Drivers have been warned that accelerating in a leisurely way to save fuel might actually be costing them MORE at the pumps.
The majority of motorists might think that the best way to improve fuel economy is to be gentle on the accelerator and to maintain a slow and steady pace.
This week a study by Kia showed just that - with 31% of respondents saying they'd adopted tactics like ‘accelerating less often’ and ‘keeping to a lower speed’ to try and save money on fuel.
But is being hesitant with the throttle really the best way forward?
It might not be, if you examine the science.
Counterintuitively, because of the way that modern engines are less efficient in lower gears, you could be better off using a heavier right foot to get up to speed than dawdling, particularly when going from a 30mph zone to a national speed limit road or motorway.
Graham Conway, Managing Director at Select Car Leasing, comments:
“When you look at the science behind fuel economy, the data on acceleration and getting up to the speed limit is really interesting - because it runs contrary to what the vast majority of people might expect.
“And your ‘money saving’ method of driving tentatively in the face of the cost of living crisis might actually be costing you more cash.
“What the science tells us is that an internal combustion engine has the highest efficiency when it’s under ‘full load’, ie, full throttle.
“As a rough rule of thumb, taking longer to get up to speed does not use less fuel, because your engine is having to use fuel for a longer period of time than if you get up to speed with traffic in a more brisk manner.
“There also appears to be a sweet spot when it comes to acceleration. Going hell for leather off the lights with your foot to the floor won’t help fuel economy.
“But aiming for two-thirds of maximum throttle while getting up through the gears as quickly as you can is recommended by many.
“All in all, Driving like Miss Daisy may not reduce your fuel bill.”
Ultimately, you want to end up cruising in the highest gear with the lowest revs to save the most on fuel when you’re at your desired speed.
But you need to get to that point first - and many experts suggest that the sooner you get to that cruising speed, the better.
Mr Conway adds:
“The longer you sit in the poor MPG zone, the more petrol or diesel you’ll use.
“You should actually accelerate up to 60 mph in a brisk manner - and as safely as you can - but while also using the lowest revs you can.
“That means fast gear changes through the rev range so you hit that 60 mph cruising speed - and you can then back-off the throttle.”
In 2015, an Egyptian study looked at fuel consumption when a car - a mid-sized Kia hatchback with a 1.6 litre petrol engine - was driven in three different behaviours - ‘aggressive’, ‘normal’ and ‘mild’.
The experts from Cairo University, Giza, observed how ‘the fuel consumed per manoeuvres decreased as the degree of aggressiveness increased due to the fact that the vehicle time spent during acceleration was less’.
A separate study by Dutch and Swedish researchers suggested having the throttle at ‘two thirds’ to flat-out was the sweet spot for fuel consumption when accelerating - so long as you’re rowing through the gears quickly.
Speaking in 2005, Mark Dougherty, Professor and Head of Department of Computer Science International staff at Dalarna University, said:
“It's not commonly understood by people who drive. They think that the way to get the best fuel economy is to accelerate very gently, but that proves not to be the case. The best thing is to accelerate briskly and shift.
"Don't give it everything the car has, but push down when you're going to shift, using maybe two-thirds of the available power, and change through the gears relatively quickly."
And just last year, experts from two Polish universities - Opole University of Technology and Wrocław University of Science and Technology - drew similar conclusions.
The research looked at the ‘acceleration intensity on energy consumption and drive efficiency during a road test for a passenger vehicle’ - namely a Toyota C-HR with a 1.2 litre petrol engine.
The car was accelerated from 20mph to 75mph. And, again, the academics found that going easy on the accelerator was not the best way to maximise fuel efficiency.
They wrote:
“It is advantageous, in terms of energy, to accelerate the car intensively at low gear ratios to reach the assumed final speed or distance. This leads to a significant reduction in the energy consumed by the car’s powertrain.”
The same goes for automatic cars.
Select Car Leasing’s Graham Conway says:
“With automatic gearboxes, you also shouldn’t be too hesitant with your right foot. Give the car enough acceleration to change up through the gears in a short amount of time.”
When it comes to electric cars, the jury is out - for now - though it appears to be that speeding up gradually and gently is a way to protect range in a battery electric vehicle.
Potential fuel saving cost of ‘accelerated’ driving.
Imagine you have a petrol car with a stated figure of 50 mpg.
If your driving behaviour means you’re not reaching that figure, instead only averaging 45 mpg, over the course of 8,000 miles you’ll pay an estimated £1,374 in petrol (with petrol at 170p per litre)
If you change your behaviour to hit the 50 mpg target, over 8,000 miles you’ll pay just £1,237 in petrol.
That’s a potential saving of £137 a year.
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