I'm a new F150 owner and have recently changed from the stock 32" tires to a 33" tire. Should I pay the $65.00 to get the speedo reprogramed? I don't think I will ever go back to stock size 275x65r18.
My concern is that over time my mileage will be a lot higher than what is actually shown. Plus oil change intervals will be off as well. Will it affect the NAV unit in any way?
Any F150 owners in North Alabama with FORSCAN who can do it cheaper? I live near Decatur.

 

curious how they are reprogramming the speedometer

 

 

 

I reset mine. Went from stock 255/55/20 to 285/70/17. Verified via GPS that the speedo is correct after the change. I already had the SCT so there was no reason to not change it.

 

Went from 32s to 33.5s. I'm not worried about speedo calibration and will likely never change it.

 

I recently went up to 275/70/18's. Mine is off by 2mph now. I am probably going to have mine recalibrated. I called the dealer about it and they told me that the exact tire size that I changed to will have to be in their system that they use in order to make mine accurate again. At that time he could not tell me if my size is in the system or not.

 

I wouldn't pay the $65. I would buy an OBD adapter, get Forscan for free, then correct your speedo and change a ton of other settings to your liking. You do want the speedometer calibrated, if nothing else than to keep your shift points optimal.

 

Do you mind sharing how you did this using the sct?

 

It's one of the settings you can choose in the SCT programmer. You just calculate the theoretical diameter of your tire, pick the closest choice in the SCT menu, change it, then use a GPS or smart phone GPS speedometer app to check and make sure the setting was accurate. If not, you can change to the next larger or smaller size to fine tune until it is dead on.

formula for tire dia: [(tire width X aspect ratio X 2) /25.4] plus rim diameter

(285X0.70X2)/25.4 plus 17 equals 32.7"