Nicholas Rufford and Andrew Frankel took two Citroëns on a real life economy drive and got a startling result: the C1 supermini with the gasoline engine got better mileage that its diesel counterpart.
They started the test “as an attempt to prove Citroën’s contention that, if driven gently in an out-of-town environment, its new diesel-powered C1 supermini would return 100mpg.” They brought along a petrol-powered C1 only to support prevailing wisdom that a diesel is more economical than a petrol-powered vehicle.
Instead, the petrol C1 “stole the show” by achieving 85.5 mpg, “putting it well ahead of rivals and, in the process, casting doubt on the wisdom of buying a diesel car at all, particularly at the budget end of the market.”
Their “real world” test:
They “filled the cars until they would take not one more drop, did a lap of the M25 in convoy, and filled them again. Why the M25? Because it is the most used road in the UK and, some claim, Europe. Better still, because it is circular you can start and finish at the same point, meaning the results are not skewed by wind or gradient.”
“We returned to Clacket Lane services, 2hr 23 min after we had left, having averaged 49mph for the 116 miles we traveled round the M25. And we were greeted by two very distinct surprises.”
“First was that the diesel C1 got nowhere near 100 mpg. In fact it swallowed 6.38 liters of diesel, giving it an overall consumption figure of 82.7 mpg, astonishingly close to the 83.1mpg claimed by Citroën on the extra-urban cycle. But our jaws didn’t really drop until we refilled the petrol-powered C1.”
“Despite having a more powerful engine (68 bhp v 55 bhp) than the diesel, we could not get more than 6.17 liters into its tank, despite spending an age adding fuel almost by the drop to make sure it really was truly full. This meant the petrol C1 had not only beaten its diesel sister, but smashed the official claim of 68.9 mpg.”
“This was, of course, just one test, conducted entirely on a motorway with the specific aim of extracting maximum economy from both cars. Even so, the test does call into question the wisdom of buying a small diesel car particularly when, in the Citroën’s case, the £8,445 C1 diesel is £1,100 more expensive than the identically specified petrol C1.”
“You’ll pay more to insure the diesel and, typically, more to put fuel in, too. Yes, it is likely that the C1 diesel will depreciate more slowly than the petrol version but it nevertheless seems hard to construct an argument in favor of the diesel — it doesn’t even emit less CO2 — particularly when you factor in how much more enjoyable (and quicker) the petrol C1 is to drive, with its fizzy 1 liter three-cylinder engine relative to the comparatively rattly 1.4 liter four-cylinder diesel.”
The authors suggested that you could expect similar results with C1 clones, i.e., the Toyota Aygo and Peugeot 107, i.e., identically economical for petrol, neither is yet available with diesel power. (All three are produced in the Czech Republic.)
Others at the top of the subcompact class for fuel economy include:
- Fiat’s diesel Panda, with 76.3 mpg on the extra-urban cycle,
- VW’s diesel Lupo / Fox (produced in Brazil) with 78.5 mpg,
With competition from an increasing number of superminis (cars with four or more seats) and minicars (two-seaters), e.g.,
- Renault Clio and Modus
- GM-Daewoo Aveo (produced in Korea)
- Daihatsu Charade
- Ford Fiesta
- Honda Jazz
- Hyundai Accent
- Kia Rio and Picanto
- Opel Corsa
- Suzuki Swift diesel with 51 mpg.
These cars are designed expressly for economy. (Compared to the 85.5 mpg that the petrol C1 achieved in this test, the much-vaunted Toyota Prius hybrid seems meager with only 67.3 mpg, which is nonetheless better and much more comfortable than many superminis.) Subcompact fuel economy comes at a cost, as the authors attest:
“Traveling at the same speed as lorries, we lost count of the number trying to bully us out of their way. And when you drive something as little as a C1 (and looking in the rear view mirror you see) your entire rear window full of a Dutch, heavy goods vehicle, you suddenly understand the meaning of intimidation.”
While the authors may have disproved one adage — diesel is (always) more economical than petrol — this test may have bore out another adage: an underpowered vehicle is less economical. And, while this test took place in London, it could be good news for U.S. car buyers since the gasoline powered Toyota Aygo is quite similar to a Scion Xa now available in the U.S.
The test results also could be reassuring to those U.S. car buyers most interested in fuel economy since diesel powered passenger cars are less available in the U.S. than in Europe.
Unfortunately, the authors lacked a Mercedes Smart Car or other fuel cell hypermini to test, even though the test along the same road by a different fuel cell vehicle are underway. It nonetheless is interesting to compare their results to another comparison between gasoline, diesel, CNG and hybrid powered Honda Civics, especially since Honda is studying whether to offer diesel-powered vehicles in the United States.