Throughout the history of Formula 1 racing, the main goal of the constructors has been to improve the designs of their cars in order to implement the latest technological advances. As has been proved by results of recent seasons, Ferrari's design is on top of the pack, and looks to stay that way.
	The same philosophy was still being employed back in 1976, when one F1 team of the time, Tyrrell, decided to embark on a project that they hoped would revolutionise R1 racing, and so put them in the same position that Ferrari are in now. At the time, a lot of work was being done on finding ways to reduce lift on the front of the car, thus minimising the drag on the car as a whole, and giving it the ability to enter and leave corners at a greater speed. One of Tyrrell's designers, Derek Gardner, reasoned that by reducing the diameter of the car's front wheels to just 10 inches, they could be placed completely behind a front fairing, and so giving the car the reduced lift that was needed.

This posed the immediate problem that the contact area with the ground, and therefore the car's grip, was reduced. It was at this point that an idea was put forward that seemed groundbreaking at the time: to add another pair of same-sized wheels behind the front pair, both steering, to make up for the lack in grip. This had the extra advantage of having four smaller disc brakes, which gave the car faster cooling, better airflow to the discs, and a large gain in brake pad size. Of course, this in turn caused problems with wheel lock: if only one set of wheels locked at a time, the effective wheelbase of the car would be changed. To fix the problem, the team used a special triple master-cylinder system, with each cylinder feeding the brakes on one of the three axles. The development was named Project 34, or P34.

	The car was produced, and was entered into the 1976 Grand Prix Championship. Unfortunately, despite being radical, the car did not fair as well as the team had hoped, despite Jody Scheckter driving the car home to a victory, closely followed by his teammate Depailler, at the Swedish Grand Prix.
After two seasons the car was dropped, and for a while constructors stuck to traditional four-wheeled cars. However, in 1982 Williams tried to repeat Tyrrell's formula with the FW08B, still believing that the theory behind it was correct. The same story kept cropping up in testing however, that there was no noticeable difference between the car and any other four-wheeled version. Before they could continue with further development, the FIA outlawed four-wheeled drive in F1. Later they outlawed four wheeled steering, and then made four wheels mandatory, and specified that only the front two could steer. This obviously put the lid on any further developments in the story, but the question remains: how did this radical idea ever leave the drawing board considering its fate? Tyrrell undoubtedly sunk millions of pounds into the project, with little reward. "At the time there was little to no CAD (Computer Aided Design) software available to the automobile industry," says Steve Ings, design engineer with TWR and Land Rover. "All the initial design and calculation was done manually, and the first time vehicles were properly tested was once a full-scale mock-up had been produced. By that time the company would have already put a substantial amount of money into the project, and if it didn't work as planned, the likelihood is that they would have cancelled the project straight away." With the advent of specialist CAD programs for the automobile industry, all scenarios can be worked out at the press of a button, and by the time a car has got to the physical testing stage, the designers are pretty much completely certain that it will work to standard. "These sort of post-production problems have been all but wiped out in the last twenty years.'
http://silverstone.fortunecity.com/saturn/8/cars.html#SIX
http://www.f1nutter.co.uk/index2.php?url=/tech/6wheels.htm
http://www.ddavid.com/formula1/tyrp34.htm