Tri-Magnum
Excitement on Three Wheels
 

The mention of 50-mpg fuel economy normally implies econobox driving - the proverbial tradeoff between performance and fuel economy that most of us accept as a necessary evil. But performance and fuel economy are not necessarily inversely related. Tri-Magnum is an excellent example of how ultralight construction can result in both high fuel economy and sports car performance. This motorcycle-based three-wheeler outperforms most production sports cars, and still delivers fuel economy roughly equivalent to that of the original motorcycle. The key constant is the power-to-weight ratio. With 80 hp and a 1,200-pound curb weight, Tri-Magnum has a power-to-weight ratio of 15 pounds per horsepower, which equates to a 3,500-pound car with a 233-hp engine.
         The original Tri-Magnum was built around a Kawasaki KZ900 motorcycle. However, the Honda Gold Wing, especially the model with the electric reverse, is an even better choice. The Gold Wing's 6-cylinder opposed engine is smooth-running, it develops maximum torque at a comparatively low rpm (better for automotive application), and is more fuel-efficient that the KZ900 engine. The chassis consists of a stripped motorcycle, minus the fork and front wheel, which is then attached to a VW Beetle front suspension assembly using a simple framework. The motorcycle drive train is used as is, including its lightweight and efficient 5-speed transmission.
         Tri-Magnum's styling is both functional and in character with its aggressive performance. Slippery aerodynamics, engine cooling requirements (either air-cooled or water-cooled), accessibility to the cockpit and engine compartment, ease of construction, and safety considerations are all integrated into the design. The impact-absorbing foam-filled front bumper, which ties into the frame with massive steel members, is designed to spill air onto the body. Body lines flow smoothly from front to rear where they break sharply around taillight nacelles to create a clean separation point. The rear-facing duct on top and the two shark-gill louvers on the sides are designed to draw hot air from the engine room while cool air is ducted into it from underneath. A small electric fan, located just ahead of the engine, or on the radiator of a water-cooled machine, keeps it cool at idle.
         The lift-up canopy, though exotic, is simple, functional and strong. It leaves the main body area integral for maximum strength. When the canopy is open, it presents an entirely open cockpit so you don't have to duck under a low roof line when getting in and out. The canopy is counterbalanced with two air cylinders, the type used on automotive hood and decks, so it is easy to lift and stays up by itself. A steel framework is laminated inside the canopy for extra strength and rigidity. Seating is side-by-side, and the seat, which is contoured from head to knees, is molded into the car's body. Passengers ride between the two front wheels for maximum side-intrusion protection. A solid bulkhead forms the rear of the cockpit where it also serves as a roll-member.
         Driving Tri-Magnum is as unique as the vehicle itself. Shifting is done with the jet-fighter-style control stick that emerges from the floor between the occupants. The control stick carries the handlebar controls from the motorcycle, which are now stacked back-to-back against each other (one from each side of the handlebar) where they are within easy reach. The motorcycle clutch lever is also mounted on the control stick. To shift gears, grab the control stick, squeeze the clutch lever, then move the stick either forward or rearward, depending on whether you are up-shifting or down-shifting. The stick is connected via a short link to the foot-lever that is normally used to shift gears on the motorcycle, so the shift pattern is identical. Accelerator and brake pedals are mounted on the floor, just like those of a conventional automobile.
         Due to its forward-biased center of gravity, Tri-Magnum understeers, just like most conventional automobiles. Pushed hard in a turn, she will float to the outside, rather than spin out. During a three-wheel-locked stop, Tri-Magnum's rear floats slightly to one side, then rights itself and floats slightly to the other side, with no tendency to swap ends. Because of its low center of gravity, which is located forward near the side-by-side wheels, the margin of safety against rollover is equivalent to a standard four-wheel car. Tri-Magnum was featured in Mechanix Illustrated magazine, February 1983. 
         Click on the link in this sentence for more information on three-wheeler handling dynamics. Click on this link for information on the FRP/foam composite used to build the body.

The New Edition of the Tri-Magnum Plans Includes:

• Vastly expanded, 80-page, large-format construction manual with over 130 photos and illustrations.

• The manual describes how to set up the motorcycle, build the body, and install upholstery, widows, hinges, and all of the other items that go into this specially constructed vehicle.

• There is a new chapter on three wheel vehicle dynamics.

• Plans provide the most complete information on one-off construction using urethane foam.

**If you've ever wanted to build a special vehicle of your own design, the Tri-Magnum plans will be an invaluable aid.