My 17's are killing my back
 

OK..so I am a wimp....BUT the 17" run flats ( Dunlop) on my 03 MCS w/JCW are like riding on rocks.....I like the 17" wheels but would like to go to a softer riding tire...Run Flats are not mandatory as I know part of the hard riding is the run flat thing....anybody have a suggestion ? Can the stock 17" wheels also handle a plus size such as going from a 205 to a 215 to get better road "cushion"...any help is most appreciated.

Yes the 17" wheels work fine with 215/45-17's. I've done it for years.

I just put 215/45-17 Goodyear F1 GS-D3s on my Webspokes.
They are definately softer than the Dunlop run-flats.
The steering response is not as quick but more air has helped that.

DSST sucks.

Switching to Alta Springs and 15" tires was ABSOLUTELY the best thing I did for ride comfort. It's like a new car!

http://i44.photobucket.com/albums/f3...i/IMG_3925.jpg

I have run 17's with 215's Perada Spec 2's and it's a great seup IMO.

i dont know about alta springs cause from wat i hear they are
higher rate than the H-Sports but there is no concrete data on
them.

but the 15's will help greatly.

I've got Dunlop Sport Maxx (non-rf) 205/45-17s on factory wheels with stiffer aftermarket springs, and it rides better than stock.

You can also easily run 215/40-17, 215/45-17 and 205/50-17 on the 17x7" wheels.

You may not be an average person when it comes to jarring to your back. Arthritic conditions and disc problems often are inflammed by constant loading from a too stiff ride no matter if it is relatively stiff.

Things to improve your ride smoothness:
* Be sure your suspension is aligned to factory specs- you have a 2003 MCS, has it been aligned since you bought it? If not then do it with a four wheel thrust alignment.
* Make sure your tire pressure is correct about 33 psi is OK for 2 people
* Make sure that your stock shocks are not leaking
* Don't add lowering springs
* Consider FSD shocks someday
* Change to non runflats either 205/45-17 or 215/45-17 or 225/45-17. Key is 45 series tire not 40 series or lower sidewalls.
* Change to a tire that offers more comfort rather than too heavy on performance at the sake of comfort. Ultra High Performance Summer tires like General Exclaim UHP offer a smoother ride.

Finally get to a MINI event and go for a ride in various MINIs with non runflat tires and stock suspension and see what you think? Is it any better to you?

Consider 16x7 rims with 205/55-16 tires or 15x7 rims with 205/55-15 tires if you want to go with taller sidewalls and even more comfort. These sizes do offer some decently handling tires and usually rim and tire weight is less than what you have now so a bit better performance, doesn't have to cost that much.

If you want to keep your rims and use 215/45-17 tires then for comfort see
http://www.tirerack.com/tires/survey...ter=17&type=MP
Max Performance tires
Goodyear eagle F1 GS-D3 and Dunlop SP Sport Maxx are good.

http://www.tirerack.com/tires/survey...er=17&type=UHP
Ultra High Performance Summer tires
General Exclaim UHP or Kumho Ecsta SPT for value

http://www.tirerack.com/tires/survey...=17&type=UHPAS
These are Ultra High Performance All Season tires
The top two are really good handling and good comfort- Yokohama ADVAN S.4. and Bridgestone Potenza RE960AS.