He is saying to not mix tires / rims / diameters amongst the 4 touching the ground. If they are the same then there is no damage. If the 4 are of different diameter then there is damage.Are you saying a 275 55 20 tire is going to hurt the drivetrain on a sport?
275/55/20 tires all round are fine. You also should get a spare of the same diameter. Do not use the donut spare.