talkgtr: You're Right!!! 18" wheels would certainly affect the ride harshness. Especially with 45 ratio tires, very little sidewall. better handlung Yes, firmer ride, Yes, less comfortable ride, absolutely.
BTW, on a tire thread here, I mentioned that I replaced my 16" standard wheels with 17" Legacy Limited wheels. Originally, installed new Cooper RS3-As as a UHP all season tire, 225/50/17s. They were too harsh, although exhibited excellent handling right out off the lift. Cooper offers a 45 day Test Drive on all their tires. I opted to switch to 215/50/17s CS4s (an HP all season Touring model tire). Much better ride. I changed to 215s from 225s followig the advise of my Subaru Dealer and the Mavis Tire dealer. That size is the recommended size for Premium & Limited Models (2010) with 2.5i. The LGT and the 3.6rs have 225 / 50 /17s... The slightly wider (215mm vs 225mm) applying the same ratio of 50 would provide a very slight Height (sidewall) increase over the 215s. When I compared the Cooper ZEONS RS3-As to the CS4s it was with different sizes (225 vs. 215s). So, the tire change is not really apples to apples...I can say the ZEONS are a truly Ultra High Performance tire (UHP) category. They could not get them to balance just right. The Subaru dealer told me to switch out of them since these tires were one step below - Racing Tires accordomg to the dealer's tire guy. They did examine the tires that Mavis mounted, rebalanced them for me and told me the ZEONS would never really balance properly due to the nature of the tire (UHP) for my Subbie. That's when i decided to switch them to the CS4s at the specified size (215s) - couldn't be happier with the decision - especially at $110 per tire mounted & balanced at Mavis Tire. No problem with the switch as well.