Here is an interesting article in Cruiser magazine on the issue.
But here's the problem; Car tires are fundamentally unsuited for use on motorcycles. Moreover, that's not just my opinion but also the opinion of every tire engineer I've ever discussed this with. We all understand that the dynamics of motorcycles and cars are vastly different. As such, they demand different types of tires and at the risk of great over simplification I'd point out that if a car type tire worked well on a motorcycle everything from a moped to a MotoGP bike would be wearing them as standard equipment. The fact that they can even be used on a big cruiser says more about the way those bikes are designed and ridden than it does about the suitability of using a car tire on one.
According to most of what I read on the Darkside (and similar forums) none of that matters. Some dispute the facts provided by the tire manufacturers and at least one guy said he didn't much care what the facts were. He liked his car tire and even if side by side testing showed that the motorcycle tire was superior, he was going to keep on running it. It's hard to argue with logic like that.