All New Mazda MX-5 - In Depth

Press Release

Weight Reduction as the Top Priority

 

Mazda’s “Gram Strategy�¾The Ultimate Weight-Saving Imperative

 

There’s a natural tendency for curb weight to rise when car manufacturers respond to market demands for more comfort, greater occupant protection, and better environmental responsibility.  Realizing that this is contrary to the JInba Ittai goal and that extra weight has a dramatically negative influence on driving, cornering, and braking performance, Mazda engineers made every gram count.  (In the English measurement system used in the US and elsewhere, one pound equals 454 grams.)  Their “gram strategy� assessed weight in the smallest possible increments.  For example, simplifying the rear-view mirror’s design trimmed 84 grams (0.19 lb).  But applying this strategy throughout every nook and cranny of the MX-5’s design proved to be a very effective means of building a very light sports car that met all of its market demands.

 

Targets were set for the total vehicle’s weight�at 1,128 kg or 2,487 lb for the base MX-5�and also for the weight of individual parts and systems.  All 16 Product Module Teams (PMTs) then set about designing the components they were responsible for with their weight targets firmly in mind.  Major opportunities for saving weight by changing the decklid from steel to aluminum and the engine block from iron to aluminum were naturally accounted for in the initial targets.  Only then, in order to close the gap between each PMT’s weight target and the weight of the components they were responsible for, was the gram strategy employed.

 

Mechanical prototypes were carefully scrutinized for every possible weight savings opportunity.  More than 100 PMT engineers also examined three-dimensional models of the upper body and interior components in search of excess weight.  Later, when completed running prototypes became available, they too were studied part-by-part, detail-by-detail for ways to trim weight one gram at a time.

 

Notebooks compiled list a total of 573 ideas representing a total of 43.589 kg (96 lb) that were considered as weight savings measures.  Of course many were rejected as unsuitable from strength, reliability, or crash-performance standpoints.  But a lot of ideas�like trimming metal flanges, eliminating excess quantities of lubricant and shortening the length of fasteners�were employed to achieve the MX-5’s ambitious weight target. 

 

Well before the gram strategy was employed as a final measure to reach the weight target, the basic unibody was designed using high-strength, low-weight materials capable of delivering the desired rigidity and the lowest practical weight.  Three fundamental weight-saving policies were:  to use thin material in large cross-section structures within the wheelbase in the interests of high rigidity; to use the minimal amount of sheet metal in overhang areas; and to incorporate as much ultra-high-strength steel in the thinnest possible gauge to meet crashworthiness goals.

 

High-strength steel comprises 46-percent of the new MX-5’s body structure by weight.  Twelve percent of the unibody is made of ultra-high-strength steel which has nearly three times the yield strength of ordinary steel.  The net savings attributable to this approach is approximately 10 kg (22 lb).  The complete body-in-white weighs 247.5 kg (546 lb) which is 1.6 kg (3.5 lb) less than the previous MX-5 in spite of major reinforcements added to improve crashworthiness and dimensional increases necessary to accommodate larger-stature occupants.

 

Use of aluminum for the hood, deck lid, power plant frame, front suspension control arms, rear hub carriers, rear brake calipers, and rear suspension spring seats trimmed additional grams.  Furthermore, the new engine’s intake manifold and cam shaft cover are molded of lightweight composite-plastic materials.  The block of the previous 1.8-liter engine was cast-iron while the new 2.0-liter engine has an aluminum block with thin cast-iron cylinder liners.  With accessories added, the net weight savings attributable to the engine alone is a substantial 19.1 kg (42.1 lb).

 

Mounting the power steering pump and the air-conditioning compressor directly to the engine block eliminated separate brackets weighing 3.2 kg (7 lb).  Using a hollow tube instead of a solid rod for the front anti-roll bar trimmed another 2.4 kg (5 lb).  Use of aluminum pipe and optimization of fixed structures in the steering system achieved another 0.6 kg weight saving.

High-strength steel has also been specified for seat backs and cushion side frames yielding a net savings of 4.8 kg (10.6 lb). 

 

The gram strategy also met success in brake and steering systems. 

 

In final form, the new MX-5 is larger, more powerful, more capable, more comfortable, and more useful.  It offers several new features and greatly improved occupant protection from collision injury.  Yet, thanks to Kansei Engineering and Mazda’s gram strategy, the MX-5’s base curb weight is only increased by approximately 10 kg (22 lb).

 

While saving weight is a top priority for achieving JInba Ittai, because a lower weight improves every aspect of performance including fuel efficiency.  Other concerns were the stiffness of the unibody structure, the height of the car’s center of gravity, 50:50 weight distribution, and the MX-5’s moment of inertia about a vertical (yaw) axis.  (A lower yaw moment of inertia quickens the vehicle’s responsiveness to the driver’s steering commands.)  Each of these parameters strongly influences the final design’s overall fun-to-drive characteristics.

 

A stiff body structure is an essential ingredient in the feeling of oneness between the car and its driver.  Thanks to shrewd analysis and the application of advanced materials, the new unibody is 22-percent stiffer in bending and 47-percent stiffer in torsion compared to the previous MX-5.

 

Moving the engine rearward by 135 mm (5.3 in) was a major step towards balancing front-to-rear weight distribution and reducing the yaw moment of inertia.  Both the battery and the fuel tank were shifted forward to new locations closer to the center of gravity.  The fuel tank was also lowered substantially.  Slanting the top of the radiator forward also helped lower the center of gravity.  The MX-5’s total yaw inertia is reduced by a significant two-percent. 

 

With two occupants on board, each axle carries approximately 50-percent of the load (50:50 weight distribution).  (Fully loaded with fuel and luggage, the rear wheels carry slightly more weight than the front wheels.  At curb weight�no driver, no luggage, full fuel tank�there is a slight weight bias in favor of the front wheels.)

 

World’s First Friction Stir Spot Welding between Steel and Aluminum

 

One example of advanced technology employed to save weight is spot friction welding used to join steel stud plates to the MX-5’s aluminum decklid panels.

 

It is normally difficult to join aluminum and steel by welding.  To overcome this problem Mazda developed new welding technology that employs a special high-speed spinning tool.  As the blade edge of the welding tool spins and comes into contact with the aluminum, the heat generated by plastic deformation of the aluminum softens the steel sheet directly beneath.  Continuously applied pressure removes the zinc plating from the surface of the steel sheet, bringing the aluminum and steel sheet into direct contact and joining them.  The zinc serves to prevent bimetallic corrosion that normally occurs at this point.  Thanks to this spot  friction welding technique, the large current used in resistance spot welding is not required, and each weld is completed in a few seconds.  Mazda engineers have applied for 20 patents to cover this innovative technology and expect to use it extensively in the future to achieve worthwhile weight savings in other vehicles.

 

Design

 

The exterior design of the new MX-5 began with the understanding that two previous models had earned a large and enthusiastic following all over the globe in large part to their appearance.  With this in mind, the most distinctive styling elements�specifically the curves and proportions evident in the side view�were retained in the new third-generation design that still celebrates the fundamental appeal of a lightweight sports car.

 

Exterior Design

 

Simple. Contemporary. Fun. Friendly. These are words that capture the essence of a successful lightweight sports car.  But achieving simple, clean elegance in a new design that will appeal to a large number of customers located around the globe is no small feat.  The MX-5 design process required over a year of dedicated effort in three studios, an endeavor that was led by Mazda’s chief designer Yasushi Nakamuta.  To inspire his team with the theme of the new third-generation car, Nakamuta provided these words of guidance, “The MX-5 has become an icon for the lightweight sports car.  As a result, the new MX-5 should convey FUN and MODERN styling while paying homage to the original (first-generation) design.  It should exemplify lightweight sports car functionality and athletic solidity.  By embodying the simple, approachable design elements in a fresh way, it will be quickly and easily identified.�

 

After visiting Mazda studios in Irvine, California, Frankfurt, Germany, and Hiroshima, Japan, and studying conceptual sketches produced by the three studios, Nakamuta combined their work in the above design concept summary.  Various pertinent details�such as the length of the wheelbase, packaging requirements, potential customer delight features, and new technologies�were then passed down to the global design team.  Working with quarter-scale clay models, a total of seven design proposals were crafted. 

 

Three of those models�one from each studio�were then selected for completion as full-scale clay models.  US designers were asked to pursue the “newness� direction with an even trendier and more revolutionary design.  Europe held true to its evolutionary path.  Hiroshima designers focused on the creation of an oval motif stressing compactness.

 

When those three full-size clay models were examined in the presence of the current MX-5 and three key competitors in a wide-open area at Mazda’s Miyoshi proving grounds, it was clear that the American design looked fresh, new, and attractive but it lacked the feeling of compactness.  In contrast, the European and Japanese proposals both embodied the desired compact roadster image.  So the selection was narrowed to two proposals for the final selection:  the very clean and compact proposal developed by the Hiroshima studio did the best job of capturing the distinctive lightweight sports car spirit of the original MX-5 with new surface expressions and a wealth of updates.

 

In a sports car, the impression of athletic muscularity comes more from the movement and expression of body contours than from its character lines.  With this in mind, designers focused on light reflections and shadows in the body shape to achieve an appearance that varies with viewing angle.

 

The first- and second-generation MX-5 exterior design is a rounded shape with a wide footprint, large-radius corners, and deep side contours.  A key change for the third generation is the elimination of the coke-bottle-shaped center section; instead, the designers employed an entirely new oval shape in which the seating area is now the widest portion of the car.  The oval shape makes for a roomier interior, and while assuring the latest in crash-safety, expresses the compact look befitting a lightweight sports car.

 

Prominently flared fender arches emphasize the width and importance of the wheel tracks while aggressively rounded nose and tail shapes express the MX-5’s leanness, athleticism, and simplicity. 

 

With respect to the second-generation MX-5, the third edition is 40 mm (1.6 in) longer, 40 mm (1.6 in) wider, and 15 mm (0.6 in) taller.  The length of the wheelbase is increased by 65 mm (2.6 in).  So the resulting basic dimensions for the third-generation MX-5 (North-America specifications) are:

·          Wheelbase:  2,330 mm (91.7 in) 

·          Overall length:  3,990 mm (157.1 in)

·          Overall width:  1,720 mm (67.7 in)

·          Height:  1,245 mm (49.1 in)

·          Track, f/r:  1,490/1,495 mm (58.7/58.9 in)

 

Major Exterior Design Elements

 

Key MX-5 side-view design details are:

·          A low, flowing shoulder line with a slight wedge shape conveys a sense of forward motion and speed.

·          Crisp surface treatments on softly rounded side surfaces create reflections and shadows that draw the eye from front to rear areas.

·          Strong fender arch lines wrapping around the wheels are a statement of Mazda design DNA.

·          Door mirrors that continue the elliptical theme established by the original MX-5.

·          Five-spoke 16-inch aluminum wheels that radiate a sense of simplicity and strength.  Ten-spoke 17-inch aluminum wheels that suggest one set of five spokes superimposed over a second set of five spokes, lending a high-quality, sporty impression.

 

The more prominent front and rear highlights are:

·          The inboard position of the head- and taillamps impart a sense of compactness.

·          The rounded grille opening is carried over with modest alteration from the original MX-5 design.

·          A shorter and more aggressively rounded hood opening line facilitates a cleaner and more dynamically contoured front bumper fascia.

·          The headlamp design is a major update from previous MX-5 configurations.  The lens cover is shorter in height but steeply slanted to sweep around the corner of the car. 

·          The taillamps combine the traditional and immediately recognizable elliptical shape from previous design generations with highly contemporary materials.

·          Seat backrest hoops add an eye-catching detail in the rear view.

 

The soft top is recontoured to provide a sportier, more classic appearance with a flatter upper surface and a longer rear contour that flows smoothly into the deck.  The lowered shape blends smoothly with surrounding body contours so well that no separate cover is needed.  The new Z-fold design creates a more impressive roof.

 

The detachable hard top has a sweeping shape that widens out to the rear windows, expressing a lighter, more modern and aggressive look.

 

Carefully tuning the MX-5’s exterior shape yielded good aerodynamic performance which enhances the feeling of pace and stability at high speeds.  Side skirts, tire-area deflectors, and the front spoiler are designed to control air flow under the body and along its sides, thereby minimizing the creation of drag-increasing vortices.

 

Eight shades of paint are offered.  Out of these there are four newcomers:  Galaxy Gray and Copper Red, which are suitable for a modern sports car image, and True Red and Marble White for the more traditional sports car look.