3.31 and Speedometer Cal.

[Lariviere_Performance]

My F350 has the 3.31 rear ends and came with the 18" wheels. Factory 20" were not an option with this rear end when it was ordered. I now uprgraded to 20" wheels. I went to the dealer to re calibrate my speedometer. At first they said they could do it. After about 2 hours they said it wouldnt take the calibration for bigger tires since it is not a factory option with that rear end. Not that it is a major problem, but does anyone have a fix or insight on this issue??

[Nthorseman]

...I'm thinking your warranty will now go a fair bit farther than it did before...you may not want to change and just do the speed adjustment in your head or watch your GPS...