By Gracus Bloom — Car Enthusiast News

There are production cars that become classics, and then there are automobiles that were never really intended to become production cars at all. They were rolling experiments—machines built to test styling, aerodynamics, engines, suspension systems and ideas that might eventually find their way into future automobiles.

Among the most fascinating examples came from Daimler-Benz and Mercedes-Benz, particularly during the 1960s and early 1990s. Three cars in particular tell a remarkable story: the Mercedes-Benz SLX, the C 111, and the C 112.

They were separated by decades, but they shared a common philosophy: build something spectacular, learn from it, and see where the technology leads.

And for today’s car enthusiast, they offer a fascinating look at what happens when automotive designers are given permission to experiment.

The Mercedes-Benz SLX: The Supercar That Almost Happened

The story begins with the Mercedes-Benz SLX design study, developed during the mid-1960s.

At the time, Mercedes-Benz had a problem. The spectacular 300 SL Gullwing had established an enormous reputation, but the company did not have a new mid-engine supercar ready to take its place.

Mercedes designers Paul Bracq and Giorgio Battistella worked on a radically different idea: a mid-engine sports car with a much more exotic proportion than the company’s conventional front-engine automobiles. Mercedes-Benz says the design study was created in the mid-1960s and became a full-size wooden model in 1966, followed by wind-tunnel testing. (Mercedes-Benz Media)

The SLX was particularly interesting because the mid-engine layout moved much of the vehicle’s mass toward the center of the car.

That meant the designers could create a much shorter nose and a tapered rear section while giving the car a distinctly exotic silhouette.

The concept also featured retractable headlights, substantial side air intakes and a highly integrated bumper design. It looked less like a traditional Mercedes touring car and more like something from a European endurance-racing paddock. (Classic Car Trust)

Where was the SLX showcased?

Here’s one of the fascinating parts of the story: the SLX was not publicly showcased when it was originally created.

The full-size model spent decades within Mercedes-Benz’s collection. It eventually emerged publicly at Techno-Classica Essen in Germany in 2019, where enthusiasts finally got to see the unusual wooden prototype. Mercedes-Benz Classic included the SLX in its 2019 display alongside the C 111 family. (Mercedes-Benz Media)

In other words, a concept that had been hidden away for roughly half a century suddenly became a star of a major classic-car event.

The SLX also became an important stepping stone toward Mercedes-Benz’s next generation of experimental sports cars.

From SLX to C 111

If the SLX was the road not taken, the C 111 was Mercedes-Benz’s spectacular attempt to see what the road ahead might look like.

The first C 111 made its public debut at the International Automobile Exhibition, or IAA, in Frankfurt in September 1969. Mercedes-Benz describes it as a rolling laboratory rather than a conventional production-car project. (Mercedes-Benz Media)

And what a laboratory it was.

The car had an extremely low wedge-shaped body, upward-opening gullwing doors, a fiberglass-reinforced plastic body and a mid-mounted three-rotor Wankel engine.

The first C 111 produced approximately 280 horsepower from a 1.8-liter three-rotor Wankel engine and was rated at about 260 km/h, or roughly 162 mph, in Mercedes-Benz’s historical specifications. (Mercedes-Benz Media)

The car immediately attracted attention.

The orange metallic paint, black detailing, gullwing doors and ultra-low profile made it look like something from a science-fiction movie.

C 111 technical snapshot

Mercedes-Benz’s own historical material notes that the C 111 was capable of approximately 0–100 km/h in about five seconds. (Mercedes-Benz Media)

C 111-II: Four Rotors and 350 Horsepower

Mercedes-Benz wasn’t finished.

Only about six months after the original C 111 appeared, the company unveiled the substantially revised C 111-II at the Geneva Motor Show in March 1970.

This version used a four-rotor Wankel engine producing approximately 350 horsepower.

Mercedes-Benz listed a top speed of approximately 300 km/h, or 186 mph. (Mercedes-Benz Media)

That was extraordinary performance for 1970.

The revised machine also had a redesigned body and was intended to be more usable than the first experimental car.

And then something very unusual happened.

People actually wanted to buy it.

Mercedes-Benz says the company received numerous purchase offers, but the C 111-II remained an experimental vehicle rather than entering production. (Mercedes-Benz Media)

For car collectors today, that is part of the C 111’s mystique.

It looked like a production supercar.

It drove like a supercar.

It generated enormous public interest.

But you couldn’t simply walk into a Mercedes dealer and order one.

Who Designed the C 111?

The C 111 is often associated with Bruno Sacco, one of the most influential designers in Mercedes-Benz history.

Mercedes-Benz’s historical material says Sacco had formal responsibility for the design direction of the C 111 and C 111-II, while Josef Gallitzendörfer and Peter Pfeiffer were involved in the design work. Mercedes-Benz later described Sacco as having shaped the company’s Wankel experimental vehicles. (Mercedes-Benz Media)

That distinction matters because concept cars are rarely the work of a single person.

A designer establishes proportions and surfaces, engineers determine what can actually function, aerodynamic specialists test airflow, chassis engineers work on suspension and handling, and manufacturing specialists determine whether the concept can actually be built.

The C 111 was essentially a four-wheeled engineering laboratory wrapped in spectacular bodywork.

The Wankel Gamble

Why did Mercedes-Benz pursue the rotary engine?

The Wankel engine offered a radically different approach to internal combustion.

Instead of pistons moving up and down inside cylinders, the rotary engine uses a triangular rotor moving within an approximately oval-shaped housing.

The attraction was compactness, smooth operation and high power potential relative to engine size.

But the technology also presented challenges.

Mercedes-Benz eventually abandoned the Wankel development program. Its historical account points to fuel consumption and emissions as important reasons the company stopped pursuing the compact rotary engine. (Mercedes-Benz Media)

Yet the C 111 experiment was far from wasted.

Mercedes subsequently transformed the C 111 concept into a family of record-setting experimental automobiles.

The later C 111 record cars used diesel and gasoline engines, proving that the basic platform could serve as a laboratory for entirely different technologies.

The C 111 Becomes a Record-Breaker

The C 111 story took an unexpected turn in the 1970s.

Instead of becoming a production supercar, the C 111 became a high-speed research machine.

In 1976, Mercedes-Benz used the C 111-II D, equipped with a turbocharged five-cylinder diesel, for record attempts at the Nardò test track in Italy.

The company subsequently developed the C 111-III and C 111-IV.

The final gasoline-powered C 111-IV became one of the most spectacular members of the family.

In 1979, it achieved a recorded speed of 403.978 km/h, or roughly 251 mph, at Nardò. (Mercedes-Benz Media)

That is an incredible transformation.

A car originally created to investigate rotary-engine technology eventually became a platform for proving that diesel and gasoline power could be pushed to extraordinary speeds.

Technical Performance: C 111 vs. C 111-II

The progression is easy to appreciate when the numbers are placed side by side:

The later record cars should not be treated as direct production versions of the 1969 C 111. They were progressively modified research and record vehicles.

But the family resemblance was deliberate.

Then Came the C 112

Fast-forward to 1991.

Mercedes-Benz once again rolled out a futuristic supercar prototype, this time called the C 112.

It debuted at the Frankfurt Motor Show in 1991. Unlike the earlier C 111, the C 112 was designed around the idea of a road-going high-performance car packed with advanced electronic and aerodynamic technology. (Petersen Automotive Museum)

The C 112 was powered by a 6.0-liter V12 producing 408 horsepower.

It featured rear-wheel drive and a six-speed manual transmission, along with technology that was astonishingly advanced for the early 1990s.

Among the most interesting features were:

• Active suspension
• Active aerodynamics
• Rear-wheel steering
• Electronically controlled rear spoiler
• Electronic tire-pressure monitoring
• Advanced cruise-control technology
• Electrohydraulically operated gullwing doors

The Petersen Automotive Museum identifies the C 112 as the first Mercedes-Benz to incorporate the company’s Active Body Control concept. (Petersen Automotive Museum)

C 112 technical snapshot

Mercedes-Benz’s research documentation identifies the C 112 as an experimental vehicle intended to test active driving-dynamics systems. (Manuals+)

The C 112 Was Almost a Production Car

The C 112’s story has another remarkable twist.

According to the Petersen Automotive Museum, nearly 700 potential orders were placed for the car, but Mercedes-Benz ultimately decided not to put it into production. (Petersen Automotive Museum)

Imagine being a wealthy enthusiast in 1991, seeing this silver gullwing supercar at the Frankfurt show, and telling Mercedes-Benz you wanted one—only to discover that the company wasn’t going to build it.

The C 112 demonstrated technologies that eventually appeared in later production vehicles.

Mercedes-Benz documentation identifies examples including active suspension technology, active rear spoiler technology, electronic tire-pressure monitoring and advanced distance-control systems as technologies that later found production applications. (Manuals+)

That is perhaps the most important role of a concept car.

The concept itself may disappear, but the technology doesn’t necessarily disappear with it.

The Concept-Car Performance Graph

The evolution from SLX to C 111 to C 112 illustrates how rapidly Mercedes-Benz’s experimental sports-car program changed.

The numbers show an increase from 280 horsepower in the original C 111 to 408 horsepower in the C 112—a gain of about 46%.

But horsepower wasn’t the only measure of progress.

The C 112’s electronics, suspension controls and aerodynamic systems represented a different kind of advancement.

Speed: From 1969 to 1991

The interesting story here is that maximum speed stopped being the only headline.

By 1991, Mercedes-Benz was investigating how electronics could help a high-performance car stay stable, change its aerodynamic characteristics and control its suspension.

That philosophy sounds remarkably familiar today.

Aerodynamics: The Invisible Part of the Concept Car

One of the most important differences between a conventional automobile and an experimental supercar is the amount of attention paid to airflow.

A car moving at high speed must push air out of the way.

The shape of the body determines how much aerodynamic drag is produced and how much downforce or lift is generated.

A simplified relationship for aerodynamic drag is:

Fᴅ = ½ ρ Cᴅ A v²

Where:

• Fᴅ = aerodynamic drag
• ρ = air density
• Cᴅ = drag coefficient
• A = frontal area
• v = vehicle speed

The important part for enthusiasts is the velocity squared term.

If speed doubles, aerodynamic drag doesn’t simply double—it increases dramatically.

That is why the designers of cars such as the C 111 and C 112 spent so much effort sculpting the body.

At 300 km/h, airflow is no longer a minor styling consideration.

It becomes a major engineering problem.

Why These Cars Still Matter

The SLX, C 111 and C 112 demonstrate three different eras of automotive experimentation.

The SLX explored the idea of a Mercedes mid-engine supercar.

The C 111 became a rolling laboratory for Wankel engines, lightweight body construction, aerodynamics and eventually record-setting diesel and gasoline power.

The C 112 moved the experiment into the electronic age, combining enormous V12 power with active suspension, active aerodynamics and electronic driver-assistance technology.

And none became a conventional production car.

That is exactly why they remain fascinating.

A production automobile has to satisfy accountants, regulators, manufacturing engineers, dealers and customers.

A concept car can ask a much more interesting question:

What if we tried this?

Today’s Restoration Challenge

For the classic-car industry, experimental vehicles create a special challenge.

Restoring a 1960s production Mercedes can already require specialized knowledge of metalwork, paint, trim, mechanical systems and period-correct components.

A one-off concept car is another level entirely.

The body may contain unusual fiberglass construction.

The interior may use experimental materials.

Mechanical components may not correspond to a production parts catalog.

And the paint can be just as important as the shape.

The C 111’s famous orange “Weißherbst” finish has become part of the car’s identity. Mercedes-Benz continues to feature the color and the C 111 in its heritage displays. (Mercedes-Benz Media)

That is where the modern restoration industry comes into the picture.

A collector looking for a good autobody technician isn’t necessarily looking for someone who can simply repair a dent.

Restoring an experimental automobile can require someone who understands body contours, composite materials, historical finishes, panel alignment and the visual language of the original designer.

Likewise, shops hiring for experienced autobody painter positions may find that vintage and collector automobiles require a different skill set from ordinary collision repair.

The Vintage Daimler Lesson

Perhaps the biggest lesson from these automobiles is that the future rarely arrives in a straight line.

Mercedes-Benz experimented with rotary engines.

It moved toward diesel record cars.

It experimented with active suspension and active aerodynamics.

Some technologies disappeared.

Others eventually found their way into production cars.

And some ideas simply became beautiful automotive history.

For today’s enthusiast, following these cars can also make a great reason to plan a European automotive vacation. Museums, classic-car events and major auto shows can turn a normal trip into a rolling history lesson—and careful travelers can search for cheap travel deals before heading overseas.

In 2026, Mercedes-Benz is celebrating 140 years of automotive innovation, and the company’s current heritage displays continue to pair historic experimental vehicles with modern interpretations. At the 2026 Aurora event in Sweden, Mercedes-Benz displayed the C 111-II alongside the modern Vision One-Eleven, showing just how long the influence of the original experiment has lasted. (Mercedes-Benz Media)

That may be the ultimate compliment to an old concept car.

The designers may have failed to put it into production—but decades later, people are still talking about it.

And sometimes, the car that never made it to the dealership becomes the one enthusiasts remember the longest.

3 pictures to accompany the article

Image note: The SLX was a full-size design/mock-up rather than a production running car; its original public exhibition came decades later. The C 111 image represents the 1969 experimental car, while the C 112 image represents the 1991 Frankfurt concept. (Mercedes-Benz Media)

Additional technical chart

Source basis: Mercedes-Benz historical specifications for the C 111 and C 111-II, plus Petersen Automotive Museum specifications for the C 112. (Mercedes-Benz Media) 

Experimental Mercedes power: C 111 to C 112

Published manufacturer and museum specifications for three landmark experimental sports cars. The SLX was a non-running design study, so it is not included in the horsepower comparison.

Published top-speed figures for selected Mercedes experimental cars

Manufacturer and museum figures for the C 111, C 111-II and C 112. Later C 111 record cars are separate record vehicles and are not included in this comparison.

Power-to-displacement comparison

Horsepower per liter calculated from published engine specifications for the C 111, C 111-II and C 112.

What if we built the car of the future right now?

The answer was a parade of concept cars that looked as though they had escaped from a science-fiction movie. Some were engineering experiments. Others were styling exercises designed to attract crowds at auto shows. A few were serious attempts to determine whether the public would actually buy something radically different.

Among the most fascinating were Ford’s two-wheeled Gyron, the lightweight Mustang I, Chevrolet’s mid-engine-inspired Corvair Monza GT, Chrysler’s jet-age Turbine Car, and Pontiac’s sleek XP-833 Banshee.

Some ideas disappeared. Others quietly influenced cars that came years later.

And, naturally, car enthusiasts still argue about which one should have made it into production.

1. 1961 Ford Gyron — The Two-Wheeled Car From Tomorrow

Manufacturer: Ford Motor Company
Model: Gyron
Year: 1961
Designers associated with the project: Alex Tremulis, Syd Mead and others
Marketed/positioned as: A futuristic experimental and design-research vehicle

If there was ever a concept car designed to make people stop walking and stare, it was the Ford Gyron.

The Gyron looked more like a spacecraft than an automobile. Instead of four conventional wheels, the design envisioned a two-wheel vehicle stabilized by gyroscopes. Ford presented it at the 1961 Detroit Auto Show as a glimpse into a futuristic transportation system. The Henry Ford records the Gyron as a 1961 Ford concept and notes that the full-size show car ultimately used small outrigger wheels because a sufficiently large gyroscopic system was too expensive for the show vehicle. (The Henry Ford)

The actual show car used a small electric motor and could move at approximately 5 mph. It wasn’t a practical high-speed automobile, and it wasn’t intended to become a normal Ford dealership product.

Its revolutionary feature wasn’t horsepower.

It was vehicle balance.

The concept anticipated a world in which electronics, gyroscopes and computerized controls could keep a narrow vehicle upright. Modern enthusiasts immediately see echoes of technologies later used in electronic stability control, self-balancing vehicles and autonomous mobility experiments.

The original full-size Gyron was unfortunately destroyed in the 1962 Ford Rotunda fire. (The Henry Ford)

Gyron technical snapshot

The Gyron proves that a concept car doesn’t need 500 horsepower to become automotive history.

Sometimes looking completely crazy is enough.

2. 1962 Ford Mustang I — The Little Roadster That Helped Start a Legend

Manufacturer: Ford Motor Company
Model: Mustang I Roadster
Year: 1962
Market positioning: Lightweight, affordable, sporty car aimed at younger buyers

The Mustang I is one of the most important concept cars of the decade because it demonstrated that Ford could build a small, inexpensive sports-oriented automobile rather than another enormous American cruiser.

The actual Mustang I was extremely light. The Henry Ford lists the car at 1,544 pounds, with a 91-cubic-inch, 60-degree V4, a four-speed manual transmission, and 109 horsepower at 6,400 rpm. (The Henry Ford)

That doesn’t sound impressive today.

But consider the weight.

The Mustang I was essentially a tiny road-going laboratory. Its aluminum body panels and steel tubular space frame helped keep weight down. The engine was mounted in the middle of the car, and the car used independent suspension.

Mustang I technical chart

The car was never simply intended to be the production Mustang sitting in showrooms.

Instead, it helped Ford explore the concept of a compact performance car that could attract younger Americans. The eventual production Mustang would be substantially different, but the Mustang I helped demonstrate that the market was interested in a smaller, sporty Ford.

That was revolutionary from a marketing standpoint.

Ford had discovered that youth itself could become an automotive market segment.

The concept also showed how engineers could use lightweight construction rather than simply increasing engine displacement.

3. 1962 Chevrolet Corvair Monza GT — Mid-Engine Thinking Before It Was Cool

Manufacturer: Chevrolet / General Motors
Model: Corvair Monza GT
Year: 1962
Market positioning: Experimental sports car and design/engineering exercise

The Corvair Monza GT looked like Chevrolet had taken a European sports car, put it through a wind tunnel and then sent it to a science-fiction movie.

GM’s own Heritage Collection describes the Monza GT as an experimental concept with highly aerodynamic lines developed through wind-tunnel testing. The rear body section hinged upward to expose the air-cooled six-cylinder engine, while the forward-opening canopy provided access to the passenger compartment. (General Motors)

The car’s most important contribution was its mid-engine configuration and packaging philosophy.

Instead of putting a large engine far forward, engineers experimented with placing the powerplant closer to the center of the vehicle. That could improve weight distribution and handling.

The Corvair connection also made the project particularly interesting because the production Corvair already used an air-cooled, rear-mounted flat-six.

The Monza GT took that basic concept and pushed it dramatically toward sports-car proportions.

Corvair technical comparison

The production Corvair engine family included 145-cubic-inch six-cylinder engines producing 80, 102 and 150 horsepower in various configurations, with three-speed, four-speed and Powerglide transmission choices. (General Motors)

The Monza GT was important because it demonstrated that an American manufacturer could seriously investigate packaging ideas associated with exotic European sports cars.

It also influenced later GM design thinking.

For enthusiasts, it remains one of the most beautiful examples of the early-1960s “what if?” school of automotive design.

4. 1963 Chrysler Turbine Car — The Jet Engine Comes to Main Street

Manufacturer: Chrysler Corporation
Model: Chrysler Turbine Car
Years: 1963–1964 consumer experiment
Market positioning: A futuristic alternative to the conventional piston engine

If the Gyron looked like the future, the Chrysler Turbine Car actually attempted to power a car with a technology borrowed from the jet age.

Chrysler had been researching automotive gas turbines for years. The 1963 Turbine Car was the most famous result.

Chrysler and Italian coachbuilder Ghia produced a limited run of turbine-powered cars, and approximately 50 were placed with consumers as part of a nationwide user evaluation program. The Drivers Foundation records the engine at 130 horsepower and 425 lb-ft of torque. (Hagerty Drivers Foundation)

The car used a regenerative gas turbine and a modified three-speed TorqueFlite automatic transmission.

Chrysler Turbine technical chart

One of the most fascinating aspects was its ability to operate on a surprisingly broad range of fuels. The Drivers Foundation notes that the cars were tested with fuels ranging from kerosene to gasoline and even unusual combustible liquids. (Hagerty Drivers Foundation)

The turbine had fewer reciprocating parts than a conventional piston engine and ran remarkably smoothly.

So why didn’t we all end up driving turbine cars?

Fuel economy, emissions, cost, throttle response and the practical realities of mass production worked against the concept.

Still, Chrysler’s experiment was enormously important.

It demonstrated that an automobile company was willing to spend years and millions of dollars investigating an entirely different propulsion system.

The Turbine Car wasn’t merely a show car.

Real people drove it.

That makes it one of the most ambitious automotive experiments of the decade.

5. 1964 Pontiac XP-833 Banshee — The Corvette Fighter That GM Wouldn’t Build

Manufacturer: Pontiac / General Motors
Project: XP-833
Year: 1964
Later commonly known as: Pontiac Banshee
Market positioning: Small, affordable two-seat sports car

The Pontiac XP-833 may have been one of the most dangerous concept cars ever created—not because it was mechanically dangerous, but because it threatened to compete with another GM product.

The project was championed by Pontiac chief John DeLorean and envisioned as a lightweight two-seat sports car. The car used a fiberglass body over a steel structure and a compact wheelbase.

The prototype’s six-cylinder engine was a 230-cubic-inch overhead-cam inline six, producing approximately 165 horsepower, and power was sent through a four-speed manual transmission. (Supercars)

Banshee technical chart

The design team had also considered a more powerful version. Sources document a planned 215-hp Sprint configuration, while another prototype used a V8. (Hemmings)

The Banshee’s styling was perhaps its greatest achievement.

Its long nose, short rear deck, hidden headlights and low profile previewed styling themes that appeared in later GM products. The MotorCities historical account identifies the XP-833 as a two-seat fiberglass Pontiac developed under DeLorean’s direction.

But GM management ultimately feared that a small Pontiac sports car would compete with the Corvette.

So the Banshee was stopped.

And that is one of the great “what ifs” of American automotive history.

1960s Concept Car Power & Technology Chart

Concept-car specifications can vary by prototype, configuration and historical source; some figures are estimates rather than standardized production ratings.

Why These Cars Still Matter

The 1960s concepts were not simply exercises in making strange-looking automobiles.

They were laboratories.

The designers were experimenting with:

• Lightweight construction
• Fiberglass bodywork
• Mid-engine layouts
• Turbine propulsion
• Gyroscopic stability
• Aerodynamics
• Independent suspension
• New seating arrangements
• Hidden headlights
• Advanced instrumentation
• Youth-oriented marketing
• New approaches to vehicle packaging

Some of those ideas became mainstream.

Others disappeared almost immediately.

The most interesting part is that Detroit was willing to build a physical machine to test an idea.

That required engineers, machinists, model makers, fabricators, electricians, welders, painters and skilled assembly workers. A concept car might begin as a sketch, but eventually somebody had to turn that sketch into steel, aluminum, fiberglass, glass, rubber and thousands of individual components.

That is where the automotive trades entered the picture.

Even a futuristic concept required people who understood how to fabricate panels, assemble electrical systems, align mechanical components and finish a vehicle properly.

And decades later, that same craftsmanship remains important to the collector-car world.

A beautifully preserved 1960s concept or production automobile can require an exceptional restoration team. Finding a good detailer can make the difference between a respectable classic and a show-quality vehicle, while an experienced autobody technician was needed for a difficult restoration may need to understand metal shaping, fiberglass, period construction techniques and modern preservation methods.

The Real Legacy of the 1960s Concept Car

Perhaps the greatest lesson from these cars is that automotive progress isn’t always a straight line.

The Gyron never became the transportation system of the future.

The Mustang I did not become the production Mustang.

The Monza GT remained a concept.

The Turbine Car never replaced the piston engine.

The Banshee never became Pontiac’s affordable two-seat sports car.

Yet every one of them contributed something to automotive history.

The 1960s were a period when manufacturers weren’t afraid to put radical ideas under bright auto-show lights and ask the public to imagine something completely different.

And for car enthusiasts today, that’s exactly why these machines remain fascinating.

They weren’t just cars.

They were arguments about what the automobile could become.

Image/source note for City-Paper

The four images above are presented as historical/editorial visual references. The Mustang image is from Ford’s archival collection, while the Gyron material is documented by The Henry Ford; the Corvair Monza GT is documented by GM Heritage; and the Chrysler Turbine image comes from historical automotive archives. Image licensing should be checked before commercial republication. (The Henry Ford)