We're often asked questions about four-wheel-driving, especially on the differences between four-wheel-drive modes in modern vehicles.
CarAdvice reader Stacey owns a new Mitsubishi Pajero Sport and wasn't sure which modes she should be using during regular driving and off-road driving.
Q: Hello. We just bought a Mitsubishi Pajero Sport and we absolutely love it. We are planning on heading away over the holidays and plan on doing some pretty mild off-road driving in and around our camp site. What is the difference between 2H, 4H, 4L and what does the differential lock do?
A: Great choice on the car Stacey. It scored highly during our recent Family 4x4 SUV Comparison.
In fact, one of the reasons it scored so highly was because of the flexibility of its all-wheel drive and four-wheel drive system.
During regular driving, the vehicle is normally driven in 2H, which is its two-wheel, rear-wheel drive mode. This mode reduces fuel consumption by just sending torque to the rear wheels and also gives you the flexibility of being able to drive on all surfaces — more on this later.
Unlike some of its competitors, the Pajero Sport can also be driven in 4H mode on all surfaces. This mode engages the front axle and the car's onboard computer determines how each wheel behaves when torque is being distributed between the axles.
Some vehicles in this segment enable four-wheel drive by virtue of a locked centre differential, which evenly splits torque between the front and rear axles. These vehicles can't be driven on high-friction surfaces with the wheels turned due to the potential of differential wind up. Differential wind up can occur when the centre differential is locked and the wheels are turned on high-friction surfaces.
The car attempts to force both axles to rotate at the same rate, which can't happen due to varied turning radiuses between the axles. This then causes the wheels to try and spin on the spot and rotate at the same speed. This eventually causes tension in the differential.
The Pajero Sport then has an additional set of features for off-road driving. It can be put into a four-wheel high-range, or four-wheel low-range mode, with the centre differential locked, where a low-range gearbox is used as a torque multiplier. This mode should only be used when off-road.
This mode evenly splits torque between the front and rear axle and can be used in combination with the rear differential lock to further increase off-road ability.
The effect of low-range is lower speed, but more accuracy with torque delivery. It's suitable for situations off-road where bursts of torque would unsettle the car.
Like the centre differential lock, the rear differential lock will split torque between the two rear wheels to ensure they both receive drive, even when one wheel is off the ground.
To help demonstrate this, we lined up a tricky hill that features undulations and uneven portions of terrain. While it may not look difficult, this hill causes the Pajero Sport's all-wheel drive system to continuously shift torque delivery and ultimately forces it to try drive wheels while others are off the ground or have very limited traction.