great tool. That should be enough for him to pick the right size wheel...
"glt, you said a lot of stuff in that last post. one thing is slightly off, though...bigger rims are more for looks and handling and not to lessen the wheel well gap. if anything, bigger rims will highlight the wheel gap. the only way to lessen wheel gap is with lowering."
EXACTLY. But the "sporty" look IS achieved by closing the gap by getting the car lower to the ground and bigger wheels that are enough to cover the side gaps too. Wheel gaps are not only up and down but to the sides of the wheels as well. A combination of bigger rims, right tire and a reasonable drop will get that look and still keep the ride confortable enough to make the car drivable every day. You don't see many people lowering their cars and keeping the stock 15s with /65s on do you? It just does not look right. Also putting too big a profile on big rims takes away from the sporty look or at least the look most go for with low profiles now days. They would just look like a bigger version of the stocks and will actually raise the car if you go too big on the tire profile. That is why most stay with /40s or /45s. Bigger rims like 19s and up even stay in the /35 range. So for looks you will have to go to bigger rims which look more agressive and the correct tires as most have pointed out here. Those rims have to be big enough to compensate for the loss of sidewall on the sporty tires so they fill the gaps mostly on the sides at least as good as the stocks and so you don't have to slam the car 3 inches to get the tire close to the edge of the wheel-well on top. More reasonable drops of around 1.5 inches will also keep you away from needing a camber kit to save the tires. Depending on the car and personal taste you have to find the balance in wheel size, tire and drop keeping in mind that with smaller wheels you will need bigger profile tires which is not what you may want and maybe a bigger drop, too big a wheel with low profiles will fill the sides but most likely enhance the top gap like you said and if you drop it too much it can result in rubbing the tires on the chasis, etc.
Best thing to do is know what you are going for, compare to others to see what they did and what you like in places like www.cardomain.com and you will make the right choice. That is what all my babbling was getting too :-).
ps- sorry, I do talk a lot! :-)