In early 2018, not long after Mazda Motorsports and Penske Racing Shocks developed new dampers for Spec Miata, the two companies began development of suspension for the Spec MX-5, a grassroots series designed to serve as an intermediate step between Spec Miata and MX-5 Cup. Faster, more accommodating, and just as straightforward as its predecessor, the Spec MX-5 was designed as a driving tool, first and foremost. The difference would be made by the driver, not an engineer.
Building on what it learned from Playboy MX-5 Cup cars, which raced from 2008-2015, Mazda knew that the NC-based platform should be given even more attention than its predecessor. Mazda Motorsports decided to give the car a more comprehensive overhaul from the start, mainly to avoid future problems and costly late-stage updates.
In addition to Playboy Cup, the NC also had been campaigned in Pirelli World Challenge and IMSA ST, as well as the Skip Barber school cars. So, even though these were pro-series cars, there were plenty of recently retired cars to retrofit and integrate into the new club fleet.
For that reason, they limited the amount of adjustment possible. Building on the success of the Spec Miata shock absorber updates, Mazda Motorsports picked Penske again as a technical partner.
Mazda provided a car to Penske to measure dimensions, which revealed that some of the rear suspension was binding and twisting. This inconsistency was a common criticism from drivers in the aforementioned series. How would they encourage the rear suspension to move in a way that made the cars progressive, playful and fast?
Penske began by switching from a 3” beehive spring to a 2.5” linear spring. Then, after fitting a slimmer shock inside, the company hired Andrew Carbonell, Tom Long, and Joel Miller to sort out the new suspension. The Penske staff was on-site to make adjustments and optimize the valving specifically for Spec MX-5, changes to the shocks and the bleed valves. After Penske supplied another four renditions of valving, it had a new shock ready to make the Spec MX-5 a great car.
The sheer scale of CAD drawings Mazda provided to Zeta Performance Technologies and Penske to optimize the car enabled a rapid rate of development. The two companies wanted a car that would suit drivers of all skill levels, require minimal upkeep, and remain affordable, so they did their homework up front. It was a considerable amount of labor to get the car to this stage, but Mazda knew that the customer would appreciate the effort they made.
The way the three parties interacted, and all teams’ respective engineering staff made it possible to supply the customer with a turnkey product.
Once chosen, Penske went to instrument the car, set a baseline, and determine where its shock’s shortcomings were. This required the use of a shaker rig, which helped engineers get a better picture of what was truly happening on track.
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A prior partnership between Penske and Zeta Performance Vehicle Technologies led to Mazda hiring the latter to serve as an engineering/consulting service with one vital piece of equipment: a shaker rig.
The four-post shaker rig places wheel pads under the tires and, with the aid of a hydraulic ram that pulls and pushes on the rig, it assesses most of the vertical loading in the comfort of an office. This style of rig does not assess lateral loading.
“All suspension will struggle to work at higher frequencies. We were looking for the lower frequency response, and trying to optimize in the critical handling areas,” said Aaron Lambert, GM at Penske.
There are a couple of major procedures a shaker rig will perform, and both help add detail and certainty to a picture drawn by the drivers. The rig also allows engineers to trust their data and make specific changes to the suspension without burning up consumables or spending as much time at the track.
The basic sign sweep entails running through a wide frequency sweep of a chassis, generally from one to 30 hertz. At a certain point in any harmonic range, the suspension will effectively lock solid and cease to work, thereby transferring all that load to the tire and defeating the suspension’s purpose. The shaker would help them determine if there were any unusual harmonics, as well as any chassis-to-suspension or suspension-to-suspension interference.
The other need this rig serves is the ability to view specific on-track occurrences in greater detail. This procedure, called track replay, requires a couple of days of work. On the first day, engineers instrument the car and ensure the data they’re receiving is correct. Back in the lab, they can isolate the same sort of curb strikes and oscillations they witnessed from the sidelines, repeat it as many times as necessary, and study these situations closely. Track replay also helps the team remain objective. Provided the data can be trusted, they can learn precisely what the suspension is doing without pesky driver subjectivity and elemental variation muddying their findings.
However, driver feedback still plays an important role at the end of the day. Though the data and the rig analysis help determine the peak figures of whatever variable is of interest, the driver knows that there are times to make a compromise in the name of greater overall performance. For instance, a shaker rig might help the team determine how to increase compliance in the pursuit of peak grip levels, but the roll incurred would make the car hard to drive. For reasons like that, the driver’s role cannot be underestimated, even if their subjectivity may irritate engineers from time to time.
There were several considerations they had to make. First: where is the car going to be used? There’s always a compromise between mechanical grip and platform control. Mechanical grip, the minimization of tire contact patch variation, would take precedence.
Engineers used this rig to sort out the chassis as much as possible, because they had a specific build ethos they had to adhere to. The dampers would be responsible for fine-tuning, while the big picture would be painted by status springs, geometry, sway bar settings, and cross weights, among others.
There were several considerations they had to make when trying to sort out the chassis. To determine the car’s pitch sensitivity, they analyzed how the front and rear worked in unison. What are the response frequencies at each end? If the sprung mass is bouncing wildly, will that cause too much weight transfer?
“The contact patch load variation had to be considered, too. In tuning suspension, we have to make sure we don’t strip the car of control in searching for contact patch consistency. It can’t be too soft,” said development driver Tom Long.
With a range of parameters to work within, Zeta set out to study the transfer functions. Everything relied on these functions, where engineers were looking at the response of the hub versus the response of the sprung mass, etc.
“If we can get our peak grip numbers slightly higher on the rig, fantastic, but it can’t leave the ranges established by our data,” Long said. “Driver comfort and tire life were factors that would temper the outright grip levels.”
Then, to study curb strike, they would isolate its effect on one side of the car, then at the front axle, then at both front and rear ends. They asked themselves: how would these jolts affect the car’s stability? Would it damage the car?
Since the suspension was doing its job, there was no longer undue stress placed on the hubs, and front ball joints were not nearly as fatigued as they once were. No longer wear items. They do address wear concerns with the RX-8 hub bolt-on upgrade.
Because Mazda Motorsports anticipated a wide array of drivers to take the wheel of a Spec MX-5, it was adamant about making the car approachable. Drivability took precedence over outright performance. Drivability was crucial since the car was destined for a club-level series. It also softened the learning curve a little. Mazda recognized there were a few ways to make the car a little faster, but couldn’t make that additional speed accessible to the amateur.
“It wasn’t just about avoiding driver intimidation. The car could be more responsive without being undrivable, but the car wouldn’t necessarily work as well over the long haul. For instance, the pro might run the car slightly stiffer and maintain the tire performance over the course of a race by fine-tuning their throttle inputs, but the amateur would be in over their head and likely overdrive it,” Tom Long added.
K & C Machine
The other device instrumental in developing the Spec MX-5 was the kinematic and compliance machine, which assesses the fundamental design of the suspension. The typical K & C machine moves more slowly than the shaker rig, but unlike the shaker, it studies the lateral loads through a combination of axial folding and longitudinal folding. It also reads tire deflection, and gives the team a sense of how the suspension changes throughout the full range of movement.
By moving through the suspension travel at relatively slow speeds on the K & C machine, instrumentation allows the team to understand caster, toe, camber, roll center changes, and it can give some input on certain stiffness points in the chassis.
It represented a serious challenge for Penske and Zeta, two companies that work at the higher levels and, as such, are more interested in peak performance. This car, however, was devised, at least in part, to help move young kart racers along the path toward MX-5 Cup in IMSA.
Ultimately, the Penske/Spec Miata project started an approach to refining race vehicles, which Mazda and its technical partners still use to this day. All the shaker rig/valving information and experience from the first project was then used to inform the development of the subsequent Spec MX-5 project. This information never gets lost. It is passed on with every generation.
With development of the Penske shocks for Spec Miata, the same approaches to acquiring shaker data, shock pot testing, and recorded track data were retained, as were the same capable people and the same rigorous testing protocols.
It was a case of rinse and repeat on the Spec MX-5 project, but without the constraints of later-stage development on the Spec Miata project. Even though the Spec MX-5 project wasn’t quite a blank slate, Mazda Motorsports and Zeta Performance Vehicle Technologies proved the importance of laying the right foundation, which makes it possible to put a competitive, enduring, straightforward series together, and it shows in the results.
