How does a 4x4 car differ from SUVs?

  • 19/08/2015
  • Author: Dariusz Wojdas

Many people, including drivers, often confuse SUVs (Sports Utility Vehicle) with off-road vehicles, even though they don’t have much in common. With this in mind, how can you distinguish between a typical 4x4 car and an SUV?

As an interesting fact, over 90% of cars described as “off-road” in the USA are not even four-wheel drive models. This feature is absent from some versions of the Jeep Grand Cherokee, a model typically regarded as an off-road vehicle. Moreover, even cars fitted with a 4x4 drive are not fitted with off-road reduction gearboxes or 4x4 inter-axle locks (although the Jeep Grand Cherokee is available in such versions). These same models are then advertised as off-road vehicles when sold in Europe, as well.

Almost all vehicles sold in Europe with an off-road appearance, such as true off-road vehicles and crossover SUVs, have a 4x4 drive. It is always worth remembering, however, that you should not push an SUV too hard over rough terrain.

Furthermore, to help complicate the issue, smaller city crossovers and compact crossovers are found with both four-wheel and two-wheel drive versions. Confusing, isn’t it? Below, to help clarify the situation, we have described the most important differences in the construction of these vehicles.

SUV or 4 x 4

Many 4x4 car models lack an off-road reduction gearbox

How to distinguish an off-road vehicle from a SUV

Basic differences

To be considered an off-road vehicle, a given model must be fitted with a reduction gearbox, which reduces the speed in every gear by half, ensuring it is easier to get over difficult obstacles like mud and sand). Because of this gearbox, such a vehicle cannot have a transverse engine, because they cannot be fitted to the specialised gearbox. It must also be fitted with a full inter-axle lock - this prevents damage to the transmission when driving off-road.

Typically, the reduction gearbox and inter-axle lock on off-road vehicles must be operated manually. As such, you can look for a suitable level or switch in the cab of the car. If these features are absent, you are most likely dealing with a crossover 4x4 car.

Any car which is not a true off-road vehicle must not be driven through water deeper than its ground clearance, or on rocks. Even driving in ‘normal’ first gear is considered too fast and can even lead to clutch damage (if the vehicle has a manual gearbox).

Many four-wheel-drive vehicles only have a ‘pseudo’ inter-axle lock and lack the reduction gearbox. Examples of these can be found in:

  • The Land Rover Freelander II.
  • The Jeep Patriot/Compass
  • The Third-Generation Toyota RAV4
  • The NIssan X-Trail.

In these cases, such a lock is provided by a multi-disc friction clutch, which is not a complete solution by itself. It does not ensure full locking at high loads, which can be encountered when driving in sand or muddy terrain.

There are also cars which have a reduction gearbox, but do not a have full inter-axle lock. Common examples include:

  • The first-generation Mercedes ML
  • The Subaru Forester manual

The vehicles mentioned above can be classed as crossovers - the category which involves SUVs. Most of these vehicles do not have any switch or level enabling direct control or operation of the drive system, as in the cose of a Haldex clutch.

SUV differ from 4 x 4 and should not be used on mud

SUVs should not be driven in the toughest terrain,
they are not true off-road 4x4 cars

Frame construction

Further differences between off-road vehicles and SUvs can be found outside of the drive system. Off-roaders, for instance, feature a lengthwise frame, which is usually separate from the body, although in some cases it can be welded to it. In the case of crossovers and SUVs, this structure is usually based on car floor panels.
 
Off-road vehicles have a significantly more rigid cab and body than crossover variants, in terms of both bending and twisting rigidity. If a car lacks the frame found in off-road vehicles, any attempt to drive it on rough terrain may crack the floor panels, or even damage the body welding. This is one more reason why SUVs should not be driven in all-terrain conditions.

Suspension and engine

Furthermore, off-road vehicles have a much harder suspension, featuring a larger wheel pitch, which is much more resilient. This helps enable driving on both poor-quality roads and off-road terrain. The suspension of crossover vehicles is similar to that of ordinary cars. During any aggressive off-road driving, the suspension roads and arms may begin to crack or bend.

The engine in off-road vehicles is also constructed quite differently:

  • The lubrication system is designed for use in different positions, including on steep upward and downward slopes.
  • The cooling system can work at a much higher rate, as it maintains the appropriate temperature when driving for a long time with a low speed and at a high engine load.

Additionally, it features solutions which protect against flooding, such as an inlet system that makes it difficult for water to be sucked by the engine and the high positioning of water-sensitive engine components. It may also use specific engine components which are resistant to flooding.

The powertrain in off-road vehicles, consisting of the transfer box, clutch, axle differentials, gearbox, drive shafts, drive joints and axle shafts, is also rather resilient. It is designed to transmit large torques at low rotational speeds, protecting against both the risk of flooding and contact with the surface (by means of a lengthwise frame). The electrical and electronic devices are also waterproof, including all the various controllers, servos and sensors.

Interestingly, despite the fundamental differences in their construction, the prices of off-road vehicles and SUVs in the same class and size are similar.

4 x 4 is more resistant to external factors as water, sand, etc., than SUVs

The sensitive elements of true off-road
4x4 cars are resistant to flooding with liquids

Differences in handling between 4x4 off-road vehicles and SUVs

Even though they are both 4x4 cars, off-road vehicles and SUVs handle differently This is a result of the difference in 4x4 drive systems, the distribution of weight between axles, the tuning of the suspension and their overall construction.

The engines and gearboxes in SUVs are usually positioned transversely in front of the vehicle’s front axle. This means that the front of such a vehicle is almost twice as heavy as the rear. A similar situation exists in most front-wheel drive cars. Such a weight distribution, in combination with a four-wheel drive and the automatic additional drive on the rear axle, causes understeering. Other than this, the vehicle then handles like an ordinary car with front-wheel drive.

SUV or off-road vehicle – the choice is yours

Because of the lack of consistency, the same 4x4 car may be classified as either an off-road vehicle or an SUV. It all depends on the type of equipment provided. It is possible, for instance, to buy certain vehicles with a 4x4 inter-axle lock and a reduction gearbox (making it an off-road vehicle) or without these features at all (classifying it as an SUV). Such options are provided by a number of ranges, including the VW Touareg and the second generation Mercedes ML.

Do you own an off-road vehicle or SUV and don’t know what specific tyres to buy for it? If so, get in touch with the Oponeo customer service team. We are more than happy to provide additional information and help you choose the right tyres. 

About our 4 x 4 expert

Dariusz Wojdas holds a Master of Engineering, specialising in automotive technology, and is a graduate of various Polish universities: Silesian University of Technology, Opole University of Technology and the Officers’ Automotive Engineering College. For more than 20 years, he has been a licensed rally driver and an expert in off-road, four-wheel-drive and sports vehicles (for civilian, sporting, rallying and military use).

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