I remember when people went crazy trying to nitpick the probability of spherical "wheels" when "I, Robot" came out and Audi had designed a car with exactly the type of system being mentioned. The general consensus, and even Audi agreed, was that spherical wheels would really only work "in the future" when roads weren't as gritty and mechanical as they are now. They would really only work when roads were smooth and made of some yet-to-be-invented material that wouldn't crack or break in pieces under regular use.
