How much differentiation is it possible to bake into two cars built off the same architecture and assembled on the same line? Apparently pretty darned much in the case of the MX-5/124 "Fiata" siblings, and there's even a remarkable amount of variation among the three trim series of the 124. The drivetrain is the heart of any sporting roadster, and the Fiat and Mazda four-bangers feel utterly unrelated in terms of feel, linearity, and certainly sound. The myriad elements of suspension tuning offer yet another set of knobs that FCA has turned in order to tailor the various 124 variant personalities to suit Fiat's Mediterranean brio.

The Fiat's rugged iron-block 1.4-liter MultiAir turbo engine pulls with far less linearity than Mazda's naturally aspirated, free-revving, all-aluminum 2.0-liter. The Fiat boasts a little more horsepower—164 for the Abarth and 160 for lesser 124s versus 155 in the Mazda—and a lot more peak torque—184 lb-ft versus 148. But more important than the numbers is the feeling. This older-school turbo suffers boost-lag right off the line followed by a rush up to a point where perhaps a MultiAir cam-phasing event seems to put a second knee in the curve. These discontinuities in the torque curve were joined by a few other flat spots in an Abarth automatic we sampled, begging the questions, is this test car having an off day? And if not, is tuning for that extra 4 hp worth the trouble it creates in this lumpy torque curve? On the plus side, when revved to its redline with either transmission, the engine pulls smoothly from a speed that's safely above those non-linearities in the next gear.

Read our First Test on the 2017 Fiat 214 Spider Classica right HERE.

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See all 39 photos

Fiat uses the exact same Aisin B400 six-speed automatic that Mazda fits, though the heavier Fiat gets a slightly shorter axle ratio. There's a much bigger difference between the manuals, where Fiat uses a third-gen Miata six-speed box fitted with its own unique ratios. Axle gearing also differs greatly between the Fiat and Mazda manuals to suit the very different torque characteristics of these engines (and the Fiat's added mass). Mazda's fourth-gen setup specs a fairly rare and very short 1.00:1 sixth-gear ratio backed by a tall 2.87:1 axle ratio, whereas Fiat has a slightly wider gear-ratio spread (5.17 versus 5.09) with a traditional overdrive sixth gear and a 3.45:1 axle ratio. Fiat's overall gearing is 3.3 percent shorter in first to provide stout launch feel and 1.7 percent shorter in sixth gear relative to the Mazda—a curious choice that still nets the smaller Fiat engine an extra mile per gallon in highway economy (35 to 34). The in-between gears are 2.5 to 6.7 percent taller in the Fiat, which may contribute to the Miata Club's 0.2- to 0.3-second advantage in acceleration versus the 124 Abarth from 30 to 70 mph.

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The Fiat engine adds 100 or more pounds to the front axle, which does nothing to improve steering feel or dynamic handling and probably contributes considerably to the full second of additional time it takes a 124 Classica to lap our figure-eight course relative to the Miata Club. Abarth tuning wins 0.7 second of that time back but trails the MX-5 by 0.3 second and 0.01 average g. Neither company will provide directly comparative data on spring and damping rates or anti-roll bar configurations between the Miata and 124, but we can tell you what changes differentiate the Classica/Lusso suspensions from the Abarth: front spring rates are 1 percent stiffer, rear spring rates are 14 percent stiffer, and with that change the rear anti-roll bar is softened by about 7 percent. The bushings and damping rates are essentially the same.

Miatas seem to roll a lot more in turns compared with other similarly sporting cars, and this trait has not been tuned out of the Fiat. In any trim level, the 124 also seems to heel over in turns, though the added stiffness in the rear of the Abarth does seem to reduce roll and neutralize its understeer a bit. The suspension tweaks abet its more aggressive Bridgestone Potenza RE050A rubber, sized to match the Miata Club's 205/45R17 Bridgestone Potenza S001tires, in delivering roughly the same lateral grip (0.94 versus 0.95) and 6 feet shorter stopping distance from 60 mph (104 versus 110 feet). The Classica's smaller and softer 195/50R16 Yokohama Advan Sport V105 tires probably bear most of the responsibility for its 0.85 g lateral grip and 113-foot stopping distance.

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See all 39 photos

Among the three Fiats, it's no surprise to learn that the Lusso is by far the most comfortable; its cushier seat even makes it seem like it rides smoother than the Classica despite its 17-inch wheels. It also seems more posh and comfy than any available trim level of MX-5. Clearly, if you're looking for a boulevardier roadster, this is your choice. The Classica on 16s feels like it subdivides the other two—not quite as sharp as the Abarth or as pillowy as the Lusso. As such, for many it may be the Goldilocks choice and the one that seems to most closely match the Miata's demeanor. Choose this one if you really just prefer the Fiat's styling. Folks planning to track their roadster will be best served by the harder-edged Abarth, especially if they're willing to aggressively shop the Abarth/Mopar go-fast catalogue. Any turbo engine can be tweaked to produce more power, so those who've longed for a Mazdaspeed Miata can make their wishes come true in the Fiat aftermarket.

2017 Fiat 124 Spider Abarth 2017 Fiat 124 Spider (Classica) 2016 Mazda MX-5 (Club) BASE PRICE $29,190 $25,990 $29,420 PRICE AS TESTED $34,680 $27,285 $32,820 VEHICLE LAYOUT Front-engine, RWD, 2-pass, 2-door convertible Front-engine, RWD, 2-pass, 2-door convertible Front-engine, RWD, 2-pass, 2-door convertible ENGINE 1.4L/164-hp/184-lb-ft turbo SOHC 16-valve I-4 1.4L/160-hp/184-lb-ft turbo SOHC 16-valve I-4 2.0L/155-hp/148-lb-ft DOHC 16-valve I-4 TRANSMISSION 6-speed manual 6-speed manual 6-speed manual CURB WEIGHT (F/R DIST) 2,490 lb (54/46%) 2,428 lb (54/46%) 2,313 lb (52/48%) WHEELBASE 90.9 in 90.9 in 90.9 in LENGTH x WIDTH x HEIGHT 159.6 x 68.5 x 48.5 in 159.6 x 68.5 x 48.5 in 154.1 x 68.3 x 48.8 in 0-60 MPH 6.3 sec 6.5 sec 6.0 sec QUARTER MILE 14.8 sec @ 93.5 mph 14.9 sec @ 93.2 mph 14.5 sec @ 93.9 mph BRAKING, 60-0 MPH 104 ft 113 ft 110 ft LATERAL ACCELERATION 0.94 g (avg) 0.85 g (avg) 0.95 g (avg) MT FIGURE EIGHT 25.7 sec @ 0.71 g (avg) 26.4 sec @ 0.67 g (avg) 25.4 sec @ 0.72 g (avg) EPA CITY/HWY/COMB FUEL ECON 26/35/30 mpg 26/35/30 mpg 27/34/30 mpg ENERGY CONS, CITY/HWY 130/96 kW-hrs/100 miles 130/96 kW-hrs/100 miles 125/99 kW-hrs/100 miles CO2 EMISSIONS, COMB 0.66 lb/mile 0.66 lb/mile 0.65 lb/mile

124 vs. 124 Abarth vs. Miata: How Do They Perform on the Figure-Eight Course?

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These charts illustrate how closely the 124 Abarth and MX-5 Club perform on this course, with the Classica's lines almost always lower in amplitude. The MX-5 out-brakes the Abarth coming into the first curve (the sharp downward red spike), and the opposite is true on the second one. Note that once the cars enter the steady-state cornering portion on both ends of the course, the Miata always gets a spike of longitudinal acceleration that suggests perhaps the driver braked past the ideal speed. Generally, it's the fact that the red Mazda longitudinal acceleration line spends more time above the purple Abarth line that accounts for the MX-5's 0.3-second win in this race.