Also named K tail, the body style created in 1938 has not always been used correctly. However, its principles have made it a cornerstone for modern car design
Aerodynamics is treated like royalty in the car world. Investing in it makes the vehicle faster, quieter, and more fuel-efficient all at once. The reason is simple: reducing aerodynamic resistance means reducing the effort to navigate through the surrounding air. Then again, this is another case of easier said than done.
In fact, that proverb illustrates this article’s topic quite well. In short, there was a time when a car designer discovered an optimal shape in terms of aerodynamics. However, putting it to practice is so difficult that it never became popular. Fortunately, the laws of physics allowed another, more feasible, shape to come.
Boxy car design in the past
It is easy to imagine that things were different a century ago. Early car models were only concerned with taking people from A to B. In terms of design, their bodies would merely wrap seats and engine. The car industry would only care about refining design in the 1930s, when proper roads became more numerous.
That change paved the way – pun intended – to higher cruising speeds. At first, automakers would address the issue by building stronger engines, but that implied demand for better brakes and higher mechanical resistance, not to mention that cars would be less safe. Dealing with all that would make costs skyrocket.
Fortunately, there already were some people working on that. Hungarian designer Paul Jaray realized that, before giving the car more power, much could be accomplished by reducing its effort. He materialized his studies into the Stromlinien in 1923, a racing car totally designed according to the laws of aerodynamics.
Under pressure
Images like the one above represent aerodynamic studies in the wind tunnel. In short, several air jets flow through the car to show how its body displaces air as it moves forward in the real world. The Concept IAA above is highly aerodynamic because air flows over its body with low disturbance from beginning to end.
As you can imagine, things were the opposite a century ago. Those boxy shapes accumulate air in front of the body and form a sudden drop behind it. As a result, air pressure becomes high in front of the car and low behind it. The combined effect is a force that pulls the car backwards. Not exactly desirable, right?
The main aerodynamic resource brought by the Stromlinien above was the teardrop shape. The smoother front and rear ends disperse air more easily on its way through the body. The pressure difference is lower, and that negative effect is minimized. Using the industry’s jargon, the car’s aerodynamic drag is reduced.
Paul Jaray in practice
The teardrop design was so promising that it quickly attracted the industry’s interest. Paul Jaray took the next step and collaborated with some companies to take his creation to the streets. Czechoslovakian Tatra was a prominent early adopter: the 77 was the first mass-produced car to be aerodynamically optimized.
The car had several mechanical innovations for its time, such as hemispherical combustion chambers and overhead valves. The teardrop design did its part by lowering aerodynamic drag to 0.36, which is still good nowadays. The result was a top speed of 93 mph despite 4,000 lb of weight and 75 hp of power.
In the other side of the Atlantic, the Chrysler Airflow was the first car to embrace streamlined design, as it was called. Those guidelines had everything to become a new market trend, and that actually happened for a while. Unfortunately, the teardrop design had consequences which only practical use could reveal.
The birth of the Kammback
Since that tapered design was mostly theoretical, high benefits would only come after extensive research. That is hard enough today, so we can only imagine how it was before computers existed. The latter would also make manufacturing excessively complex. Both issues would inevitably lead to higher overall costs.
As if that was not enough, actual driving brought more problems. The teardrop shape harmed headroom on the rear seats and forced the rear part of the body to be too long. Besides that, there was little height available for the glass area, which made maneuvering more difficult. That design was just not practical.
Overall, the industry tried to solve the problem by doing the opposite of what it used to do, but it caused other problems. In the late 1930s, several specialists were working on a surprisingly objective idea: since the teardrop design led to an excessively long rear end, what about chopping off some of that length?
Wunibald Kamm in car design
Truncating the teardrop design like that made the rear fascia end in a vertical surface. It turns out that, at high speeds, the profile creates a controlled turbulence over which the surrounding air can flow. In other words, it is possible to make air flow just as smoothly without building the complete teardrop rear end.
German professor Wunibald Kamm applied that concept in practice with the BMW coupé shown above. It reached a drag coefficient of 0.25, which is still excellent nowadays and was 29% better than the original vehicle from which it was derived. The Kamm coupé was developed to compete in the 1940 Mille Miglia.
While the Kammback was still complex to build, it was much more practical. The truncated rear made cars shorter and gave designers more flexibility to provide adequate headroom. Now, since the auto industry adopted it all around the world, there are cases of all types. Some of them definitely deserve a closer look.
Kammback in the market
The Citroën SM above is a good example: it has a teardrop rear end that was vertically truncated. You can see that it creates a smooth air flow because there is no windshield wiper: dirt only accumulates in places that form considerable turbulences. It actually goes further by adding a partial cover on the rear wheels.
On the other hand, the AMC Eagle Kammback is almost ironic. It has a regular horizontal roof that ends in diagonally truncated rear; none of that follows the original concept. It is one of many examples where the car achieved good aerodynamics, indeed, but with solutions that are not what Wunibald Kamm created.
In general, the industry spent decades using only the general principle behind the Kammback. By tapering the rear in any way, it becomes close to the teardrop shape and brings a little bit of its benefits. The Opel Kadett E is a rare case when the company chose to go further at the expense of reducing rear headroom.
Kammback in electric cars
This design was ostracized for a long time because the industry had other priorities. It would only become common again in the past few years because of the global push in favor of electric cars. Authorities need them in large numbers, but people will only buy them if they are capable enough for their normal use.
Just like ninety years ago, applying stronger powertrain (or larger battery packs) is not effective because it is expensive and increases weight, which is counterproductive. Making the body more aerodynamic helps a lot and is much easier to put into practice now that the auto industry can use computer-aided design.
The result is that the Kammback has become popular again especially among dedicated electric cars, such as the Hyundai Ioniq and the Toyota Prius. Their rear end could be longer before the vertical cut-off and their bumper could be smoother, sure. But practical use will always demand concessions here and there.
The Kammback is an intriguing case of applied engineering. It is not concerned with making aerodynamic design possible, because the teardrop design had already accomplished that. Instead, it acts as a practical alternative; it makes the principle applicable in reality. What other cars with that design do you know?
Sources
- Exploring Kammback History and Examples—and Why the Design Makes Sense – Automobile Magazine
- The Kammback Caused Some Turbulence in Automotive-Design – Dyler
Danillo Almeida has explored his passion for cars in two distinct ways. The first one is his graduation course in Mechanical Engineering, which will hopefully lead to a job position in the field. The other one is expressing his knowledge and opinions on the matter through writing. Almeida has already contributed to blogs, stores, and websites in general writing automotive content in many formats.
