Just got a 98 cummins 12 valve, it already has 315's on it, I was told that the speedometer was about 10 mph off. Anyone know how can I go about recalibrating it?

You may be able to get a different gear set for where the speedo plugs into the tranny. Go down to the Dodge dealer and see what the choices are

The 4x4 shop I used to work at kept them around. The 1/2 ton dodges use them so the biggins might use them also. it is a colorkeyed gear for the speedo drive in the t-case. I don't remember how many teeth to change for the MPH change.
Brian

Thanks, Ill run by the dealer when I get the chance.:D

Check and make sure your VSS is in the t-case. It goes into the tailhousing, and has a wire loom going to it. If it is there, great, the gear is ~$12. You will have to figure out how far off your speedo is, which gear you have now, and do the math.

However, at least the 24 Valve '98s have the VSS in the rear axle. I don't know how the '98 12v's are setup. My '97 is in the t-case.

Pete

I had the dealer bring out the handheld programmer on my 04' Ram 2500. I put the BFG 315's on it. They don't have the option to pick you tire size, but they can punch in the revolutions per mile for the tire. The 315's are between 604-606. I put in 606 so when my tires wear down a bit, it will be right on.