I have to admit that I know next to nothing about this so bear with me. After reading about the Goodyear Integrity tires hyroplaning etc. I am seriously considering new tires. I have noticed many posters recommend the 195 60 15 size as opposed to the 185 65 15 size supplied by Toyota. What is the advantage of this and would this affect the speedometer reading or MPG in any way. I have also noticed that some posters have recommended tire pressure as high as 42/40. How does this help and does it cause a choppy ride. Finally I am wondering how these higher pressures would affect the car on snow and ice.