speedometer calibration problem

[soutthpaw]

Ok this is weird, I used to be able to adjust tire size and get a corresponding response from the odometer... but now it won't do it... also tried changing the tire size with AE and having the chip disconnected and set the truck to stock... it is showing about 4mph faster than actual regardless of the vehicle speed. as compared to my tomtom gps.... I tried changing the pulses per revolution to 20 on one tune too and that didnt work either.....
If the wife gets home soon I am gonna try some other stuff and also run the live data on AE to see what the MPH shows that way

[88Racing]

First off I have no clue on what or how you are going about entering the actual tire size measurements?
Are you using a formula to get the measurement?
If so does the formula take into account for squish?
Squish=The loss of circumfrance of the tire due to the vehicle weight.

[soutthpaw]

That's cuz we are talking about real tuning software not Gryphon for Gassers. AE has a tire size adjustment under the ABS PCM diagnostics.... Minotaur has settings for Revolutions per mile... that value is available in the specs from the tire manufacturer for my new tires is 634... also a pulse per revolution of the speed sensor. its snowing and dark now so may wait on playing with it till later

[cleatus12r]

Changing the revs/mile in the PCM programming will only mess with shift points and speed limiter functions.

DJ, your "problem" lies in the ABS module, not the PCM at all. If the speedometer is changed, the odometer will change too as there is only one input to the instrument cluster.

I wasn't aware that AE would change the ABS data output to the PCM....
Hmmmmm.

[soutthpaw]

yep it will and the last time I messed with it I was able to bump everything up so setting the tire size at 35" I was able to ge it like 10-20 mph over what it was supposed to be but for some reason I cannot get it to drop the last few MPH.... maybe I will contact AE and see what they have to say about it.... need to mess with it some more first... I tried setting it to stock tires size a few times which is 1 1/2 inches less diameter... but it doesn't change

[cleatus12r]

I know that the older trucks only allow for a change so many times before they just quit allowing it anymore. Not sure about the Super Duty-based trucks (or Excursions )

[88Racing]

Originally Posted by soutthpaw

That's cuz we are talking about real tuning software not Gryphon for Gassers. AE has a tire size adjustment under the ABS PCM diagnostics.... Minotaur has settings for Revolutions per mile... that value is available in the specs from the tire manufacturer for my new tires is 634... also a pulse per revolution of the speed sensor. its snowing and dark now so may wait on playing with it till later

Take it easy on a Gryphon gasser who wants to learn some more about the oil burners. There's a scary thought!
Being a mod has it's advantages and disadvantages.
Thanks for enlightening me on how it's calculated

[soutthpaw]

Sorry I couldn't resist that one ya made it too easy

I did talk to Bill a long time ago and remember telling me it usually did not change the speedometer... but it did correct the speed for the shifting strategies. Ill check with the dealer on if there is a limit on the abs module for changing the tire size... if so, maybe the ABS module can be reflashed to reset that