Will I need to recalibrate my speedo?
 

Hey - right now I have 16.5x12 rims with 39x15 Mickey Thompson Baja Belts. I am thinking about getting the 39x18's, a guy offered me a great deal on a set plus a good bit of $$ on a trade in for the tires I have now.

My question is - if I get the wider tires will I have to recalibrate my speedometer? I would assume no, since they will be the same diameter and overall height, but is anyone an expert in these matters that could verify this???

thanks!

The speedo only cares about the circumference of your tires. Wider tires wont change this. I imagine you already adjusted it for the tires you have so you're good to go.

True, I already had it recalibrated for the 39x15's. Thanks Drake! I think I will get the new monster's for the holidays!

how did you recalibrate?

F150aGoGo,

This thread explains what's involved with recalibrating a 1997-1998 4R70W:
https://www.f150online.com/forums/sh...threadid=98075

The 1999 and later models require that the computer be reprogramed by an aftermarket computer chip. Or, at the dealership.