I just replaced my stock 18" wheels with Ford f-150 stock 20" wheels. The used 20" wheels have only about 4,000 miles on them, but I have a slight shimmy in the front end now that wasn't there with the 18". I checked the tire pressure and found it was 38 psi in the front and 40 psi in the rear. I have adjusted them all to 40 psi and it seems to have gotten worse. What is the best thing to do at this point? The tires are Pirelli Scorpion ATR's 275/55.

 

Either have them rebalanced, or try rotating the fronts to the rear to see if it makes a difference.

 

I had the same problem with 20", the tire place rotated high speed balance the works and still I have a slight shimmy from time to time

 

Thanks everyone, but after driving with them for about 40 miles it seems to have gone away. I do find the 40 psi a little harsh. I am thinking of droping the pressure down to 38 psi while I'm not hauling anything but passengers.