Generally speaking, the optimum driving speed for fuel economy is 55/56mph, which is what car manufacturers typically use to quote fuel consumption figures. However, fuel economy is dependent on a number of different factors such as tyre pressure, excess weight in the boot, presence of roof racks, driving style, etc.
While reducing speed is an effective way of reducing motoring costs, motorists are advised to slow down only when it’s practical to do so, taking into consideration the type of road, the speed limit and the current driving conditions.
The RAC has come up with the following tips to help motorists improve their fuel efficiency and save money:
Fuel economy tips
- Less fuel equals more fuel - If you tend to be an urban driver, only have half a tank of fuel – less weight will help fuel economy
- Plan your route - Consider making one round trip rather than several short trips. Once the engine is warm it will operate at its most efficient whereas several cold starts will increase fuel consumption even though the total mileage could be the same - visit the RAC Route Planner to help plan your journey in a more fuel efficient way
- Make sure you maintain your vehicle – regular maintenance and servicing improves the efficiency of your vehicle. And therefore can improve your fuel consumption
- Slowest speed, highest gear – the secret to achieving a high mpg figure is driving at the lowest speed you can, in the highest possible gear. This optimum fuel economy speed will be different for every car. The Audi A6 ultra’s was 52mph in seventh gear on the flat. While there is an ideal speed, road conditions and gradients don’t often allow you to do that speed so you have to improvise and learn to adjust your driving according to the road ahead. Also, if you were to maintain one speed, either manually or by using cruise control, you would never achieve maximum fuel economy
- Maintain momentum – keeping the car moving is key to fuel economy. Obviously this depends on traffic conditions and what’s happening on the road ahead, but slowing down and having to accelerate again naturally uses more fuel
- Gentle right foot – having a light right foot and ensuring all acceleration is gentle is definitely important, but fuel-efficient driving is all about not upsetting the equilibrium of the car
- Lighten the load – don’t keep unnecessary items in your boot as they add weight to your vehicle, which affects fuel economy. On average, every 50kg will increase your fuel consumption by 2%. This is based on the percentage of extra weight relative to the vehicle's weight so it affects smaller vehicles more than larger ones
- Don’t get dragged down – don’t leave your roof bars on because they create wind resistance and cause your car to use more fuel through the ‘drag’ effect. Roof bars tend to weigh between 3kg to 5kg but the aerodynamic factor is greater. An empty roof rack affects fuel consumption by about 10%
- Keep the pressure up – make sure your tyres are inflated to the correct pressure as indicated in your owner’s manual. This will vary depending on the load you are carrying: if you have four passengers and luggage then you will need your tyres inflated to the maximum recommended pressures
- Warm engine – consider making one round trip rather than several short trips. Once the engine is warm it will operate at its most efficient, whereas several cold starts will increase fuel consumption even though the total mileage could be the same. This is why the Record Road Trip team kept going almost continuously, only stopping for 20 minutes at a time
- Lose your cool – don’t use your air conditioning unless you really have to as it uses engine power and therefore increases fuel consumption
- Don’t forget the basics – make sure you maintain your vehicle as regular maintenance and servicing improves efficiency, and can therefore improve your fuel consumption
Rebecca Jackson’s advice: “To set any kind of fuel efficiency world record you have to be looking ahead as much as possible to pre-empt oncoming hazards. This is a good general driving habit but it was absolutely crucial for us. It’s all about keeping moving and not losing momentum. Accelerating from being stopped is very costly in fuel consumption terms and so is going up any steep incline.
“We tried not to use the brakes as much by easing off the throttle to reduce speed. If you can keep moving slowly rather than stopping in traffic that’s good, but you do have to be conscious of not being a pain to other drivers by leaving too much of a gap behind the car in front.
“You need to listen to the engine to make sure you don’t use excessive revs but you need to use enough, so it’s a fine balance as you don’t want the car to be labouring too much either.”
Andrew Frankel’s advice: “If you are coming up to a roundabout you need to know whether you will be able to get through without slowing down too much by adjusting your speed very carefully before you enter.
“And, if you have a hill coming up you need to judge not just the gradient, but its likely duration too. If you can see it’s just a short rise it’s better to coast up, lose the speed and stay in gear rather than change down early. Each hill is therefore different and there is of course an element of guesswork.”