The Dark-Side revisited Gaining traction in exchange for control

Darksiders will tell you that running with a car tire on the back of a motorcycle is better because it has a better contact patch in the rain. A true Darksider will swear to the end of time that the car tire is better and safer. The amazing thing is that even the tire manufacturers say the tires are not designed to ride on their ridge. 
The rounded tire used on motorcycles today are designed for a smooth transfer of weight from one side to another, and the casing is made to disperse the weight evenly. One thing you won't see on racing bikes is a tire that doesn't allow for a quick smooth cross over from one turn into another.

The car tire does not allow for the smooth transfer, the ridge fights the bike, and presses the entire bikes weight and driving force onto the tires edge. This not only makes the bike less agile in the corners but it places undo force and heat into the tread side.

The weight transfer during a corner has also been shown to roll over the tread section rapidly. The motorcycle has to push harder on a turn to lift the tire to it's edge rather than the smooth transition of a rounded tire, this has been known to catch riders unaware when the banking continues further.