the wider the tire , the more drag it has or rolling resistance.. stofter compounds will also increase this as well because of fiction, though compounds have a very small affect compared to tire width.. if you look at any eco car they have like a 185 tire with the hardest compound possible, this is to help roll better down the road, thus using less energy...in the braking area, wider tires are heaver most of the time, the heaver the wheel and tire combo, the more the brakes have to work to slow the rotating mass, better pads will help give you that instant responce and bite your looking for... wider tires will give more grip on the road, with means better stopping, tunring, and accel.... softer compounds will incease this again.. remember that your car can ONLY perform as well as your tires.. 500hp dosnt mean s*** if you cant put it down,, $2000 coilovers dont mean s*** if the tire dosnt grip to turn the car.... i have 215-45-16 azenis on mine.. this tire is heaver, wider,much, much softer and a little taller due to the ratios.. i lost a little accel, and wider tires will hydoplane easyer, a little of that bite on the brakes...BUT now the car is a hero in the corners, massive amounts of grip, stops on a dime, launches out of the hole with much less tire spin.... next year im getting black team dynamics pro race one wheels, 15x7.5 and the new azenis in ther 225/45/15 size... more grip, less weight...