If you tow beyond the manufacturer’s limits you are treading on very thin legal ice. Understanding your responsibilities differences is critical if you intend to tow in a safe and prudent manner. Towing beyond any vehicle’s manufacturer’s weight ratings-or without regard to the properly equipped limitations a vehicle’s manufacturer places on the towing vehicle relates directly to the law of negligence and places may expose you to liability.
http://www.randolphwolf.com/blog/towing-liability-for-overweight-loads/