Haven't posted one in the last hour or so, so here's more ignorance questions for ya.
 

Ok, I know the dimensions of a tire, say 18 x 10, are relative to the circumfrence (18) and the width (10).

My first question is, when you go to bigger circumfrences, does the width also always automatically increase too?


Second question is, assuming that the width is the same, what is/are the advantage/advantages, if any, of having say a 18 or 20 inch tire over say a 15 or 16 inch tire? I know that the wider the width, the better the traction, as there's more tire surface hitting the pavement, but how does a bigger circumfrence help performance?

If you increase the overall tire/wheel diameter beyond what it is stock, its just like putting a higher gear in the rearend. I went from 245/45s to 255/45s and it would appear I lost a 1/10 or so in the 1/4 because of the .3" increase in tire diameter. Also, the bigger the wheels are, the more effort it takes to get them rolling and get to them stopped. I won't go beyond a 17" rim unless I get brakes that require 18"s.