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).
4WD is manually engaged and provides continuous power to all 4 wheels while engaged.
AWD detects slippage in traction and adjusts power to other wheels to provide traction as needed.
“4 wheel drive” involves direct command from the driver via switch or setting. “All wheel drive” is basically on standby when the vehicle is starting to slip and automatically engages it. Both have their pros and cons.
Sexist version (but true)
4WD is 4 men all working together in unison to complete a specialized job in the best way possible. 2 of them will be fine sitting down and watching the others work and willingly pitch in with the same effort when asked.
AWD is 4 women who are mostly in tune with their best friend on the same axle… But the other 2 girls don’t need to know you 2 hang out more…. So when you need the other girls help, just ask. The effort you get from the 2 other females may vary depending on their hormone levels on that particular day.
Four wheel drive is normally used in trucks to cross rough terrain at low speed and comes with a bunch of features to give the driver control over how the wheels work.
All wheel drive is normally used in sports cars and is simpler as it doesn’t have all the fancy features of four wheel drive but also works just fine at high speeds.
Branding and marketing.
Sometimes companies use “full time 4wd” or “AWD” to indicate that there’s no manual switch between 2WD and 4WD, and that all four wheels turn most all of the time, but there’s no hard fast rule
Now there are actually dozens of different unique mechanical configurations that can be used to drive all four wheels of a car/truck that use different combinations of differentials, clutches, viscous couplings, helical or planetary gearing and switching gearboxes combined with electronics to turn things on and off with buttons or automation. It actually gets really fuzzy and situational deciding which wheels are driven at different times with some modern systems. The only thing they all have in common is that they are set up so there is a way to drive all four wheels, and at any given time, the car is driving somewhere between 1 and 4 of them.
Now it’s “Quattro” “4-matic” “active-4” “S-AWC” or whatever the company wants to call it to describe its “special sauce” for driving 4 car wheels from one or more engines/electric motors.
All wheel drive, or AWD, is always on. All 4 wheels get turned by the engine. However, this causes a lot of unnecessary, and damaging, wear and tear on regular drive trains (the stuff that connects the engine to the wheels). So they are designed to be “loosey goosey” so they don’t get damaged from moving at high speeds. But this means less power is actually applied to all the wheels.
4WD is only meant to be trained on when 2 wheels is simply not enough to get you moving. Usually used when in snow, mud, loose dirt, etc., And usually because you are stuck, or afraid or being stuck, and not moving fast. However, this causes excess strain on the drivetrain when moving at high speeds, and especially when turning. So you really shouldn’t have it on when you don’t need it.
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