recalibrate speedo's
 

What is the biggest size tire I can get without having to recalibrate my speedo's. the tire i have now are stock. I have '97 f150 4x4 with a 5.4 engine everything is stock. I was thinking of putting on some bfg's mud terrain.

Everything other than stock will throw your speedo off, just depends if it's 2 mph or 20. I went up to 37's on mine and regeared to 4.56's. I had my Superchip reburned to the new set up and my speedo is dead on! Without it, I was 20 mph off. I've heard the 97-00 were easy to recalibrate.