first off the first number is how wide the tire is in millimeters not centimeters. If the tire was 215 centimeters wide that would be like 8 feet wide. second the next number 65 is a measurement of the side walls. once again, this is in millimeters, not centimeters. Like someone else stated this is a percentage of the overall width of the tire as well. the last number is the radius of the tire (the distance around the tire) this is measured in inches. Then there is a letter that comes after the radius which is the speed rating of the tire (the maxinum speed the tire can be saftely traveled on) the higher the letter the higher the speed, example A= very slow Z= very fast. The next size tire is P225/65 R 16 but if I were you I would go with something like a 245/50 R 16 This would look much better, since the middle number is lower your sidewalls will be shorter (i.e. a lower profile tire) This is a much better look for a sports car and all of the top end sports cars have a low profile tire. I own a 04 cobra and run 315/35 R 17 on the back . Your only hold up will be the width of your rims, I think you have 16''x8'' rims so putting 245's on will be no problem. Check with the guys at discount tire, they really do a great job at knowing what tires you are able to put on what cars/rims.
These guys putting you on 60 series tires are just trying to make you drive slow. Your speedo will have about a 4 percent error making you think you are going faster than you really are. Just get some 225/65-16's and you will be fine. don't do 60's unless you plus up your wheel an inch in diameter. Not much in the 60-17 to choose from for tires. You probably would have to go to 18's to even find many tire lines to choose from 235 or 225/50-18. ASE Cert Auto Tech, SCCA member since 1978
The next wider size would be 225/60R16. This is how the tire sizing works. The first number is how wide the tire is in Centimeters. The second set of numbers is a the sidewall, but this measurement is a percentage of the overall width of the tire. So in your case (tire size you have given) your Tire is 215 Cm wide and 146.25 Cm tall (side wall). The last set of numbers is the rim size. Here its 16inches.
the guys who said the 225/60/R16 are better in order to keep a better mph reading because if you change the width of the tire, you have to change the height also. for instance the wider you go the shorter you have to go in order to keep a stock height so if the first number goes higher than the second has to go lower