Calibrating speedometer

[riverjig]

I have a 1996 4.0 Ranger. I have 31" tires on it and the speedo isnt correct. I almost certain that the speedo is electronic. How do you calibrate it so the speed is accurate?

Im trying to do a sensor bypass for the drive cycle and not having an accurate speedo is making it difficult.

 

[greenpus]

Got An Electronic Speedometer (1995-Up): <~~~~~click on link

 

[trader007]

what i did was install a micro atx computer into the back jumpseat with a touchscreen lcd monitor mounted in the dash. setup some custom front end software and installed a usb gps receiver. the computer can determine my vehicles actual speed within .1mph based off the gps readings.

i think i did it the hard way though.