My truck is in for another ring & pinion change for the Howling over 65mph. By the way, they have the fix according to my dealer, and I'm just awaiting parts.

While it's in I asked them to re-calibrate my speedo for my 20" wheels that were on the truck when I took delivery of it. They said that it can't be done.

Is this true? I figured they could do it with so many people upgrading their wheels & tires.

 

I sure hope it can. I paid a local dealer $43 last year to do mine when I switched to 18" wheels. Hope I didn't give them money for nothing.

 

What is your overall tire diameter? I've been told that Ford can recalibrate the speedo to correct for up to 37" tires. A buddy of mine had it done on his 04 F350. I can't see why they couldn't do the same for an F150.

 

P275/55/R20 is the tire size.

 

10.83 inches wide by 5.95 inch x 2 plus 20 = 32.00 inches

Assuming your tires have a lot of tread, they may be 33 inches to 34 inches tall. The stock Long Trails, etc. are often 33 inches.

Have you tested the speedo, say with a GPS? The factory ones usually read a little high. After I increased my tires from 30 to 30.6 inches, it is more accurate.
So if they are off only a little, the dealer can't adjust them in small increments.

You can get a tuner, of course, and set it the way you like.

Of course, most likely, the dealer 'technician' just doesn't know how to do it.
Chris

 

With that size in diameter ... you should be fine ... even though they probably don't have that size as an option in the computer... just get your revs/mi and they can pick a size that closely matches.