I recently reviewed a three-wheeled vehicle design I executed in 2009. It was a rush job, done under a pressing deadline, so at the time I didn't have the luxury of considering the proposal in its broader context. My review, however, did give me the time to better assess the overall state of three-wheeled vehicle development. What I found surprised me.
First, some historical context: The vehicle I was designing—call it EUV, for "electric utility vehicle"—was a low-speed urban utility vehicle, similar to the Westward GO-4. You're probably familiar with the gas-powered GO-4. In fact, a GO-4-driving parking enforcement officer has probably ticketed you in some major American city. These are certainly not motorcycles, but they are motorcycles in their DNA. The GO-4 is a modern response to Harley-Davidson's three-wheeled Servi-Car utility vehicle, an extremely popular and practical service vehicle produced by The Motor Company from 1932–'73 and still used by some police departments as recently as the mid-'90s.
The American financial crash ended the EUV project prematurely, but what of three-wheeled development more generally? In terms of sheer diversity, three-wheeled development outpaces the two- or even four-wheeled variety by a considerable margin. Some three-wheelers have one front wheel while others have two wheels in front; there is even one lone exception with all three wheels in-line. Not to mention, sidecars.
Single-front-wheel designs suffer from an inherent stability problem—what OEMs confronted when they built, then soon discontinued, three-wheel ATVs. Instability is particularly an issue with short-wheelbase, high-center-of-gravity trikes, which are still sold for road use today. There are ways to lessen this instability. Designs that keep both rear wheels flat while allowing the forward chassis to lean like a motorcycle—Honda's Gyro scooters and the Dutch-made Carver tandem two-seater, for example—overcome this problem.
Two wheels up front effectively address the stability issue, and again there are flat and leaning versions—as well as sit-on and sit-in versions, wide track and narrow-track versions, and, well, let's just say there is a bewildering range of diversity.
The best-known flat design right now would have to be the Can-Am Spyder, which combines an automotive-type front suspension with a motorcycle-type rear end and uses controls and seating similar to what's found on a motorcycle. Campagna's T-Rex design has been around for some time and uses a similar suspension layout to the Can-Am but with automotive-type controls and side-by-side seating for two. Still other versions of the flat three-wheeler are almost completely automotive, using front-wheel drive, like the recently announced Elio three-wheeled car.
Then we come to the most interesting (at least to motorcyclists) of the double-front-wheel trikes, the leaning designs. Several wide-track versions of these have been prototyped and/or put into limited production—even Harley-Davidson patented a design in the late '90s called the Penster—but the trend here is to a narrower track that keeps the overall width close to handlebar width for safety reasons. The best known of these is Piaggio's MP3 maxi-scooter lineup, available with up to 500cc displacement. Gilera and now Quadro make similar machines, and even Yamaha has entered the fray with its Tricity concept. To give an even fuller sense of the tri-scene's creative ferment, consider Peugeot's Hybrid 3 Evolution leaning, three-wheel-drive maxi-scooter concept. The front wheels are driven by an electric motor in each hub; a supercharged, gasoline-powered, 300cc engine drives the rear wheel. Regenerative braking helps to charge the batteries. One model even has a roof.
Just naming the wide variety of three-wheelers that have been introduced, prototyped, or proposed in the past decade would have easily filled this column. Just when it seems like every possible future has been shown, someone finds a new way to add two plus one to equal three. It seems like we've come a long way from the simple Servi-Car.