While a four-wheeled motor vehicle will perform perfectly well for most purposes so long as two of its wheels are driven, writes Jeff Daniels, traction is much improved when all four wheels are driven. This improved traction allows poor terrain to be crossed more slowly and carefully, with less chance of becomingimmobilised, and confers the ability to negotiate steeper gradients. Full use of these abilities calls for significant drive torque to be available at very lowspeed, hence 4WD vehicles for "off-road" use are generally provided with a step-down transfer gearbox which allows the overall gearing to be significantly lowered when necessary.

The advantages of the light-duty 4WD vehicle for off-road operation was first fully realised during the Second World War with the emergence of the Willys Jeep. The value of such vehicles for agricultural, industrial, forestry and construction industry use (as well as military) created a ready market for warsurplus vehicles and encouraged a handful of vehicle manufacturers to develop new designs more suited to civilian use. Thus the later 1940s saw the emergence of the earliest Land Rovers and more advanced "civilianised" Jeeps. Other interpretations of the concept emerged in the early 1950s, notably the Toyota Land Cruiser BJ of 1951 and the original Nissan Patrol of 1952).

Although developed to meet a civilian need (though often with their commercial viability enhanced by way of military orders) such models were still essentially working vehicles. It was only during the later 1960s that the concept began to emerge of a working 4WD vehicle with a sufficient degree of "civilisation" to appeal to the more general consumer. This trend was accelerated in the early 1970s by the appearance of the Range Rover whose sales consistently exceeded the planned figure. By the end of the 1970s the number of models competing for this new market had risen considerably. It certainly was a new market, not least in that many of the 4WD vehicles sold into it spent little if any time off-road, except perhaps in North America where the "all terrain" environment is easier to access. In short, consumers were buying these vehicles almost entirely on the strength of their "tough, aggressive" appearance and some perceived but essentially "fringe" advantages: greater mass leading to improved survival in a collision, higher eye-line affording better driver visibility. This was the generation of 4WD models to which the term recreational vehicle (RV) was first applied. The major American manufacturers had created their own models for the RV market in the form of the Chevrolet Blazer and Tahoe (and their other GM-badged siblings), the Ford Explorer, and the Dodge Durango.

The vehicles forming the original RV generation were of substantial size - the Range Rover, the later-series Nissan Patrol and Toyota Land Cruiser, the Jeep Cherokee and the Mercedes G-wagen prominent among them. Towards the end of the 1980s the main manufacturers began to introduce somewhat smaller, cheaper vehicles exemplified by the Land Rover Discovery of 1989.

The SUV class emerges
There had long been a sub-class of smaller, lighter off-road 4WD vehicles, almost entirely of Japanese origin (Daihatsu TAFT, Suzuki Jimny). Towards the end of the 1980s new and more capable "compact" models were introduced (including the Daihatsu Feroza/Sportrak, Suzuki Vitara) and these began attracting new customers and opening up a market sector which the larger manufacturers could not ignore. In Europe, General Motors launched the Frontera, essentially developed by Isuzu, and Ford developed the Maverick in collaboration with Nissan, which marketed the vehicle as the Terrano. However it was Toyota's introduction of the RAV4 in 1994 which defined the apparently ideal package for the attractive compact 4WD vehicle which became known as the Sport Utility Vehicle (SUV). The RAV4 was quickly followed by rivals such as the Honda CR-V and Land Rover Freelander - so quickly that it was clear many product planning teams had been thinking along the same lines. The attraction of this segment was shown by the speed with which newcomers prepared suitable models: a good example is provided by the Korean manufacturers, with the rapid appearance of the Hyundai Santa Fe, the Kia Sportage and the Ssangyong Korando (Daewoo took over the ailing Ssangyong and made its 4WD models an integral part of its own range).

A further sector of the "consumer" 4WD market was opened up in the later 1990s with the appearance, mainly in the USA, of a new generation of large RVs with luxury equipment, commanding higher prices and representing greater value-added. The Japanese manufacturers began the trend with the Lexus LX450 (later 470) and the Infiniti QX4, which were quickly joined not only by home-grown American rivals - Lincoln Navigator and Cadillac Escalade - but also by the all-new BMW X5 and Mercedes M-class, both manufactured in new US plants. This class has now been joined by the Volkswagen Touareg and a technically allied model, the Porsche Cayenne. These newer models place greater emphasis on road-driving pleasure and are essentially "large SUVs".

Light trucks, a major factor in North America
There was, however, more to the American picture than this. In the US market, pickup-configuration vehicles classified as "light truck" (by American definition, up to 10,000 pounds gross vehicle weight) also became extremely popular not only for their ability and convenience in a range of driving environments but also because they continued to offer the kind of engine size and performance which was largely denied to the conventional passenger car by the CAFÉ requirement. The typical light truck, still with a pickup load space, now often incorporates a 4/5-seat cab with an extremely high standard of equipment. To begin with, light trucks were generally rear-driven but 4WD versions became increasingly popular. The light truck class accounted for almost half of the US market for "personal" vehicles in the early 2000s and getting on for half of them were equipped with 4WD. Light trucks have been subject to their own CAFÉ requirement for several years but the standard (27.5mpg for passenger cars, 20.7mpg for light trucks, US gallons) is more relaxed, as are exhaust emission requirements. Thus the vehicles can still be offered with large-capacity V8 and V10 engines of a kind rarely seen in conventional passenger cars.

For CAFE purposes the US Federal definition of a light truck is remarkably wide in its scope. It includes "vehicles that transport property on an open bed; or provide greater cargo-handling volume than passenger volume; or permit expanded use through the easy removal of seats; or can carry more than 10 persons; or can provide temporary living quarters." In addition, it extends the classification to any vehicle "designed for off-highway operation, having either four-wheel drive or with gross vehicle weight exceeding 6,000 pounds and with four of the five following characteristics: approach angle of at least 28 degrees, breakover angle of at least 14 degrees, departure angle of at least 20 degrees, running clearance of 20 cm or more, and/or axle clearances in the front and rear of not less than 18cm."

This definition means that "light truck" embraces all RV/SUVs and minivans (MPVs) as well as vehicles with pickup-type bodies. It also means that any vehicle with 4WD can be rated as a light truck so long as it complies with the "characteristic list" which is not especially demanding in engineering terms. Subaru actually increased the ground clearance of its US-market 4WD Outlander in order to have it reclassified as a light truck rather than a car. In any event, as a result of this historical evolution, the US market for 4WD vehicles now embraces a number of segments including:

  • Traditional "workhorse" vehicles such as the Jeep Wrangler,
  • Large-size RVs such as the Chevrolet Trailblazer, Ford Expedition and
    Jeep Grand Cherokee,
  • The SUVs, which seem now to be subdividing into a larger and a smaller class, the former including the Ford Escape and Chevrolet Blazer, the latter the Honda CR-V, the Toyota RAV4 and the Land Rover Freelanderamong several others,
  • The Luxury RVs/SUVs including the Lexus, Infiniti, Lincoln, Cadillac, BMW and Mercedes models, plus the VW Touareg/Porsche Cayenne and theRange Rover,
  • The 4WD versions of the light pickup trucks including the Ford F150 - the world's biggest-selling single vehicle model series - and its rivals from GM and Chrysler, plus US-built newcomers from Honda, Nissan and Toyota.

Road-going 4WD
During the 1980s there also emerged a trend to equip purely road-going cars with 4WD. This trend was mainly established by the Audi Quattro although there had been earlier examples, notably the Jensen FF, while Subaru (Fuji Heavy Industry) was already making 4WD cars in Japan. In the road-going case, the requirement was again to achieve optimum traction, but on low-friction road surfaces rather than slippery off-road conditions. The benefits were most evident in high-powered sporting cars which benefited not only from reduced wheelspin and better acceleration in adverse conditions but also, it was claimed, superior handling and ease of control. In such cars, there is no requirement for intermediate step-down gearing.

In the early 1990s especially many powerful road-going cars, especially in Europe, were equipped with 4WD for these reasons. At one time the majority of European vehicle manufacturers offered road-going 4WD models and promoted them with some enthusiasm, but by the mid-1990s there efforts had waned and the number of models considerably reduced, most of the remaining volume being claimed by Audi with its quattro range. Aside from Land Rover and Mercedes-Benz, the European manufacturers showed little interest in developing off-road RVs or SUVs. In some cases, for example Renault, the emphasis shifted to light "multi-surface" 4WD models with raised ground clearance and underbody protection. On the other hand, within the last few years, Jaguar has introduced a new road-going 4WD model, the X-type.

Demand for purely road-going 4WD cars has not evolved to anything like the same extent as for off-road vehicles, partly because lower-cost technical alternatives, such as traction control systems, have become fully developed and widely available in the last decade.

Most recently, Europe has shown much greater interest in a new market segment which has emerged for so-called "crossover" 4WD vehicles, which set out to combine the features of a road-going estate car with those of an SUV. New models in this category have been announced by Audi, Saab and Volvo. Such inherently high value-added products have enjoyed considerable initial success. Many of them are explicitly aimed at the US market.

The need for 4WD?
It has been pointed out before that many of today's RVs, SUVs and light trucks spend little if any time off-road and that logically, these vehicles do not need 4WD. It could be argued that it is the SUV image which is important, not the fact that all four wheels are driven - with a system which inevitably adds weight and cost, and reduces overall mechanical efficiency.

There is a divergence of opinion between manufacturers and in different markets as to whether 4WD should be standard. Those manufacturers whose reputation is built on a strong tradition of 4WD refuse to contemplate offering outwardly identical vehicles with 2WD. Land Rover is the most outstanding example of this attitude. On the other hand, the vast majority of RVs, SUVs and pickups sold in the USA offer 4WD as an option, the "standard" configuration until very recently having been rear-wheel drive (RWD). Smaller SUVs are now turning to transverse engines and front-wheel drive (FWD) as their standard drivetrain configuration. Toyota offers its RAV4 in both 4WD and rear-drive versions. Honda, on the other hand, builds the CR-V only as a 4WD (it does, however, also build the "SUV image" HR-V with a choice of 4WD or FWD).

In many European markets, 4WD buyers fall into two very different groups. On one hand are those who buy "workhorse" vehicles for agricultural and allied purposes; on the other, a significant number of customers, often city-dwelling, buy SUVs for what might be termed their cosmetic value. A survey carried out some years ago by Michelin, researching the likely pattern of demand for replacement 4WD tyres, revealed for example that more than half of all Range Rovers in the UK were registered in London postal districts. It remains an open question whether this second group in any way benefit from the capabilities of 4WD, or would even be aware whether or not their vehicles were so equipped. Despite this, the vast majority of "SUV character" vehicles sold in Europe are 4WD, while in the USA buyers seem more willing - and are afforded the opportunity - to balance their real need against the additional weight, cost and fuel consumption of the 4WD option.

Expert Analysis

Automotive 4WD transmissions: technology, markets, suppliers and manufacturers - forecasts to 2010

The advantages of the light-duty 4WD vehicle for off-road operation were first fully realised during the Second World War. By 2004, the main world markets have long since arrived in a situation where all retail vehicle buyers were aware of 4WD, mainly through the consistently strong growth in sales of vehicles ostensibly intended for off-road operation. This report deals with aspects of the 4WD transmission market and technology, downstream of the main gearbox (manual or automatic). It therefore concentrates on the centre differential, final drives, propeller shafts and associated components. Written by multiple award-winner Jeff Daniels, this impressive report looks at 4 wheel drive technologies, markets, suppliers and manufacturers, and forecasts out to 2010 by transmission type by region globally, for Europe, NAFTA and Asia.

To find out more about this report, download your sample or to order your copy, please follow this link