Speedo/Odo correction

orygunf150 · #1 Sat, April 4th, 2009, 01:52 PM

Reading this thread
http://www.ford-trucks.com/forums/836709-odo.html
I am also wondering, does changing the tire size on our programmer also change the Ford speedo or just the programmer? My Ford speedo is a few mph off but the Gryphon reads about right, (according to my GPS).

Sburn · #2 Sat, April 4th, 2009, 02:04 PM

Quote:

Originally Posted by orygunf150

Reading this thread
http://www.ford-trucks.com/forums/836709-odo.html
I am also wondering, does changing the tire size on our programmer also change the Ford speedo or just the programmer? My Ford speedo is a few mph off but the Gryphon reads about right, (according to my GPS).

If your Gryphon matches your GPS, you're fine. Odo will also be correct. Your speedo will be 3% higher than your actual (GPS) speed because Ford set it that way.

***Jackpine*** · #3 Sun, April 5th, 2009, 12:19 AM

Quote:

Originally Posted by Sburn

If your Gryphon matches your GPS, you're fine. Odo will also be correct. Your speedo will be 3% higher than your actual (GPS) speed because Ford set it that way.

Very good, Sburn! I hadn't thought of the speed difference in terms of percentages.

That explains why it's only about 1 mph fast in the 40 mph range and is 2 mph fast in the 70 mph range.

And, back to the OP's question - yes! Programming the PCM with a new tire size set in the programmer DOES change the dashboard speedometer too. The PCM controls the speedometer readout in the new trucks.

- Jack