I have a 2005 Cooper S with very nice 18" Chrome wheels and low profile tires. It also has an aero kit. It looks great but this combo gives a very rough ride. What wheels and tires would smooth things out. Thanks

 

I don't think the aero kit has anything to do with the rough ride. A couple of things that others may need to know in order to help are; what size tires are you now running, and what brand are they? Has your MINI been lowered?

 

If you are running run-flats, get rid of them. If not, a higher profile tire will, obviously, smooth out the ride.

 

Do you have stock suspension or upgrades?
When is the last time you had alignment done?
What are the alignment settings?- stock?

Rough ride can be caused by many things-
Bad uneven roads
Lower profile tires- 35 series
Hard or stiff sidewalls- BF Goodrich g-Force T/A KDW2
Too much air in tires- try 36 psi front and rear
Misalignment- toe settings not same right to left, too much rear camber from dropping suspension
Rim size is passively involved- smaller rims are light and allow for tires that are more comfortable, 18" rims are heavy and usually have small sidewall tires.
Broken suspension part like a worn shock
If you have coilovers that are adjustable try settings that are less stiff- try 30% less than full soft and adjust from there.