There is no possibility of an 18 riding better than a 17. You have less give in the sidewalls which just means bouncing from one ridge to the next. The natural 'Stiction' in the suspension means that effort is needed before the spring works. Without sidewall deformation ride comfort is zero.
Got 18s? Park it up and look at it. Don't bother with road use!
Whats on your car then?
There IS every possibilty that the ride is better on 18s.
It IS better. (I m not making it up! I ve just driven 900 miles on them!)
Its a little firmer overall, but it barely registers bumps that would cause a huge bang, accompanied by a judder throughout the whole car on 17s and sometimes even for the car to be thrown off course.
This is because larger wheels smother bumps better. The pay off is a slightly firmer ride overall, but its much more comfortable than on 17s, which where a bit softer, but crap over bumps. I used to weave all over the place avoiding as many bumps as I could ,even small ones, for fear of the car distintergrating, on 17s. Now I can drive over 90% of bumps without worry! In fact I now drive over them deliberatley instead of avoiding them! Obviously the handlings improved too, so its a win win situation as far as I m concerned. I was expecting to hate the ride on 18s and even thought I might end up going back to 17s, but no.
I ve sat in a GT and you can see the rim/kerb if you look in the door mirror, as you can in virtually all cars, so thats no reason for kerbing, I agree with jug, people should learn to judge distance correctly.