May not want to swap tire sizes on that Ram just yet..

[dpatt67]

I had made a post a week ago about switching wheels and tires on my '13 Ram 2500 from it's factory size of 17" to the '14's 20" size. I got the tires and TPMS sensors switched over to the 20" wheels and then took it to the dealer to have the computer flashed to recognize the new size for the speedo. No go. All the truck would recognize is the factory size. So, if you are looking to change tire sizes on your late model Ram and want an accurate speedo and odo, you are probably out of luck. I post this to let others know that late model vehicles don't want you to change them, even tire sizes.

[bguy]

If you're not changing the overall diameter of the tires there's no change needed for the speedo. IIRC anything less than 4% error is acceptable.

[camp-n-family]

The dealers are only able to calibrate to sizes that the truck could come stock with. The largest option are the 17's. There are aftermarket programmers that can recalibrate the speedo on the newer trucks. Hypertech and bullydog seem to be the most popular. See here