When the TWIKE was invented 36 years ago, it was a closed three-wheeled recumbent bike in delta design. Today, we still adhere to the original construction method. This is because, in addition to regulatory reasons, it also has a number of technical advantages. Time and again, customers ask us why we stick to the three-wheel model approach. Why not four wheels? Why one wheel in the front and two in the back instead of the other way around? Well, there are several good reasons for this tricycle model. On the one hand, we were able to build up extensive experience with the “original TWIKE”, and on the other hand, the approval process allows us to start economically with the small series. However, the main reason lies in the technical advantages.
Bottom-up: From bicycle to TWIKE
The first TWIKE was built by tech-savvy students at ETH Zurich with a heart for environmental protection and a penchant for cycling, and was demonstrated at the 1986 Vancouver World’s Fair. Their vision was a lightweight, covered bicycle for two people plus luggage that would be used in urban areas. They designed an aerodynamic recumbent with side-by-side seats and decided on the delta arrangement (one wheel in front, two wheels in back) that still exists today. This provides the necessary stability and at the same time allows a higher payload on the rear axle without critically shifting the center of mass.
The students at ETH Zurich wanted to turn a bicycle into an e-vehicle that has a sustainable drive system, can seat several people and complies with the safety standards required in road traffic. Their starting point was the bicycle, not the car, so the idea of the TWIKE 3 was a “bottom-up” rather than a “top-down” process. Why do we still hold on to the delta arrangement today?
Advantages of the tricycle: simplified approval, lightweight construction and agility
One of the main reasons why we are sticking to the three-wheel concept for the TWIKE 5 has to do with the vehicle’s registration. Registration procedures for three-wheelers are significantly less costly than for four-wheeled passenger cars. The difference here is a single-digit million amount (for a three-wheeler) to a mid-three-digit million amount (for a four-wheeled passenger car, vehicle class M). The lower initial costs allow cost-effectiveness even in small series production.
In addition, the approval for the L5e vehicle class is not limited in performance (in contrast to the four-wheeled L7e class), which allows us to launch the new TWIKE 5 with a maximum speed of 190 km/h. In the U.S., tricycles are also classified as “motorcycles” if they meet certain motorcycle criteria (e.g., handlebars instead of steering wheel). The associated lower registration requirements are another good reason for us to hold on to the tricycle with a view to possible expansion into the US market.
But there are good technical arguments above all. After all, in order to build an e-vehicle that is both powerful and has a long range, saving weight is of enormous importance. This is because the more weight a vehicle has, the more energy is needed to move it. However, since the TWIKE is supported on only three wheels, the otherwise higher torsional stiffness requirements around the vehicle’s longitudinal axis are reduced. This alone holds some lightweight potential, and further weight could be reduced by saving on other components.
With its two wheels on the rear axle, the Delta three-wheeler retains the same reliable handling as a passenger car, even on critical road surfaces. At the same time, loading luggage hardly changes the riding stability of a Delta tricycle. And last but not least, a low center of gravity and the development of a camber-active rear axle made it possible to achieve the cornering agility of a modern sports car.
In our next update, we will go into more detail about the technology installed in the new TWIKE.