I've taken delivery of an MCS with Sport Package 17s (Crown Spoke A/S). I come from the mushy world of Hondas and Toyotas. I test drove an MCS and I was happy with its noise levels. IIRC, it had 16s.

I have two real concerns: bumps on highways tend to derail the car (I pretty much drive in white-knuckled mode) and they're communicated very clearly back to the driver . Number two, road noise at 75 is pretty high.

Now I've read through tons of posts, and it looks like people attribute ride quality and road noise issues to run-flats in general, greater wheel diameter, and the (crappy nature of?) stock run-flats as well. I'd like to do something about the road noise. Should I wait to see what happens towards the end of the break-in period? If I went with 16's and a decent 'grand touring' tire, would I see a significant reduction in volume? Could I get away with good grand touring 17's?.

I have a feeling I'll own a set of 205/50/16s on S-Lites soon. The only thing that'll suck about this, for me, will be shelling out another $200~ for the TPMS sensors. You live, you learn. I should've test driven both cars with 16's and 17's.

 

If you think your car has twitchy handling now, then don't even think about modding the suspension. Though you could mod it to dull the response, but then what is the point then?

I would advise against s-lites, they are really heavy and detrimental to the car's dynamics. You will actually feel the car get more sluggish and the gear changes get rougher.

 

The model tire you get can make a big difference in road noise. The quietest tires do give up something in cornering and braking. I ended up with Pirelli P-Zero Nero M+S for a balance of handling and road nosie.

A 16" wheel and non-runflat tires will soften the ride. Don't get S-Lites. A heavy wheel will give you a worse ride than a light wheel. I bought a set of Rota RB 16x7 and run 205/55-16 Pirellis on them. The Rota RB can be had online for $575 shipped for a set of four. They are a little hard to clean, but only weigh 14 lbs. each. Rota has other designs that are worth looking at.

I also have a set of CenterLine RPM 17-7 with Michelin Pilot Exhalto PE2 205/45-17 tires. They are louder and rougher than the 16" Pirellis, but quieter and smoother than the Dunlap runflats that came with the car. The 17" do feel a little more responsive than the 16" but the difference is fairly subtle in everyday driving.

The derailing is sometimes called trammeling. Some tires will trammel more than others. Changing to another tire model may solve that for you.

 

We noticed that the stock Dunlop run flats get pretty noisy as they wear. We have 24k miles on ours and are about to replace them.

The decision of 16 vs. 17 is up to you but do get an alignment from a good shop. That might help.

I personally like 16s on this car. Gives just the right amount of sidewall for a comfortable ride.

 

Tramlining is when a tire tends to follow ruts in the road (can be super annoying as you literally have to fight the steering continuously). See Tirerack's explanation - http://www.tirerack.com/tires/tirete....jsp?techid=47.

The tendency for bumps/potholes to derail the Mini I partially attribute to stiffer suspension, highish center of gravity, lighter weight, and to some degree front wheel drive (after all, the drive wheels being the same as the steering wheels means the car tends to be propelled in the same direction the bump may have thrown the steering off to). Of course tires do make a difference, but I have found that even with really grippy non runflats the Mini will still get upset/thrown off line.

 

You don't have to go with a Grand Touring tire to get comfort but it is possible.

In Grand Touring All Season tires there are few choices for 17x7 rims that will fit the MINI, small would be 215/50-17 which is much taller than stock at 25.5".

Better size for Grand Touring tires would be 205/55-16 but that is also a bit taller than stock at 24.9" but not too bad if you have stock suspension.

Bridgestone Turanza Serenity $118 each
and
Michelin Primacy MXV4 $125 each for H speed rated, $146 for V rated
and
Goodyear Eagle ResponsEdge $111 each (205/50-16! for $123)

If you are serious about Grand Touring then 15x7 rims and
185/65-15
or
195/60-15 would be ideal for street use and light weight

If you have a large budget and care about wheel gap then you can consider various street coilovers that allow for ride height adjustment and control over stiffness/dampening. This improves handling and ride smoothness.