In one of the Facebook groups I follow a member posed this question: “Anyone tried a car tire on the rear of their bike...lots of info on you tube...just wondering?”
Well that question started a flame war of the like not seen since the PC-MAC conflagrations of the last century. Aside from sidecar rigs (Petunia over at Arizona Adventure Dude, for example) which often sport automobile tires, I’d never heard of anyone putting them on a regular, two-wheeled, motorcycle. Until now. And to say there are advocates for this would be an understatement. The car tire disciples are many, they are vocal, and they even have a name for themselves – Darksiders.
As with many things on the interwebz, there are many opinions but very little solid evidence one way or the other. Some positions make a certain amount of sense (http://www.roadandtrack.com/car-culture/a8606/why-so-called-darksiders-prefer-auto-tires-on-their-motorcycles/) while others rely simply on the passion of their arguments to make their case.
As a lay person with no practical experience other than 40++ years of riding, I find the very idea of putting what is essentially a flat-profiled tire on a vehicle intended to lean to be disconcerting, if not downright frightening. Tire design is not rocket science, but it is complex. Different vehicle types impose different loading factors and forces that determine a tire’s characteristics such as sidewall flex, compound hardness, profile, and so on. So to take a tire designed for one set of conditions and stake your life on it functioning properly under a completely different set of conditions strikes me as idiotic in the extreme.
UPDATE: For anyone who really wants to get into the minutiae of this topic, here's a great link: http://www.goldwingfacts.com/forums/10-reference-faq-forum/400426-design-differences-between-car-motorcycle-rim-tire.html.