Designing A 4-Wheeled Bicycle - A Quadcycle. Need advice from anyone with knowledge on bikes!?

I'm in the process of designing a 4 wheeled mountain bike - or as i call it, a Quadcycle, for my A Level Product Design Major Project. I am confident it will work, it will need a fair amount of suspension but what other factors will bear thinking about? It will need gears too... Any information / ideas at all on this subject will be greatly appreciated - materials, existing products, constraints, experiences... anything! Do you think it's a cool idea? Any feedback is appreciated!Designing A 4-Wheeled Bicycle - A Quadcycle. Need advice from anyone with knowledge on bikes!?
try going to http://www.rhoadescar.com/


and go to the showroom. they sell some interesting looking productsDesigning A 4-Wheeled Bicycle - A Quadcycle. Need advice from anyone with knowledge on bikes!?
In addition to Andy's link, I would contact John Castellano. This man invented the sweet spot full suspension bike, which is still my favorite design. He has also designed off road wheelchairs. If anyone can get you started in the right direction, I'm betting he can. He's also cool enough to answer emails himself. Check him out below:
http://www.americanspeedster.com/
Your major constraint is horsepower.





All of the things you need to do to make a 4 wheel human powered vehicle are working against it.





1. Weight. You are adding a significant number of components, and every one of them has a mass. None of them add to horsepower.





2. Rolling resistance. 4 wheels have nominally twice the rolling resistance of two.





3. Aerodynamics. You will be adding aero drag with extra frame components and wheels. A recumbent position would offset this to some degree, but you've ruled that out.





As my brother discovered when he designed and made a 2 wheel drive bicycle, the additional drivetrain power losses made it nothing more than an interesting design exercise. There were were only a very few limited circumstances (like loose sand) where the 2 wheel drive would outperform a standard bike, and the power required made those rides exhausting and short.





Back in the early 80's when AWD cars like the Audi Quattro were the hot new thing in racing, the rule of thumb was that the improved traction/handling/control of the AWD was offset by power losses unless you had well over 100hp to work with. Its a mighty good cyclist that can generate more than .5 hp for more than a short time.





Not saying you shouldn't do it - it will be a valuable learning experience. Just pay attention to weight and drag, and don't expect any kind of spectacular results.