This is a note received from May Villamin, Senior Admin/Training Materials Specialist:

We understand that some touring bike riders use a car tire on the rear wheel, but the Motorcycle Safety Foundation strongly recommends that a car tire never be mounted on a 2-wheel motorcycle. The MSF and the major motorcycle tire manufacturers helped the Motorcycle Industry Council develop their Tire Guide - see page 7 at: MIC_Tire_Guide, which states:

"And never mount a passenger car tire on a motorcycle rim; the flat profile of a car tire is incompatible with the dynamics of a vehicle that leans as it corners, and the section of the tire in contact with the rim (the “bead”) is incompatible with motorcycle rims."