Owned my ranger for about 2 weeks now and my Speedo is off more than 10mph only know that because I'm using my stereo receiver GPS mph as a just in case. Driving with traffic in a 40mph zone unit says 40 and Speedo is at about 53. I know the former owner bought the truck from someone who had rims on it but he isn't sure of the size. Is there a way to calibrate this thing so it's closer to actual size? I delt with computers that adjusted it automatically this is really my first vehicle that isn't 2010 or newer that I have to do the work on.

 

You should always include the YEAR of your Ranger in your post

If its 1997 or older it will use a speedometer gear on the transmission or transfer case(4WD), it can be changed to match tire size

If its 1998-2000 then GEM module can be programmed for correct tire size

2001 and up the Computer can be programmed for correct tire size

If it has 4Wheel ABS the module can be programmed in some years

1995 and up you can use a Dakota Digital SGI-5E for speed calibration that can be changed any time, i.e. if you change tires size winter and summer or off-road, on-road

 

Yeah sorry it's a 99. I posted on Facebook and my buddy is the service manager for a Mazda dealership that still has the Ford computers for the few Mazdas built by Ford they still work on he may have me come in and get that fixed because I have the tire size that's recommend by Ford. Just trying to get this thing as close to right as I can. Thank you for that in depth information. It helps a lot.

 

In 1999 Rear ABS he can program the GEM module for tire size, or if its 4WABS then he programs the ABS module.

You should have the RPM(rotations per mile) for the tire size, go here: https://tiresize.com/calculator/
Enter your tire size and "calculate"
Revs/Mile is at the bottom, write it down, he will need that

 

@RonD Hooked up my OBD2 connector and opened torque on my phone. The phone is showing what speed I should be going which is spot on thanks to the town I live in having those speed signs up just before graduation time. I think my speedo has taken a crap on me and I'm going to have to get another one.

 

Is it always off by the same amount regardless of speed? There is a way to recalibrate the needle.

 

Yes, you can pull out the cluster and apply 1.5volts then reset needle to about 72MPH

Video here: youtube.com/watch?v=WVz6ilGiTBY

Test yours first before pulling off the needle, if its at 62mph then yes take off needle and put it back on at 72mph
If its showing 72mph then there is another problem, not sure what it would be?

Or get a speedometer from wrecking yard