I am starting a FXS build, which is quite different from what I've built in the past. I have found recommendations on tire sizes, but I would like to know the pros and cons of the differing sizes. The track I'll be racing on is a 1/6 mile dirt oval (Jackson Speedway in Michigan). I have found that 15x8 tires on 8x8 rims for the rear are common. What are the advantages of that size over a 12x9? I am planning on using 11x5.5x6 Hoosiers on 6x6 rims for the front. Also if I were to go with the 15s, could I make a 15in diameter plate to use until I get the tire and rims? Or are the tires not exactly 15? I'm sure it depends on air pressure as well. Thanks in advance.