I put 18" winter tires instead of 20" for my 2018 Platinum F150. Now I'm trying to find a way to adjust the speedometer. My dealership says they cannot do it, and companies like Superchips cannot do it yet either.

Any suggestions?

 

Depending on the size of the 18s, you may not need to do anything. What are the tire size of the 18s & 20s?.