Originally Posted by
chrisabn
mmm this will be tricky to explain since the old tube is now in somewhere in the city trash. There was a hole right along the middle, about 3 inches long and about as wide as the tube itself. It was roughly opposite to where the valve is located. Although I was told that something could've been potentially wrong with the rim or the tube had been poorly seated, .....
Here's another possibility, but it would only apply if you have narrow rims.
When a tire is mounted
(see sketch) there's a sort of hourglass shape, with the tire above, then a narrow area between the beads (3), and the space inside the rim below the beads.
As you fill the tire, the properly positioned tube fills the tire at about 5psi, spanning the narrows. With more pressure, the section across the narrows blows down into the space below. Since the tube is sticking against the tire, only the narrow section expands, so it's effectively stretched 2-3x the rest of the tube. The end result is that this hyper-stretched section can burst, just like an overinflated balloon.
If this is the cause, you'll see evidence in the form of stretched areas elsewhere on the belly side of the tube.
Meanwhile if the tire is handling nice at 70psi, you might as well stay there, though there's no assurance you won't have the same problem, nor that more air will trigger it.
Originally Posted by
chrisabn
I probably should mention again that when I inflated to 100 psi, the pump piston started to feel incredibly hard - it was quite an effort to do that. (Is that normal, anyway?)
.
Yes, pumping force is directly proportional to pressure. The pump is a piston, and the force needed is equal to the pressure X the cross sectional area of the pump's cylinder. That's why high volume pumps are fat (move lots of air per stroke) and high pressure pumps thin, don't move much air, but have a better ratio of pressure to pumping force.