97 and back with speedo gear in the trans is affected by gear or tire change, since the speedo pickup is in the trans and upstream of both gear and tires.

98 and forward with speed sensor on tone ring of the diff are not affected by gear change, but it is affected by tire size.

 

I mean that the way our trucks are set up, it doesn't effect our speedos, due to where the sensors are placed.

I apologize, I was being to generic by stating that all Rams don't need it. I bow to vaughan's correction. My statement only works for 1998+ Rams.