I have the lousy stock 31.1 diameter tires on my Fx4 and Iam looking at putting on a 285/70 (32.7" diameter) Will that extra 1.6" take away all my get up and go and turn it into a pig? I have a 3.55 rear L/S diff on a 5.4L

 

I went up a little over an inch with 355s and I am not sure I even noticed the change and I only have a 4.6.

At 40 mph your rpms will drop by less than 100 with the taller tires.

 

Personally I think even 33's are good enough with 3.55. Any bigger is when I'd regear to maintain performance.

Adrianspeeder