Mazda3 SKYACTIV: The Truth Behind The EPA Fuel Economy Numbers

Mazda makes fun cars. Too few car buyers care. Mazda has been losing buckets of money. What to do? Mazda is betting that a focus on fuel economy without going hybrid will reverse their fortunes without costing them a fortune. To deliver big mpg gains, and further enhance the driving experience as well, the folks in Hiroshima have creatively re-engineered conventional engines, transmissions, suspensions, and body structures, with an emphasis on light weight and improved efficiency. But talk is cheap. Do Mazda's "SKYACTIV" innovations actually deliver?

The suspension and body of the 2012 Mazda3, the first car to get SKYACTIV, haven't changed. The former remains the best aspect of the car while the latter (along with the interior, Mr. Whipple-worthy dash pad notwithstanding) remains the worst. Refrigerator-white paint and undersized wheels don't help.

The bits that have the largest impact on fuel economy—the engine and transmission—have been replaced. The old 148-horsepower, 135-pound-feet 2.0-liter four-cylinder engine managed EPA ratings of 24 miles-per-gallon city, 33 highway with a four-speed automatic transmission and 25/33 with a five-speed manual.. The new 155-horsepower, 148-pound-feet 2.0 achieves a much more competitive 28/39 with a new six-speed automatic and 27/38 with a new six-speed manual.

How did Mazda achieve these impressive gains? For starters, a much taller top gear with either transmission. Perhaps the oldest trick in the book, and one I've long wished for in my 2003 Protege5 (which struggles to top 30 mpg on the highway largely because its archaic 2.0 is spinning close to 4k).

Beyond this, the automatic transmission employs an energy-wasting torque converter (a fluid coupling) only for what these do best: smooth takeoffs. Once the car is moving the torque converter locks up and a computer-controlled multi-plate clutch manages shifts. Other automatic transmissions have either a torque converter (usually) or a multi-plate clutch (rare—only the Mercedes-Benz MCT used in some AMG models leaps to mind). Mazda's innovation: both in the same transmission. The upsides are takeoffs as smooth as those of a conventional automatic and shifts with the direct feel and efficiency of a manual transmission. The downsides, of course, are cost, complexity, and curb weight, as you have two systems instead of one. Mazda has mitigated the weight gain by making the torque converter more compact than it would be if it had to handle all shifting. The quick shifts are an achievement in themselves. Single-clutch automated transmissions have been widely considered an evolutionary dead end, as they're neither as smooth nor nearly as quick as a dual-clutch automated transmission. But, through extensive tweaking of the transmission's electronic controls and mechanical bits, Mazda has gotten its box about as close to a dual-clutch system as a single-clutch system is likely to get.

As for the power part of the powertrain, the new direct-injected engine incorporates clever combustion chamber design, sophisticated fuel injectors, and lightweight parts to reduce internal friction and permit an ultra-high 12:1 compression ratio. This compression ratio is actually down from 14:1 in other applications and locations, because a "SKYACTIV" 4-2-1 exhaust header won't fit in the Mazda3 and Americans prefer regular unleaded gas.

The pudding? Results in previous TTAC tests have been mixed. Brendan achieved 33 mpg. But Derek managed only 25 mpg in town in an automatic and 26 mpg with a healthy helping of highway miles in a manual.

What gives? Brendan drove his car as if it were a rental. Which it essentially was, only rent-free. Derek drove his pair in the Canadian winter with high rolling resistance Blizzaks. Also, his typical trip was only six miles. Engines are terribly inefficient when warming up from very cold temps. With the ambient temperature near freezing, the blue light that indicates a cold engine (in place of the absent temp gauge) stays on for about two miles. The Blizzaks likely knocked off another mpg, judging from Tire Rack tests. Then again, the trip computer likely added at least one mpg, as these devices are wont to do.

For my own tests, I had an automatic car briefly from a dealer and a manual for a week from Mazda. Driving the automatic after the engine had warmed up with a light foot, I observed a trip computer average of 34.6 in suburban driving. Pretty good. But returning on the highway with the engine spinning a leisurely 2,100 rpm at 70 mph (the posted limit), the car managed only 33.5.

I had more of an opportunity to experiment with the manual transmission car, which, like Derek's, was shod with Blzzaks. Traversing the suburbs in my normal, semi-casual style, I observed about 27.5 on the trip computer—virtually identical to my old-tech Protege5 when handicapped by winter tires. Spot on the EPA number, yet somehow disappointing.

It turns out that the SKYACTIV Mazda3 is especially sensitive to driving style. Driving with a very light foot, shifting short of 2,000 rpm, and paying extreme attention to impending red lights (so as to get off the gas as soon as possible), I managed a high of 41.0 mpg on my standard drive from home to the kids' school (with a trip computer reset after the engine had warmed up). Now this is more like it!

On the highway, though, the manual transmission car fared no better than the automatic. Speed is a big factor. First, air resistance rises at the cube of velocity. Second, engine speed increases in lock step with vehicle speed, and at a certain rpm efficiency begins to fall off dramatically. Driving at a steady 78 mpg, the trip computer reported 30.6 (again close to my nearly decade-old Protege5). Drop ten mph, and the number ticked up to 31.3. Drop down to 62, and it took a larger jump, to 33.6. Perhaps at the double nickel the promised 37 would materialize—but I just can't drive 55! The implication is clear – the EPA highway figure is only going to happen at speeds much lower than most of us drive.

The new SKYACTIV powertrain also makes the Mazda3 more fun to drive compared to the former 2.0-liter engine. Though it delivers little in the way of visceral thrills, the SKYACTIV four revs very smoothly, and pulls well at high rpm. For me the automatic succeeds mostly by never calling attention to itself. Shifts are quick and smooth in the rush to get into top gear and when downshifting readily in response to a heavy right foot. For big grins, the manual remains the way to go. Throws have the tight, precise, well-oiled but direct feel of a rifle bolt. I can't recall a better-feeling linkage in a front-wheel-drive car. Yet all is not perfect: the knob atop the shifter is far too tall, affecting both comfort and the perceived length of the shift throws. Not much of a problem—mods don't come simpler than replacing a shift knob.

Bottom line: your satisfaction with the Mazda3 SKYACTIV will depend on your driving style and expectations. Expect good looks? Eye of the beholder. Fun to drive? It'll deliver given sufficiently frequent curves and a willingness to live a grunt-free lifestyle (Texan torque junkies need not apply). Fuel efficiency? Highly dependent on driving style and conditions. Replicate the driving style and conditions of the EPA's tests, and you'll meet or exceed the EPA's numbers. Intensively employ the pedals, drive short distances in cold weather, or exceed 55 on the highway, and those numbers aren't happening.

Suburban Mazda of Farmington Hills, MI, provided the automatic-transmission car. They can be reached at 877-290-8110.

Mazda provided the manual-transmission car with insurance and a tank of gas.

Michael Karesh operates TrueDelta.com, an online provider of car reliability and real-world fuel economy information.