't lose ( schrader valves ).

What you have described is neither a snake bite nor a pinch flat.

"Pinch flats (Snake Bites). This flat is identified by one or two distinct puncture marks on a tube, as if it were bitten by a snake. These are usually caused by striking something like a pothole or curb with low tire pressure. The tube becomes pinched between the tire and rim from the abrupt impact, puncturing it."

This has been part of proper tire installation since the beginning of time. But thanks for sharing.

Sounds like you really needed to use more air in the tube when installing it.

I NEVER use tools to mount a tire, only to dismount.

My only punctures were from low air, since todays tubes leak badly. (Well that my opinion when I have to re-air tires at least once a week.)

-SP

Idle curiosity: What causes the double puncture in a snake bite? I recently hit a pot-hole and got the usual two holes. They were positioned along one side of the rim and in line with the edge of the rim, about 1/2" apart. So why always two holes?

Rim and street/trail hazard pinches the tube between them, the slamming force, punching a hole with the rim edge.

a rim has 2 edges..

The two slits (holes) are from where both sides of the rim punctured the tube, when the rim bottomed out upon impact with the pot hole.

OP, thanks for your extensive research, but during your 15 years of exhaustive field testing, this thing called The Internet has developed, and it contains many resources that provide similar tutorial info about how to install tubes...

Three points of contention to the above.

1. Pry bars (tire levers/irons) should be avoided in remounting if at all possible. It is very seldom necessary with proper technique and can easily damage a tube or even the rim. As the OP noted it's usually effective to get the tube out from under the bead by manipulating the tire and tube, rather than using a tool.

2. There will be more slack to install the 2nd bead if you start opposite the valve stem (air nozzle) and finish just to one side of it. If you mount first at the valve stem it interferes with pushing the tire toward the center of the rim where the radius is smaller.

3. One important step is after both beads are mounted to push the valve stem into the tire, push the tire toward the rim, and then gently pull the valve back out.

I was so hoping this thread was going to die a quick death 2 days ago.