Developing and Installing the Suspension for a Spec MX-5

If the NC MX-5 Miata stands out from its predecessors in terms of power and size, it should be remembered that it boasts some improvements in the suspension department as well. With a five-link rear suspension allowing for independent camber and toe adjustment, the NC’s suspension setup saves the user some of the frustration that comes with adjusting the NA/NB Miata.

To help compensate for its added heft, the NC also has the most room under its haunches — and this allows it to run a 235-section-width tire without rubbing. Just these two assets alone make a compelling case for the NC, but they’re not the selling point. With Penske, Eibach, and Zeta Performance aiding in the development of the Spec MX-5 racecar’s suspension setup, the NC has proven itself as one of the most capable in the Miata family. That is why, despite the size, it has what it takes to be a real contender.

To get a greater understanding of how the NC was shaped into the Spec MX-5 scalpel, we consulted Josh Smith, Technical Development Lead at Mazda Motorsports. Smith has been involved with this car since its inception in the Playboy MX-5 Cup series some years ago. After the Playboy MX-5 Cup car left the world of pro racing, it looked for avenues into club racing with some success. The NC MX-5 has competed in Touring 4 T4, Super Touring lite, NASA’s Super Touring 4 and 5, and a few others.

The Playboy MX-5 Cup car used a sophisticated Sachs shock with a reasonably wide range of adjustability, and they were also quite friendly, which made many of them attractive propositions for a predictable school car. Skip Barber bought many of them after the series disbanded.

When the spiritual successor was introduced half a decade later, Mazda Motorsports could piggyback off the work done for the Playboy car and optimize handling characteristics and outright grip, as well as make the car more approachable for the relative newcomer.

Finding The Last Iota

If the Spec MX-5 shod in Toyo RRs can lap most North American circuits 4 seconds faster than a second-generation Spec Miata on Hoosier slicks, that says something about the success they’ve had with extracting the last few drops of performance from this platform.

It’s a relatively simple arrangement, though it is somewhat more sophisticated than the suspension found on earlier generations of Miata. With the NC, they decided to include a 12-pound helper spring at each corner to prevent the main spring from getting loose in the spring seat when the suspension is unloaded due to suspension travel. Additionally, since the rear of the chassis has been rough on spring hardware due to misalignment when converted to a linear race spring, Penske developed an aluminum isolator sleeve to house the helper spring to remedy this issue.

The lower shim for the rear shocks.

The main spring rates may surprise some. Despite a little extra heft compared to the preceding generations of Miata, the Spec MX-5 suspension runs very close in spring rates. Up front, it uses 700-pound linear springs and 400-pound linear springs on the rear. The front suspension uses the OEM strut tower brace standard for cars with the 17-inch wheel option and uses the offset lower control arm bushings already offered by Mazda Motorsports to achieve the desired camber settings.

For all the additional items present with this kit, the shocks themselves were kept quite simple. The Penske single-adjustable sealed shocks give racers options without the need for an engineer typically recommended for double-adjustable shocks. This gives the ambitious driver a taste of suspension tuning in a competitive environment where they can establish a foundation for understanding more complicated suspension tuning later down the road. Best of all, this is done in a class where driving still plays a larger role in their success. In other words, they can learn how their suspension functions without their relative inexperience in this area seriously limiting their potential.

A fixed front sway bar and an adjustable rear limit the range of adjustment. This accommodates an experienced driver looking to eke the last hundredth from the setup, as well as the uninitiated, who can’t allow a lack of suspension knowledge keep them from being competitive.

Interestingly, the design of the NC’s suspension simplifies and complicates suspension tuning. “The NC has more factory adjustment than the first two generations,” Smith began. “The front design is very similar, but the rear gains a five-link arrangement with individual camber and toe rods.” This means a greater range of adjustment overall and a different approach to sorting it out. “Don’t attempt to set these cars up like you would a Spec Miata—it becomes undriveable,” warned Smith.

Clearly, the suspension was designed with Mazda’s four pillars in mind.

Zeta Performance putting the NC through an arduous shakedown on a shaker rig.

Bringing in the Right People

“We spent a lot of time on the shaker rig,” Smith chuckled. To make the chassis as predictable as possible, they teamed with Zeta Performance to put it through a grueling period of development. Using a 150 mm/second constant peak velocity sine sweep heave profile, their shaker rig sends force through four actuators, one under each tire, vertically in sync with one another. The test profile is a sine wave utilizing a constant peak velocity and a degrading displacement magnitude.

Mazda Motorsports sought to improve pitch response to maximize overall grip and drivability.

The reason for the focus on this phase of development was to help refine the pitch behavior of the car—essentially, how the front responds relative to the rear. Pitch response is defined as an imbalance in the front and rear response magnitude and phase. Too much of this results in unwanted weight transfer between the front and rear axle and inefficient use of the available grip.

The Right Amount of Adjustment

Once they were able to dial out as much imbalance as they could, they adjusted the damping based upon the pitch response—not in order to achieve a certain handling balance. When balance becomes an issue, there is some range of adjustment available.

“For instance, on very rough tracks or in the rain we may need to open all four dampers equally from the standard damping setting. Reducing the control in the system to account for limited grip at the cost of decreased roll control,” Smith elaborated.

“In other cases, we may need to open the rear dampers to tighten the balance of the car or close the rear dampers to free up the balance of the car. In these situations, we are sacrificing mechanical grip for balance—a sacrifice sometimes necessary, but one which should only be used when other options such as adjusting sway bars and ride height have been exhausted.”

Wyatt Couch’s Spec MX-5 suspension comes together in pristine fashion, thanks to help from sponsors Maas Brothers and the $20,000 scholarship from Mazda Motorsports.

Partly due to the limited range of adjustment and partly due to suspension tuning done beforehand, achieving all of this is fairly intuitive. “We did our homework before releasing these shocks to the public,” said Smith.

This means that the ideal range of adjustment has already been isolated, so a driver won’t run the risk of dialing the car out of competitive range. Simply put, each of the eight clicks on the Penske shocks makes a noticeable difference.

Another Easy Installation

Like with their cage installation, Wyatt and Dave Couch made sure to prepare as thoroughly as possible. The first order of business was inspecting the suspension for signs of fatigue. Despite the car’s mileage, the undercarriage and all the related components were in great condition. The bushings were great, the suspension arms showed no cracking, and the subframes were solid. Well, mostly.

As per Mazda’s recommendation, they replaced the hubs, rear axles, and uprights with the sturdier, drop-in items from a Mazda RX-8. Along with these upgrades, they felt it would help to replace the aging ball joint boots.

They then sent the subframes and arms off to Maas Brothers for powdercoating. Once they returned, dressed in gloss white, it all easily fell into place. However, being the first time Dave and Wyatt had worked with the five-link rear, it took them a little longer than with their other racecar, an NA-generation Spec Miata.

Different from previous generations, the NC MX-5 features a five-link rear suspension to provide separate adjustments for camber and toe.

In slid the arms, on went their Penske shocks, and then they crowned it all with four cherries on top: their red top hats. Like so many of the accent pieces in the engine bay, they powercoated these bits their signature metallic red.

“I just wanted to give a massive thanks to Penske Racing Shocks for partnering with me on this build,” Wyatt added.

The two still have to give their Spec MX-5 an alignment — something they’re not too familiar with doing when the five-link rear is involved. They have all the necessary equipment, but this father-son team only have a few weekends left to get things ready before their first race at Utah Motorsports Campus. However, if their previous performances are anything to go by, it’s fairly safe to assume they’ll get this black beauty dialed in very soon.

Image courtesy of Wyatt Couch, Joshua Smith


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