If you're driving a vehicle that can switch between 2WD and 4WD modes, what happens if you accidentally (or deliberately) get on the highway when in 4WD mode? Is that in any way dangerous? Or is driving in 4WD mode on a highway safe?
The short answer is: Yes, it can be safe to drive in 4WD on the highway as long as you're going very slowly and so does the rest of the traffic around you. In other words, only during severe road conditions that require you to.
To understand why, we need to recap some of the info we covered in the post about when to use 4WD and what this system is even good for, other than the very obvious case of off-roading adventures.
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First, let's talk about capabilities.
4WD vs. AWD and which vehicle has what
I've been reading a LOT about this topic and talked to a bona fide mechanic about it too. It can absolutely get confusing, especially with so many vehicles now boasting some type of drivetrain that isn't your regular 2-wheel-drive.
If that's not enough, these systems work a bit differently in various car models.
Many people think AWD is just another name for 4WD. Arguably, language being what it is, when most people think that, it may actually be the linguistic case. However, there is a fundamental difference.
Let's talk drivetrains
The drivetrain is the mechanism that transfers power from the engine to the wheels. Simple enough.
The only question is - how many wheels does the drivetrain send that power to?
In a 2-wheel drive, the answer - as you may have guessed - is two. One pair of wheels - usually those in the front - is connected via an axle to the engine itself. As the pistons rotate the crankshaft, the energy is delivered to the front wheels only. The rear wheels? They just join along for the ride, fairly passively.
The 4WD Setup
In a 4-wheel drive, you have an additional rear axle. The power from the engine goes to both sets of wheels - front and rear. It's as simple as that.
As a result, with a 4WD drivetrain, you have control over the rear wheels, as well as the front. If the front wheels lose their grip on the road for any reason, the vehicle can still accelerate or decelerate by controlling the rear wheels.
Traditionally - i.e. in the previous century - 4WD was a big deal. Few vehicles were 100% 4WD. If you went offroad with 4WD truck, you had to bring it to a full stop, literally get out, grab a lever and connect the rear axle to kick the vehicle into 4WD mode. Then along came SUV's and off-roading just for fun. People really preferred to stay inside their SUV or truck so new systems were developed with which you could engage your 4WD systems with the push of a button.
This history lesson serves a point: With an older vehicle, you still need to switch between 2WD and 4WD. Witn many newer trucks, 4WD is a fixed feature. Nothing to think about with those - your truck is 4WD and will be that always. With others, there's only 2WD drivetrain available, so again, not much in the way of making a conscious choice on the part of the driver.
With older models, you need to engage 4WD when needed and disengage it when not needed.
Before we move on to talking about how to engage your 4WD and when, a word about AWD.
AWD stands for All-Wheel-Drive. This name is confusing because if you have 4 wheels and you're using a 4-wheel-drive, you're really using all-wheels. Which would make a 4WD the All-wheel-drive in any 4 wheeled vehicle, right? Unless you have a dually with six wheels...
Actually, AWD means something a little bit different.
In an AWD drivetrain there is a special mechanism that switches between 2WD and 4WD driving on its own. When the vehicle senses that two front wheels aren't enough (usually by gauging the temperature) it automatically locks in the rear axle and transfers engine power to the rear wheels too.
So, to sum this up -
The question of whether or not it's safe to use 4WD on a paved highway is really relevant only to older trucks and SUV's where the driver needs to engage and disengage the 4WD mechanism. As a driver, it's perfectly natural to wonder if maybe you should stop and disengage the 4WD abilities when returning to the road. And it's also natural to be worried about safety.
How to engage your 4 Wheel Drive
This differs between brands and models. Your best bet is to look in the user manual and follow the directions there.
You may notice both 4L and 4H settings. This basically means low gear and high gear while in 4WD mode. Low gear - just like with 2WD - means more torque, only this time the torque is going to all four of your truck's wheels.
Here's a fantastic video of testing the various settings in a Toyota Tacoma. The guy explains about the different gears and performs tests in off-road terrain to show how they move the truck differently. It's a fantastic demonstration of the difference between 2WD and 4WD when going off road -
Can You Drive on a Highway in Four-Wheel Drive?
All this begs the question: Can you drive on a highway in four-wheel drive?
Sure, you can. In terms of safety, there is no problem with sending torque to all four wheels. Sometimes you should. I mentioned possible scenarios in a previous post about when to use 4WD drive. To recap:
Use 4WD if -
- If the terrain is wet or slick.
- In rainy or snowy conditions
- When hauling or towing uphill or downhill
Which 4WD gear to use when driving on the highway?
Be sure to set your truck or SUV to 4H four-wheel drive. This way, you can drive at normal speeds when on the road. Remember, 4L simply means using lower gears in 4WD mode. If you try to use 4L while driving in highway speeds, you're going to reach high RPM's without gaining much speed. That's not good for your vehicle at all.
Using 4H, you’ll get all the traction you need so you can safely reach your destination at a reasonable speed. There’s no need to ever use 4L four-wheel drive for highway driving.
Also, in most vehicles, if you’re already on the road and the conditions suddenly change, you can switch to 4H four-wheel drive while you’re driving. This is not the case with 4L four-wheel drive, when you must slow down significantly or even stop.
4WD increases your traction. That's important when the road doesn't provide enough friction (as in the case with snow, ice or water on the road). It's also relevant when you're moving a heavyweight on a steep grade. 4WD can add some more traction and help you fight against gravity.
That's when you need to.
Technically, you could drive in 4WD on any paved road, but the problem is that you'll be locking the differential ration between your wheels. That can be dangerous when you're trying to turn the vehicle and need the wheels on either side to move at different speeds.
So, driving in 4WD should be done slowly and only when road conditions require it.
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So, you can potentially safely drive on the highway in 4WD - but should you?
Unless the need arises, you shouldn't engage 4WD on the highway or any asphalt road in a vehicle that has that option.
While you can absolutely use four-wheel drive in inclement weather for highway driving, you should not use it when the highways are clear.
As mentioned above, driving in high-speed with 4WD on means your wheels on both sides of the truck or car always turn at the same speed. That's fine if you're driving straight ahead, but any turn of the wheel to the sides at high speeds could be extremely dangerous.
In addition to that, you're simply 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 using them unless you actually need to.
Moreover, driving in 4WD mode means your engine is using more gas. It needs this to create enough horsepower to rotate four wheels - not just two. Generally speaking, 2WD has a better fuel economy. When you're the one switching between the two modes, you get more control over your fuel economy.
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. Again, check the video I posted above - the guy tests traction control as well 4WD modes.
A few more tips
Here are some ways you can stay safe and prolong the life of your truck or SUV when in four-wheel drive:
- Learn how to navigate situations like getting trapped on a snow pile or in the sand. You’re not trying to turn the wheels too fast in these situations.
- Four-wheel drive tends to use up a lot more gas due to the added torque. In fact, the more settings that come with your truck or SUV, the more these will suck up gas. You shouldn’t always have to use a four-wheel drive for the reasons mentioned above. You can significantly reduce your gas totals by only activating this setting when you have to.
- Remember that you’re only getting added traction in wet and snowy weather when four-wheel drive is activated. It does nothing to augment your stability, braking skills, and handling. It’s up to you to exercise good judgment when driving with a four-wheel drive. You must still brake slowly and conscientiously. You also shouldn’t drive faster than what you’re comfortable with.
Thoughts? Leave me a comment below!