2009 Toyota Corolla; photo by Greg Wilson
2008 Honda Civic; photo by Grant Yoxon
2009 Toyota Corolla (photo by Greg Wilson, top) and 2008 Honda Civic; photo by Grant Yoxon. Click image to enlarge
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By Jim Kerr

Autos’s 50-litre ChallengeTM was a real life evaluation of the fuel economy you could expect to achieve with thirteen compact cars priced at under $20,000. Each car was filled with 50 litres of regular gasoline and when the last droplets had been sucked into the engine, the cars quietly coasted to a stop. After the odometer readings were tabulated and corrected with our GPS, I was asked why I thought the Honda and Toyota cars achieved better fuel economy than the others.

First, let me explain that there were more similarities with this group of 13 cars than there were differences. All the cars were four-cylinder models. Interestingly, the top three finishers, the Corolla, Civic and Vibe all had 1.8-litre engines, so it would be correct to assume that smaller engines deliver better fuel economy. However, the Pontiac G5 had the largest engine at 2.2 litres and still finished in the top half of the group.

Curb weights were close, with the lightest car in at 1,187 kg and the heaviest at 1,390 kg. Moving additional weight uses more fuel and it might have had more of an impact if we had included more stop and go city traffic but the Vibe at number three was the heaviest and the Civic at number two was the lightest, so curb weight doesn’t necessarily mean that much on the highway as long as they are close.

The Focus, Civic, Mazda3, and Lancer were equipped with manual transmissions. You might think a five-speed manual gearbox would give an advantage, but the final axle ratio on manual transmission equipped vehicles is often steeper to allow drivers to start out smoother. This causes the engine to rev faster on the highway and use more fuel. Unless the gearing is the same, an automatic might actually give better fuel economy on the highway.

Of the automatic transmissions, six were four-speed models, two were CVT’s (continuously variable transmissions), and the VW Golf had a six-speed automatic. More gears typically give better fuel economy, but in the Golf’s case, the engine had only two valves per cylinder instead of the four valve heads found in most others. The Golf also felt more spirited, so I suspect the fuel programming in the computer was designed as much for driving performance as it was for economy.

That brings me to the real answers to fuel economy. Rolling resistance, including wind drag, driving style and vehicle fuel injection programming are likely the biggest factors in variances in fuel economy. We switched drivers often to reduce this as a factor, but it only takes a few quicker accelerations to make a significant difference. The winning Corolla achieved only about 0.3 litres/100 km better fuel economy than the Civic, and drivers could easily make this difference.

Vehicle drag from outside influences should have been equal. However, you can’t tell by simply looking at a vehicle whether it will slip through the air easily. Engineering expertise and attention to details are what make the difference here. As consumers, we can only go by the manufacturer’s reputation on previous vehicles, what we like and the reports of other drivers.

Finally, the program in the engine computer can be tailored for fuel economy, performance, or sometimes both, but never at the same time. The Corolla seemed to have a mild, conservative manner to it that I am sure was the biggest reason it topped the group. The Civic was a little more spirited. That additional fun does use more fuel, which would also explain why some other cars such as the Mazda3, VW Golf and Dodge Caliber used more fuel.

Looking for economy? Any of these cars would be a fine choice but the expertise of Toyota and Honda has still put them at the top of the economy chain.

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