Small Cars: Petrol or Diesel?

U

ntil recently, most small car diesels (by small car, I essentially no bigger than a Fiesta sized) always felt rather compromised compared with their petrol powered brothers. This is because most cars used rather large, heavy “atmo” diesel engines. There are a great many examples of small cars in the 1980s and 1990s being fitted with large diesel engines of 1·7 litres or larger - the Peugeot 205, Ford Fiesta, Renault Clio, Seat Ibiza and Volkswagen Polo being examples. Some small cars came with smaller diesel engines, (or 1·4 or 1·5 litres in capacity) such as the Peugeot 106, Citroen Saxo, Rover Metro, Vauxhall Nova, then the Corsa. Generally speaking, these smaller capacity diesel engined cars offered greater economy, but less performance, then their larger engined cousins. But they usually had the advantage of having less weight to lug about, especially over the front wheels.

The trouble with having a big, heavy engine over the front wheels is that it can lead to the car feeling very nose heavy. The Fiesta 1·8 diesel weighs approximately 100 kg more than the equivalent petrol model: all of this weight sits over the front wheels. In some cars, this can cause handling problems (my 1990G Fiesta diesel had downright evil handling, as you’ll see here). All too often, the diesel models were given similar suspension settings to petrol models with the similar power output (usually around the 1·1 litre in capacity), with perhaps a token stiffening up front.

Also, the extra weight of the diesel engine knocked fuel economy as well as performance. These diesel cars are usually no more than ten percent more economical than their petrol powered cousins.

Study the next sized class of cars, the Escort / Focus / Astra breed, and engine sizes and car weights increase. This immediately reduces the weight penalty associated with having to lug about a heavier engine. Move up to the Mondeo class, and the diesel engines are usually around the same size as the typical petrol equivalents (more often than not, sporting a turbodiesel rather than an “atmo” diesel). This still further reduces the penalties.

As the weight penalty decreases, so the economy benefit increases.

But does anybody else remember the Daihatsu 1·0 three cylinder turbodiesel from the 1980s? They had the right idea back then!

More modern diesel engines have reduced in size and weight, improved emissions, power, torque and efficiency, and of course, are fitted into much modern cars. The PSA group’s 1·4 litre HDI (to be fitted into Ford’s Fiesta, and perhaps the Focus and 2003 Ka) and the Volkswagen / Audi group’s 1·4 three cylinder TDI unit are just two examples. These newer, smaller engines have effectively tipped the balance back into the diesel’s favour.

Elsewhere in this website you’ll find articles on a Ka TDCi or a Ka fitted with the Peugeot XUD engine.