Hi Ed,
I checked the size of my tires on my chevy based TD. They are P195 75/R14. I run the tire pressure at mfg recomdations. I also had a shake in my car upon the completed assembly. I found 2 things that helped. The tires on the car during assembly, though new, had flat spots from setting for extended periods. The other thing I found, the front shocks, even though they were new, were leaking oil. I was able to match them to a new set of gas charged shocks and she drives like a dream. I hope this helps. Good luck.
Bill Hursh NY