Adjusting speedometer for different tire size

[2015EB]

I changed the wheels and tires on my car. It now has Sumitomo HTRZII 275/40/18's on the rear. According to tire rack the Revs are 783. Using my SCT X4 I put the revs to 785. My speedometer is still off by 2mph. I've adjusted the revs to 780 and it is still off by 2mph. Any help from people adjusting their speedometer with aftermarket wheels. Do these cars only go by the rear wheel speed sensors or do they read the fronts too? I have staggered wheels on the car. Thanks for any help.

Jason

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