mention of 50-mpg fuel economy normally implies econobox driving or an
expensive hybrid. But
you do not have to give up good looks or buy a high-priced vehicle in order to
cut down on gasoline. 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 performs
like a production
sports car, and it still delivers fuel economy roughly equivalent to that of the original
motorcycle. The key constant on performance 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. Built on a Honda Gold
Wing, a GL1800 for example, power-to-weight ratio comes in at about 10
or 11 pounds per horsepower - or roughly equivalent to a 3,500 pound car
with 350 hp engine. And if that's not enough, there are lots of
add-ons that will increase power output, including turbochargers.
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 as smooth as any automotive
engine, it develops maximum torque at
a comparatively low rpm (best for automotive application), and it's more fuel-efficient
that the original 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 in a turn, she will float to the outside, rather
than spin out, unless of course you push past its limits. 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 family sedan.
Tri-Magnum was featured on the cover of Mechanix Illustrated magazine.
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.
Length: 146-1/2 inch
Width: 65 inch
Height: 42 inch
Tread: 58 inch
Front Brakes: Drum
Curb Weight: 1125 lbs
Ground Clearance: 4-1/2 inch
Turning Circle: 32 feet
Fuel Capacity: 4-1/2 gallons
Seating: Two, side-by-side
Power Train: Kawasaki KZ900 (or Honda
Gold Wing, preferably with electric
Power: 81hp @ 8500rpm (according to the
Transmission: 5-speed, constant mesh,
return shift (motorcycle transmission)
Front Suspension: VW Beetle
Construction Cost: Approximately $3500,
plus the cost of the motorcycle used as a
The New Edition of Tri-Magnum Plans Includes:
- Expanded, 80-page,
large-format construction manual with over 130 photos and
- The manual describes
how to set up the motorcycle, and how to build the body, and install
widows, hinges, and all of the other items that go into this specially
- There is a new chapter on three wheel vehicle dynamics.
- Plans provide complete information on one-off construction using urethane foam.
- Plans include a set of 13 large, 17 x 22 inch drawings.
**If you've ever
wanted to build a special vehicle of your own design, the Tri-Magnum
plans will be an invaluable aid.