Correcting spedometer for tire size

[rammertide07]

My goal is to get my odometer right, for servicing and fuel milage reasons. Anybody know how many gallons can be held in the tank and packed up the neck?

And according to the gps vs the odometer... for every 46 miles on the odomater, I have actually gone 50 miles.

Thanks guys

[Longshot270]

If it is just for your personal use then you can adapt a little formula for finding the correct tire size on the programmers. You take the GPS mileage and divide that by the odometer mileage (resulting in a number around 1.08). Multiply that number back to your odometer to find the true number of miles you've driven in that time frame...or does this also sound funky?

[rammertide07]

Originally Posted by Longshot270

If it is just for your personal use then you can adapt a little formula for finding the correct tire size on the programmers. You take the GPS mileage and divide that by the odometer mileage (resulting in a number around 1.08). Multiply that number back to your odometer to find the true number of miles you've driven in that time frame...or does this also sound funky?

Well the spedometer is right up untill 35-40mph....then it starts to get off. So sometimes its right...sometimes its wrong. Will A MODIS not correct for the different tire size?

[907DAVE]

Its worth a try, but I dont know for sure.

Also be aware, the ABS module can only be re-flashed 6 times IIRC, so try and get it right the first time.

[rammertide07]

Originally Posted by 907dave

Its worth a try, but I dont know for sure.

Also be aware, the ABS module can only be re-flashed 6 times IIRC, so try and get it right the first time.

Well that is great Thanks

[cleatus12r]

As Dave has pointed out (thanks Dave!):

The SD trucks have to have the vehicle speed sensor data changed in the ABS module to correct the speedometer/odometer. You have 6 chances to get as close as you can.

The OBS trucks have the programmable speedometer/odometer module. The series of steps you listed there are to reset the speedometer/odometer on those trucks.

Either find a way to reprogram the ABS module for the tire size, buy a VSS inline correction box (such as the Tru-Speed), or do the math a suggested by Longshot270.

[rammertide07]

Thanks for the input guys. Think I'll try that truspeed calibration. Shopping around and found it about $100 cheaper than normal list price.