Unsprung weight , I doubt if you will notice the difference , unless its a race car and you are looking for everything that you can get . get a set of bathroom scales and check them , at least you will get a rough idea . I made my own wheels for the Exa 13x 10 weighing 2.5 Kg, because I couldn`t bye anything . The only real difference between 16,17 ,18 etc is the larger the wheel the smaller the profile and the harsher the ride.