sonal mobility naturally points to the three wheel platform. Three-wheel vehicles ... tires will breakaway and slide bef
Technical series
Benefits of the
Three-Wheel Platform
The idea of smaller, highly-efficient vehicles for personal mobility naturally points to the three wheel platform. Three-wheel vehicles are inherently simpler and lighter, they have lower manufacturing costs, and when correctly designed, they can deliver superior handling response. Superior handling comes from a three-wheeler’s lower polar moment of inertia, which is a technical way of describing the layout’s quick reaction to steering inputs. In terms of resistance to rollover, a correctly designed threewheeler can be as resistant to overturn as most four-wheel vehicles. The XR3, for example, has a rollover threshold that is roughly equivalent to that of a conventional four-wheel compact car. It can withstand lateral turn-forces of about 1.20g. Since passenger car tires have a friction coefficient of approximately 0.80, a 1.20g rollover threshold means that tires will breakaway and slide before turn-forces cause the vehicle to overturn. In comparison, SUVs have a rollover threshold of about 0.80g to 1.20g, which means many SUVs have less resistance to rollover than the XR3.* Three-wheelers are inherently lighter and less costly to manufacture. In comparison to a four-wheel vehicle, an equivalent three-wheeler has 25 percent fewer wheels, tires, brakes, and suspension components. The drive train is often more simplified as well. And because a three-wheel vehicle is supported at only three corners, the frame does not have to be beefed up to withstand the high twisting loads typical of a vehicle that is supported at four corners. This inherent mechanical simplicity naturally results in a lighter and more energy-efficient vehicle. A correctly designed three-wheel vehicle can light new fires of enthusiasm under tired and routine driving experiences. This layout points the way to a new category of personal transit vehicles of much lower mass, far greater fuel economy, and superior handling response.
Inherently Responsive Design A well designed three-wheeler is one of the most responsive machines one will ever experience over a winding road. Superior responsiveness is mainly due to the threewheeler's rapid yaw response time. Yaw response time is the time it takes a vehicle to reach steady-state cornering after a quick steering input. A softly sprung four-wheeler will have a yaw response time of about 0.30 seconds, and a four-wheel sports car will respond in about half that time. A well designed three-wheeler can reach steady-state cornering in as little as 0.10 seconds, or about 33 percent quicker than a high-performance sports car. Quick steering response has nothing to do with the number of wheels or how they are configured. It is a by-product of reduced mass and low polar moment of inertia. A typical three-wheeler is lighter and has approximately 30 percent less polar moment than a comparable four-wheel design.
* Large, high-profile SUVs have a rollover threshold of 0.80g to 1.00g.
Rollover Stability A three-wheel vehicle can equal the rollover resistance of a four-wheel vehicle, provided the location of the centerof-gravity (cg) is low and near the side-by-side wheels. Like a four-wheel vehicle, a three-wheeler's margin of safety against rollover is determined by its L/H ratio, or the half-tread (L) in relation to the cg height (H). Unlike a four-wheeler, however, a three-wheeler's half-tread is determined by the relationship between the actual tread (distance between the side-by-side wheels) and the longitudinal location of the cg, which translates into an "effective" half-tread. The effective half-tread can be increased by placing the side-by-side wheels farther apart, by locating the cg closer to the side-byside wheels, and to a lesser degree by increasing the wheelbase. Rollover resistance increases when the effective half-tread is increased and when the cg is lowered, both of which increase the L/H ratio. A simple way to model a three-wheeler's margin of safety against rollover is to construct a base cone using the cg height, its location along the wheelbase, and the vehicle’s effective half-tread. Maximum lateral g-loads are determined by the tire's friction coefficient. Projecting the maximum turnforce resultant toward the ground forms the base of the cone. A one-g load acting across the vehicle's cg, for example, results in a 45 degree projection toward the ground plane. If the base of the cone falls outside the effective half-tread, the vehicle will overturn before it slides. If it falls inside the effective half-tread, the vehicle will slide before it overturns. Base Cone Analysis of Rollover Margin of Safety
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