So What's the Diff?
Prologue – I’d love to tell you that this article is the result of a long focus group about how to reach my key audience but sadly, this is not the case. Nope. This little gem is the result of me trying to explain to my family (primarily my mother and my inquisitive bevy of sisters) just what the heck it is that I do for a living. So, here’s the glossed-over version in approachable terms.
So, what’s the diff? If you think I’m referring to the difference, probably more than you think. The diff I’m talking about is the differential, as in a key component of your drive train.
The differential is that big round thing in the middle of your axle, which, in case you weren’t sure what an axle is, it’s the stick of metal that joins your wheels together. You have one between your front wheel and another between your rear wheels. Your differential is basically the brain of the axle, it’s the piece that allows you to turn corners and ultimately controls your traction.
At first glance, most people think that all of their wheels are spinning at the same time and this is true, until you turn a corner. When you turn a corner, you need to make your car arc around the corner. To do this, the wheel on the inside has to make a little arc and the wheel on the outside has to make a big arc. If your wheels are spinning at the same time you’d have to have to equal arcs and this would prevent you from being able to steer the vehicle effectively. Think about a geometry compass, in order to draw an arc or circle, one of the compass points has to remain stationary while the other point moves. When a vehicle moves, the inside wheel isn’t quite stationary but it’s moving much slower than the one on the outside end of the axle. The differential is the piece that more-or-less controls the wheel speed allowing you to turn in a fluid motion.
Two-wheel drive, four-wheel drive or all-wheel drive, it all comes down to the traction and your traction is controlled by your differential.
2WD
Contrary to its title, two-wheel drive does not mean that two of your four wheels are powered. Actually, you only get to control one wheel and then the other three basically follow it. Think about a tricycle, the wheel in the front guides the two fixed wheels in the back to do what the driver wants.
If you've ever heard you car being referred to as 'front wheel drive' or 'rear wheel drive' your car is probably a two-wheel drive vehicle. In a front wheel drive car, one of the wheels in the front is leading the way and in a rear wheel drive car, one in the back is the pushing the way.
AWD
On an all-wheel drive vehicle, you get power to one wheel in the front and one wheel in the back so you have twice as much traction, which means more control. While the premise is similar, an all-wheel drive is not the same as a four-wheel drive because it’s designed specifically to work on the highway because it does not have a low-range transfer case, but more on low-range later. Occasionally, an AWD has an option to switch between 2WD and AWD because a 2WD is more fuel efficient than AWD mode but it will never have an option for low-range. An AWD will fare better that a 2WD in inclement weather but they are not suited to off-pavement activities.
4WD
This brings us to 4WD, which is power to one wheel in the front and one wheel in the rear and the option to switch in to low-range. Low-range is an option that changes your gear ratio and allows your transmission to slow down allowing you to have greater control while driving in difficult terrain where your tires won’t be able to get a lot of traction, like on a slimy boat launch, snow covered road, muddy trail or extremely sleep inclines.
Why does it matter how many tires have traction? Because if, in your 2WD car, you have one tire on the ice and the other three tires on dry road, your highway-minded differential will only send power to the tire that is slipping on the ice. You have three other potentially useful tires to drive you out of the situation but your differential won’t let you use the other tires, and you’re stuck spinning on the ice going nowhere. The same thing would happen if you had a tire lifted off the ground, all of the power would go to the tire in the air so it would be spinning but you’d never be able to move.
If you have an all or four-wheel drive you have the benefit of the second powered tire. So, if one of your front tires is on the ice, your rear tire with power may be able drive you out of the situation.
Lockers
And then there are lockers, short for locking differential. So far, I’ve been discussing how the differential allows the wheels to turn at speeds independently, but there are some circumstances where we want them go at the same speed. That way, we can control the wheels when a tire is slipping and the vehicle won’t move because all the power is going to that slipping wheel. Like, if you are on that slimy boat launch and trying to get your boat out of water but the truck is just spinning out, Lockers allow you to make the wheel spinning time lock together so that you can take control of that other tire and drive out.
Some lockers are mechanical, and some are selectable and you can put them in the front axle, the rear axle or ideally both, which we call a fully locked vehicle.
A mechanical locker typically stays engaged all of the time and uses a clutching mechanism to allow the differential to disengage enough to get around a corner and it requires some handling skill because the vehicle will not always act in a predictable manner. The mechanical locker cannot be manually disengaged, it guesses when it thinks you should disengage.
A selectable locker typically allows your vehicle to drive exactly like normal and then when you find that you’re just spinning a rut in the mud or for some reason stuck and not going anywhere, you flip the switch and drive out of the trouble area. As soon as you’re clear of the obstacle, you disengage the locker and carry on as usual. The advantage of the selectable locker is that it can be turned off. Being able to turn the locker off means that you will always have perfectly normal vehicle handling, you’ll be able to steer and you’ll experience no additional wear to your tires or fuel economy because you won’t be powering those additional wheels all the time
Selectable lockers can be engaged electronically, pneumatically or by a manual action.
ARB Air Lockers
ARB Air Locker locking differentials are engaged using pneumatic air pressure. ARB uses air instead of electricity or a manual action because air is the most efficient way to produce the power required to keep the differential engaged. Air also puts the least amount of draw on the vehicle’s electrical system and an air line is much cheaper and easier to repair than either an electrical or a manual action that would use a cable.
Whether, it’s a two-wheel drive, all-wheel drive, four-wheel drive or fully locked there is a drive train that’s right for you and I hope this article helps you choose. And, for those of you who were afraid to venture off the pavement, I hope you now know that there is no such thing as a trail too treacherous if you have sufficient gear.