Im getting 17's for my focus and i see that there are different types to choose from!
Some say 205/40/17 and then some say 215/45/17! I get what the 17 stands for but not quite sure what the first two numbers are saying!
First number is the width of the tire (in MM). The second number is the series. The series is how tall the sidewall is. Like say the series is 40, the sidewall height is 40% of the width of the tire. Also http://www.tirerack.com/tires/tiretech/general/size.htm has a good explanation.