That’s not a Geo Metro

1983 General Motors TPCLess of a show car and more an engineering testbed, this little guy was developed by General Motors, independently from any division.

The acronym TPC stands for Two Person Commuter. The purpose was to see how far the engineers could push the fuel economy envelope, and learn what they could along the way. To achieve their goal they openly cut a couple of corners, aside from those around the body’s edges.

Efficiency to the max
I’d like to start by saying, I am not certain that 1983 is the correct year for the TPC. One book I referenced labeled it a 1982, as do some websites that discuss it.

However, I’m leaning towards 1983 since every contemporary article that I found about it was from mid 1983. Further, although the press release oddly omits any reference to a year for the TPC, it closes with “5/83,” an apparent date, on the last line. (If anyone has anything else to share that could clear that up, please comment.)

So even though this little guy may lack a specific birthday, it did have a specific purpose: efficiency. TPC lived up to that purpose, impressively.

According to Robert J. Eaton, then GM vice president in charge of staff, who was quoted in the release, the TPC “was built to measure the practical limit of fuel economy against the design of other cars throughout the world.”

In the end, this creation of the GM Advanced Product and Manufacturing Engineering Staff, achieved 68 mpg city and 95 mpg highway based on the Environmental Protection Agency’s testing from the period. The car was so efficient that it got away with a four-gallon gas tank which would equate to 270 typical commuter miles or up to 380 miles of normal highway driving, according to GM. This was achieved by several methods.

1983 GM TPC front three-quarter

First off, the TPC weighed a mere 1,070 pounds. GM points out that their lightest production car at the time, the Chevrolet Chevette, weighed 2,200 pounds.

That astounding weight, or lack of it, resulted, at least partly, from its diminutive size. It was 46.3 inches tall, had an overall length of 128.4 inches and a wheelbase of 80.2 inches. Constructed mostly of light-weight steel, the entire front end, doors and rear fenders were made of aluminum.

The second thing that contributed to the TPC’s efficiency was its little, itty-bitty 0.8 liter, three-cylinder motor that weighed only 120 pounds. The press release did not include power output estimates (one website reported 40 HP and 40 pound-feet of torque).

The release did, however, talk about performance. It reported a 5.3-second 0-30 MPH run. To go from 30-60 MPH, it took “less than 13 seconds.”

1983 GM TPC rear three-quarter

Further efforts for efficiency on the mechanical parts included zero-drag drum brakes on all four wheels and low rolling-resistance tires. The suspension, front and rear, was a transverse-mounted composite plastic beam design, said to combine the functions of spring, control arm and roll bar in one.

Another factor in its efficiency was its shape. Tested in the wind tunnel at GM’s Aerodynamics Laboratory, the TPC’s aerodynamic drag coefficient was 0.31. That figure was attained via flush glass; rear-view mirrors that were mounted inside the cabin; flush tires, wheels and wheelhouses; and the smoothing and rounding of corners on the body.

So, what did I mean by saying GM cut a couple extra corners to reach its maximum potential? Mr. Eaton also stated that “To make the TPC competitive on a world-wide basis, some minor government emission and safety standards peculiar to the United States were excluded.” Meaning, some things like those low-mounted headlights probably wouldn’t meet US crash standards and it wasn’t likely to pass a smog test.

Regardless, that was some forward thinking on the part of GM’s engineering and marketing teams.

Below is a great picture of the TPC sourced from a book titled, Cars Detroit Never Built, by Edward Janicki. Click on the thumbnail to see a larger version.

1983 General Motors TPC front left