Bicycle Mechanics - Tire, upon inflation, comes off of rim

I recently ordered 2 of the Tri-Sport tires from your online store and have been using them for a while. However, twice I have left my bike and come back to find a flat in the back where it *appears* to have been a pinch flat perhaps (a 5" gash with a star shaped hole in the tube). Well, I dismised the first one as a pinch flat but have meticulously checked the 2nd time for pinching, and it still happened. Well, I just got new tubes and decided to see if I could do better installing the tire next time.

Now I just put on my tire, and upon inflating to 15psi or so, I check the tire for pinching and all that--looks good. Then I inflate to about 80psi. Seems fine so far. I let it sit for a minute and then I notice the tire is coming off the rim, while still inflated at 80psi. Wow! I quickly deflate the tire in case it pops. I reseat the tire and do this 2 more times, each time discovering that the tire is coming off the rim.

It now seems that perhaps the way I have received flats in the first place was because of the tires coming off the rim while I was away. The higher pressure in the tires (~85 psi) then blew the tubes.

The wheels are old (from 80's Schwinn), rim strips are new, and tires are new. Is this possibly from a defective tire? My front one has never given me trouble.

Thanks,

Adam

The tire may be a bit oversize but the real problem is your old rim. Current rims have "hooked beads" which are an inward facing ridge of metal just inside the outer perimeter of the rim. These "hooks" match a groove around the tires bead area and the two interlock to keep the tire on the rim at high pressures. Your old rim lacks these hooks but your new tires are designed to work with them.

Is your front rim the same vintage or a newer replacement?

Yeah the front rim is the same and its the same tire (Specialized's cheapest road tire, the tri-sport). The front has never given me trouble but then it also has less weight on it too--

Maybe the tire is just too cheap?

Mark the tire and rim where the tire starts to come off the rim. Take the tire off and reinstall with the marks 180 degrees from each other. If the problem follows the tire, problem with the tire, if it follows the rim, problem with the rim.

For the record, "pinch flat" means a flat that you get when you hit something hard while riding, like a rock, and pinch the tube between the rock and the rim. They don't result in 5-inch holes in your tube ;) Pairs of little 1/4" holes, yes.

The problem could be a lot of things, including rim tape or rim strips that are getting between the tire and the bead and preventing the beads from getting under the rim's hook edge very well (assuming it's got hooks). I'd advise using cloth rim tape that lays in the bed of the rim, covers the spoke nipples, but is not so wide that it rides up into the bead area.

It also could be what HillRider said... your old rims just aren't ready for 80psi tires, or your tire's a little oversized, or maybe one rim is a little undersized (manufacturing tolerances).

Specifically what rims, tubes and tires are you using? Sizes? You aren't actually giving us a whole lot of information here.

I'll also add that I don't have an online store...

Hillrider is right. I owned a 1969 Schwinn Super Sport with old style rims, the non-hook bead rim kind. Try to put over the recommended maximum 70 psi and POW - off goes the tire and the tube would be ripped with a huge hole.

I did, however, have the same thing happen on a hook bead rim. It was a Sun rim and no brand of tire would stay on it. It turned out that the rim was made too small, a manufacturing defect. The way Sun handled the problem was very disappointing, but that's another story....

It's easy to check for this type of thing. Measure the perimeter of a known good rim with a sewing type tape (they will lay flat on the OD of the rim, unlike a carpenter type tape measure) and compare to the rim in question.

2 things:

1-If the problem follows the tire, problem with the tire, if it follows the rim, problem with the rim;

2-I don't have an online store either.

Rafael

put on some rim tape.

sd

Mark the tire and rim where the tire starts to come off the rim. Take the tire off and reinstall with the marks 180 degrees from each other. If the problem follows the tire, problem with the tire, if it follows the rim, problem with the rim.
This man is right. Do this.

Betcha the tube is pinched between the tyre and rim... You gotta push the stem up into the tyre before putting air in... Then pump to 2psi and pull the tire sideways to see down the gap between the tyre and rim to make sure there's no tube visible.

Thanks for all the replies. I didn't get a chance to mark the tire and install it 180 degrees from the rim, but I will do that when I get a chance (damn finals...).

I'm pretty sure it's not pinch flats. I do check them for pinching with the tire but never find anything.

I do not think there is a rim "indention" that keeps the tires in place. It looks like it just goes smoothly straight up. These wheels *are* pretty old, being from the 80's, and perhaps this is the problem. But I'd still like to have at least 80 psi since anything less than that (and even that) seems to be kind of flat and causes lots of resistance...

I actually just realized something that may have caused the problem. Someone mentioned that perhaps the wheel is too small. I actually just tightened some of my spokes because some of them were hideously loose (without truing or anything, I just tighened the loosest ones and kept going around until they sounded about the same pitch), and this may have shrank my wheel size--not dramatically, but maybe enough to cause the wheel to be too small for the tire? I may have *overtightened* them, which I doubt, but it is possible.

My tire size is 27x1 1/4" and so is the wheel (I think--this is what size tire WAS on the wheel). They seem to fit really well too.

Specialized says that I can send the tire back and they can issue me a replacement. At least that's an option over Christmas break when I won't be riding my bike for 2 weeks anyway (going back home from college). But I'm not sure if its worth the shipping to them for like $5 for a $13 tire.

I'll do that trick and try to find out if its the tire or the rim. Thanks guys!

Adam