what’s the difference between 4-wheel drive and all-wheel drive?
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They’re often used interchangeably and inconsistently in marketing which doesn’t help. There’s also a variety of different drivetrain configurations which don’t always line up into clear box’s and an exception to every rule (mostly weird Subaru’s and ranger rovers)
In the simplest scenario you’ve got a traditional 4wd that’s 2wd until you engage the front wheels. Your front and rear propshafts are forced to rotate at the same speed. There’s also a selectable low range.
A simple AWD system has a differential in the transfer case that lets the front and rear propshafts turn at different speeds. You can still lose traction if one wheel is off the ground. To prevent that more modern AWD systems can have various limited slip differentials that allow some difference between propshaft speeds. How those work is well outside an eli5 answer, some are physics based others are computer controlled.
There’s also the AWD haldex system which are primarily front wheel drive but when wheel slip is detected engage a clutch to connect the rear axle and provide power to the rear.
A constant 4wd system generally consists of centre differential (like a simple AWD system) but adds the ability to lock it so front and rear propshafts turn together. Plus a selectable low range.
True 4 wheel drive is somewhat of a misnomer unless a vehicle is also fitted with lockable differentials in both front and rear axles. Often a gwagon is hyped up as it can be “triple locked” (centre, front and rear), so can any lt230 based Landrover (defender classic, range rover classic, disco 1/2) and off-road is the same as a part time 4wd with front and rear lockers (like a wrangler).
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