Energy crisis: How to maximise your fuel efficiency when driving

An energy expert says every time you put my foot on the brake, you're spending money. Photo / Quin Tauetau, RNZ

By Nik Dirga of RNZ

With the Iran war leaving supply chains choked off, pain at the pump is rising, but you still need to drive. How can you get the most out of your tank? Here are some options.

The price of 91 petrol is now heading towards $4 a litre in some parts of the country, the Government is mulling weighing in and some have begun to hoard petrol before possible shortages.

Feeling uncertain? Get used to it, for now.

“Nobody has a clue about future petrol, diesel and aviation fuel supplies and their costs,” Massey University emeritus professor in climate mitigation and sustainable energy Ralph Sims said.

There are plenty of other options – public transport, biking or walking if you can, pivoting to electric vehicles – but not everyone can easily take up those alternatives.

If you’re looking to “fuelmaxx” your efficiency, here is more of what experts suggest.

Petrol has risen to more than $3 per litre. Photo / Nick Monro, RNZ

Combine your errands

NZ Transport Agency Waka Kotahi (NZTA) estimates that short trips use 20% more fuel when your engine is cold.

So if you can manage to tie together things like school runs with the grocery shop and a run to the chemist, you can save your overall petrol consumption, AA fuel spokesman and former general manager of the Energy Efficiency and Conservation Authority Terry Collins told RNZ’s Afternoons.

“Do it all in one trip when the car’s warm – save the fuel, tick off all those little jobs, instead of making them independent trips every time.”

Steady on the acceleration, mate

Sims said that the majority of drivers can save up to 20% of fuel use with a few simple changes.

“Most people don’t understand how to drive a car efficiently,” he told RNZ recently.

“I see people accelerate to a red light and then brake heavily, and if you’re running on low tyre pressures, it consumes much more fuel.”

Collins said a lot of it boils down to how you’re driving.

“When we hop in a car, what we really want is momentum – movement. So what we do is we use the fuel to gather momentum, but I see every day people wasting that momentum by braking unnecessarily.

“They’re not anticipating the traffic in rush hour, so they’re driving up behind the next car and putting the brakes on. If they could look ahead a number of cars and see that everybody already had their brakes on, they could just drift up behind the other car very slowly and brake.

“Every time you put your foot on the brake, you have lost that momentum for the fuel that you’ve paid for. So think that every time I put my foot on the brake, I’m spending money.”

Driving efficiently can save up on fuel.

It’s worth watching your speed on highways, too – Sims said that typically a car at 110km/h uses 10% more fuel per kilometre than when travelling at 90km/h because of greater air friction.

Once upon a time, manual or stick shifts were typically more fuel-efficient than automatic transmission vehicles, but thanks to improved technology, that’s changing and modern automatics are often as good or slightly better than manuals.

The more you carry, the more you use

Carrying heavy loads will obviously slow your car down, but there are also smaller drags to be aware of.

Modern cars are carefully designed and put through wind tunnels to get the most aerodynamic shape possible, Collins said.

Even leaving roof racks on your car that you never use can add to the drag.

“The moment you put those roof racks on, you’re disturbing all that air flow.

“People think ah, they’re okay, but you’d be surprised how much that aerodynamic change affects your fuel consumption.”

New tyres or keeping your old ones properly inflated makes a difference.

Keep up your maintenance

Don’t just think about car services as a way to get your next Warrant of Fitness ticked off. Regular care for your vehicle’s systems can save you money in the long run.

“One of the things we often overlook is just the simple thing of checking your tyres,” Collins said.

Under-inflated tyres can add 10-12% to your fuel bill, he said.

“You’re just adding drag ... It’s working harder to get that momentum I was talking about earlier.”

Your tyre’s correct pressure should be listed on the vehicle label inside the door or in the handbook. It’s best to check the pressure when the tyres are cold to see how yours are looking.

A dirty air filter or fuel filter can also compromise your efficiency, while old and worn spark plugs may mean you’re not getting enough ignition.

“Just that simple servicing on a regular basis to make sure those jobs are done are [sic] going to save you in the vicinity of 10 to 20 per cent of your fuel bill,” Collins said.

Some cars have technology designed to make them more energy efficient. Photo / Nicky Park, RNZ

To A/C, or not to A/C?

This is one of the great existential questions of driving – is it better to wind down your windows or pump up the air con? Studies have had conflicting results and ultimately, it’s better to be flexible.

“While it’s more fuel efficient to have it on at 100km/h than it is to have the windows down creating drag, the air con can use around 10% more fuel,” the AA’s website states. “You may need to find that balance of comfort and economy.”

A lot may depend on how old your car is and how well-maintained the engine and air con systems are.

It’s best to mix and match if you can – windows down and air con off when you’re at town speeds and windows up and air con on if you’re on the motorway.

In general, any other unnecessary widgets on your car may also be creating a drag – such as leaving your rear window defroster on long after it’s done the job, or those heated seats when there’s no need to.

Use the technology if you’ve got it

Many newer vehicles are equipped with auto stop-start systems which automatically shut off the engine when a vehicle is in congestion or at traffic lights. As soon as you take your foot off the brake, the engine restarts without delay, Ford New Zealand said on its website.

“Your climate control fan, audio system and headlamps still work while your engine is off for your comfort,” Ford noted.

Collins said some people turn off these features on their vehicles, but it’s counterproductive if you want to save money.

“Some people find that annoying – it’s there for a reason. It’s because those cars have to meet energy efficiency standards ... So every time you turn [that feature] off, you’re actually defeating the purpose of saving fuel.”

Collins said he often commutes over a hill and said there are many tricks you can use to avoid consuming excess fuel. Gravity can help to be your brake when going up a hill and going down, other methods can help keep your foot off the accelerator – such as using those other driving modes you may often ignore on the gear shift.

“I have an automatic but I put it in sports mode, which holds it in gear longer. That acts as an engine brake, so I don’t really need to brake on a lot of the corners. I just go through them smoothly, not touching, and my fuel consumption’s on zero.”

And if you can, avoid rush hour

Sitting idling in traffic will waste significant fuel, so – if your job allows it – consider off-peak travel to avoid those long queues, or working from home certain days a week if your employer permits.

Avoiding rush hour can cut back your fuel use. Photo / Sylvie Whinray

Sims said that many of these steps are easy, but changing habits is harder.

“It’s all pretty basic and the science is well understood for cars, trucks, and buses. But to change human behaviour is always the challenge.”

He called for the Government to step up fuel conservation messaging.

Sims said the Government needs to urgently run a national education campaign (similar to what was accomplished during Covid times using all media opportunities) to inform drivers how they can save both fuel and money.