aight, imma complete moron when it comes to readin sizes, if i want a WIDE tire, which # do i look at? which is wider here, 215/35/18, 215/40/18, 225/35/18, 225/40/18?
Anyways, the first number is how wide (in millimeters) the tread is. The wider, the better for acceleration.
The second number is how wide the profile is (profile is the part between the rim and the tread). That number is not how wide the profile is in inches, but rather how wide it is percentage wise to the tread width.
EXAMPLE: The first tire's profile would be 75.25 millimeters. I just took 35% of 215 to find that out.
Rule of thumb is, wider the profile, better your ride will be. IMHO, a smaller profile looks best, but you will make your ride rougher, and you always risk bending your rim if you hit a pothole, or get a flat.