why can't I get my speedometer accurate?

[02CCSB]

I've been battling this thing for weeks.

Adjusting revs per mile in the TCM, pulses in the ECM.

No matter what I'm out 15% to the low.

It's a 3.73 gear truck with 325/60R20 Nitto Terra Grapplers

[tokymon]

i just adjust in the ecm and messure the tires and put that in not what the tire calc says. (ie. tires= 35x12.5x16 but messure only 34.5 tall)

[Wheelz]

Post up the tune and ill look at it later tonight

[minytrker]

i just adjust in the ecm and messure the tires and put that in not what the tire calc says. (ie. tires= 35x12.5x16 but messure only 34.5 tall)

THats the trick, almost every all terrain or mud tire I have measured was always off. All the low profile 22's, 24's, etc are usually dead on though.

[THEFERMANATOR]

DON'T CHANGE THE TCM, LEAVE IT ALONE! All you are doing by changing the TCM is changing your shift points and throwing your adapts off. The factory calibration is set up and should work pretty well with most combos regarding of gearing. Only make changes to the ECM for speedo changes. If you know your actual speed VS displayed speed, go into the speedo calculator select speedo fine tuning, and put in the numbers. This will get it pretty dang close.