crg53

As the title says, on a scale of 1-10, 10 being 17" wheel comfort, how much of this "comfort" would I give up if I mounted 18" wheels, and what are the most obvious differences between the two sizes in road feel and handling.

ilko

It also depends on your tires' sidewall, but on the 1-10 scale I'd say you would be at 8. Wider wheels with wider tires improve handling, at least in my case they did. You will be feeling bumps in the road more with the 18s, that's for sure. If you're after comfort, look for tires with softer sidewall such as the Goodyear F1 GS-D3. The flip side is that those tires are more prone to bubbles.

rotorheadcase

As ilko mentioned so much of the comfort is down to the tyres. On your scale it could be somewhere between 6-8. You will likely notice that the steering feels a little more "alive" in that it will squirm in your hands over less than perfect roads. It gives you a lot more feedback as to what the tyres are doing and for me that translates to feeling more connected to the car. They are more noisy as well...

If your car is a daily driver you may not be happy with the 18's but if you choose your tyres carefully you may find litte or no difference. I changed from Conti Sport 17's to Pirelli P Zero Rosso 18's and found only marginal difference. With the Yokohama Advan R Spec tyres I use on track it's a LOT more unforgiving.

Neil