Ford: Rims/Tires, 20 rims, rims tires

Question
Upgrading from 16" rims to 20" rims. As well as getting new tires for the rims. Will this affect my speedometer when I make the change?

Answer
Andrew, unfortunately yes, it will cause the speedometer to read improperly.  Depending on the year model, you may be able to take it to a dealership and have them reprogram your computer in just a few hours.  Or, you may have to pull the computer and send it somewhere to be flashed.  I own 4 trucks, and not one of the speedometers works right.  Just have a friend drive behind you and let you know how far off the speedometer is.  (if you want to save some money)  I hope this helps,   Jason