Q: Car pulls to the right after replacing the driver side rear tire.

Hi there. The tire guy was correct. Here is an analogy to consider. Let’s that you had a straight stick and that on one end, you have a round wooden block that has a diameter of 6" round. On the other side, the block was 7" round. If you push that stick; it will pull to one side. The same thing is going on with the new tire. Although it’s the same "size", it has more tread and thus is larger diameter. Also, one little known fact is that although a tire might be the same size, the standards on tire sizing offer a 5% size "cushion" for different manufactures. So, if you buy a Goodyear P225/75R15, in theory, it could be bigger or smaller than a Bridgestone in the same size. Another issue that causes this pulling issue is the tread pattern. It is possible that the suspension is not properly aligned, but I would suspect the single tire is the root cause. If you don’t want to buy a new tire, rotate the rear tires to the front, have the balanced and I’ll wager the pull goes away.