Originally Posted by daveb
I had a similar situation and when they looked closer found a fine crack in the rim. It was an American Eagle rim that came with the van.
Was the wheel aluminum?
Makalu1, are your wheels Al? They are lighter, but more expensive, subject to stress fractures, and the bead seal wears faster. You can get better, and even more expensive ones with scandium added to the alloy. This is a big issue trucking lines look at when figuring what's best for their bottom line.
Some aircraft and rocket fuselages now use aluminum-lithium alloys with possibly a trace of copper and zirconium too. This is lighter, stronger, and less stress-fracture prone, but even more expensive. I'm not sure if it can be cast as a wheel; I believe it can only be welded with friction-stir welding.
Anyway, if the wheel is aluminum a micro-fracture could be possible.