Neat surface architecture and aerodynamic form


Takio Nakagawa

―― Sudden order

The design work on the 2nd gen. Galant Sigma was nearing completion. Suddenly, an order came for the development of the Tredia / Cordia, the world cars. Reorganization of the design teams took place abruptly. Despite the fact that these were completely new models, the design development schedule was one stage shorter than usual, and the staff was very confused. Mitsubishi had started FWD with the Mirage, and the Tredia / Cordia were its upper FWD models, and were comparable to the Lancer (RWD) . The packaging was not small, not large, just right, and suitable for everyone, and was in the standard compact class in the world.

Image sketch by Eiichi Okuma

―― First of all, concept making camp in Izu

As a new attempt, a camp was held at an inn in Izu, far from the development site. The purpose of this was to brainstorm free ideas in a relaxed environment, to explore concepts, and to unify the group. As a result of the camp, a design concept was agreed upon: not to be over-designed or decorative, but to be simple, natural, and environmentally friendly.

―― Back at studio

With the results of the camp in mind, the team was divided into two groups, one for the sedan and the other for the coupe, and worked enthusiastically on idea sketches in the summer heat. Then, based on the concept, selections were made and renderings of four sedan and three coupe proposals were created. I was in charge of the Tredia, and my basic concept was a traditional notch-back style with a neat surface architecture, simple frontal shape, and smooth aerodynamic surface that would be long lasting. The front design, in particular, was simple and elegant without elaborate detailing. The upper edge of the rear wheel cut is lowered for aerodynamic effect, and the side view was sharp and clean.

Rendering by writer

Rendering by Shinichi Kobayashi

Rendering by Shigehisa Ishii

Rendering by Eiichi Okuma

―― Presentation day has come

Design presentations are extremely nerve-wracking. Chairman Kubo and other executives were present in the conference room. The presentation of the renderings of the sedan and the coupe were well done and confident. The Chairman had a keen intuition, was straightforward, and when he gave direction, he clearly judged whether it was a “no” or a “good” decision. After the design explanation, the chairman took a turn in front of the proposed renderings and indicated his decision. No detailed explanation was given, and my proposal for the sedan and Yokoyama’s proposal for the coupe were selected. It was a rare case in those days that a design direction was made in a single shot without any negative comments.

―― Competition with Italian designers ends

After the design direction was completed, the chairman said, “The design competition with Italian designers has served its purpose, so let’s call it off”. It was a strange feeling of ease. I felt relieved to be free from the pressure that had always accompanied me, and at the same time, I felt a sense of disappointment that my powerful rival had disappeared. I thought it was a sign of the significance of making our own design decisions. I regretted that I had been instructed by the executives to compete with them, but I do not deny the competition.

―― 1/1 design work in difficulty

The 1/1 design work, which translates from rendering to actual size model, was carried out by a team of three members, Shigehisa Ishii and Eiichi Okuma, under the experienced supervision of Shinichi Kobayashi, the head of the team. The team proceeded to 1/1 tape drawing, encompassing the engineering requirements while keeping the design image. The most difficult part of the process was the model making , where intensive design work is critical. The packaging, the aspect ratio, the proportions, the surface treatment, and the engineering requirements were checked repeatedly. At this stage, where the design was refined and perfected over and over again, the Tredia’s design moved closer from the designer’s image to the reality of the car.

The side view of the clay model

The modeler’s ability greatly influences the quality of the design. From the detailed clay modelling to the painting and final installation of the outfitting parts, the modeler’s skill goes a long way in creating an image of the actual car. I am very grateful to all the modelers for the excellent models.


studio view


clay modeling

―― Wind tunnel testing, another important issue

The wind tunnel test on the 1/5 model was conducted by Okuma and his colleague Itsuhei Kori, who was in charge of the wind tunnel test. The work involved adding and removing clay of the model to find the optimum shape for aerodynamic performance, and measuring the aerodynamic drag and the lift each time. Repeat the test by making small changes to the narrowing and cross-sectional radius of the front fenders, rear quarters, and cabin, as well as the sloping angle of the rear window and the bottom height of the front and rear bumpers. The results were incorporated into the clay model being made in the studio, but it was inevitable that many of the results could not be reflected in the design due to conflicts with the desired design image.

Effect of aero cover confirmed in wind tunnel test

―― Pursuit of further aerodynamic treatment

Once the aerodynamic characteristics of the exterior were roughly understood, it was necessary to further improve aerodynamic performance by reducing the effect of turbulence under the engine compartment, which was a major source of drag. At first, an air dam was installed under the front bumper to forcefully cut the flow into the engine compartment, but eventually an aero cover was installed that covered the entire area from the bottom of the bumper to the engine compartment, which proved to be very effective. In addition to this, smoothing the underside of the floor was also found to be effective. (FF vehicles have an advantage over RWD vehicles in this respect.) Other measures were also taken to minimize the gap between the door sash and the glass to prevent wind noise and stains on the side windows behind the door mirrors.

Also, as in the design of the Galant Sigma, the side lines were made continuous to the rear, and the upper edge of the rear wheel cut was lowered to hide the tires and reduce aerodynamic drag. This creates a smooth and stretched design. This process, however, usually requires the tires to be inward, but this was avoided by clinching the flange of the wheel cut.

Summary of aerodynamic improvements based on wind tunnel test results

―― Test driving prototype cars reveals many things

In general, there are many things to be checked: production checks, design checks, driving checks, and quality checks, but driving tests are a valuable experience for designers to gain insight into many things. The appearance on the road is important, as is the fit of the car with the cityscape and standing on the road, and the stability of the car. In addition, the Hokkaido snow driving test with the test team was a great opportunity to learn things that were not possible in the city, such as grasping the road surface conditions, how fast snow accumulates, what to do when visibility turns to white snow, and how to handle the steering wheel on ice.

FRP model of final design

―― As conclusion

Despite the sudden start, the design process went very smoothly based on the concept created at the Izu camp, and development was completed and launched with a small number of design study models and no major technical problems. Whenever a car is launched, there is always a mixture of anticipation and anxiety. However, sales of the Tredia did not grow as expected. There are various perspectives in evaluating a car, but design has a large impact. I think we did our best, but…. . There were many things that we were able to do and many things that we were not able to do, but when the design was finished, the reflection began. This reminds me of the words of Professor Keith Teater, a design consultant for Mitsubishi, and the dean of Art Center College. ” A car should not only be beautiful and gentle, but it should also have a certain level of awesomeness, like a yakuza’s scar on the face.” In other words, a car needed to distinguish itself as a unique entity.

The front of the Tredia

August 2021