Why Three Wheels Are Better Than Four

When it comes to automobiles, the conventional wisdom is you need four wheels or more. So why are there cars driving around with three wheels? We'll take a look at the science (and the economics) of tossing out one of your wheels.

Tripods are good for cameras, artistic-looking tables, or even tricycles, but their utility is limited when it comes to cars. And yet, throughout history, there seem to be a number of people who have decided that an even number of wheels on a car is a sign of a shameful lack of spirit. Three-wheeled cars have been around since the late 1800s. The first of the three wheelers was made by no less a vehicular luminary than Karl Benz - whose name might be familiar to car experts. It's obviously not stability that makes people design these. What's the attraction?

Why Three Wheels Are Better Than FourS

To begin with, there are two kinds of three-wheelers, deltas and tadpoles. Tadpoles are also called reverse trikes, because they have two wheels in the front with one wheel in the back. Because they taper off towards the back, they look a bit like a cross-section of a bird's wing, and the let air flow past them like one, too. The air parts at the front of the car, and flows smoothly inwards towards the back. The car is extremely aerodynamic, especially at higher speeds, and so is extremely fuel efficient. The two wheels in the front make the overall design stable, while the back wheel is attached to the engine and accelerates the car. It's easy to see why that might be helpful. Many tadpoles are basically more-stable motorcycles with a lot of protection for the rider.

And then you have deltas, which include cars like the Reliant Robin. This is a normal car-shaped car that appears to be balancing precariously on a single wheel in the front. Obviously, its weight is distributed so that it won't simply tip over if you kick it, but it is unquestionably less stable than a four wheeler, especially when it goes fast. Why on earth would that be a popular car? To answer that, we have to go back to Mr Benz, and his early car design. One of his biggest challenges was getting a car to steer. Imagine your car is turning in a circle. At first you think that the wheels have to be facing the same way. After all, it's just one circle. But it isn't. The inner wheel is a car-width further towards the center of the circle than the outer one. So while the outer wheel describes a wide circle, the inner wheel, if it is to keep pace with the outer one, will have to describe a smaller, tighter circle in the same amount of time. They can't be pointed the same direction. The relative tilts of these two wheels have to sync up in every imaginable curve. That's hard to design, and hard to build. Car manufacturers have found ways to do it, but poor old Benz settled for taking away those two wheels and putting in one wheel. The car then steered as simply as a tricycle. Move the wheel, move the car.

This made for a much cheaper steering system, and so for a much cheaper car. Combine that with the fact that the delta cars also were smaller than normal cars and used less gas, and there was a huge savings to the consumer. They were quirky, but they were also affordable, utilitarian cars perfect those who were willing to drive them slowly and carefully. Whenever gas prices go up, three wheelers go back into fashion. The last Reliant model was introduced in 2006. I think the world is ready for more.

Top Image: Dash

Second Image: Pavol Freso
Via How Stuff Works, Ars Technica, and Car Bibles.