Why Are Pickup Trucks and Vans Rear-Wheel Drive?

Have you ever noticed that nearly all full-sized pickup trucks and commercial vans are rear-wheel drive? Ever wonder why that is? If not, Now you do. Haha! Our trap worked!

The reason for rear-wheel drive being the norm, after most other vehicles moved to front-wheel drive, is three-fold: frame design, weight distribution, and powertrain size. The first two reasons work together while the latter is because of the requirements of the others.

Framing and Weight Distribution

Most full-sized pickup trucks, vans, and many sport utility vehicles use what’s called a body-on-frame design. This type of vehicle design dates back to wagons and carts that had more than one axle. In simple terms, the framing is designed separately from the body work so that the frame is fully independent of the body. The body (doors, windows, fenders, etc.) of the vehicle has its own framing independent of the support frame and suspension (together called the chassis).

Until recently, the body-on-frame design was what all vehicles were designed with. Small or large, every vehicle utilized it. That changed in the 1960s as the now-common unibody (short for “unitized body”) began to replace body-on-frame designs for passenger vehicles. Unibody vehicles allow more interior room, better ride quality, and are generally lighter in weight.

But heavier vehicles, like full-sized pickup trucks, big SUVs, and vans, retain the body-on-frame design. This framing allows for more weight to be carried and for the larger drivetrains that are required to power a vehicle hauling or pulling that weight. This frame design and the rear-wheel drive it comes with also changes vehicle dynamics on and off the road.

Most of the added weight (cargo) carried by a van or truck will be carried at the rear, nearer to the rear wheels. The truck’s cargo bed and the van’s cargo space are both behind the front axle and drivetrain, pressing more on the rear axle than on the front. Similarly, a big SUV is also more likely to have more of its passenger weight towards the rear.

That rear-focused weight distribution means that the vehicle is likely to be tilting towards the rear, lifting the front wheels. That affects traction both front and rear (in opposing ways), which affects vehicle control. An independent frame allows designers to account for varying weight distribution levels as the rear gets heavier or lighter. A ladder-type independent frame can bear the weight, and better distribute weight inequalities than can a unibody design, where weight and stresses need to be largely in balance. Ladder frames are also inherently less apt to twist or rack from lateral stresses due to weight movement or changes as the vehicle maneuvers.

The larger and more robust body-on-frame design used in trucks and vans also allows for heavier suspension components to further help distribute the load across the axles. In a pickup truck, for example, the front suspension is usually lighter (compresses easier) than the rear, allowing the stiffer rear suspension to lever some of the cargo weight forward for more even distribution.

Having the majority of the vehicle’s weight on the rear axle means better traction for those wheels and tires. Which is why rear-wheel drive is preferred. A RWD platform also has inherently better handling characteristics in most at-speed maneuvers than does a front-wheel drive vehicle. Specifically, when under a heavy load, a RWD vehicle will have lower understeer properties (slipping of the front tires) than will a FWD vehicle with a similar load. The load itself, being rear biased, helps keep the rear tires from slipping, lowering oversteer as well. These two things help keep the loaded truck or van from becoming unstable when turning.

Powertrain Size

The other metric for rear-wheel drive platforms in pickup trucks, vans, and sport utilities is the size of the powertrain. Because these vehicles are generally expected to carry more weight and are more likely to have a low-geared four-wheel drive system in place, their powertrains are generally larger. It’s more difficult to fit a larger engine sideways with a transmission into the relatively small box of the engine compartment.

Even with today’s turbocharged engines with smaller footprints and displacements, a rear-wheel drive platform still makes more engineering sense. The engine and transmission for a load-bearing and/or towing vehicle like a truck or van are more robust. Bigger jobs mean bigger machines. By placing the engine and transmission in line with the vehicle’s length, torsional rigidity is easier to achieve. It helps counteract the twist of the transmission under the force of the engine.

Because vehicles like trucks and SUVs are expected to tow trailers of similar or heavier weight, having the engine, transmission, and drive axle’s differential in line helps maximize torque output and minimize stresses on the components. A transverse setup (engine sideways, transmission attached to front axle) would change that dynamic for the worse.

Rear-Wheel Drive FTW!

These are the main reasons that most pickup trucks, SUVs, and vans are rear-wheel drive. With the loads they’re expected to carry, trailers they’re expected to tow, and powertrain capabilities they’re expected to have, these vehicles must use a RWD architecture.