Today I Discovered The Difference Between 'Four-Wheel Drive' And 'All-Wheel Drive'

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You know what would be really handy? If a trained rally driver with access to a bunch of all-wheel drive and four-wheel drive vehicles helpfully explained the difference between these two ever-more confused terms. Oh wait, here he is!

This is Wyatt Knox of Team O’Neil Rally School. You may remember him from teaching my coworker and I how to take control of a car if your driver gets shot, and how to do a PIT manoeuvre, and, well, a lot of other things. Wyatt is a two-wheel-drive national rally champion, and knows his stuff. It is with this in mind that Wyatt explains why an older Subaru STI can be considered 4WD while even the coolest Ford Focus RS cannot, and where trucks and Land Rovers and Jeep Cherokees all fit into that.

Four-Wheel Drive: 100 per cent of the power is sent to the front and rear of the vehicle. That means you have a transfer case or locking center differential.

Part-Time 4WD: This means you can have the vehicle in 2WD or you can engage, usually, a transfer case to lock the front and rear together. Your front tires are turning at the same rate as your rear tires, which is what makes this good in the mud and snow, and what makes your dad yell at you to DON’T PUT IT IN 4WD ON THE ROAD you’ll chew up the tires.

Full-Time 4WD: This means all four-wheels are being driven, just not necessarily with front and rear locked together, though the car will let you lock everything together with a locking center differential. This is a differential in the middle of the car that locks the front and rear together so that everything spins at the same rate, giving you that 4WD. A Subaru STI with a locking center diff will, as Wyatt says, be 4WD if you look at it this way.

All-Wheel Drive: No transfer case, no locking center diff, either. Power can be sent to the front or rear, but it’s not locked together, so you’re not skittering around corners. Having this ability to keep things unlocked makes AWD cars driveable in normal situations.

Part-Time AWD: Power normally goes to either the front or rear of the car, but the car can send power to the other end, usually if it detects that the normal drive wheels are slipping. These are, like, front-wheel drive vehicles until the front wheels start spinning or, alternatively, rear-wheel drive vehicles until the rear wheels start spinning.

Full-Time AWD: Power is always going to all wheels, but it’s variable how much goes where. You have a center differential but it’s variable, like a viscous center diff or a clutch pack.

I am, of course, no expert, so just listen to Wyatt explain things and he’ll be clearer than I am.

The confusing part is that over the years, car companies have made big money selling all-wheel drive to increasingly scared Americans, and the number of terms about what’s on-demand and part-time and full-time have exploded. Moreover, just because you have 4WD doesn’t mean your vehicle is invincible in all conditions. Even if you’re locking the center of your car, if your front and rear differentials are open diffs that can’t lock, you can still end up spinning two lone wheels on a slippery surface.

As such, a lot of these arguments are kind of academic.


This story originally appeared on Jalopnik.


Comments

    AWD is good but I understand that after your tires are part worn and you get a puncture and shred one tire. On a rear wheel drive you buy a pair of tires. But on an AWD you have to buy 4 tires.
    The reasoning is that the drive train suffers wear if two tires are not exact and after an interval your gears and everything wear out and you’re are up for big bucks.
    A friend explained it like your LSD is working all the time instead of just with wheel slip conditions.
    You can limp home from your holiday but look to replacing them soon.
    So all four tires have to be the same wear pattern and if you have to replace one, you’re up for 4.
    I know tires should be in good condition any way, just bear in mind if you decide to buy an AWD

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