Front-engine, four-wheel-drive layout
In automotive design, an F4, or front-engine, four-wheel drive (4WD) layout places the internal combustion engine at the front of the vehicle and drives all four roadwheels. This layout is typically chosen for better control on many surfaces, and is an important part of rally racing, as well as off-road driving.
This layout is also the drive train of choice for off-road pickup trucks and SUVs. It allows these vehicles to get the most traction without sacrificing cargo or passenger room. The center differential is often not present in these vehicles, meaning the 4WD system does not allow any difference in front and rear axle speeds. For normal road driving, these vehicles are shifted into 2WD mode, preventing damage to the transfer case, though full-time systems cannot go to 2WD mode.