I have 17 inch rims on the Ram. I love the 20's though. If I switch can the dealer recalibrate the speedo. What about the gears, does the tires size affect this ?

 

The need to reclibrate your speedodepends on what size tire you use (ie. 275/60). If the tires on the20's have the same diameter as your 17's you will be OK. However, if you get taller/shorter tires you will need to recalibrate.</P>


As for gear ratio - Yes tire size alsoaffects the overall gear ratio.</P>

 

Here is a formula to figure out tire diameter: (1270 is a constant number)</P>


tire diameter = (<U>section width x aspect ratio</U>)+ rim diameter
1270 </P>


Forexample a 265/70/17 tire is approx 31.6" tall.</P>


(<U>265 x 70</U>)+ 17 = 31.6
1270</P>

 

Thanks BlueHemi, I programmed that formula into my Scientific Calc.