Full disclosure: I’m a longtime Miata fan. And by longtime I mean since mid-1989, the year I obtained, through a series of fortunate connections, one of the three original Chicago auto show display cars. But this was no blatant attempt to butter up a journalist – I barely knew how to spell the word. At the time I worked for the Department of Defense and was racing SCCA showroom stock on the side.
It was destined to be a racecar. I was assured it’d be quick, but doubts surfaced when I arrived at Mazda’s dealer training center to pick it up. “Oh, it’s that cute Elan-looking thing,” I probably said. But my mind was utterly changed when I eyeballed its double-wishbone suspension and other cleverly engineered features hiding beneath its skin. In subsequent years of racing – and eventually restoring – that car, I spent uncountable hours being impressed by it.
I can safely say that the new ND Miata (2016 - present) is the best yet. It’s lighter than it has been in 20 years, and that’s some trick considering the relentless march of safety requirements and expected convenience features. This car is actually 1.3 inches shorter from nose to tail than my NA Miata, but it’s also 2.4 inches wider and rolls on a wheelbase that is 1.7 inches longer.
But it is the suspension that has always made the Miata great. This look under the skin of a 2020 Mazda MX-5 shows why the ND is the best Miata in that arena, too. The fact that this is an RF model doesn’t much matter one way or the other.
As it was the first time I laid eyes on one, things got off to a promising start as soon as I pulled a wheel off. It’s clear that this is no mere strut suspension, as we can see a coil-over shock and glimpses of aluminum.
The apparent stars of the show are the A-shaped upper wishbone (green arrow) and the L-shaped lower wishbone (white). Miatas have used this layout from Day One, but aluminum didn’t enter the picture until the NC generation.
For 2020, Bilstein monotube shocks (green) come on the Club and Grand Touring models with a manual transmission. This setup was part of the GT-S option package in 2019. The standard shocks are also monotubes, but they’re not Bilsteins and they’re tuned a bit softer.
The upper control arm (yellow) is mounted low down such that its ball joint (white) resides within the barrel of the front wheel. This low position increases the stresses within the arm and at its pivot points, but this car is not heavy enough to make that a consideration. It also avoids the cost and complexity of the tall and curvaceous knuckle that would be needed if this had a high-mount upper arm. Such a move would probably spoil the Miata’s low hoodline and low center of gravity because the shock towers would have to be further-strengthened, too.
Besides, this layout allows the entire suspension to be mounted to a compact and sturdy subframe that can be installed into the car as a unit. I love the utter simplicity and straightforwardness of this approach. It suits the Miata very well.
The front bump stop is hidden inside the bellows that protects the shock’s shaft and upper seal.
The rear lower control arm pivot (yellow) reverts to the fore-aft bolt orientation it had in the NA and NB generations. The NC Miata’s rear bolt came up from the bottom, but that orientation made it hard to accurately damp vertical suspension motions. Such a bushing orientation works with struts, but it introduces unwanted vertical movement when a coil-over bolts to a wishbone.
Either way, the extreme rearward position of the rear bushing allows it to take the edge off the longitudinal component of sharp-edge potholes and the like. Such sharp pulses come in at the ball joint (white) and get turned through 90 degrees so they press in on the rear bushing, with the forward bushing (red) acting as a pivot. The forward bushing will take up some of this, but you can see there’s not much room between its mounting flanges.
Here we can see the all-encompassing front subframe (yellow) and how it contains the mounting points for the upper and lower wishbones. In other views we’ll see how it also houses the stabilizer bar pivots and the steering rack. The engine mounts to it, too. I’ve always loved the tidiness and simplicity of this design, not to mention how easy it is to service.
Hey, we were just talking about you. Here’s the point at which the stabilizer bar (yellow) and front-mounted steering rack (green) mount to the subframe.
The MX5’s coil-over shock and stabilizer bar link attach to the lower wishbone. The spring/shock assembly looks to be about 70% out from the pivot, which means the shock will compress 0.7 inch for each inch of wheel movement. But it leans inward some, so its efficiency will be slightly less than that. How much? It’ll be the cosine of whatever that angle is from vertical when the car is on the ground. If we say that’s 25 degrees, the COS key on my calculator says 91 percent. So 0.7-to-1 becomes 0.63-to-1. The stabilizer link has a similar lean to it, so by the same token its pivot-based 0.55-to-1 motion ratio drops to 0.5-to-1.
The ND Miata has something that previous Miatae have not had: an aluminum front knuckle (yellow). They’re really serious about reducing unsprung mass. The steering connects forward of the axle centerline, which is the best way to go if you want precise steering and crisp turn-in response. It’s easy to pull off here because the MX-5 has a longitudinally-mounted inline-four engine that is pretty compact.
As usually happens, front mounted steering leads to rear-mounted brakes. But this view also shows how the knuckle has been configured to put the upper ball joint (green) right where the designers wanted it.
The MX-5’s single-piston sliding calipers may not be that impressive to look at, but I can say from experience that they stand up to hard use. They’re easy to service in the field, too.
At the rear, we can see another coil-over Bilsten shock and a pair of links. The prior NC generation had a multilink suspension, too, but early Miatas had a double wishbone setup back here.
But the last-generation’s multilink differed from this one. The forward upper link (left) angled forward, and the rear upper link (right) was much closer to straight. They’ve made the change here because the ND is a much smaller car. The space ahead was needed for pure structure.
The view from below shows this to be a five-link multilink. The angled link (green) at the bottom still points forward, and it works with the forward lateral link (white) to define the wheel’s fore-aft position and resist cornering loads. The longer rear lateral link (yellow) mainly manages wheel toe. If it doesn’t look like that just yet, stay with me.
Nothing much different in this view. I just like the convolutedness of it all. And it’s a good overall view that helps it all sink in.
The shorter lateral link (yellow) is the camber link. It mounts lower on the knuckle, so its eccentric will primarily influence camber. This also puts it in the best position to brace cornering loads (red), which pass through it to a substantial subframe cross-brace. My NA Miata was open across under the differential, and supplemental bracing was added in subsequent years. This extra beef is much-needed.
The longer lateral link (green) is a toe link because its mid-height and rearward knuckle attachment point will create more of a steering effect when its eccentric is turned. The clear difference in the length of these links will cause the front of the rear tire to tuck in slightly as the car heels over and compresses the outside suspension in a turn. This measured dose of roll understeer helps the car turn-in predictably and hold a steady line through fast sweepers.
Meanwhile, the small rear stabilizer bar link (white) connects to our toe link about halfway along its length, indicating something like a 0.5-to-1 motion ratio. It’s a small stabilizer bar that doesn’t need to generate a lot of roll stiffness to balance the chassis, so a simple link will do. The coil-over Bilstein (blue) mounts directly to the knuckle for a 1-to-1 motion ratio.
The rear knuckle is quite compact and is made of aluminum.
The rear brakes are simple-yet-effective single-piston sliding aluminum calipers and solid rotors. This car weighs barely more than a ton, so we’re not looking at undersized stuff. The back side has a cable-operated mechanism that squeezes the caliper when you set the parking brake.
The 2020 Club and Grand Touring come with a limited-slip differential. It’s not a Torsen differential as was sometimes used in past years, but is what Mazda calls a Super LSD. This diff has conical friction elements enveloping the side spider gears, with centrally-positioned springs to preload the friction surfaces.
But the key element that makes the Miata so brilliant isn’t what sort of limited slip you have, or even if you have a limited slip at all. The secret is how that differential is mounted.
The differential housing is supported by one bushing on either side, each of which bolts to the rear subframe. But two mounts doesn’t sound like enough. We need to see what else is going on.
The nose of the differential is firmly mounted with a pair of long bolts (yellow) to what is the Miata’s most distinctive and most hidden design feature. It’s what blew me away the first time I examined that old Miata.
It’s called the Powerplant Frame (PPF), and it’s a large aluminum C-channel (green) that runs the length of the car and connects the nose of the differential firmly to the transmission case itself. There is absolutely no axle windup with this setup. The nose of the differential cannot tip up, the driveshaft universal joints do not articulate. It gives the MX-5 uncommonly good on-off throttle response.
The PPF connects to the transmission case (green) with four bolts. The distance between the upper and lower pairs represents the height of the PPF’s C-channel section. This is nothing less than a structural bridge that binds the engine and transmission to the differential and gives the drivetrain, quite literally, some backbone.
Earlier I mentioned that Bilsteins can’t be paired with the automatic transmission. It has to do with the cross-bracing that spans the car body under the transmission and the PPF. The cross-bracing simply doesn’t fit with the bulkier automatic transmission. But the stiffer upgraded suspension needs the cross-bracing to work properly, so you can only get the Bilsteins with the manual transmission.
These asymmetric-tread 205/45R17 Bridgestone Potenza S001 tires are mounted on 17 x 7-inch wheels, and at 38 pounds, the combination is admirably light. It turns out the aluminum suspension bits we saw earlier were NOT some kind of engineering penance paid to offset porky tires and wheels. Instead, it’s just another sign that the Miata engineering team really does want to make the best affordable lightweight sports car it can. And that’s exactly what hooked me from the start. Well, that and the fact that it proved to be surprisingly fast on a racetrack.
Contributing writer Dan Edmunds is a veteran automotive engineer and journalist. He worked as a vehicle development engineer for Toyota and Hyundai with an emphasis on chassis tuning, and was the director of vehicle testing at Edmunds.com (no relation) for 14 years. And, as we learned today, he also worked for the Department of Defense and was racing SCCA showroom stock on the side.
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