oldbobcat said:
Let me get this straight. You've got a Schraeder valve and a rim drilled for a Schraeder valve.
Is the bulge coming out the valve hole or is it at the tire casing where it seats on the rim. If it's the tire casing, release most of the air pressure, push the valve stem into the tire to ensure that the tube is inside the tire and not pinched between the bead and the rim. On narrow tubes, the hard rubber surrounding the stem can cause the tube to get pinched here. As you re-inflate slowly, check that the tire is correctly seated on the rim.
you got it straight, oldbobcat.
this tube/tire combo had been mounted for about 18 months, yet only recently this bulge popped thru...pretty amazing, too, since there's very little clearance in between the rim metal where the valve stem hole is, and the valve stem itself.
I did end up letting out most of the pressure, then replaced the tube, destroying the old tube by cutting the valve portion of the tube out with a pair of scissors..
when I inspected the valve area of the tube which had the bulge (after cutting the valve out) it appeared to me that there were 2 layers of rubber around the valve, and that air pressure had "sneaked" between the 2 layers, and managed to pass 2 walls of rim metal, through tight clearance, to pop out the other side and form this bulge.
pretty impressive display of what 100 psi can do, eh!?
thanks!
geardad