rotational weight. again the width of the tire and also the diameter of the the do not affect the contact patch. weight and air presure do. for an example, if you had a 3000 lb car and 30 psi in your tires the contact patch will be the same size no matter what tire u use 22" down to 12". Actually its an old racers trick. You can weigh your car by going out and using paper and a ruler. here is a link
http://www.rockcastle.org/activities.../weighcar.html