Speedo correction after tire size change?

[cu440da]

I just bought a '96 F150 and it needs tires badly. It has the tiny 235/75-15 on it now, but the factory upsize was a 265/75-15. I would like to go to the larger tire, but I want the speedo to read correctly and since I am a Mopar guy I do not know how the Fords adjusted for tire size.

How do you make the speedometer adapt to tire size changes?

Thanks!

 

[LocuMob]

I use a speedometer app on my phone that uses GPS to determine out of calibration Speedos. It should be fine going with stock size tires, as long as the previous owner didn't correct it when they went smaller. Do they have any of those trailers that tell you your speed vs speed limit near you? That's another way to check if it's close.

 

[cu440da]

Currently, my speedo reads correct with the smaller factory tire size. I want to upsize to the larger factory tire option, and want the speedo to read correctly after that.

I used the google, and found that there is an electronic adjustment for my truck. No hardware to swap, just a simple reprogramming that can be done at home.