Dear Tom and Ray:

I have a 1996 Jeep Cherokee that I bought used last year. Recently, it has developed a shimmy at speeds over about 50 mph, and it feels like the tires are bouncing all over the road. On gentle turns, it feels out of control, like it is going to roll or leave the road. I've taken it to a tire-and-alignment place, where the mechanic said I simply needed to have my tires balanced. That didn't fix it. This really scares me. I'm a new driver (I'm 17), and I don't need anything else to worry about while driving. -- Alex

RAY: This is not something you want to fool around with, Alex. A front-end vibration could be anything from a bad tire to a wheel getting ready to fall off. Do you want to wait and see which one it is?

TOM: We didn't think so. If you think the alignment-and-tire guys are good guys, you can go back to them and tell them that the wheel balancing didn't fix the problem. Have a mechanic drive the car with you, so you can say: "See? You feel that? That's the problem I'm talking about."

RAY: It could be many things, Alex, or a combination of things. For instance, the shimmy could be caused by a bad tire or a bent wheel from that curbstone you hit last summer (you forgot about that, didn't you?).

TOM: And the "bouncing all over the road" could be the result of severely overinflated tires. Some new drivers think that if 30 psi is good, then 45 psi must be better. That would cause very scary handling in a Cherokee.

RAY: Bad handling could also be explained if you had put the vehicle in four-wheel drive at some point and then forgot to take it out. The Cherokee has an old-style four-wheel-drive system that cannot be driven on dry pavement. Why? Because on dry pavement, it causes dangerous and erratic handling!

TOM: And if you happen to have a seized universal joint in your front axle, too, that could cause a shimmy when you're in four-wheel drive. So check those things first.

RAY: But it's just as likely to be a bad ball joint, a bad tie-rod end or something else that could lead to a wheel falling off. So you absolutely want to have a competent mechanic inspect the whole front end and find out what's going on under there.

TOM: You're right to be concerned, Alex. And you want to fix this -- whatever it is -- right away. And get back to your Cherokee's normal, slightly safer, lousy handling.