Lt295/70/17
#1
03-03-2011, 01:31 AM
Lt295/70/17
Ok so I searched "speedometer calibration" and honestly the only thing that helped me was this:
"Stopped at my Friendly Dodge Dealer this morning on the way to work and inquired about the procedure for programming the CAB. He looked in the service manual, looked in a couple others and finally dragged out the Chassis Diagnostic Manual. There, in section 29A, it explains the procedure needed to program the CAB for specific tire sizes. [The CAB sends a pulse stream to the PCM, which drives the speedo/odo; to change the calibration, the CAB needs to be told, among other things, the number of teeth on the RWAL sense ring and the rev/mi of the installed tires.]
So, if you change your tire size and your dealer hasn't a clue as to correcting the speed/odo, point him to the Chassis Diagnostic Manual, section 29A. It's all there.
NOTE: the 98 1/2 models do not use speedometer gears and the speed metering is taken from the ABS sensors. To change "gears" for different tire sizes requires reprogramming of the PCM. Dealers have been having problems with this procedure, and many axle ratio/tire size combinations are not available."
But my real question is since these tires are basically 33.5 inches my speedometer is going to be off right? Or will I not have to worry about it? Granted I shouldve gotten my tires on today but I guess it takes a full week to ship tires from West Texas to Colorado I guess I will just have to wait and see how much its off if so.
"Stopped at my Friendly Dodge Dealer this morning on the way to work and inquired about the procedure for programming the CAB. He looked in the service manual, looked in a couple others and finally dragged out the Chassis Diagnostic Manual. There, in section 29A, it explains the procedure needed to program the CAB for specific tire sizes. [The CAB sends a pulse stream to the PCM, which drives the speedo/odo; to change the calibration, the CAB needs to be told, among other things, the number of teeth on the RWAL sense ring and the rev/mi of the installed tires.]
So, if you change your tire size and your dealer hasn't a clue as to correcting the speed/odo, point him to the Chassis Diagnostic Manual, section 29A. It's all there.
NOTE: the 98 1/2 models do not use speedometer gears and the speed metering is taken from the ABS sensors. To change "gears" for different tire sizes requires reprogramming of the PCM. Dealers have been having problems with this procedure, and many axle ratio/tire size combinations are not available."
But my real question is since these tires are basically 33.5 inches my speedometer is going to be off right? Or will I not have to worry about it? Granted I shouldve gotten my tires on today but I guess it takes a full week to ship tires from West Texas to Colorado I guess I will just have to wait and see how much its off if so.
#2
03-03-2011, 10:57 AM
#3
03-03-2011, 11:52 AM
Grand Champion
And an odometer error since you will no longer be ticking off miles correctly.
I had my local dealership calibrate mine twice, once for 33's (285's) and once for my 35's. Both times, they went to the web and looked up the revs/mile of my new tire size on 1010tires calculator:
http://www.1010tires.com/tiresizecalculator.asp
On my '99, that is the only value needed in the PCM table to adjust the speedo and odometer. It worked perfectly both times. The first time, he even let me go back to the shop and watch him do it. He showed me the menues he went through on his scan tool to get to the correct setting in the PCM, and then how he changes it. I was amazed at how many menues and variables they have access to change. Wish I had that programmer/scan tool they use.
I had my local dealership calibrate mine twice, once for 33's (285's) and once for my 35's. Both times, they went to the web and looked up the revs/mile of my new tire size on 1010tires calculator:
http://www.1010tires.com/tiresizecalculator.asp
On my '99, that is the only value needed in the PCM table to adjust the speedo and odometer. It worked perfectly both times. The first time, he even let me go back to the shop and watch him do it. He showed me the menues he went through on his scan tool to get to the correct setting in the PCM, and then how he changes it. I was amazed at how many menues and variables they have access to change. Wish I had that programmer/scan tool they use.