This post was originally posted by me on a different blog on Nov 7, 2011:
If you’re considering an overland vehicle and 4×4 capabilities are important to you, then you’ll probably be as interested in this topic as I was when I started really researching the capabilities of various types of 4×4 vehicles.
First, the caveat: Some of this is new to me, so if you see any errors here please say so in the comments.
I’ll define an “all wheel drive” vehicle vs. a “4×4″ vehicle as the difference between having a “low” range. A low range selector specifies different gearing in the transfer case, giving the vehicle many times more power due to the lower gearing. So for example, certain models of the Honda Element are “AWD,” because it delivers power to all four wheels while a Jeep is a true 4×4. (Speaking of Elements, if you want a cool camper option for an Element, check out the ECAMPER — but that’s off-topic for this thread.) In this thread I’ll only be referring to true 4×4 vehicles.
What the jargon means: Open vs. Limited Slip vs. Locking Differentials
(If you don’t know what a differential is, take a look at this video before you read the article below. Skip to minute 1:50 unless you want to see the cheesy motorcycle antics!)
Even though many brands advertise their vehicles as having four wheel drive, the truth is that due to the open differentials on the axles, power only goes to the vehicle with the leastwheel grip. An open differential is necessary on paved roads because the outside wheel travels farther than the inside wheel in a turn, but on trails or off the beaten path, a fully open differential will only cause you problems.
Auto manufacturers work to correct this problem with “limited slip” differentials. These are still open differentials, but the slip is mitigated using several mechanisms: Usually either the brakes or a change to the differential design. The Toyota Tundra, for example (which we’re considering as the base of a camper) comes with something called “AutoLSD,” which sounds trippy but means something much more mundane: “auto limited slip differential.” It engages the brakes of a the tire that’s slipping to send more traction to the tire that’s not slipping. You can watch a video showing the difference between an open differential and AutoLSD here.
It’s imperfect though. Braking the tire that’s slipping can cause the brakes to overheat, and as you can see from numerous videos like the one below, LSD is not the same as having your differentials locked.
Some vehicle manufacturers offer locking differentials as part of the standard or options packages. For example, the 1/2 ton Nissan Titan pickup offers an optional electronic locking rear differential, while theToyota Tundra only offers AutoLSD.
Despite the locking differential advantage of the Titan, I’m still partial to the Tundra due to its superior performance in other areas and much better worldwide availability of parts over Nissan. And if I really wanted to, I could install after-market locking differentials.
And that’s where it gets really interesting. More about full locking differentials after these two videos, which showcase the differences: