Joel,

It sounds like using a car tire on a motorcycle has some of the characteristics of using too wide a motorcycle tire. For instance, if you were to test the stock Triumph Rocket III vs. the Rocket III Tourer, the former has a 250mm wide motorcycle tire and the latter has a 180mm wide motorcycle tire. The wide-tired one has to be "steered" all the way around the turn lest it follow its natural tendency to go straight and ride into the next lane and off the road. The narrower tired Triumph is like our stock T's, you can push the handlebar to start the lean and then not worry about it through the rest of the turn. The thing I have against too-wide tires on a motorcycle is it is a lot of work to keep pushing that handlebar hard from the start of the turn to the end of the turn.

Fred