i had 19s on my 986 and for the most part, the ride was terrible. some parts of certain fwys would produce a horrible cowl shake. i had them on the car for about 2000 miles and then took them off. tires were new, size 225/275. i've gone back to lightweight 10-spoke 17" carrera wheels and put the 19s on my 996 C4S with wider tires, 235/295. the 911 rides fine with the 19s, the tire width and profile are the same as stock 18s, so the speedo is a bit off and the car sits higher by a half an inch. getting back to the boxster, i would only go to 18s and not 19s.