Q: Why do the rear tires on my Model S wear out on the inside edge?

Because the 2012-2020 Model S and Model X carry a lot of natural rear camber, especially cars on factory air suspension, the rear tires lean in at the top and scrub the inner edge while the outer still looks new. That eats the inside of pricey rubber like a Michelin 255/45ZR20 before the tread is used up. The factory rear arms are not adjustable, so a shop can only dial it out by aligning very low. To reach neutral camber and stop the wear, you need an adjustable rear arm.