I am going from a 235/85R16 (31.9" tall) to a 285/75R16 (32.85" tall). Does this warrant a speedo recalibration?

 

Your current tires are stock? They are almost equivelent diameter to the ORP package. Ford does not have program to handle larger than stock diameter tires. Your change is not that much, but your speedo will be reading abit slow. For a 2000, to reprogram the speedo for larger than stock ORP tires, you would have to have a custom chip programed.

 

Yes they are stock - if you don't pay for a tire "upgrade" from Ford, this is what you get. My first stop after picking it up Saturday morning will be the tire shop!