With the 37s, obviously the speedo is off. Can the dealer reprogram the ecm to correct the issue or is the fix only obtainable with aftermarket programmers/modules?

 

I don't know about on a 06 but on my 07, they can't do it with 37's.

 

The AutoEnginuity scan tool will do it, if you don't mind paying the freight. It's not cheap. Two cautions though:

1. You will need one of the enhanced Chrysler versions. It has to include the ABS module. I know the full version has it. I don't know if the cheaper non-body version has it. You would have to ask.

2. Be sure to ask if you will be able to set the pinion factor manually on your 07. They did not have that feature in there for my 05, just tire size choices, which did me no good. I talked to them about it, and their software programmer added it and sent me a beta version to test. It will be in release 7.1. I assume it will do the manual pinion factor for all years, but I am not certain of that, hence the advice to ask.

If you do buy it, expect to have to calculate the correct the pinion factor yourself, taking into account the deflection in the tires from the truck's weight. Search DTR for a post on how to do it.

Edit:

One last thing, the vehicle software contains a rationality check. If the check fails, it kills the ABS system, turns on the ABS dash light and Brake warning light. When I used Toyo's non-deflection-including revs per mile figure for the pinion factor, my speedo read real high and the ABS light came on after about ten miles.

Apparently the software uses some sort of algorithm to determine if the stored tire size is rational. If it doesn't think it is, you will get the ABS light. There is no way I know of to overcome this without having an inaccurate odo and speedo. I didn't check, but the rationality check failure may kill the cruise control as well.

From my experience, I think it may be possible that 37s are so big that the rationality check will fail, even with a correct pinion factor. I don't know this for a fact, but I suspect it may be the case based on my admittedly limited experience playing with pinion factors.

 

dealer did my 06. just dont know about 37's

 

they can do any size all they do is change the Revolutions per mile in your computer and send you back on the road... Here this might help
http://www.miata.net/garage/tirecalc.html

 

No they can't. The dealer scan tool is limited to specific brands of tires in specific sizes for the latest years. It will only set the pinion factor for tires that actually came with the trucks. If you put on any other type or size of tire, you are out of luck. There is no longer a provision to set the pinion factor independently.