If you changed your gear from stock to say a 5:13, would your speedo be off plus or minus? And if you changed tire size from stock to 33 inches would that make it plus or minus? I know it might sound simple, but I'm trying to settle a debate.

 

Larger tires will mean the speedo is gonna be slower than your actual speed.

 

If you get a tuner you can change the wheel size yourself to keep the speedo accurate. One of many benefits to owning a tuner.

 

Your dodge dealership can also correct your speedometer and in result odometer for larger tires for a small fee. I had that done when I got my 265/75 r16s.

Not sure if they are limited though.

 

I have a tuner. This was just to settle an argument I was having with a co worker. I wanted him to hear/see it from somebody other than myself.

 

Gears have no effect on speedo, since the sensor reads ring gear RPM. 3.21's or 4.88's will still be turning the same RPM with the same tires and same MPH. Tire diameter will affect speedo accuracy.