Back in the mists of time, I judged a car only by its racetrack performance and its ability to get me a date – acceleration and speed were at the top of my list. But in the past few years I've been on a different automotive quest, hunting for the car that can carry me the furthest on a single litre of fuel.
Yes, I've turned into a hyper-miler – one of those economy nerds who obsess over the fuel-flow meter instead of the speedometer. Efficiency testing may lack the rush of lapping a racetrack, but it has its own rewards – I have spent countless happy hours exploring the mysteries of hybrid drive systems, theorizing about stoichiometric efficiency (geeky, yes) and trying to hit the 100-mpg mark (the everyday driver's equivalent of the four-minute mile).
Now it's time to have a look at my findings. There are five main categories of powerplant available on the car market today – gasoline, diesel, hybrid, plug-in hybrid, and pure electric. I've driven them all for extended periods, and have come to some conclusions about what works, what doesn't, and what the average consumer should buy.
First – a pure electric vehicle is the most fuel-efficient choice of all. Does that mean you should buy one? No. A conventional gasoline-powered vehicle is the least-efficient of the five choices. Does that mean you shouldn't buy one? Not necessarily.
Here's a breakdown of my results with each type of powerplant, and the pros and cons of each. Before we get started, bear in mind that true efficiency starts with choosing the smallest, lightest, most aerodynamic car that will do the job for you. For some drivers, that may mean a giant SUV. For others, it means a fuel-sipping subcompact – our missions vary.
My testing of pure electric vehicles quickly showed me that these are the most fuel-efficient vehicles on the road today. (With BMW's subcompact Mini-E prototype, I easily got the equivalent of more than 125 mpg without altering my driving style.) This is due to the inherent efficiency of electric drive systems. According to the U.S. Department of Energy, electric vehicles convert up to 62 per cent of the energy loaded into them off the grid into actual power at the wheels. This is about three times as efficient as a gasoline-powered car, which wastes up to 83 per cent of the energy contained in its gasoline (among other things, the energy is lost to the friction of moving engine components, and in the form of heat that goes out the tailpipe). But the electric car's efficiency comes with some deal-breaker limitations, which include high cost and reduced space (a battery is many times larger than a gas tank).
But the real killer is range limit: even the most capable electric cars can only go about 400 kilometres on a charge. And when you run out of fuel (electricity, in this case) you need to find a place to plug in (if you can) and a good book (a full charge may take many hours). Although I enjoyed my time in electric cars, I would not choose one as a primary vehicle, and I cannot recommend the pure electric, except to a small subset of consumers. Infrastructure improvements (read "charging stations on every corner") and improved power storage systems (like lightweight ultra capacitors that can be charged in minutes) have the potential to render the battery obsolete and make the electric car an excellent mainstream choice. But they're not here yet – so the most efficient car on the market remains a bit player.
With the exception of pure electrics, these are the most fuel-efficient vehicles you can buy. To understand why, let's look at the Toyota Prius, a car that is virtually synonymous with the hybrid genre. On a series of extended tests with the mid-size Prius, I was able to do better than 55 mpg (5.5 litres/100 km) on the highway without trying hard – and when I worked at it, I could achieve more than 65 mpg (4.3 litres/100 km). There are two key factors behind this efficiency – an extremely well-engineered powertrain and excellent aerodynamics (that ant-eater shape gives the Prius extremely low drag).
Like other hybrids, the Prius uses a sophisticated system to store, deliver and recapture energy. The gas you put in the tank powers a gasoline engine that works in tandem with a large electric motor. The brakes act as generators, recapturing energy and pouring it back into a large battery located in the tail. It all works seamlessly and brilliantly, taking you down the road on minimal fuel. I have tested a long list of hybrids, including subcompacts, luxury sedans and SUVs. All were markedly more efficient than their non-hybrid counterparts. Unlike pure electrics, hybrids have no range limitations, and they use gasoline – the most readily available fuel in the world. The hybrid's downsides include higher initial cost, reduced towing capacity, and a slight reduction in luggage space due to the large storage battery. But if you want a super-efficient vehicle that will let you go where you want, when you want, this is it.
Plug-In Hybrid (PHV)
This is a variation on the standard hybrid, with an enlarged battery that you can charge at night. This lets you drive using the battery alone – but when the battery is drained, a gas engine kicks in, giving you unlimited range. I have tested two cars that feature this technology: the Chevrolet Volt and the Toyota Prius PHV. Both are excellent, but each is optimized for a different mission. The Volt has an extremely large battery, and will go up to 80 km before the gas engine kicks in. The Prius PHV will only go about 25 km on battery alone. Both cars achieved spectacular mileage. (The calculations get complicated, but I did better than 100 mpg in both after gas and electricity used were factored in.)
Of the two, I considered the Prius the better engineering compromise – the 25-km battery range let me run urban errands for weeks on end without using any gas and, when I went beyond battery range, the PHV was almost as efficient as a regular Prius, with highway mileage in the 4.5 litres/100 km range. The Volt was spectacularly efficient while running on its battery, but not once the gas engine kicked in – the massive battery needed for that long electric range turns into dead weight once it's depleted. For all-round performance, the Toyota PHV was the winner, but the Volt is not a bad choice. The downsides of the PHV include high initial cost and reduced luggage space thanks to those big batteries. I would recommend a plug-in hybrid to anyone who lives in an urban environment.
I am a fan of diesel engines – I like their low, rumbling sound, their Clydesdale-like torque and their longevity. Then there's the built-in efficiency – a litre of diesel fuel contains more energy than a litre of gasoline, and a diesel burns its fuel more efficiently than a gas engine thanks to its higher compression ratio and combustion temperatures.
I achieved more than 50 mpg in the VW Golf TDI – this is a car beloved by hyper-miling fuel economy buffs, and I soon understood their passion. Thanks to its small size and aerodynamics, the Golf is a relatively efficient car with any engine, but the diesel put it over the top. The BMW X5 diesel SUV also demonstrated the fuel-efficiency of this powerplant choice – on a trip to the deep south, my wife and I did more than 27 mpg (10.4 litres/100 km). That may not sound particularly impressive until you consider that this is a large vehicle, and that our load included a 400-pound garage compressor. The diesel isn't the absolute efficiency champion, but it's up there. Should you buy a diesel vehicle? Yes – at least if you can. (In the North American market, the choice of diesel vehicles is limited.) Other caveats include higher initial cost and fuel availability issues – diesel fuel can be harder to find than gasoline. (Note that many GPS systems will find diesel stations for you.)
Gasoline Internal Combustion (IC)
Although it's the least efficient of the five powertrain options, the four-stroke, gas-powered engine is is still the optimum choice for many drivers. Although it lacks the technical chic of the hybrid or the electric, the IC gas engine gets the job done: driving carefully, I have routinely hit more than 50 mpg (5.6 litres/100 km) in gasoline-powered cars like the Toyota Yaris and Honda Fit, and have done better than 60 mph (4.7 litres/100 km). (As always, efficiency depends on more than just the power plant – aerodynamics, weight and driving style will determine how far a given engine will carry you on a litre of fuel.) The gasoline engine still has some major attractions, including low cost and fuel availability (you can buy gasoline anywhere).
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