How to Improve Fuel Efficiency

last updated 30/05/2018

The purpose of this article is to explain how you can improve your fuel efficiency and save on fuel costs. A nice by-product is that you save the environment too. There’s heaps of information already on the internet on this topic, but I thought I’d deliver it from a slightly different point of view and focus on a couple of things that in my opinion have the greatest scope to improve your fuel efficiency. I have another page on hilux fuel efficiency. That article focuses on my actual fuel use whilst touring around Australia, and its relationship with speed.

What Efficiency is Achievable?

In Australia the official fuel efficiency figures quoted for vehicles is an Australian Design Rules (ADR) calculated value and is often optimistic. Most people use more fuel than indicated – around 15% more in city cycle and 34% more in country cycle according to a study on in service fuel usage. This is not vehicle manufacturers purposely misleading you. The tests are done independently according to a well defined standard and form a good basis for comparing fuel efficiency between vehicles. The tests are not designed to predict your real world fuel usage. There are too many variables to make that possible. The ADR values are good for making relative comparisons between vehicles. Most people use more than the ADR calculated values.

In city driving conditions, you should be able to use less fuel than that indicated by ADR. City driving should also use less fuel than on highway runs. Why do people generally always use more fuel in city conditions compared to highway? Driving habits is the main answer. This will be explained below. My Hilux has a combined ADR rating of around 8.5L/100km. With a vehicle fully loaded for touring, I can get it down to around 7.9L/100km city driving. That’s with a tonne of gear in it and heaps of crap on the roof. Unloaded and milking it for all she’s worth, I’ve gotten it down to less than 7.0L/100km, and that’s with a steel bullbar, canopy, dual batteries and storage drawers. Six-point-something litres per hundred. Pretty good for a big 4WD. That’s with good traffic conditions and taking driving style to the extreme so isn’t reasonably achievable in the long term, but it does give you an idea about how much better you can do than the ADR figure if you try.

hilux average fuel consumption

Unloaded and with the engine at operating temperature, cruising at about 60km/h in top gear yields a fuel consumption of around 6 L/100km. That’s the theoretical limit of what fuel efficiency could be achieved in the hilux provided the engine was never cold and road conditions were perfect. It’s not possible to average at the theoretical limit but you can try to get as close as you can by driving correctly.

For highway driving, you may be able to achieve around equal to the ADR figures – maybe slightly more, maybe slightly less, depending mainly on cruising speed. Apart from cruising speed, driving habits are less important for highway driving. Fuel consumption is dominated by speed.

Before going into the details of improving fuel economy, let me first give you the best way to save a butt load of fuel. It’s best for the environment, it’s best for your health, it makes you live longer, it makes you happier and it’s best for your wallet. Avoid using your car. A car is a several tonne machine designed to carry several people and their stuff hundreds of kilometers. What a ridiculous tool for the job of carrying one person on short commutes. Ride your bike!

What Consumes Fuel?

In this article, we’ll assume that the energy released from burning fuel gets consumed by the following five factors and look at how to mitigate each one:

– Wind Resistance / Drag. Friction between the air and your vehicle opposes movement.

– Mechanical Friction. This is friction in the engine, friction in the drivetrain, and friction between the tyres and the road.

– Thermodynamic losses within the engine. Heat engines waste energy according to the laws of thermodynamics.

– Engine overheads. This is energy consumed by the alternator, fuel pump, oil pump, water pump, cooling fans, air-conditioner, sucking in air, pushing out exhaust etc.

– Acceleration of mass. This is the energy that increases the speed of your vehicle.

Wind Resistance / Drag

Pushing air out the way of a moving vehicle consumes energy. Wind resistance or drag is proportional to speed squared. For example, doubling speed results in a 4 times increase in drag. So at low speeds, drag is small, but as speed is increased drag escalates quickly and becomes the dominating energy consumer of your vehicle.

To minimize drag:

– Drive slowly. This can make a huge difference. At high speeds, wind resistance goes through the roof and your engine drinks fuel. Highway driving is where this can make the biggest difference as there is greater scope to reduce speed. Significant savings can be made by cruising at a slower speed. For example, my fully loaded Hilux, with all the extra stuff on the roof, consumes around 9.0L/100km at 90km/h but this increases to 14.0L/100km at 120km/h. See Hilux Fuel Efficiency article for more details.

– Minimize what you carry outside the vehicle. This might be stuff on the roof, in the tray, hanging on your bullbar or hanging out the window. Anything outside the car will contribute to additional wind resistance and therefore fuel consumption.

– If you are not concerned about safety, slipstream trucks. This is also called drafting. Big road trains are best. They leave a large low pressure region in their wake which reduces drag of the following vehicle. However it’s a very dangerous practice. Your whole field of view is obscured by the truck. You can’t see anything ahead. You could sideswipe an oncoming car or cyclist or other obstacle since you could drift outside of the truck’s wheel tracks and you can’t see what’s coming. Something could fall off the truck and slam you right in the face. You’ll probably die. Even if none of that happens you’ll be breathing in the truck’s toxic exhaust for long periods of time and probably get cancer.

– Avoid external modifications to the vehicle. Anything from bullbars to canopies to roof racks all negatively impact fuel economy.

– Keep the outside of the car clean. This contributes to a small but measurable improvement in fuel consumption (check mythbusters results on their golf ball effect episode).

– Slow down up hills. This offsets the extra fuel used to get up the hill with less wind resistance. You can then use the down hill to re-accelerate the vehicle.

Lucky Bay Beach, Cape Le Grande National Park

We got heaps of stuff on the roof of our Hilux, creating significant wind resistance and increased fuel consumption, especially at higher speed.

Mechanical Friction

Anything moving has friction losses. On your car the main friction losses are in your engine, through your drivetrain and between your tyres and the road. To reduce mechanical friction:

– Check your tyre pressures regularly, keep the pressures up, and adjust them according to load. More load means you need more pressure. Ensure your pressure is, at minimum, equal to that shown on your vehicle’s tyre placard. I always keep my tyres at a slightly higher pressure, and increase it further according to load (always ensure you stay below the maximum pressure specified on the tyre). Tyre pressure has many compromises. For more information check out the article on tyre pressure. If you’re not sure what the best pressure is for your requirements, then use the tyre placard details as a guide and check with your tyre shop.

– Get regular wheel alignments. If your wheels aren’t aligned they are fighting against each other, causing increased friction as well as increased tyre wear. Avoid hitting bumps or curbs at speed to reduce misalignment.

– Avoid chunky or aggressive looking tyres. They develop more rolling resistance. There are a few tyres specifically designed to minimize rolling resistance, but they aren’t widely available. It may be an option to pursue.

Bridgestone D694 mounted to hilux before being inspected and rotated

I’m running all terrain tyres rather than more aggressive off road tyres. All-terrain tyres offer several advantages when on bitumen, one of them being better fuel economy.

– Minimize engine RPM. Less revs mean less friction in your engine. Use the highest gear possible and drive slower. Engine rpm should never exceed the rpm where maximum torque is achieved.

– Short shift when accelerating. This means shifting to higher gears earlier, thus minimizing RPM during acceleration.

– Keep your lubricant servicing up to date and use the correct lubricants according to your manufacturer’s specification. This includes engine oil, gearbox oil, differential oil, greasing of bearings and universal joints. Some 4WD vehicles also have a separate transfer case with it’s own oil. How often should you service your car? Click here for my explanation. In my opinion, follow the manufacturer guidelines.

– Purchase vehicles with a manual transmission. Automatic transmissions have higher drivetrain losses. Quoted figures by manufacturers are usually for combined city / highway cycle so the difference between manual and automatic may not be much. But if you’re doing lots of city driving the difference grows. Low rpm at low speeds and constant slippage in the torque converter in an auto gearbox causes poorer fuel economy. Also an automatic gearbox is bad for driving style. You’re more likely to waste fuel accelerating and braking all the time in traffic rather than holding a steady speed with a manual gearbox. I’ve found I can easily beat the manufacturer’s specified fuel consumption in a manual but not so easily with an automatic.

Thermodynamic Losses

This is how efficiently an engine converts heat energy into kinetic energy and is governed by an engine’s design and the laws of thermodynamics. It’s basically fixed for a given engine. In my opinion, after market fuel savers, performance chips, gas injection, magnets and any other fuel saving device don’t work. If there existed cheap fuel saving devices that worked, they would be exploited by vehicle manufacturers. The manufacturer isn’t going to throw away fuel for nothing if it can be saved cheaply. Gas injection is a special case, where it does actually change the combustion process within the engine. It is claimed that it increases the burn rate which yields improved efficiency. I doubt it’s true. Burn rate and peak combustion pressure are timed to provide optimized energy extraction according to the engine’s design. Faster burn rate doesn’t necessarily mean more efficient. Actually sharp spikes in combustion pressure can be less efficient. Claimed efficiency gains from gas injection would likely be from the extra energy released from burning the gas. It is no different to injecting more fuel. Apart from buying a different engine, smaller engine (lower overheads), or an engine that runs at higher compression (eg diesel), you’re stuck with these few options:

– Run your motor at it’s most efficient RPM. This is at around maximum torque, when compression is at its maximum. Check your vehicle’s manual for the rpm that yields maximum torque. However it’s not that simple – this is in conflict with minimizing mechanical friction as identified in the friction section above. Most efficient RPM is a compromise between thermodynamic efficiency and friction losses. Under light loads, friction dominates and minimizing engine RPM is more effective at reducing fuel consumption. With higher loads, thermodynamic losses become more significant so it may be more efficient to operate at higher RPM closer to the maximum torque RPM. This may be the case when towing a heavy load or going up a long hill. Under these circumstances you may be better off using a lower gear. However, most of the time, minimizing RPM yields the lowest fuel consumption.

– Avoid large diameter tyres. Bigger tyres offset the overall gearing which was chosen by the manufacturer to optimise fuel efficiency.

– Ensure your air intake, ignition system and fuel delivery system are working optimally. This means checking and maintaining the air filter, air monitoring instruments, oxygen sensors, exhaust sensors, spark plugs, ignition coils, engine tuning, fuel injectors and fuel monitoring instruments.

– Buy smaller engined cars. Cars these days have oversized engines to give good performance. It means that most of the time the engines are under-utilized and are operating inefficiently, wasting fuel. Even the smallest, least powerful modern vehicles are ridiculously fast, relative to the job they need to do. There is no need for large engines.

– Avoid short trips with a cold engine. An engine’s efficiency is poor when not at operating temperature. I have no good data, but based on trials using my trip computer, short cold trips can use a massive 80% more fuel compared to longer trips at operating temperature. Combustion efficiency is low when the engine is cold. Then there’s increased losses from engine, gearbox and diff oils that are too thick. Additionally short trips involve a disproportionate amount of idle time / low speed travel. Walk or use a pushbike for very short trips. Consolidate multiple errands into a single trip. When you need to use a car put the reason on a list and wait until several items are on that list before using the vehicle.

Engine Overheads

There’s not many things you can do to reduce engine overheads that actually work. Turning off electrical loads will make so little difference it will be hardly noticeable  Perhaps keeping your engine properly serviced and lubed according to the same idea of reducing mechanical friction above will help minimize engine overheads. Otherwise:

– Avoid Idling. Park the car and get off your ass instead of using the drive through. Stop the engine if stopped in heavy traffic.

– Turn off your air-conditioning. Toughen up. Drive around in your undies and no shirt to keep cool. Take a spray bottle with you and spray yourself with water when you get hot. Open your windows. Apart from when driving above around 100km/h, it is more economical to open windows compared to running the air-conditioning. Most of the time (all of the time for city driving), opening windows is more efficient.

– Performance or low restriction air filters don’t make much difference. There isn’t much energy consumed pulling air into an engine. If there was then vehicle manufacturers would look at ways to reduce it, for example through low restriction air filters. I’ve done a test on one of my old cars completely removing the air filter. There was no noticeable difference to fuel efficiency, but it did make the engine sound louder. There is evidence that suggests manufacturer supplied paper filters are the most efficient at removing contaminants over the life of the filter. Other filters compromise filtering ability, reduce engine life, and insignificantly improve performance / fuel efficiency. Have a search on the net to see some of the studies.

– Increasing exhaust size is commonly thought to improve efficiency. Actually a larger exhaust reduces fuel efficiency because it makes the engine less efficient over the bottom half of its rpm range which is where it typically operates. Exhaust size is a compromise between flow velocity and resistance to flow. Bigger isn’t necessarily better. A smaller exhaust is more efficient under low exhaust volume (low RPM). A bigger exhaust is more efficient under high exhaust volume (higher RPM). Exhaust flow comes out in pulses as each exhaust valve opens. A smaller exhaust diameter increases flow velocity so the the gas has more inertia and the constant stop / start of exhaust flow is smoothed out. This means the engine doesn’t need to work as hard to re-accelerate the exhaust gas every time an exhaust valve opens. Also a smaller exhaust pipe means less mass of gas retained within it, again allowing the engine to work easier as it isn’t accelerating as much gas on each exhaust stroke. However a smaller pipe has a greater resistance to flow in the usual sense and will generate more back pressure at higher exhaust volumes. The manufacturer picks a size that, according to their design, is the best compromise. A smaller exhaust is better to save fuel because driving to save fuel also means minimizing rpm. Maintaining exhaust size whilst reducing resistance to flow will improve efficiency. This can be done by using low restriction catalytic converters and mufflers / silencers, however the gains are almost imperceivable and the increase in noise is significant. Vehicle manufacturers aren’t going to restrict exhaust flow unnecessarily if there is a practical and legal way to improve it without compromising emissions and noise. Completely removing the exhaust system provides the most efficient solution, but this is very noisy and illegal. See Exhaust Pipes: Is Bigger Better for more details.

Acceleration of Mass

Ok here is the silver bullet. The miracle cure. Well there’s no miracle cure, but along with driving slower to reduce drag, the tips in this section are the most effective in reducing fuel consumption. One in particular deserves to be singled out: Stop accelerating towards a situation where you will need to brake. Drive with the goal of minimizing brake usage and you will use less fuel than the ADR rating. You can save maybe around 30% in fuel costs by following the points in this section.

Driving in the city is at slower speeds compared to highway. So your wind resistance is less, your mechanical friction is less and your engine rpm is lower. Why does city driving use more fuel then? The answer is the energy consumed accelerating the vehicle after having to slow down. This really chews the juice. To minimize the energy consumed accelerating your vehicle, follow these points:

– Stop accelerating towards a situation where you will need to brake. This is tantamount to throwing money in the fire. Change your driving habits so that braking is minimized. Braking turns your hard earned cash you just spent accelerating your vehicle into waste heat. Why spend money heating your brakes and wearing out your vehicle? Anticipate conditions. Look ahead. Plan your speed. Slow down gently. Slow down under the natural rate that your vehicle slows when your foot is off the accelerator pedal. Get your foot off the accelerator pedal early enough so that you hardly have to brake. This includes when you are approaching slow moving traffic, red traffic lights, roundabouts, corners and intersections. If you are driving in stop / start traffic with repeated acceleration and braking cycles, do not stop / start. Try to pick a speed where you no longer have to stop / start. Try to judge the average speed of the stop / start traffic so that you can drive at a constant speed. Make it a challenge to try to drive all the way through the stop / start traffic without using the brakes. Stop accelerating to the rear end of vehicles and slamming on the brakes. This saves you heaps of fuel and reduces the risk of accidents, including the risk of you ramming up the rear end of those in front, and those behind you ramming your rear end. Apart from saving fuel, it also saves time. The time it takes for you to work to pay for the fuel you have unnecessarily burnt. The time it takes for you to work to pay for the unnecessary wear and tear that you’ve inflicted on the vehicle. If you drive impatiently, accelerating hard and slamming on the brakes, it’s only a matter of time until you cause an accident, either in front or behind you. In that case  changing driving habits would have saved you a huge amount of time.

– Do not drive aggressively. Avoid becoming angry or impatient. Various studies have proven that driving aggressively increases fuel consumption significantly. It’s been verified by academic institutions as well as on an episode of Mythbusters. On the episode it was found that driving stressed / agitated increased fuel consumption by a whopping 68%!

– Smooth out your speed profile. Minimise speed variability. This means trying to travel at a more consistent speed. Avoid acceleration and deceleration. Travel at the traffic’s average speed rather than constantly speeding up and slowing down with traffic.

– Avoid the fast lane. The fast lane is full of people who think a continuous cycle of speeding up and slowing down is a good idea. This makes it harder for you to smooth out your speed profile, since you’ll be influenced by the wildly erratic speeds of the vehicles ahead and behind you.

– Generally accelerate slowly and drive slowly to minimize the amount of kinetic energy you waste during any unanticipated slow downs.

– You should be annoyed every time you touch the brakes. Every time you use the brakes you should think to yourself “Dam I’m an idiot I’ve just thrown away money due to my own poor driving. I accelerated unnecessarily which caused me to unnecessarily use the brakes and waste fuel”. You drove badly. You could have anticipated the conditions better. Build an emotional case to help you remember to do a better job next time.

– Don’t carry around unnecessary weight in your car. If there’s stuff in the car that doesn’t need to be there for the trip you are undertaking, then take it out. Imagine you are riding a push bike. In that case you’d definitely jettison any unnecessary weight. Extra weight is a huge burden when pedaling under human power. However pushing your foot harder on the accelerator pedal is very easy, not much of a burden on you physically, but it is a burden to the environment and your back pocket.

– Avoid larger diameter tyres, which are not only heavier in mass but also have much higher rotational inertia. This results in an equivalent weight penalty much more than the extra weight of the tyre.

– Buy lighter cars. Cars these days are unnecessarily heavy, packed with features for the sake of pandering to fashion and trends. They are bulky and bloated with weight. Seek out lighter cars if you want to save fuel.

More Advanced Options

There’s a community of people called hypermilers who go to extreme measures to save even tiny amounts of fuel. It’s an interesting hobby where, if you want to, you can really push the limits on what can be achieved. Most of the methods are aimed at improving aerodynamics. Not only is it a great hobby, it will also make you rich. I have not personally tried any of these initiatives but some of the things hypermilers do include:

– Fix flat panels to the underbody of the car. This reduces aerodynamic drag.

– Fix flat panels over the rear wheels (called wheel skirts or fender skirts). This reduces aerodynamic drag. You can’t do the front wheels since they need to be able to steer, unless you create skirts that can swing out of the way to accommodate the turning wheels.

– Cover your wheel rims with flat panels or “moon caps”. This reduces aerodynamic drag.

– Fold in your external mirrors or remove them completely. This reduces aerodynamic drag.

– Remove the air-conditioner system completely. This reduces weight and mechanical losses from turning the pulley.

– Remove anything else that you can live without. Floor mats, sound deadening, seats, interior panels, electric window motors, whatever. This reduces weight.

– Remove the power-steering pump and replace the steering system with one designed without power assist. This reduces weight and eliminates the engine power that the power steering system uses.

– Tape up any gaps in the body of the vehicle. This includes gaps between body panels, around light fittings, etc. This reduces aerodynamic drag.

– Pulse and glide. This involves controlling the vehicle’s speed between an upper and lower limit by accelerating rapidly and then shutting off the engine. This improves thermodynamic efficiency by operating the engine at a higher load. It also reduces engine overheads since the engine is switched off for a large portion of the time. Note coasting with the engine off is illegal in most jurisdictions and can also be dangerous. Power steering will be lost and the steering will become slow and heavy. Power brakes will be lost (vacuum assist is usually still good for a couple of braking cycles with the engine off). You could accidentally lock the steering wheel and run off the road or into traffic.

– Install a kill switch and push button start so you can easily shut down and restart the engine at traffic lights. This will also help with pulse and glide by eliminating the risk of locking the steering wheel as well as reducing distraction / workload related to fiddling with the keys.

– Install a boat tail / kammback. This is a streamlined aerodynamic aid fitted to the rear of a vehicle. It reduces the low pressure system at the rear of the vehicle and significantly improves aerodynamics.

– Block out gaps in front radiator air intakes. This reduces aerodynamic drag at the cost of reducing the radiator’s cooling capability. Make the blocking panel removable so you can take it out on hot days.

– Remove the alternator. This saves weight, reduces mechanical losses and eliminates the engine power that would go into charging the battery and running electrical loads. You won’t be able to run any electrical stuff (fans, headlights, etc) and you’ll need a way to keep your battery charged. Perhaps a solar panel on the dash board (don’t put it outside, too much wind resistance). You won’t be able to drive at night.

Becoming a Fuel Miser

I take great pleasure in seeing my trip computer report record low fuel consumption. I think about the extra dollars in my pocket topping up my beer fund and allowing me to enjoy longer and more frequent camping missions. I think about the good that I’m doing for the environment, minimizing carbon emissions and reducing my consumption of finite resources. It’s also an interesting and satisfying challenge to see you low you can go.

Driving slower and avoiding the brakes are the main techniques that will save you the most fuel. You may find driving this way annoying or unpleasurable. It’s a balance between what driving style you enjoy, how much you’re prepared to pay for it, and how much fuel you want to save. For me there are other things I want to spend my money on, so I try to minimize fuel consumption as much as I can. One day I think I’ll even pursue some of the hypermiling techniques.

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See also:

Diesel vs Petrol

Exhaust Pipes: Is Bigger Better?

Emission Systems: Worth Tinkering?

Hilux Fuel Efficiency

Why No Performance Chip?

How Often Should I Service My Car?

Why a Ute? Why Toyota Hilux?

How to Catch Barramundi

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more articles by outbackjoe

35 replies »

  1. Hi joe thanks for posting such good information. I have a 2012 hilux TD3litre just wondering what your thoughts are on fuel filter changes as it common rail should I be changing it every 5000km do you think? And is it worth putting a second filter on? And which fuel station has the best diesel is it BP? Thanks mAte.

    • Hey Julian I wrote an article about vehicle servicing. Replacing fuel filter is an example I go into detail. Have a look here:

      I replace my filter on my Hilux diesel every 100,000km. Ridiculously small service intervals on the fuel filter serves no purpose. It does more damage than good. Many people like the idea of a second filter but I don’t think it’s necessary. I have never heard of fuel system issues due to particles getting through the filter. Water is what damages the fuel system and no amount of filtering will remove water. So an extra filter just adds more pressure drop and more load on your pump and may not offer any advantages. If you want extra piece of mind add a water monitoring system.

      I don’t know what the best fuel is. Every person has a different opinion. I fill up anywhere and never notice any difference. Filling up at one place will help with holding them accountable in the event of fuel contamination issue.

    • A very in depth, but i thought a bit on Diff Ratios would have been interesting
      In Europe all vehicle have such a better final drive for hwy driving.
      So many of our AU vehicles rev their guts out at 100ks…..
      I know you run into other issues doing this (more engine load) but there must be a goldilocks ratio for economy on flat Aussie roads

      • Hey ol mate i don’t think manufacturers put different final drive ratios in vehicles for the Australian market do they? I’d thought with fuel economy being so important these days all modern vehicles come out with top gear optimized for fuel efficient cruising. I don’t think I’ve seen regearing appear on hypermiling sites although I’ve not looked exhaustively. It may seem some cars rev too high but as an example when people put bigger tyres on some 4WD vehicles you’d expect improved fuel economy but actually economy gets worse and is restored when diff ratios are modified to match factory gearing with the factory tyres. Since fuel economy is improved with lower gearing it proves the source of the increase in fuel consumption is gearing and not heavier tyres or rolling resistance or whatever. High speed is high load and at high load there comes a point where dumping heaps of fuel at low rpm is not efficient.

  2. quick one regarding the larger tire diameter, they might have extra weight but they do drop the RPM slightly depend on how large the tire is which means improving fuel efficiency but compared to its weight and roll resistance I don’t know if it will be worth it. what do you think?

    • Hi Abdullah in my experience with modern vehicles, the gearing is already optimised for maximum fuel efficiency. Fuel efficiency is massively important these days. In old vehicles there may be some scope to stretch gearing through larger tyres. I don’t think so in modern vehicles.

      I know that on my model Toyota Hilux, people who install larger tyres suffer poorer fuel economy. Some people offset this by changing the diff ratios to bring the overall gearing back to stock. This restores fuel economy.

  3. Hi joe , I am just wondering I have a o8 Hilux sr5 TD , 4×4 , when I bought it the guy put A/T 31 inch by 15’s , I just bought a second Hand set of 17 ‘ rims and WAIT FOR IT 265/70/17 muddy s that came with it , second hand. Just been told they are 32’s and won’t be ideal to use .. They guy from a shop says I should get a transmission fan cooler or change the diff ratio, as the bigger Tyres will make the transmission work harder and cause possibly a transmission to blow up ! In time especially in sand ( not that I go in sand or off-road very much ! But I intend to !;) I just want the best for my Hilux , my pride and joy . Thoughts ?

    • Hey nic bigger tyres definitely put more stress on the drivetrain. I know of people who have put bigger tyres on and then regeared the diffs to bring back performance and fuel economy. Some people just leave the diffs and tolerate the effect of bigger tyres. Not sure if anyone’s transmission has blown up from bigger tyres but the extra wear will accumulate with time and could eventually cause a failure. Even with a regear the axle shafts and cv joints will still suffer from the extra torque and the increased risk of failure.

      There is no best. It depends what you are trying to achieve. If you want best fuel economy, reliability and on road performance then keep the tyres stock. If you want some extra ground clearance then go bigger. 31 inch isn’t a bad compromise. That’s what I run. Not so big that you feel it or that you need to fork out for a regear.


  4. Thanks for a great article. My fuel consumption has dropped from 10.5L/100 to 9L/100 just by reducing speed from 110km/hr to 90km/hr (my driving is all country roads). I have a diesel (+turbo) powered Ford Ranger manual 5spd and stick to 1800-2000 rpm whenever possible.

    You rightly emphasise that it is dangerous to follow trucks closely, but you have failed to say the same about ‘coasting’ with the engine off. You say it is often illegal – true – but you don’t say why it is illegal. Turn the engine off and you are in a very DANGEROUS situation. The brakes will cease to function effectively, the steering will be difficult, and you will probably engage the steering lock (!!!) and be unable to steer the car at all !

    Thanks again for a great article. It is the only one I’ve seen that raises the drag squared issue of wind resistance which is why car speed is so important when it comes to reducing fuel consumption. Having flown fast aircraft for many years I know the physics. Essentially the wind resistance is made up of profile drag, skin friction and induced drag. Cars suffer from the first two and driving slower is very effective in achieving marked reductions of those drains on fuel consumption. (Induced drag is caused by the wings producing lift causing vortex turbulence. Reducing induced drag is the reason why ‘winglets’ are now on aircraft.)

      • Hi Joe just wondering what are your thoughts on fitting an oil catch can to hilux d4d? To reduce soot build up on the Intake pipes? Ive heard egr blanking plates may solve the issue but I think it will cause more problems? Also heard of pcv filters can reduce but can’t find any suitable for hilux Cheers Julian

      • Hi Julian yeah catch can is a good thing. I’m in the market for one myself actually. Keeps the egr and intake clean. I know heaps of people who use one. I don’t like blocking egr, too many negative side effects.

  5. I learnt how to drive in old tractors that typically had no brakes in working order. Great way to learn to anticipate whats coming ahead and to slow down in time – might not have been great for the cluch when stopped on a hill though!

  6. Good article except for the incessant “save fuel by not driving” quips, like seriously dude, you either think your readers are stupid or you think you are a comedian. When people come to read an article about how to save fuel, ‘don’t drive’ is bloody slap worthy and potentially punch worthy in some country towns.

    People know that if they leave their car in the Garage, it will not use fuel and are obviously reading ‘how to save fuel’ articles in reference to when they are driving not when the car is off…I’m sure you get that…don’t be a

    • Wow there you’re a bit sensitive dude it’s just an article with some words, the world still loves you.

      Yeah you’d think it’s obvious that if you drive less you save a lot of fuel. But then people often use a 3 tonne 4WD to go fetch a couple of litres of milk and then complain about how much money they spend on fuel. I think some people don’t realise how effortlessly they could replace some short trips with walking or cycling because everyone else is using 3 tonne 4WDs to do it and it seems so normal. I think it’s a valid point to make. Fair enough if you think it’s not valid, we can still be friends.

  7. In regards to wider tyres vs narrow tyres affecting fuel economy, does contact patch discussed in you’re “Why Wide Tyres Don’t Help In Sand” have an effect or are there different things in play here?

    • Hey Klint narrow tyres don’t inherently have less rolling resistance. Actually at the same pressure, with all other things equal, a wider tyre has less rolling resistance because it deflects less. Tyres designed for efficiency are designed for super high pressure so they deflect less. The are kept narrow so they are light weight and present less wind resistance. I might tidy up the article to make it more accurate.

  8. Man, after recently buying a very popular 4WD magazine it’s so refreshing to read an article with genuine technical discussion, and not just fed general statements in order to sell the reader aftermarket sh*t. Thanks Joe!

    • Yeah the 4WD culture is a bit confused. Status and respect is awarded to the person with the most mods. It should be the other way around, more respect for people who do more with less.

  9. Very informative article! May I ask your opinion on the matter of short shifting and minimizing engine rpm. I drive a Toyota Kijang/Innova, with a 2KD engine (with turbo). I’m not trying to be a smartass, but I’ve watched a vid from youtube channel ‘engineering explained’ saying that turbocharged engines should not be lugged. What is the sweetspot of driving at lower rpms but not lugging the engine? Thank you.

    • Hey Iyzburg engineering explained is bloody good, I’ve watch many of his videos. The low speed pre-ignition and rich fuel mixture risks that are mentioned in the video I don’t think are valid in a modern engine with its sophisticated control system. And the gearing disadvantage is just a performance issue.

      In any case, lugging is low rpm at high load. Short shifting is done to save fuel. Accelerate gently. Gentle acceleration is light load. Do it only on level road. If you want to accelerate faster or if going up hill then let the engine rev higher.

      I dunno where exactly the optimal gear change would be under light load. Shift up so that in the higher gear the engine can accelerate at the rate you desire with only light throttle input. And make sure engine rpm stays high enough so the engine feels smooth and quiet. Satisfy those conditions whilst shifting up as early as possible. If you’re concerned about over-fueling do some experiments with accelerating at low rpm whilst having someone monitor the exhaust pipe. If everything in the engine is working properly you’ll probably never see any smoke but if you do see smoke under certain conditions of load / throttle input / engine rpm then try to avoid those conditions.

  10. Thanks Joe I was only minutes away from buying a 3″ stainless exhaust catch can and chip until I stumbled upon your article very informative thanks mate but I might still buy the catch can what’s you opinion on these

  11. So refreshing to read something that is
    A: intelligent
    B: well researched
    C: not combative ridiculing and basically counterproductive
    I searched ways to make my 84 4Runner more fuel efficient and all the foruomake fun of this goal and talk only about increasing power noise and overall stupidity. They add to this a slurry of insults for whomever doesn’t share the goal of acting like an absolute pindick. Thank you for your excellent work. Maybe it’s time I left America and came to live among you guys who don’t seem to suffer from such a macho complex. Plus I love to fish

    • Hi Alexis I’m afraid the 4WD culture is pretty bad in Australia too. Although probably not as bad as in USA the king of the consumer sucker.

      So much is about the car and the modifications rather than what you do with it. If you can save fuel it means you can do more with it so should be a high priority. More fishing less sitting in a cubicle at a job you hate paying for dumbass toys that sit in the garage.

  12. Howdy Joe
    Ive recently bought a 2016 hilux sr and am concerned with fuel economy as i’ve always owned smaller cars. Its pretty stock standard with a tray. Places like ARB sell ARMAX ECU’s for fuel efficiency. Whats your take on modifications like this. im concerned they may have long term negative effects on the engine.

      • Thanks for the advice. I’ve got the “average fuel consumption” down to 9.5 driving sensible although I’m only getting 660kms to 80L which would suggest the avc display is bull. I’m hesitant to add a bullbar and driving lights as I don’t want to increase the consumption any further. I’ve read some acticles saying that the fuel light on the 2016 hiluxs were a bit dodgy and people were getting another 150kms out of them but I’m not willing to risk it!

      • You gotta measure your economy based on how much fuel you pump in and distance travelled.

        Most mods worsen fuel economy. What sort of driving you doing? City? What tyres?

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