Driving is believing: Don’t trust manufacturers’ mileage claims

February 10th, 2011 by Philip Brasor & Masako Tsubuku

Though revenues were initially spurred by the government’s eco point system, hybrid cars are definitely the way to go for carmakers right now. Last month, sales of Honda’s Fit hybrid outpaced those for Toyota’s Prius hybrid, which had been Japan’s best-selling car since March 2009. Though consumers seem to be getting on the environmental bandwagon, the real appeal of hybrids is economical: They use less gasoline. Or, at least, that’s what we’ve been led to believe.

Tell the truth: Prius at Tokyo dealership

Actually, it’s difficult to know what to believe, according to the mobile telephone site E-Nenpi. Nenpi is the Japanese word for gasoline mileage, and people who subscribe to the site have helped the company that runs it, Iidosha, compile mileage statistics for almost every Japanese car model. Iidosha is of the opinion that the mileage figures supplied by car manufacturers in their brochures are unreliable, since they are based on tests that have no relation to real driving conditions. The Ministry of Land, Infrastructure, Transport and Tourism has apparently picked up on this skepticism and recently announced it would demand “improved” reporting on mileage testing.

Presently, the standard testing method in Japan is the “10.15 mode,” which utilizes a fixed roller in a government-run facility. Automobiles “drive” on the roller at different speeds and an average mileage figure is calculated from the results. Starting in April, however, the standard testing method will become the “JC08 mode,” which reproduces actual road driving conditions more closely. This method, however, has already been used by most automakers for several years and is usually listed in current brochures alongside the 10.15 mode figure, thus causing unnecessary confusion.

E-Nenpi doesn’t trust either test. The site asks its 500,000 subscribers throughout Japan to do their own mileage calculations based on gasoline bought and kilometers driven. Apparently, about 100,000 subscribers participate through cell phone uploads, and while there are no officials on hand to verify the results of each contributor, 100,000 is a pretty decent sampling and certainly more credible than any figures you’d get from the 10.15 mode tests. According to Toyota, the Prius gets 35.5 km per liter for the 10.15 mode test and 30.4 km per liter for the JC08 mode test. However, E-Nenpi comes up with 19.3 km per liter. That’s 45 percent less than the official 10.15 mode findings, and, apparently, that’s one of the better results. E-nenpi finds even greater discrepancies in the findings for other Japanese models.

In America, consumers always take manufacturers’ mileage claims with a grain of salt, if only because whenever companies advertise such results they are required by law to state that these results are provided “only for purposes of comparison,” meaning that you can’t take them at face value. That also seems to be the case in Japan, except, of course, that the government doesn’t require automakers to state it so clearly in ads (it is there in the fine print on the brochures). The problem is that foreign carmakers have been complaining about these discrepancies for years. Foreign models sold in Japan have to undergo the same 10.15 mode test, and for some reason the results are always lower than those for domestic cars, albeit more realistic. The Fiat 500, for instance, tests at 19.2 km per liter, whereas the E-Nenpi survey gives it 16.8 km per liter. That’s a 12 percent discrepancy. This smaller gap, in fact, seems to apply to all foreign cars. Why the difference?

The Asahi Shimbun asked the land ministry this question and the ministry’s reply was almost shocking in its candor: Domestic carmakers provide their own computer programs for their 10.15 mileage tests, and also use their own specially trained drivers for the JC08 road tests; while foreign car companies provide data of “driving conditions” in their own country for the 10.15 program and hire local drivers for the road test.

In other words, domestic carmakers know how to work the system to get better results while foreign carmakers do nothing special. Iidosha’s comment is that Japanese carmakers look upon mileage results as a marketing tool, while foreign carmakers look upon the same results as something consumers can use for comparison’s sake. As the president of Iidosha told Asahi, Japanese carmakers, like Japanese students, are good at “tests” but bad at “actual competition.”

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