Smaller rims, rally cars do not have big wheels.

On normal roads, cornering will be better with 17-inch rims with the lower profile tyres - lower profile tyres do not distort as much during cornering, meaning more rubber stays in contact with the road. Top speed and acceleration are not affected much by rim size. You may find the larger rims improve both, but only because of the better grip and the fact that lower profile tyres are normally inflated to higher pressures.

Have you ever wondered why there aren't more cars out there with rubber-edged rims? If lower profile tires are better, and sidewall flex is the root of all evil, then why not run 5-profile tires on "plus-10" rims and eliminate sidewalls completely? Well, there are a few reasons. Like Old School, I also would split the difference and go with 16s. The 17s have less sidewall flex which will improve cornering but the price you pay by moving the majority of the wheel's mass to the outer edge will hurt acceleration. Additionally, having too little sidewall flex will cause more handling problems than it solves. In my opinion, you need about 3-4 inches of rubber between the tread and the rim to get a decent balance. What profile this is depends on the tread width of the tire.

This is actually a mixed bag. There are lots of factors to consider when choosing a wheel size. Rally cars do use 15inch wheels for the snow, dirt off road sections. But if you look, they use 17s for the asphalt sections. I can only assume that the outside diameter of the tire will be the same regardless of wheel size (ie you will run a lower profile tire on the 17s, but the overall height from bottom to top of the tire will remain the same). That being said, first off, there are way more performance tires, both brand, size and performance level for a 17 inch wheel than for a 15 inch wheel. If you want to run a 315 rear tire, good luck finding a high performance 15 that has the proper profile. Why? Because the trend has been to go with larger wheels over time. YES a larger wheel will most likely have a more rotating inertia than a smaller wheel, but you will have a bigger tire, and while not equal you must look at the big picture. A 17 inch wheel will allow you to run a much larger brake rotor. This will give you better braking, and more choices for a brake setup. Bigger wheels also will cause you to run a lower profile tire(thinner in height from rim to tire edge). Your tire and wheel setup is a part of your suspension, if you like crisp handling, and sharp responses you will get better feedback from a 17inch wheel, the tire just plain has less room to squirm under the wheel, plus the sidewall will be stiffer. Top speed should be little effected by either wheel size. Acceleration will be effected, but if the car has 300hp or more, this shouldnt be an issue. The new carrera gt has 19s and 20s. The new nissan gt-r has 20inch wheels all around. At the end of the day, you will most likely have more tire choices for the larger wheel size. You will be able to get better tires, which will give you better handling, and acceleration. Plus, performance tires are rated for higher top speeds.