Name that mechanical problem
 

I was out on a ride last week when my buddies rear tire started to intermittently wobble, enough to hit the rear brake and actually slow him down. It would last for about 15 or 20 seconds, then go away, so the tire was totally true again. Several minutes later, out of true again and rubbing on the rear brake. Lasted this way for the duration of a 90 minute ride.

Took it the LBS when we were done riding.

20 questions to figure out what was wrong.

you have me stumped. Were all the spokes in tact?

Cracked axle or a cracked frame.

It's probably the Fetzer valve.

Edit: Dangit! I need to read the signature lines in a thread before I post something like this. Curse you, Coach! ;)

misaligned flux capacitor

Another loose quick-release, with the axle moving around in the drop-outs? Or a cracked hub flange?

All the spokes were intact.

This was my thought while we were on the road. I thought that he had a broken axle. As a result we were a bit nervous on the descents to get back to the car.

But no, axle and frame were fine.

quick release and axle were fine. Hub flange was probably okay, if I had any idea what it was.

To the others (I don't know how to multi-quote), the Fetzer valve was a little leaky, the flux capacitor wasn't fluxing very well, and it was a quart low of 10W30, but alas those weren't the problem either.

Was the wheel really going in and out of true? Was a spoke thread stripped, or a spoke nipple stripped or broken? How about the rim? Was it getting thin from long-term brake rub?

I number of years ago a friend started down a jeep road when all of a sudden, POW, his front rim blew apart and wrapped one of the rim sidewalls into his fork. Stopped him immediately.

We're probably not even close, are we? Time for you to clue us in.