Buying a 4X4 car: what to consider?

You want to buy a 4x4, but you don’t know where to start. We are here to help! First, when you’re buying a 4x4 with the essential purpose of being able to bring it into the desert then there are a few things you need to understand at a high level, and that is the differences between the following types of 4x4 vehicles:

Part-time 4 Wheel Drive. A part-time 4WD typically drives in 2WD mode but has a transfer case to engage the 4WD system and provide equal power distribution to the front and rear axles. Engaging 4WD typically puts it in high range, but the transfer case also allows you to switch to a low gear ratio called low range which reduces the speed of your vehicle but increases the torque of the axles.

Full-time 4 Wheel Drive. A full-time 4WD drives in 4WD mode permanently but has a central differential in the transfer case to allow unequal power distribution for normal road use. In the desert however, it can lock the center diff allowing equal power distribution to the front and rear axles, and just like the part-time 4WD it has low range mode.

All Wheel Drive. In an AWD power is permanently distributed to all 4 wheels but through unlockable differentials. The AWD does not have a transfer case and as such does not have a low range option. Nor does it have any diff locks which means power is always distributed to the wheel with the least resistance, which is the exact opposite of what you want in the desert.

When people tell you an AWD is actually great for both on and off road you might want to question their definition of “off road”. You'll find several online blogs recommending cars like the Volvo XC70 and Subaru Forester for the UAE deserts. I’m not sure if these are sponsored or all plagiarized from the same bad source, but please be aware that AWDs are highly unsuitable for the desert. AWDs are designed for improved road performance and stability, but not for off-road purposes. Although it might do fine on a gravel road, or even bring you across the wadi, in the desert it will get you nowhere. And traction control systems with a special ‘Sand’ mode might help you cross a sabkha, but that’s about it. Besides the fact that AWDs don’t have a low range gear ratio and diff locks, they typically also lack sufficient ground clearance and suitable off-road tires that allow proper deflation.

The only problem is that some car brands these days use the term AWD for their 4WDs, so unfortunately the industry is not yet in full agreement on the terminology. Just make sure you check the specs.

Okay, so now that you know that you need a part-time 4WD or full-time 4WD and we have established that you need a high and low range option with at least one diff lock, let’s have a look at what else you need to consider:

Engine. As long as electric 4x4s are not widely available/competitive, let’s focus on the internal combustion engine which determines the power output typically measured in kilowatt or horsepower. Most 4WD have either 6 or 8 cylinder engines which should be sufficient depending on the weight of your car. Which leads to the next point.

Weight. The weight of the car should be measured against the engine capacity. You can do this by dividing the power output of a vehicle by its weight. For example, if you have a car with 300 hp that weights 3000 kg, then the PWR will be 300 / 3000 = 0.1 hp/kg. For desert driving you definitely want to be above 0.1 hp/kg.

Ground clearance & wheelbase. The ground clearance is the distance between the ground (flat surface) and the underside of the chassis. The wheelbase is the distance between the front and rear wheels (center lines). In most off-road environments, especially rocky terrain, it’s important to have a decent ground clearance, but in the desert the most common place where people get stuck is on top of the dune crest. Therefore, what’s more important is the breakover angle. Which leads to the next point.

Approach, Departure & Breakover Angles. The departure angle is the angle between the front tire and the lowest part of the front overhang. The departure angle is the equivalent at the rear. The lower the approach and departure angle, the higher the chance you will lose a bumper in the sand. The breakover angle is a function of the ground clearance and the wheelbase. As a rule of thumb: a minimum of 20° is recommended for desert driving, above 25° you’re out of the woods, above 30° you’re overspending (but who’s judging). The most common ways to improve your approach, departure and breakover angles are: bigger tires, coil spring spacers, body lift or suspension lift kit.

Wheels/Tires. A tire size (e.g. 275/75r17) includes the width in mm, the aspect ratio in % and the rim size in inches. The aspect ratio is the sidewall in percentage of the width. The bigger the tire, the bigger the ground contact surface (also known as the contact patch), but increasing your tire size will be limited by the wheel arch of your vehicle. As such 4WDs often use limited rim sizes around 16-18 inch. A smaller rim allows for tires with a bigger sidewall which has more stored air and therefore allows extra deflation, which increases the contact patch. A deflated tire gets wider and longer and can achieve an increased contact surface of 250% of its inflated condition. Another aspect off-roaders typically look at is ‘wheel travel’, which is the capacity of the axles to articulate vertically whilst the wheels maintain surface contact. Wheel travel can be increased with a lift kit.

Body strength. For desert driving we recommend sticking to an old-fashioned ladder/body-on-frame above a monocoque chassis/unibody frame. A few reasons: 1) A body-on-frame chassis has a high resistance to bending and deformation under stress. 2) It is much stronger for hauling and towing. 3) It typically provides higher ground clearance and is easier to accommodate an increase of ground clearance 4) You can separate the entire body off the frame which makes body repair easier and likely cheaper. But it has to be said that the unibody frame has been taking over a large part of the SUV market in the last 2 decades. Then again most SUV are not 4WDs and simply not designed for off roading. But with the Land Rover Discovery and Defender changing to monocoque design we could be proven wrong. Besides the frame for desert driving it's important for your vehicle to have a strong drivetrain and suspension system.

Towing capacity and arrangement. Most 4WDs have a pretty decent tow rating, but make sure you also have proper tow equipment.  On the rear it's recommended to have a proper tow hook. Different hooks are available, e.g. grab hook, slip hook, pintle hook, ball hitch, shackle hitch, etc. The pintle hook is typically a safe solution as it’s strong and closeable. In the front most 4WDs come with tow lugs which can be used as recovery points. It’s also possible to install tow lugs, shackles, or hooks, but make sure they have sufficient rating and they are properly connected to the chassis. We strongly recommend against using screw-in tow hooks as these are probably the most common failure mode in recovery operations.

What else is there to consider?

Manual vs. Automatic

Whether you buy a manual or automatic transmission is mostly a matter of personal preference. Some folks choose manual because they prefer to have total control, but these days most automatic transmissions have a manumatic function anyway which allows the driver to upshift or downshift using a gear selector. And most older 4x4s have the choice 3, 2, or 1 gear which locks out the higher gears. This was mainly introduced for downhill and towing purposes. When desert driving and especially during a slip face descent this is a good way to maintain a low speed.

Electronic Control Systems

These days a lot of cars and especially 4x4s are equipped with electronic control systems such as stability control, traction control, hill descent control, etc. We've already covered stability control. Traction control is a system which uses sensors and break actuators which are engaged when it measures a loss of traction and ensures that more torque is transferred to that wheel. For most off-road conditions it’s probably a good tool and over recent years these systems have gotten better and faster, but in the desert you typically don’t want to rely on a reactive system which interference can cause you to lose momentum. In general, our advice for the desert is not to use ‘active’ systems to provide stability, traction, or anything else. You are much better off with ‘passive’ systems such as a low range or diff lock to provide torque increase or distribution.

Besides all these technical requirements, when buying a 4x4 make sure you also factor in your personal requirements and preferences. Which 4x4 models do you actually like? What are you going to use the car for? Big family, long daily commute, etc. If you need any advice on selecting the right 4x4 make and model, check out our blog “Buying a 4x4, what are my options?”.