Data Sheet

#23 Choosing a tow car - Which Fuel?

#23 #23 Choosing a tow car - Which Fuel?

Diesel, petrol, hybrid engines and all electric have their advantages for towing. Benefit from free tow-matching when you join the Club.

Fuel filling station

There have been big changes in the car market over recent years. Following the 'dieselgate' scandal of 2015, in which Volkswagen was found to have cheated emissions tests in the US, diesel cars have declined in popularity. Petrol power now takes the lion's share of new car sales, and electric vehicles and plug-in hybrids are taking a growing share of the market.

Although petrol cars account for around 65 per cent of UK new car sales (2019), tow car drivers shouldn't dismiss diesel. This type of engine still has many advantages for towing, and the latest generation of diesels emit much less than older diesels.

In the longer term, both petrol and diesel fuels look set to be replaced by battery electric cars (and possibly hydrogen fuel cell vehicles), with a move to hybrids and plugging hybrids bridging the gap between the internal combustion engine and the fossil-fuel free future.

Growing numbers of hybrids are homologated for towing, and even some pure electric vehicles.

So, how do you separate anti-diesel fact from fiction? Are modern petrols just as capable of towing as their diesel counterparts? And are hybrids and electric vehicles now capable tow cars?

Which type of fuel is best for towing?

Diesel versus petrol

web_IMG_2287Although alternative technologies are gaining popularity, most tow car drivers are choosing between diesel and petrol. Here is a look at the pros and cons of each.

Diesels are almost always more fuel-efficient than the equivalent petrol car, and that can lead to big savings at the pumps. We have taken a basket of three popular cars (the BMW 5 Series Touring, the Kia Sportage, and the Skoda Karoq) and compared the fuel bills of a petrol and diesel model. Our calculations are based on the official combined figure, under the new Worldwide Harmonised Light Vehicle Test Procedure (WLTP) standard. The results of these new tests are much closer to the economy drivers are likely to achieve in real-world driving than the old NEDC (New European Driving Cycle) tests.

The diesel versions saved between £209.51 and £411.42 for a driver covering 10,000 miles per year, although this must be set against the higher cost of diesel cars: expect to pay a premium of around £1,000 to £2,000.

It will take many miles to make up for the higher price in fuel savings, but the greater your towing mileage the more you are likely to save. In 2013, The Camping and Caravanning Club compared fuel economy when towing with petrol and diesel cars, working with Practical Caravan and What Car?. The research showed that economy worsened far more for petrol cars than diesels when towing a caravan.

It is not just that diesels will cost less to run than petrols. The way the engines respond when the driver presses on the accelerator is also important. Diesels generally have more torque than petrols, and this is delivered at lower engine revolutions. This means that diesel engines respond more strongly in the middle of the rev range than petrols, and are better able to pull in a high gear when towing.

By contrast, petrol engines often have more power at the top of the rev range. This means the driver needs to hold on to a lower gear for longer when accelerating to get the best from the engine. To maintain speed on hills or overtake when towing, a driver will need to change gear more often when driving a petrol car.

Although this generalisation still holds true in most cases, there is a strong trend in petrol engine design for small capacity turbocharged units. By using turbocharging to force air into the combustion chamber these engines are more efficient and have torque characteristics that make them better suited to towing than most non-turbo petrol units.

For example, the 1.5 TSI 150PS engine in the Skoda Karoq and many other VW Group cars has 250Nm of torque. That's more than Mazda's non-turbo Skyactiv-X engine in the 3 hatchback and the CX-30 SUV, which has 224Nm.

It's not just that the turbocharged petrol has more torque, it's also delivered lower in the rev range. The Skoda's TSI puts out its maximum from 1,500-3,500rpm, whereas the Mazda engine delivers peak torque at 3,000rpm.

However, even an efficient and punchy turbocharged petrol struggles to pull as well as a turbodiesel. The equivalent diesel in the Skoda Karoq range has 340Nm of torque. That's a 36 per cent increase over the turbocharged petrol, enough to be clearly noticeable while towing.