How 4WD works: 4Hi vs 4Lo vs 2Hi

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A modern vehicle can do a number of things for its driver. It can regulate traction, keep your braking pressure from locking your stoppers up, and make sure your engine doesn't exceed a given rev limit. Heck, a modern car can keep you in your lane and stop you from hitting the car in front of you. There are some things you still need to know, however, and one such bit of information pertains to four-wheel-drive systems.

You have choices in your four-wheel-drive machine. You can run it in two-wheel-drive, 4Hi, or 4Lo. Knowing the differences between the three is important. For most daily driving you'll only need two-wheel-drive. The rear wheels have more than enough traction to keep you moving in most situations. Should the road get messy, however, you can switch over to 4Hi and that'll give you the ability to travel with greater available levels of traction.

How the four-wheel-drive system reacts depends on where the grip is and how the system shuffles power around. In this example, Engineering Explained host Jason Fenske uses a Nissan Frontier Pro 4X with locking center and rear differentials to show where the power goes in various scenarios.

When you're plowing through some serious stuff, it's time to put the vehicle into 4Lo. In this setting, you are in a slow-speed situation where traction is a priority. A change in gearing sends a lot of torque to the tires and keeps the speeds low. This is to help you get through a section of the road or trail where you might find deep sand, mud, or snow

You can actually see the effect of this extra torque in the video above. Doing 0-30 mph launches in the Nissan, Jason records his run times and g forces in a variety of driving modes. Due to gearing, more torque is delivered in 4Lo, and that creates the quickest 0-30 mph time. That's not what the setting is for, mind you, but it helps illustrate the torque being sent to all four wheels.

Check out the video for more about how these systems work. As usual, Jason breaks it all down in easy-to-understand language.

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