There’s nothing quiet like a get out of gaol free card. Whether it’s a winch when you’re bogged. An awning when it’s raining. Or even something as flash as a diesel heater when it’s snowing outside and your mates are freezing their socks off in a swag. But perhaps the greatest get out of gaol free card so far has been the humble diff lock. But are they still relevant in 2022 after decades of traction aid development? Let’s take a look.
The secret sauce to success off-road is pretty simple. The more traction you have propelling you forward, the less chance of getting stuck. Simple right? In theory yeah. In practice, things get a little more complicated.
Understanding the basics
Let’s take a step back and look at a 2WD ute. Only the rear wheels drive you forward. So you’re already down to a maximum of 50% traction. And those two wheels need to be able to go different speeds to account for corners. A differential is what allows one wheel to receive drive, and the other to coast. Now we’re down to a maximum of 25% traction. There’s a pretty serious design flaw in a standard (or open) differential where the easiest wheel to power is the one that gets driven. Not an issue driving around a shopping centre, but when you’re on loose terrain, the easiest wheel is the one without grip. Now you’ve got a wheel spinning uselessly on the wet grass, and 0% traction. Far from ideal.
A 4X4 system gives double the traction, by sending drive to the front as well as the rear. 50% traction. But each axle has the same issue with the differential. If both front and rear wheels are in a low grip environment you’ll have one front and one rear wheel spinning uselessly. Back to 0%.
How does a diff lock fix this, and what are the drawbacks?
A diff lock is a very simple device. It locks both wheels on an axle together ensuring both will turn at the same speed no matter the grip available. While one wheel might be spinning uselessly, the other wheel can be driving you forward still. It’s no guarantee for success, but the more wheels driving, the more chance you’re moving forward. They can be selectable with air or electronically, mechanically engaged like an auto-locker, or even be permanently locked together like a spool. The results will be similar when you’re talking grip.
But they aren’t the solution to all life’s problems. When both rear tyres are locked together your 4X4 can have a tendency to drift sideways. That’s not an issue when driving through a set of wombat holes, but when your rear end is climbing a rock ledge it can slide you sideways. Get yourself in a tricky situation with a sideways slope and a drop off on the edge and you could be in real strife with your locker engaged. The front can cause similar issues too, and will reduce your steering ability.
Put simply. You can improve the way a diff lock engages. But we’re yet to see a way to improve on how they function.
But traction control sucks
You’re 100% right there. But things are more complicated than they may first appear. Early traction control would sense that one wheel was spinning, and attempt to stop it spinning by cutting your engine’s power. Whether you’re climbing a steep rocky ascent, powering through soft K’gari sand, or halfway across Nolan’s Brook cutting your engine’s power isn’t going to do anything good.
Braked Traction Control on the other hand works by using that design flaw of an open diff to your advantage. When a wheel spins, the speed sensor can detect it, apply the brakes, and send drive to the wheel that still has traction.
So what are the setbacks?
Well honestly, there are a few. There can be a slight delay between one wheel slipping, and the other getting drive. In an early or rudimentary system this can cost you precious momentum. Platforms like the Ranger have more advanced systems that can reduce this delay drastically. Some systems will disengage when a factory diff locker is engaged too. Again, the more advanced system on a Ranger will only disengage the system on the axle that is locking. Other systems will disengage the entire system. Ironically, turning the rear locker on in this situation may make the 4X4 less capable than relying on the traction control alone.
And what are the positives?
Put simply. A diff lock is always going to behave like a diff lock. While traction control systems can be used in a whole variety of ways. Drive modes allow the ECU to understand what terrain you’re driving and respond accordingly. Want a little wheel slip and bulk throttle response in high speed sand? An advanced traction control system can give you that, a diff lock can’t. They’re also permanently engaged making the base line capability of your 4X4 higher, whereas a diff lock requires you to engage it in advance. Finally, these systems can also be used for other handy features like downhill descent control.
What’s right for me?
While traction control is no doubt more advanced than the humble diff lock, there’s no one size fits all here. In an ideal world your 4X4 will run both. Selectable front and rear lockers, and a centre if required, for when you know you need them. And a competent and un-intrusive traction control system that’ll make your rig more capable without even needing to reach for a button. Simple eh?