The question about driving in 4 wheel drive versus 2 wheel-drive, and how it affects fuel consumption has been asked quite a few times. This article will also discuss how the gas mileage differs from a 4WD driven in 4H vs 2H and then compared to a 2WD of the same make and model. We also discuss if the fuel consumption will be negatively affected if all things were equal between a 2WD vs a 4WD and which will be more frugal at the pumps.
So does a 4 wheel drive use more gas? A 4-wheel drive will use more gas since it has more drivetrain components and weight compared to a 2WD of the same make and model. 4 wheel drives have additional components such as an extra differential, transfer case, and an extra driveshaft. These components all add to the weight, friction, and rotational mass which negatively affects fuel consumption.
So now we know the short answer to the question, which is, yes it does, let us look at HOW and WHY the drivetrain components negatively impact the consumption and why the unsprung weight of a vehicle can decrease your gas mileage. Also, we look at how friction and rotational mass affects gas mileage and performance.
Let’s dig in!
Does 4 Wheel Drive Use More Gas
So we’ve established that the gas mileage of a 4 wheel drive, when driven in 2H, will be better than when the same vehicle is driven in 4H. What happens when we engage 4H? Well, when you select 4H you are engaging additional drivetrain components to send power to the two extra wheels and differential, which is usually the front wheels. What happens?
Let’s look at them in more detail now.
4WD Drivetrain components
So with 4H engaged you will essentially be activating or engaging the following components. Remember, they are all robust, weighty components that need to withstand the torque and power being transferred through the 4 wheel drive drivetrain system. That is why these components consist of really beefy, metal parts that are quite heavy.
These components consist of the following but are not limited to:
- Transfer case
- Front driveshaft
- Front axle
- Front side-shafts
- Front wheels
When you drive in 2H mode, all of the above components are not engaged at all and simply coast along. This means there is no resistance or drivetrain friction caused by these components since they are not involved in the forward propelling of the vehicle. It is exclusively the transmission, rear wheels, rear axle, rear driveshaft, and side-shafts that are active when driving in 2H. This means the power is easily transferred to the wheels in 2H. This translates into improved consumption since the engine does not need to work that hard to rotate the components and less power is lost through the system.
Additional weight
So will a 4WD vehicle, that is driven in 2WD mode return better gas mileage than a 2WD of the same make and model? Well, if you consider all the additional components and the weight a 4×4 system adds to the vehicle’s overall mass, you are looking at extra weight in the region of roughly 350-500lbs, depending on the 4WD make, drivetrain component size, and other factors. That might not seem like a significant amount of weight, however, they all require additional torque to physically move. Combine that with the internal resistance of all of the 4wd drivetrain components, resulting in additional fuel being used.
With that being said, a production vehicle that is released in a 2WD version will return the best gas mileage compared to the exact same vehicle produced in 4WD mode.
The third option is a 4WD driven in 4-Lo. This will return the worst consumption when compared to a 2WD and even a 4WD driven in 2H. Again, assuming all other factors are equal.
So best to worst gas mileage will be in the following order:
- 2WD truck
- 4WD driven in 2H
- 4WD driven in 4H
- 4WD driven in 4Lo
Yes, 4Lo comes in last since you can easily see your gas reading almost triple when using 4Lo. When I drive in 2H I get really decent fuel consumption from my Amarok 2.0 BiTdi, returning 8.5L/100km easily urban driving. Once on the open road, it can drop to 7.5L/100. That is one of the main reasons why I opted for the Amarok, it was its excellent fuel economy, and it just made sense.
However, when I engage 4Lo when doing heavy off-roading, I can usually see the l/100km readings easily climb into the 23L/100km range. Note to self, always make sure you have sufficient fuel when going off-road.
The terrain you are driving also has effects on the rate of fuel consumption. Heavy rock crawling or technical trails in 4Lo will consume more fuel than say driving in sand or on the beach in 4H. Similar to driving in the sand which will consume 16 liters per 100 km as compared to 7.5 liters per 100 km on the highway.
Driveline loss
The power reading from the flywheel to the wheels is different due to the drivetrain components and their weight. A significant amount of power is spent due to friction to spin gears, driveshafts, and joints just to transfer that power to the drive wheels. This is called driveline loss.
AWD vs 4WD Fuel Consumption
The modern AWD’s of today mostly drive in 2H mode for improved gas mileage and only once traction is lost will the AWD system kick in and activate the rear driveshaft to send power to the rear wheels in an attempt to regain traction. They usually only propel the front wheels. This is made possible by means of either a multi-plate clutch box or an electrical motor that activates the AWD system.
You can read more about that here
Gas Mileage Difference between 2WD and 4WD
So let’s for argument’s sake, compare 2 versions of the exact same vehicle, with the one being a 4WD and the other a 2WD. Which will have a higher weight and more drivetrain components? The 4WD obviously. As we’ve learned, it will have more weight, more friction, and more moving parts to be able to transfer power to the additional two wheels, differential, and side-shafts.
However, it’s the rotating mass that affects the vehicle’s acceleration rate as well as fuel consumption. This is because it requires more power to rotate all the heavy components simultaneously which results in a slower vehicle with higher fuel consumption. The rotational mass includes all assembled components that need to rotate as well as traveling with the vehicle, such as wheels, tires, gears, side-shafts.
Then there is a thing called unsprung weight which also negatively impacts performance and gas mileage. Unsprung weight is all the weight below the suspension that the vehicle needs to move, like wheels and tires. That’s why bigger, heavier wheels impact your gas mileage negatively.
Does auto 4WD use more gas
4-wheel drive Auto or 4A as it is depicted on the dial is a very ingenious concept. Essentially, when the vehicle is placed in 4A mode, it will power only the rear wheels, similar to when you are in 2H. The difference with 4A mode is the vehicle will sense when traction is lost and immediately, within split seconds engage the front wheels to activate 4WD in an attempt to regain traction.
So you are basically getting the best of both worlds. On the one hand, you have the advantage of 2H or 2-wheel-drive which returns the best gas mileage the vehicle has to offer with the added benefit of 4-wheel-drive functionality when needed. Plus, you as the driver do not need to intervene in any way, the computerized 4WD system and all its wheel sensors will do all the thinking for you, it’s fantastic!
So does Auto-4WD use more gas? Well, that depends largely on the terrain you are driving on. If you are driving on the highway or dry pavements then you will get the same gas mileage as when you are driving in 2H. However, if you are driving on a sleek or slippery road consisting of a mixture of low and high-traction surfaces then your gas mileage will naturally decrease since the vehicle will be engaging the 4WD or 4H system more often.
It is negligible and still better than leaving your vehicle in 4H permanently, especially when driving for extended periods on high traction surfaces such as highways and tarmac roadways. This will result in drivetrain binding which you can read about here.
Conclusion
So, in conclusion, it’s pretty safe to say that a 4 wheel drive will never be as fuel-efficient as a 2 wheel drive of the same make and model with all variables aside. The sheer weight, and friction, combined with rotating mass caused by the heavy drivetrain components of a 4 wheel drive will always result in lower gas mileage over a 2WD.