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.

 

[Billyg320]

Thanks for the quick response.

 

[Combatvet]

I put 1.25" & 1.5" spacers on and I'm at about 2-3 mph difference.

 

[UNBROKEN]

Spacers will not affect the speedo in any way. Just to clarify.

 

[Combatvet]

Spacers will not affect the speedo in any way. Just to clarify.

I beg to differ. My Uniden R8 used to be dead on with my speedo, once I added spacers the Uniden is now 2-3 faster than the speedo.

 

[UNBROKEN]

I beg to differ. My Uniden R8 used to be dead on with my speedo, once I added spacers the Uniden is now 2-3 faster than the speedo.

The only way to change the speedometer is to put a smaller or larger diameter tire on the car. Pushing the wheel out further changes nothing related to the speedometer. That is a fact.

 

[Combatvet]

I get you are the local expert on all things ST, and the last thing I want to do is instigate you, but you Sir are wrong. The Uniden R8 GPS speed was dead nuts with the factory speedo, until I added spacers. 2-3 MPH difference from the factory speedo to the Uniden R8, that is the difference I see on a daily basis. I'm on factory '25 wheels and tires, with 1.25" & 1.5" spacers from LP. When I get my vehicle back I will record a video as proof.