I'm currently on a Nirve Night Owl beach cruiser with a three speed hub transmission. The bike is stock except for a new chain, chain tension, and a rear rack over the wheel. I got this bike in December when forced with the choice of buying a 1000 car - or a getting bicycle and have the leftover money go towards rent. I used this bike all throughout the 08-09 Michigan (Rochester Hills) winter, putting on about 400 miles a month and subsequently know every inch of the machine.
This is just a little background as to why I would even attempt to think about taking my "Beach Cruiser" downhill mountain biking. With no front or rear shocks, no designer rims or a purpose built frame - I was able to outpace my friends with much more expensive "mountain bikes". It may have been their lack of experience, but I had the time of my my life flying down the trail. I'm going to go as often as I can before I ship out for the Navy in December. Maybe with some new tires (I've been using the same tires that came with the bike! must have a couple thousand miles on them!!).
Other than sharing my success story, I was wondering if anyone has tried mountain bike racing in say, a foldaway bike or a pedal gokart?