Is Driving In 4 Wheel Drive On Highway Safe?
You probably know that a vehicle can offer different modes or drivetrains for different driving conditions: 4WD, 2WD, AWD, FWD and RWD. However, you might be wondering how they differ, when to use what, or what happens if you accidentally switch from 2WD to 4WD on the highway. Is driving in 4 wheel drive on highway safe?
While the general short answer is four wheel drive is not recommended on flat, smooth, dry roads, it is much more nuanced, as 4WD alone have different settings.
To really answer this question, as well as the bigger issue of when to use and when not to use 4WD, we need to have a basic understanding of how 4WD works differently from the other AWD, FWD and RWD modes.
This article will cover the basics of a vehicle’s drivetrains, or engine and transmission layouts, so you will know in which driving conditions to engage them. It will cover in depth the different 4WD settings, when driving in 4 wheel drive on highway is relatively safe, how to use and maintain a 4WD system so that it will last long, plus bonus 4WD driving tips.
Different Engine and Transmission Layouts
In case you have come across these common car terms “4WD”, “AWD”, “FWD” and “RWD” but wonder what they really refer to, these are abbreviations for four-, all-, front- and rear-wheel drive. They are different types of engine and transmission layouts, or a vehicle’s drivetrain.
Each system has its own advantages and disadvantages, thus is used in certain driving situations to ensure safety and ease in controlling the vehicle. For instance, these systems will greatly affect how much fuel the car burns, or how the car performs on tough, uneven tracks.
4WD – Four-Wheel Drive
Four-wheel drive and all-wheel drive are common features of modern crossovers and SUVs. These two car terms are incorrectly used interchangeably. In fact, they are considerably different, except for the general similarity is that all four wheels receive power from the engine.
Four-wheel drive is popular in trucks and SUVs such as Jeep Wrangler and the Toyota Land Cruiser, the heavy-duty vehicles meant for wilderness exploration on tough, bumpy or low-traction tracks.
Most 4WD systems are part-time systems that can be used when required and then disabled, putting the vehicle in two-wheel drive.
In a 4WD system, each wheel will spin at the same constant rate as all the others. This will better ensure the car’s stability and traction on slippery, tough and uneven ground when driving off-the-beaten-path.
In contrast, using 4WD on regular roads is not ideal. For instance, when the 4WD car does a u-turn, the outside wheels have more ground to cover thus have to turn faster than the inside wheel, making the car hop or creating a rubbing noise when you approach full lock.
When to use 4WD:
- If the terrain is wet or slick.
- When hauling or towing uphill or downhill.
- In rainy or snowy conditions.
When not to use 4WD:
Traveling in 4WD on flat, smooth, dry roads is not recommended, as it will damage your drivetrain. Also, remember that four-wheel drive provides more torque and engages all the tires for movement, thus it doesn’t help you stop. Always travel at speeds that allow you to stop safely.
While technically driving in 4 wheel drive on highway is possible, it is only relatively safe in certain conditions. Read on to find out.
Important note: Handling
4WD doesn’t help you brake better or give you more stability in turns while braking. So slow down when you’re turning and brake sooner.
Note that while you can use 4WD in rainy or snowy conditions, 4WD doesn’t improve handling on slick ice- and snow-covered roads. If you drive faster than conditions allow, you’re far more likely to flip and roll because of your higher center of gravity.
Important note: Gas mileage
When you’re in 4WD, you’re engaging a lot more extra gears and driveshafts and keeping them spinning to create enough horsepower to rotate four wheels, not just two. This eats up more fuel than 2WD, which lowers your gas mileage. If you don’t need 4WD, turn it off and save some dough at the gas pump.
In addition, this also means you’re putting excess pressure on your 4WD drivetrain, differential case, and gears. Fixing all those parts would be very expensive so ideally, you want to avoid engaging the 4WD mode unless road and driving conditions really require.
Different Settings for 4WD
1. Four-High (4H)
In high-range 4WD, you can travel at all normal speeds. Simply put, 4H is used for driving at normal speeds when you need extra traction.
Engage this setting when you’re on the highway and wet, snowy, icy roads. It’s also good for level, loose-gravel roads, packed sand or mud.
2. Four-Low (4L)
The low-range 4WD setting is for the serious stuff: deep sand, snow, mud, crossing water, climbing rocks and ascending/descending hills.
When you use four-low, keep your speeds low, under 40 mph or so, as you’re not actually gripping the road any better but you’re applying more torque to that grip. Designed for maximum traction and maximum power, the wheels will turn more slowly in 4L than 4H.
3. Automatic Four-Wheel Drive
Use this setting when roads are variable, such as patchy snow and ice or any other combination of conditions when a tire could slip suddenly. In this convenient setting, the vehicle monitors tire traction while in two-wheel drive and automatically shifts into four-wheel drive when one of them begins to slip.
When shifting from two-wheel drive to automatic four-wheel drive or four-high, you can do so while continuing to travel at normal speeds. When shifting into and out of four-wheel-drive low, however, it is best practice to come to a stop and wait for the indicator light to stop flashing.
When to use 4H and 4L
Knowing when to use 4H or 4L is what causes the most confusion for 4WD vehicle owners, so here are some rules.
When to Use 4L:
- When you need more torque (power) for heavy pulling at slow speeds.
- When you’re climbing steep grades at slow speeds and need extra power.
- When you’re descending steep hills with a heavy load-the low gearing provides engine braking assistance.
- Don’t use 4LO to get unstuck in mud and snow. The extra torque will cause the tires to spin.
When to Use 4H:
- When you’re on slippery surfaces and driving at street or highway speeds.
- When you’re stuck in snow, mud or ice.
Now let’s look at how 4WD differs from the other modes.
AWD – All-Wheel-Drive
While 4WD is a part-time system which can be disabled, AWD is a full-time system that is “on” all the time. AWD is born much later than 4WD, is completely automated and commonly used in crossovers.
While in 4WD, each wheel receives equal power from the engine to maximize road traction, an AWD system either mechanically or electronically varies the amount of power sent to each wheel.
It can be found from the expensive Audi R8 and Mercedes-AMG E63 to the budget-friendly Subaru. It’s more complicated, but considerably more user-friendly.
Subaru’s ad campaign sums up the advantage of the AWD very well: “transfers power from the wheels that slip to the wheels that grip.” When there is a loss of traction, power from the engine is transferred away from the slipping wheels to the other wheels, helping the car quickly regain traction, thereby improving fuel economy.
FWD – Front-Wheel Drive
While 4WD and AWD have been gaining popularity more recently, most cars on the roads typically have front-wheel drive, that is the engine’s power is transferred to the two front wheels only.
Front-wheel drive is a simpler system than all-wheel drive, thus it’s more user-friendly and less expensive. You’ll need to spend a few thousands dollars more to equip your car with the AWD. Most cars have FWD, which means this system works just fine.
Since all the mechanics is located in the front of the car, a FWD car will be designed to offer more room for both front-seat and back-seat passengers. Plus there’s no transmission tunnels in the floor of the rear seats required for the AWD, which means considerably more leg room.
The second advantage of a FWD car is better traction when climbing uphill, since the power is all in the front wheels. However, this also means lower traction compared to the AFW system in normal driving situations: if one of the two front wheels loses traction and slip, there is only one wheel left to find some grip.
FWD works just fine for dry driving conditions. With the introduction of modern traction control technology and the Anti-lock Braking System (read on to find out about “ABS”), FWD is performing better and better to work well in wet conditions and even light snow.
RWD – Rear-Wheel-Drive
In short, rear-wheel drive is front-wheel drive in reverse. When you press on the gas pedal in a RWD vehicle, power is sent to the rear wheels, thus maximizing the car’s performance in acceleration. That is, the rear wheels provide force to move the car, while the front wheels decide its direction.
Even with modern technology that provide for better traction control, a RWD car is not as reliable in wet, slippery conditions compared to AWD.
SH-AWD – Super-Handling All-Wheel-Drive
This more recent system is SH-AWD developed by Honda and used in many Acura models including the TL, MDX and NSX. It is a full-time all–wheel drive system designed to achieve optimum traction and handling.
The SH-AWD does this by using an electronically controlled clutch mechanism for the rear wheels. This mechanism can distribute extra power to the outside wheels, which have more ground to cover, when the car turns. When the inside wheels loses traction, it will distribute more power to the outside wheels so they will gain more grip.
This means better traction, more stability and higher speed when cornering. This feature makes SH-AWD more ideal then the conventional AWD system in performance-oriented driving.
How To Engage Your 4 Wheel Drive
This differs between brands and models. Your best bet is to consult your user manual and follow its instructions.
You may notice both 4L and 4H settings, which basically means low gear and high gear while in 4WD mode.
Older and more basic 4WD systems must be engaged manually while the vehicle is at a complete stop and the transmission in either Park or Neutral. Don’t try to engage these systems when the vehicle is moving or you can damage expensive components.
Meanwhile, most recent 4WD systems can now be shifted into or out of 4WD in an instant at the push of a button without you having to stop the car completely. The most sophisticated and convenient 4WD systems are fully automatic. They shift into and out of 4WD automatically as the system detects the need for more traction.
Driving In 4 Wheel Drive On Highway: Can You and Is It Safe?
4WD increases your traction. That’s important in the case of snowy, icy or wet roads, or when you’re moving a heavyweight on a steep grade. These are the instances when you need to engage 4WD.
Although technically, you could drive in 4WD on any paved road, 4WD is generally not an ideal mode to use while driving on dry, flat, level roads. The problem here is that you’ll be locking the differential between your wheels, so all four wheels will be turning at the same speed.
That is very dangerous when you’re moving at high speed on the highway and trying to turn. Turning requires the wheels on either side to move at different speeds: the outer wheels have to cover a longer distance, thus will have to rotate faster.
So, driving in 4 wheel drive on highway: can you? Yes, technically you can use 4WD on the highway, but if you do, make sure it’s 4H four-wheel drive. Using 4H, you’ll get all the traction you need so you can safely reach your destination at a reasonable speed.
Do not ever use 4L four-wheel drive while driving at highway speeds. Remember that 4L simply means using lower gears in 4WD mode. If you try to use 4L, you’re going to reach high RPM’s without gaining much speed, which is not good for your vehicle at all.
In addition, in most vehicles, if you’re already on the road at a certain speed and the conditions suddenly change, you can switch to 4H four-wheel drive while maintaining your speed. Meanwhile, with 4L four-wheel drive, when you must slow down significantly or even stop.
In short, while you can absolutely use four-wheel drive in inclement weather for highway driving, you should not use it in good weather conditions. In addition, when you do need to engage four-wheel drive on highways, make sure it’s 4H setting.
As mentioned above, driving in 4 wheel drive on highway at a high speed is only safe on straight routes. Any turning at high speeds could be extremely dangerous.
Don’t Forget Traction Control Systems
Your 2WD/4WD truck or SUV should include a traction/stability control option as well. This is ideal for when you feel driving conditions are getting unsafe. From the moment you put the key in the ignition to when you park, traction/stability control should be running. (This won’t always be the case for older vehicles, so check your settings.)
Since traction/stability control is always on and four-wheel drive isn’t, you might be able to get over a small stretch of slick road with your traction/stability control alone. If you’re driving in mud, snow, or sand, though, this feature becomes less handy. This is when you want to use four-wheel drive to navigate and avoid getting stuck.
Bonus Tips: How To Maintain 4WD System
When using 4WD, you’re putting excess pressure on your 4WD drivetrain, differential case, and gears. Fixing these parts would be very expensive so ideally, you want to avoid engaging the 4WD mode unless road and driving conditions really require. This will keep your 4WD system in good shape.
In addition, 4WD systems work best and last longest when they’re used regularly and maintained according to factory recommendations. When a 4WD system sits unused for months at a time, the linkage and hub components seize, the seals dry out and the lube drains off gears.
Learn how to maximize the life of your four-wheel drive system and drive safely:
The best way to keep all 4WD components lubricated and in good operating condition is to engage your 4WD at least once every few months on wet pavement, best in a parking lot when no one’s around.
Tire size & tire rotation
The front, center and rear differentials in 4WD vehicles are designed to compensate for its shortcoming when turning a corner or changing lanes. Mismatched tires, whether they’re a different size or a different tread depth, will force the differentials to operate full time even if you’re going straight down the road.
Such overworking will lead to excessive heat and cause premature wear that can cost thousands of dollars in repair. A difference in tread depth of just 1/16 inch among tires is enough to cause early failure of the system.
Premature failure also occurs in the case of different tread brands, tread patterns and even different rubber compounds, since they can result in different traction rates between the tires. Therefore, avoid mixing different brands or tread patterns on your 4WD vehicle.
Another maintenance tip is that front tires wear faster than rear tires because they carry more weight and perform more braking and turning. Therefore, it is recommended that you rotate your tires every 5,000 to 7,000 miles to even out tire wear and minimize 4WD differential operation.
Fluid changes & Lubrication
As mentioned above, lubrication is important. Follow your owner’s manual for differential and transfer case fluid changes even if you don’t use your 4WD very often, and don’t forget to grease drive-shaft slip joints and U-joints.