What are the differences in the ride quality and handling between the 17" and 18" tire sizes? Are the 18" tires alot rougher of a ride? Is the handling better?

 

Ride quality: its a judgment call. Lets get extreme and say that the ride is more soft with 18 versus 20-inch tire. “Soft” because you have more rubber between the road and the wheel to absorb shock. So if a 18-inch tire is more soft than a 20-inch tire, than a 17-inch tire will be more soft than a 18-inch tire. How much softer? Don't know.

Handling of 17, 18, 19....inch tires. That's been covered many times so I'm not going to comment.

 

up to 18"..not really a huge difference,, but up to 19" you will feel more...

it also depends on the tires you go with etc...

 

I didnt notice any difference in ride quality going from 17" stock to 18" Nismo.

 

I went from the stock Z 17's to stock G35 18's. Not much of a ride difference but the G stock tires are waaay better.