Reflections on the potential of human power for transportation

Saturday, October 10, 2015

GM Lean Machine: The Solution to Personal Mobility, 30 Years Before the Competition

The problem is obvious to even the most causal driver sitting in traffic. Most cars have just one occupant, and for that occupant the car is much larger than it needs to be; at least twice as wide, equally long and maybe 10 times as heavy. As a result those cars consume more fuel and take up more space than is necessary.

A potential solution, while not as obvious, is rather straightforward. Make the vehicle just wide enough to seat one driver. Vehicles of this type are known as man-wide cars or narrow-lane vehicles. For two people, seat the second person behind the first in tandem. Keep the driver’s head height at sport-car level and to prevent the vehicle tipping over in corners, allow it to lean like a bicycle.

Both Toyota with its i-Road three-wheeler and Nissan with its four-wheel Land glider have recently built such vehicles.

But probably the most surprising fact is that 33 years ago, General Motors built such a vehicle. It was conceived by Frank Winchell, GM’s V.P. of engineering. With over 50 patents, Winchell was a strong creative force at G. M. He also assisted Jim Hall of Chaparral racing fame by designing and building many of the components that went into their cars. But Winchell’s most revolutionary contribution must be the Lean Machine.  GM said “it may be the first new road vehicle invented this (the 20th) century”. The Lean Machine took seven years to develop. That means work began on it shortly after the gas shortage of the early 1970s. Just as impressive as the visionary idea that such a vehicle was necessary is the design execution. It is probably as simple and as elegant an implementation of a motorized leaning vehicle as could be designed.

Ultimately the Lean Machine ended up in a GM World of Motion exhibit at Epcot. The images below are from the publicity brochure for the vehicle.

To be accurate, the Lean Machine is only a semi-leaning vehicle. The motor module, with its two driving wheels, does not lean. Only the passenger pod and the front fork lean. But, since the majority of the weight is in the motor module and since the center-of-gravity (cg) of that module is low, the overall effect allows for 1.2g cornering with 50deg. of lean.
George Georgiev borrowed heavily from this design for his leaning Varna Cargo Trike.

Paraphrasing the brochure, wheelbase is 71”, track is 28”, length is 122”, width is 36” and height is 48”. Actual vehicle weight was 350#. 

The chassis was made up of two parts. The rear section was made up of a tee-shaped frame. A rectangular tube that ran transverse to the vehicle supported the engine and the swing arms for the suspension. Attached to the rectangular tube was a horizontal spine made of a large-diameter tube. This spine ran from the back to the front of the vehicle. It was to this tube that the leaning portion of the chassis was attached

The front portion of the chassis was made up of a wishbone or Y-shaped frame made up of round and square tubing. The two legs of the Y supported the seat. The single tube portion of the Y held the steering head of the fork.  This tube also had a vertical extension that held a spherical-bearing rod end. That rod end was bolted to the end of the horizontal spine of the rear chassis. The front chassis was also connected to the spine by a sleeve bearing behind the seat. These two bearing allowed the seat and fork to rotate about the spine which resulted in the leaning action.


Leaning was accomplished by pushing on either of two levers with the driver’s feet. The levers were attached to cables that wrapped around the spine. Pushing a pedal unwraps its cable and rotates the cabin away from that pedal. At the same time the cable for the other pedal is wound up. The picture below shows a precursor to the LM. Notice the vehicle is leaning away from the driver’s extended leg.

When stopping, the driver was required to hold the passenger pod upright with his feet until a lever could be engaged to hold the vehicle upright. If the driver forgot, the pod would flip sideways, but LM did not tip over. This is a benefit of the semi-lean approach where the motor module’s weight keep the vehicle upright when this happened.

Below is a short clip of the Lean Machine in action.

To keep the nose-region low, Showa forks from a small displacement motorbike were used supporting a 3.00-10 mini-bike tire. Steering controls were 18” behind the fork, pivoting about a horizontal axis and connected to the fork through a linkage.
The engine used was from an 185cc Honda ATV with a 5-speed semi-automatic transmission driving the rear wheels through a garden-tractor differential. The engine put out between 12 and 15hp. The rear tires were 4.80-8 boat-trailer tires. The engine required a cable-pull starter which was accessed through a hatch in the motor-module cover.

The cd for the vehicle (coefficient of drag) was .35, not exceptional but the vehicle cross-section was small, so aero drag was low. 

Performance numbers were a top speed of 80mph and a fuel economy of 120mpg at a steady 40mph.
Notice that the 120mpg number does not match the 200mpg value published in the Epcot brochure. The 200mpg number is theoretical, based on a 38hp engine and a more streamlined body.

That body is shown in the mockup shown below. Notice the lack of the gap between the passenger pod and the motor module that would exist in a working vehicle. This more streamlined version had a cd of .15.  One of the reasons for this lower value is the tapered rear of the passenger pod as opposed to the flat-back rear of the actual vehicle. The line drawings in the brochure are of this tapered version.

The last model is of a flying-car version of the Lean Machine. While it looks very cool, the presence of even folded wings defeats the narrow-width paradigm of the original design.

Of course, if resurrected today, one change would be to have the leaning be computer controlled. The driver would just steer. Since leaning is a function of turn radius, vehicle speed and, in this case, weight of the occupant, the use of accelerometers and strain-gauges feeding information to a micro-processor which in turn controlled hydraulic actuators would take the guess work out of leaning.

The LM, as configured was just a one-passenger vehicle. It would be easy enough to extend the passenger pod to hold a second seat. The second seat location could also serve as a cargo compartment. And like the Messerschmitt tandem cars of the 1950’s, if the cg is located at the rear seat, the addition of a passenger or cargo would not affect the vehicle handling. More weight in the passenger pod would require less of a lean angle for a turn of a given acceleration.

Finally, the low-slung motor pod would be an ideal location to house heavy batteries for an electric vehicle. 

The technical information for this post came from a January 1983 Road and Track article by Peter Egan. The chassis photos from the Epcot exhibit came from Max Hall’s Maxmatic website.


  1. Very cool, I hadn't heard of this vehicle! Great research!

  2. They are much more stable on turns with two wheels in front and one in back.
    Three wheelers come back around every 30 years, like almost all energy conservation technologies.

    1. Your comment on stability may be true for static vehicles but keep in mind that these vehicles lean and the effects are different. Three wheel cars are by no means new but the Lean Machine, to the best of my knowledge, was the first of its kind and there have been numerous leaning vehicles since.

  3. For history and examples see:

  4. See also Chapter XIV Three Wheelers in Designing Tomorrow's Cars by Walter Korff, 1980.