Does your Duster "float" at highway speed?
My car likes to wander a bit at speeds around 70mph
Define wander
Do you mean follows the groves in the road?
You have to constantly readjust the steering to keep it going straight?
What happens if you take your hand off the wheel? Where does the car go?
The 2 to 3 hundred pounds you removed IMHO is not the issue.
My 67 dart with 319,000 on many of the front suspension parts will drive down the interstate at any speed streight as an arrow ( slight creep to the right due to the crown of the road)
I find my self moving the wheel because I perceive I need to. But if I take my hands off the wheel no need to correct.
I have about 5 deg play in my steering wheel, like 11:30 to 12:30 (2330 to 0030 for you 24hour types)
My front tires are cooper cobra 205-70R14
All 4 corners, alignment is most likely factory spec, dad did not know about the radial spec when it was last aligned.
I had a 56 pickup with 210 BFG in front and 255 BFG the rear. Drove great, I went to the mountains so I bought 2 snow tires for the rear probably around the 205 ti 210 width. 4 hours of driving hell. The back end was squirming all over the place. Not saying that is your issue but it illustrated that tires might be a huge contributing factor.
I have had tires on a commuter car the followed every grove and others that didn't ( same car, same roads, same speed)
