alt Hacker NewsThere are plenty of AWDs that operate as FWD 90% of the time, only engaging the rear as needed. (I am told this is for fuel efficiency but the logic escapes me.) But I have yet to ever see a 4WD that could be "switched" to FWD.
The clearer distinction is that a 4WD has a second gearbox (aka a transfer case) that either manually or automatically engages the front wheels, the Jeep Wrangler /TJ being the architype. That means the extra wheels cannot be triggered seamlessly. A 4FW has distinct driving modes whereas an AWD uses clutches to bounce between modes as needed.
Bluey has a couple lines about this distinction. In Australia, even small children have opinions on 4WD v AWD.
> There are plenty of AWDs that operate as FWD 90% of the time, only engaging the rear as needed. (I am told this is for fuel efficiency but the logic escapes me.)
AIUI, you lose energy because the power/torque has to go through an extra differential, transfer case, etc, before reaching the rear wheels.
Going from the engine through the transmission to the front wheels is already a 'fixed cost', but the extra mechanics (and their friction loses) to the rear wheels an 'OpEx' that you don't necessarily have to pay if you don't need to.