I have 275-60-15 tires on the rear of my car and 205-70-15 on the front. I don't have a spare in the car but want to put one in it so I am going to get another 205 for a spare. I have read that running two different size tires on the rear could cause damage to the rear end if driven too far or too fast. Does anyone know if for example, I had to put that 205 on the rear if one of the rear tires went out, how far/how fast could I go without damaging the 8 3/4 Sure Grip?