Tire material is probably the the most significant factor. Once you have the stickiest tire you can get, the next option is to increase contact area.
1cm is negligible with regular road tires (maybe a the Stig can tell the difference). Heck, going from a stock tire to a slick of the same size will get you way more return on contact area than widening it.
Still...discretion should be used when making large generalizing statements like the one above.
True, but you gotta look at the car we are talking about here.
wider wheel = more traction,but is not because the wheel itself is wider, its because you can fit wider tires.
225 vs 235 pretty much boils down to the compound of the tires. slicks? you will feel a difference. 10mm is a lot since its at all 4 corners.
but that doesnt mean that your car will run faster if you go 245 or 255.
Its all about the balance. at a certain point, the more traction you have, the more drag will produce. (especially at the rear wheel)
You have to remember wider the wheels = more weight as well.
Your tire is going to be the biggest factor here.
225 tires (good rubber) is going to be better on 8 width than 8.5 or even 9.