my taurus has 3 tires with 80% tread. 1 of the rear tires has 30% tread? on slippery down hill roads, my back end wants to wander left/right when i am coasting. i drive a section of interstate daily that has a 2 mile downhill stretch. the car gets very twitchy when i let off the gas to coast. of course icy roads magnify the situation. car feels fine in most level driving situations. gas on/off feels good. is the issue low tread tire? empty trunk? perhaps a bad cord in 1 or more tires? car has no vibration issues and tracks perfectly. front struts are new. not sure if rears are original. have 4 wheel alignment checked?
I would suggest that you check the rear anti-sway bar, as it may have become disconnected at one end.
Weak struts are also a possibility, and–of course–having one tire with much less tread is going to give you quirky traction.
One odd tire can cause odd handling. IMHO that’s a very likely source of the problem. I’m going to even go so far as to ask if the tire is probably a different make and maybe different ratings?
By all means get the suspension checked out. That’s’ prudent. But regardless of the results, I’d replace the two rear tires.
Definitely replace the rear tires. Check the 80% three carefully and replace the worst and put them on the rear.
Get the alignment and suspension checked out. These cars tend to break rear springs, the stab bar could be broken (disconnected) or a bushing in the rear suspension could have failed and one of the rear tires is wandering about on its own.
front tires are matched set. rears are 2 different brands. quite easy to find pairs of taurus rims/tires. i am sure i could find better pair and sell mine.
That’s what I figured.
I think your decision is a wise one.