275s are 275 mm wide. The second # (35 - 40 as you listed) is the aspect ratio. IE, these tires are 35% as tall as they are wide. The higher the number, the taller the tire. If you want wider the first number needs to be bigger. Wider is not alway better. What size r the rims in question?
*edit, sorry I read you post wrong. I thought you already had 275.
I,m trying to decide whether to go with a 35 or 40 sidewall.Stock size is 255x40x19 pirellis,i have seen other people going with up to 285 35,s on there stock Brembo package wheels.I know for the 285,s you have to go to a 35,but is that the case with 275,s also?