Originally Posted by Rolla

That's exactly how Gary Fisher, Tom Ritchey, Otis Guy, et al invented the mountain bike.

Keep in mind that beach cruisers tend to have hi-tensile steel frames and forks, so there's a limit to the abuse they'll take. A chromoly BMX cruiser, on the other hand, is intended for much more punishment, and companies like Transition and We The People are offering offroad klunker-style bikes that retain the look of a three-bar cruiser while offering a more robust build -- with and without a coaster brake.

Video here