Four-wheel drive versus all-wheel drive. Easy Select versus Super Select II. What does it all mean?
If my inbox is anything to go by, there’s great uncertainty out there about all-wheel drive and four-wheel drive. In reality, it’s not that simple. Or at least, not clear-cut.
Let’s clear a few things up: Firstly, four-wheel drive. Let’s define that, arbitrarily, as a system designed only for low traction surfaces, slippery underfoot, in which the drive to the front axles and the drive to the rear axles can be locked together at the same rotational speed, using Fred Flintstone engineering.
In other words, the front and rear prop shafts are mechanically locked to rotate at the same rate.
All-wheel drive: Let’s define that arbitrarily as a system designed to drive all four wheels, either continuously or occasionally, but with the front and rear prop shafts able to turn at different rates. And that means you can use all-wheel drive on high-traction surfaces (like sealed roads; dry bitumen).
The big difference: When a vehicle drives on a curve, the front end and the rear end follow different paths. Therefore, the front and rear ends travel different distances. Therefore, on a high-traction surface, the front and rear prop shafts need to spin at slightly different rates.
On a low-traction surface, the tyres can slip a bit, if the front and rear prop shafts are locked. But if you put a vehicle into four-wheel drive mode (prop shafts locked in unison) and you drive on a high-traction surface, on a curve, you will break something - at least, you open this door, and warranty will not cover you because that’s technically abuse.
So - all-wheel drive vehicles have some sort of sophisticated coupling between the front and rear prop shafts - either a differential, or a viscous coupling, etc, that allows this relative rotation. They’re more sophisticated, and therefore, more expensive.
Most all-wheel drive SUVs have a four-wheel drive mode, usually engaged with a ‘lock’ or ‘4WD lock’ button, or sometimes a rotating switch. Typically you engage that to get through some mud or soft sand - whatever. In the snow. But not for driving on bitumen - if you know what’s good for you.
I’m John Cadogan. I hope this helps. Thanks for watching.

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