I have stock 17" rims with 225/50-17 runflats. As many of your noticed, these runflats make the ride noisier and rougher due to thick sidewalls. But, it still has a high enough profile of 50 for a relatively comfy ride. Now, if I would go with a 5-spoke 18" from GS430 with its 245/40-18, how would it affect the ride quality? I'm actually thinking about 18" combo with Continental ContiProContact tires. Obviously, the profile will be lower so in theory you get more feel for the road. But, than would I balance it out with a "softer" Contis in comparison to higher profile stiffer runflats? What do you think?

Also, how would it affect handling and performance? 18" are wider which goes with a more weight distribution and results in a worse bad weather handling, one would think. Honestly, I don't have much experience with tires/wheels, and my goal is not for looks but rather to improve comfort/performance/handling/treadwear over my stock 17" w/rf. I guess the big dilemma if I should get new tires on my stock 17" or go with a bigger 18" and "comfier" tire combo to improve it even further?

If you are looking for a comfier ride, I don't think going with 18 will improve that. I do like how my stock 17 handle in this past winter. It was much better than my Acura TL. I don't think I'll give up my 17 anytime soon....Unless I move to TX or CA!

I was in the same boat this past week, but lack the bad weather aspect. I decided that I didn't want to sacrifice comfort just for some extra bling. Maybe I'll have wheel fever again in a few years and make the +1 or +2 jump from my oem 17 inchers.

Just my opinion*****

But, I don't think you will be dissapointed in the ride with the 18's from your current 17's.

Yes you will have better road feel, but I like that, better handling.
But I don't think you will be "oh no it's to rough".
It's marginal to the amount of difference youwill feel. Yes there will be some change, but all for the better in my mind....

I am at the moment just upgrading my current 245's/18/40 to just a different (PS2) tire, but next year I am planning on going to 19's 245's in the from and 19's 275/285's in the rear.

Even at that, yes the ride will be a tad stiffer compared to my current run flats, but all for the better.

Good luck with your decision.....

I guess from what I heard, (225/50-17 w/funflats) = (245/40-18 w/all-season), is this a correct assumption in terms of a ride comfort? My only big concerns is that we got way too many potholes in here, so higher profile tires should cushion that and keep rims from being damaged. And, wide tires are great for performance in a good weather, but in a rain and snow it will be a negative factor?

I did the same thing with my GS. I put 18 inchers with the continental pro-contacts all seasons. So far the ride has been great, and not too harsh. Its more precise than the 17 inch wheels when making turns or changing lanes. I think its a bit loud on the highway but its not bad, and I think the runflat tires were louder, but I can';t remember. Great tires in teh snow though.

Regarding your comment about snow handling, how do you compare it with 17" w/runflats? I'm just using a common sense here, with the same weight and less area of road contact (in case of 17" 225) you will be sinking more into the snow for a better handling. While, with wider 18" 245, you will be gliding more? Maybe its too of an extreme comparison and the difference is very subtle, but can you give me a feedback on this comparison? After the past winter and few of the nasty snow/ice storms we go in here, bad weather handling got bumped up on a list of my priorities

You are correct, a little narrower is a good thing for snow. I remember ordering wheels and snow tires for another car I have and they recommend "minus" sizing for the best results. Practically speaking though, I don't think it would be a big difference.

Pete

I don't think you'll notice much of a difference going from 17's to 18's. I know I didn't, but everyone's tolerance is different.

SGT, I assume you are talking about driving through a snow and other weather elements?

My bad, the difference I was talking about was actually road feel. I actually don't know how the snow handling would be going from 17's to 18's since I swapped before it started snowing. It feels fine in the rain, but I think the most important factor when driving in inclement weather are the tires. Size matters, of course, but I feel the tire tread, compound, and type have way more influence on handling in snow and rain.