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.
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!
Wednesday 15th of January 2020
It is illegal and unsafe to drive significantly below the posted speed limit, unless constrained by traffic or road conditions, and even if road conditions are bad, driving more than 10mph less than the speed of surrounding traffic is extremely dangerous. There are only two possible end causes of a collision: a difference in direction, or a difference in speed. Highways and especially freeways are created to allow for higher speeds to be safely achieved by directing traffic to travel in the same direction and at the same speed. If you are traveling at a different speed then the surrounding traffic than you are a hazard to yourself and everyone around you. Highways have very high posted limits. By saying that it is safe to drive in 4wd mode on highways you are suggesting that is safe to drive in 4wd mode at highway speeds. If it is not your intention to suggest this then you must specify exactly what speed range which you wrongfully believe that it is safe to drive on highways in 4-wheel drive mode.
Thursday 16th of January 2020
In my experience, when road conditions are that bad, everybody slows down, so you wouldn't be driving more slowly than surrounding traffic. Thank you for your feedback all the same and have a great day!
Sunday 12th of January 2020
YOU ARE ENDANGERING YOUR READERS LIVES WITH MISINFORMATION. The truth is, driving in the wrong mode at highway speeds absolutely could KILL you. The power of any 4 wheeled vehicle comes from one engine to two or more wheels. Whenever the power needs to be split into two directions it needs to go through a differential to split the power into two separate drive shafts. There are three different basic types of differentials: locked, open, and limited-slip. As you might have guessed, a locked differential locks the two wheels together in simultaneous rotation, while a open differential allows them to rotate independently of each other, and a limited slip differential allows some difference in wheel speed, but limits the ability for one wheel to travel faster than the other. Locked differentials are absolutely the best type for off-roading over difficult slippery obstacles at low speed. Locked differentials will kill you at high speeds because they do not allow for the two wheels or two sets of wheels to travel at different speeds as they naturally need to in order to steer the vehicle at highway speeds. In order for the vehicle to steer properly, the inside wheel will always need to travel less than the outside wheel. If the wheels are locked together in direct simultaneous unison then one-wheel will need to slip in order to keep up with the other. Once your vehicle has started to slide, it can be difficult or impossible to regain control of it. This is why locking differentials are always able to unlock and are normally driven in the unlocked position: because it is dangerous and deadly to lock a differential at highway speeds.
Tuesday 14th of January 2020
Hi Ben, Thanks for the comment. I re-read the post to make sure. We're definitely not suggesting for anyone to drive in 4WD mode while cruising along in full highway speed. This mode is reserved for very specific situations (as mentioned in the article).
Friday 13th of December 2019
Thanks for this article. One other question. If I have to drive on a highway and it is light rainy, snowy and I feel I am losing traction in 2WD, andthen switch to 4WD, can I drive over 55mph? I have a 2016 Tacoma, TRD off road, and new tires, but on slick roads in 2WD it feels like it has little traction and 4WD feels much better - but 55 can be very low mph on highway. Many articles say do not drive in 4WD over 55. But that seems really low. Please let me know what think -if you can. Thanks.
Saturday 14th of December 2019
Thanks for the comment, Jan! There are differing opinions about whether or not going over 55mph with 4WD enabled will cause damage to the 4WD system. If there is sufficient snow/ice on the highway to warrant 4WD, our recommendation is to not exceed 55mph anyway for safety reasons. If the roads are that bad, the majority of other motorists will likely reduce their speed as well. For more information, we suggest taking a look at the owners manual and/or some online Tacoma forums to see if anyone else can give a more conclusive answer based on personal experience. We hope this helps!
Saturday 27th of July 2019
Thanks a lot, very useful. I was about to buy a Toyota 4Runner that I'll use on highway in 90% and in sand and muddy forest-roads for the rest of the time. I was convinced that I need a good 4x4. But reading your article I've realized I'll rather need an AWD car like Honda Passport or whatever small/mid SUV with AWD.
Friday 29th of November 2019
Pre 2010 4runners (any trim I'm pretty sure) have full time 4wd with a push button to lock the center diff (making it act like a part time 4wd system). Also 2010+ 4runner limited models have this same system, a full time 4wd (4wd you can use all the time... Basically AWD), with selectable locking center diff for off road. Just an FYI if you did want a 4runner.