I have a 2011 S Hardtop with 16 inch wheels - I want a SUPER COMFORTABLE ride and am thinking about switching my stock 16" wheels for used 15" ones - cheaper and more rubber. >> Will the 15's fit??

 

I don't think 15"s fit over the breaks on the S.

 

15" wheels will not clear the front brake rotors on your second generation (2011) Cooper-S. 16" is as small as you can go. If you want a softer ride keep the 16" wheels and replace the run flat tires with conventional tires.
Here is a great MINI wheel/tire link. http://www.mini2.com/forum/faq.php?f...wheel_fitments

 

The brakes will not allow 15s to fit.

 

If you replace the stock run-flats with non run-flats and get a slightly bigger tire you will have what you seek. I just replaced my stock Conti run-flats with Hankook V12 Evo K110 205/55-16 tires and the ride is *much* better and quieter. And the new tires have quite a bit of grip. They also reduced my speedo error from 5% to 2%.

Cost was a bonus, too - I got them from TireRack.com for $71 ea. after $60 4-tire rebate.

 

I don't know how comfortable a ride you need, but agree that switching to non-run flats would be a good first step. Beyond that, high performance summer tires generally ride firmer (but handle better) than all season tires or touring tires, and a slightly taller sidewall (higher aspect ratio) provides a softer ride due to the additional sidewall flex.

The question is, just how far do you need to go along that continuum from maximum handling to maximum ride comfort to get the comfortable ride you want? Alex (our usual Tire Rack advisor here) can probably help you choose a tire you'll like.