Is there a difference between 20/21 inch rims/speedo

[Billyg320]

I have a lifetime warranty on any moving part on my 2020 st, I want to put the bigger black spoked rims wheels on mine to shake it up, gonna keep it forever. I currently have old man silver 20 inch rims.

QUESTION- any know speedometer changes to be made with bigger, much nicer, rims?

 

[UNBROKEN]

Tire OD is what effect the speedo, not wheel OD. You can swap to the oem 21’s with zero issues.

 

[Mustang5L5]

Tire OD difference is 0.3" but that will depend on what brand tires as there are minor differences in OD among tire models even in the same size.

If you wanted, i think you can even go into ForScan and adjust the tire size there to correct it, but i wouldn't sweat it. As you can see here, the difference is pretty negligible.