Shimmy 50-60mph, new tires, fresh balancing.... hints?

[Don Banfield <banfield@domain.elided>]

Hi,
	My car seems to have a lateral shimmy or vibration at about 50-60
mph.  Its smooth above and below that, and I even think sometimes its
smooth between 50 and 60, but most of the time you can't miss the lateral
vibrations at those speeds.
	Now the puzzle is that I just replaced all 4 tires with brand new
ones and had the wheels balanced and the alignment checked by a
(supposedly) reputable shop.  I had the tires replaced because the old
ones were out of round (visibly while spinning them by hand with the car
on a lift).  It had a much worse vibration before the new tires, which I
thought were the sole culprit, but now I'm wondering if their being bad
wasn't only a symptom.
	So, should I go back and insist that they rebalance the new tires?
Or do some form of fancier (dynamic?) balancing?
Or is it possible that something else is wrong:
	Bent wheel?
	Loose wheel bearing?
	Loose suspension components? (which?)
	unbalance brake rotors?
	new tires out of balance/round? (unlikely)

How often have you all found that shops don't balance wheels correctly?

thanks,
Don Banfield

Don Banfield					Senior Research Associate
banfield@domain.elided                   Cornell University Astronomy
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