Tires: steering wheel shaking, stock tire size, ball joints

Question
I have a 2001 montero xls with 57k stock tire size of 265 70 16 when i picked it mup from the dealership it had a highspeed shake in the steering wheel 55 mph + i changed stock bridgstone tires from ht's to at revo had them rebalanced and the problem is still there now i just put 275 45 20s on the car and the same problem i have had the 20" balanced  3 times and sometimes its worse sometimes better this vehicle is "lugcentric" should i consider finding somebody with a roadforce balancer? Any ideas would help alot!

Answer
Jason,

1)  You've tried 3 combinations of tires and wheels and the vibration is still there.  I think it's time to look somewhere else.

So try the driveline - u joints, pinion angle, brake rotors, etc.  Also have someone look for worn ball joints, tie rod ends, etc.

2)  Road force balance is not a bad idea, but see #1.

Hope this helps.