So I need some new tires and decided to swap the 18" tires and wheels my F250 came with for a new take off set of 20". Question is will I have to get my speedo recalibrated for the bigger tires and wheels?

 

What size tires do you have now?

What size tires on the 20" wheels?

It's not the wheel diameter that determines whether you need to recalibrate the speedometer, it's the overall diameter of the tires.

Just because you're getting larger wheels does not mean the tires are are larger in diameter.