The tire may not be seated correctly, and/or your rims may not be well-suited for them.
1) What rims are you using?
2) Look at the bead line (line molded into the sidewall rubber just above the edge of the rim). Is there a "low spot" where it dives down out of sight anywhere? Because if the tire can crawl over the edge of a suitable hook-bead rim, it's getting that slack from somewhere. A low spot in one place gives it slack to have a high spot in another place.
3) Check that the inner tube is not trapped between the rim and the tire bead. To check, deflate the tire almost completely and then squeeze it together so you can peek inbetween the tire bead and the rim. You shouldn't see the inner tube folded over and trapped between the tire bead and the rim.
- i have had the 'bulging' thing happen with a number of tires - most often w/the folding type, not the wire bead type...
- always make sure the tire bead is seated... my sequence is 1) inflate to 1/4 recommended pressure... 2) seat, then inflate some more... you may notice a bulge if the bead is not seated... 3) if found, deflate, reseat (i roll tire around rim on floor at 1/4 pressure), then re-inflate and you should be good to go...
- this may also help avoid pinch flats or those 'spontaneously exploding' tubes?
- the first time this happened to me i thought i received a defective-beaded tire, but after reseating the tire was good to go!
It is mandatory to check a newly mounted tire for proper seating on the rim. I inflate to about 20 psi and holding the wheel by the axle, rotate the wheel and look for uneven seating on both sides (relationship of rim to molded ring on the tire that should run about 1/16th inch away from the rim). Next spin the wheel again and look at the molded rib on the center of the tire to see that it runs straight. If it wiggles from side to side, take it off and look for the cause.
The reason to inflate to only 20 psi is to avoid blowing a tube at full pressure if there was a problem.
Yea,I'd say check your tire mounting style. I mount the bead on one side all around. With the tube inflated with enough air to not get pinched, install it.Using only your thumbs will save the new tube. I've gotten those "ta ta kaboom" blowouts too.Never a good thing.