• Yoshinori Takeuchi & Naoko Motoyoshi Chihiro Furukawa Vehicle Development Div.
  • Takayuki Kimura & Hiroshi Kawata Vehicle Development Div.
  • Katsuaki Nobukawa & Miyoko Ishikawa Drivetrain Development Dept, Powertrain Development Div.
  • Yukifusa Hattori NVH Performance Development Dept, Vehicle Development Div.
  • Tsukasa Hoshino & Kenji Sasaki Powertrain Development Div.
  • Yukiharu Asano Clay Modeler, Design Div.
  • Masashi Nakayama Next MX-5 Chief Designer
  • Shinichi Yasui Production Planning Dept, Production Engineering Div.
  • Yukio Nakamura Product Planning Dept, Product Div.
  • Tetsuo Fujitomi Powertrain Planning Dept.
  • Hitoshi Takamatsy Deputy Program Manager, Vehicle Development Promotion Dept.
  • Nobuhiro Yamamoto Program Manager

Feel the incredibly deep passion
for vehicle engineering built into the MX-5
Through the reverberating sound of the body

Takayuki Kimura
In charge of Body Development for the 4th Generation Mazda MX-5
Vehicle Development Div. Body Development Dept.

Hiroshi Kawata
In charge of Chassis Dynamics Development for the 4th Generation Mazda MX-5
Vehicle Development Div. Chassis Dynamics Development Dept.

When boating on a lake in a park, for example, we can tell what kind of material the boat is made of and how strong it is by the sound and resonance of the water slapping against the bilge of the boat on the still water surface. Then, when you start rowing the boat, the dialogue between the boat and lake surface flowing against it becomes even more detailed, as though communicating to the five senses.
The five senses of human beings are truly a wonderful thing and thus we want customers to open their senses to the reverberating sound of the body when driving the 4th Generation MX-5. After opening the doors and sitting down in those longed-for seats, contain your excitement for a while, then close the doors gently, start driving, and feel the incredibly deep passion for vehicle engineering built into the MX-5 through the reverberating sound of the body. And in doing so, remember that there were craftsmen who poured their heart and soul into the MX-5 solely for the smiles that this reverberating sound would put on the customer's face.

No competitor to surpass anywhere in the world

Kimura is a dyed-in-the-wool body craftsman who has led an engineering life dedicated to body development.
"My senior associates always told me, 'Weight is the only true measure of our engineering prowess.' To achieve a superb driving feel, the presence of superb, quality suspensions are a must. And for that, a body with high rigidity which can firmly hold the suspensions is essential. But in reality, the difficulty in body development is achieving this together with lightness. If the weight is of no concern, a highly rigid body is a simple matter. The weight does not lie. 'The trick is achieving the target rigidity together with surprising lightness. This is what clever engineering is all about,' is what I was taught and this is what is traditionally passed on at Mazda."
Kimura knows the inside and out of vehicle bodies from around the world and with the go ahead on the design of the 4th Generation MX-5 body, he already knew that there was no competitor to surpass anywhere in the world.
"One of the indices in body development is the body-in-white weight per planar projection area. It is not hard to see the relationship between body-in-white weight and area if you imagine the vehicle body sliced vertically. A car may be lightweight, but it the car is small, well, of course it's going to be light.
However, modern cars have to fulfill higher performance and safety requirements, and when we looked at their figures based on this index, we realized that all of these cars were too heavy to achieve the MX-5 driving feel that we aimed for.
Looking at this figure for successive MX-5s, the 1st generation MX-5 was the lightest, the 2nd generation MX-5 was a bit heavier, and the 3rd generation MX-5 was somewhere in between. So, we thought, what should it be with the new generation MX-5? The target I set for this value was lighter than that of the 1st generation MX-5. Then I started development with a firm belief that the ultimate Jinba-ittai to appeal to the senses could not be achieved without realizing this target lightness."
There is no rival to the MX-5 but the MX-5 itself. That was the determination in the summer of 2009.

Next in line was the rear-wheel drive MX-5
and all of us developers set our souls on fire

Kimura, who led the development of the SKYACTIV-BODY, had already identified the first truth.
"The basic philosophy was the same for the SKYACTIV-BODY achieved on each of the front-wheel drive models. Stress is distributed most efficiently by thoroughly straightening the frame structure, the skeleton of the body, which achieves new levels of both rigidity and lightness.
This logic is fundamental to dynamics and thus any engineer working in body development anywhere in the world understands this. However, there are many restrictions when putting this into practice. The various elements which make up the vehicle, such as the engine, transmission, and suspension, contact as if to obstruct this ideal layout Mazda calls the multi-load path frame. Thus, no one was able to achieve the ideal frame layout, however, through SKYACTIV-BODY development, we achieved it on each of the front-wheel drive models. Next in line was the rear-wheel drive MX-5 and all of us developers set our souls on fire."
It was about the rear-wheel drive layout in which the transmission protrudes into the cabin, it was about a compact body size, and it was about an open car which requires high strength due to a body structure centered on a floor called the platform. Development became extremely difficult.

"It was difficult. Heavy components such as the engine and transmission were shifted towards the center of the body to achieve the brisk drive feel. The positions of the seats and pedals were fixed to achieve the ideal driving position and could not be changed. Consequently, the frames cannot run straight from the body's front to back. This leads directly to a decrease in body rigidity and an increase in weight to reinforce the rigidity. We suddenly faced a huge problem which shook the foundation of body design."
The commitment to strive for an ideal MX-5 was strong in the hearts of engineers in all areas of development and no one even considered compromising the targets in the area they were in charge of. It seemed that the problems would only become more serious.
"But at the same time, the development workshops were filled with a wonderful atmosphere. We all had a shared awareness that the purpose was not to stroke each other's egos, rather it was centering on the creation of an ideal MX-5 with the power to put a smile on the face of anyone.

To make breakthroughs in achieving the ideal against
the interfering limitations required thinking things
through step by step, again and again

There is a word in the Hiroshima dialect called "yusuru". It means making mutual concession with each other, rather than stroking one's ego. Day after day, there were debates making mutual concessions over dimension changes as little as 1 mm. These debates were for making mutual concessions, not about compromising each of the ideals. It is mutual concession without compromise. The only way to make this possible was through originality and ingenuity. To make breakthroughs in achieving the ideal against the interfering limitations required thinking things through step by step, again and again."

For example, with the backbone frame, which extends front and back from the center of the body, it was a fight over space for the transmission from the exterior and space for the seats from the interior.
"Here, as a result of employing ingenuity through mutual concession on three development sides, including a transmission case with absolutely no surface asperity using casting techniques for a compact finish without loss in the rigidity, innovative seats using net material, and a panel shape which restrains the rear end of the backbone frame, all of those involved in different development areas got their way, and no one had to reduce their target values."
For example, the panel behind the engine compartment, which is called the cowl and dash, could not be large if we wanted to achieve the low bonnet and ideal layout of the brake and clutch pedals positioned underneath.
"Normally, we would want to make the area of this part as large as we can to assure torsional rigidity. But, once we knew that this was impossible, it became a matter which could only be resolved by racking our brains. We assured the target rigidity using the panel shape created through deep consideration of the mechanics. At the same time, engineers in many areas of development, who put their heads together and made their mutual concessions, came up with things like making the wiper motor more compact, and cleverly devised the shapes of the pedals and their layout. What was most difficult with this panel was, in the end, coming up with an efficiently strong shape which could also drain rain water flowing from the windshield.
The body of the MX-5 uses high performance materials where necessary, including aluminum alloy and high-tensile strength steel, and these are expensive. But if someone was to ask what is the true value of this body, our immediate reply would be that it lies in our thorough dedication to building things. In other words, it is the result of the exchange of people's voices such as 'Let's go beyond conventional thinking', and 'Let's make breakthroughs using ingenuity combining more wisdom'."

The breathtaking drive feel you can sense throughout your body.
I felt that my job was to find the key to achieving this

The development driver Hiroshi described his first impression of driving the first prototype car completed by the development engineers, including Kimura.
"It's light. Above all else, it's light. And if we get the set-up right, the drive-feel could be incredibly exhilarating. I want to get this vehicle finished."
Kawata was a 33-year old up-and-coming development driver dedicated to development of the Mazda3 at the time, but at the same time he completed those duties, he took on the big task of being in charge of the handling and stability of the MX-5.
"I started the development with a desire to give a more MX-5-unique feel to the suspension stroke. It's the breathtaking drive feel you can sense throughout your body the instant the vehicle starts off or the instant you turn the steering wheel. I felt that my job was to find the key to achieving this."
Kawata's job covered a lot of areas. He comprehensively reviewed all of the areas related to the drive feel, such as the body, suspension, steering system, and tires, and finalized those elements toward the one and only answer. Each of the operations was extremely important and difficult because they were directly linked to the expression of the sensation suitable to the MX-5. But, in the actual development, it is really the continuation of steady work.

For example, one day on the test course, Kawata got out of the MX-5 after driving it on the test course countless times diligently confirming the slight harshness remaining on the suspension, and then headed to the workshop and began carving the rubber bushings used in the front suspensions himself.
"I have carved bushings by hand, assembled them to prototype cars, and tested them many times. A car's behavior can be changed with the smallest amount of cutting depth and shape carved into a small rubber part which can fit on the palm of my hand. It may seem hard to believe, but creating the MX-5 can be compared to an uncompromising dedication to a small world, like the rubber carvings remaining on the palm of one's hand." The movement of the suspension in the very early stages must be smooth. And firm handling can be enjoyed even after the speed is increased. Sets of bushings with fresh gouge marks created by hand are piled in front of Kawata in a matter of moments, and gradually the MX-5 begins to reveal the true nature of its innovative body which Kimura has instilled in it.

In late 2014, the final road test was conducted to confirm the final specifications to be delivered to MX-5 fans waiting anxiously around the world. The MX-5 sped through the cold wind.
The body-in-white weight per planar projection area which Kimura refused to compromise on achieved a lightness surpassing the first generation NA while realizing dramatically high rigidity and extremely high stability, and having an attractive form.
The program manager Yamamoto sitting in the driver's seat drove around the test course countless times diligently confirming the feel of the carved bushings Kawata poured his heart into, and before long he returned to the area where the development engineers including Kawata were waiting anxiously. And after pausing to take a breath, he raised his right thumb straight up. The expression on Kawata's face warmed instantly and a smile spread across his face.
Absolutely the same reverberating sound which was created together with the deep emotion of the engineers at this instant will be delivered soon across the globe. You will no doubt understand the meaning of the words, "It's got to be an MX-5," when you get in the car yourself and open your senses to the reverberating sound of the body.