Bringing power to all four wheels of a vehicle is a great way to boost traction and safety at the same time.
So with a growing number of four-wheel drive (FWD) or all-wheel-drive (AWD) cars being offered, the question for car shoppers these days is: Do you need it?
Compared to only a few years ago, many crossovers and estate cars are available with FWD or AWD grip technology. Both help motorists cope more ably with corners, slippery surfaces and harsh territory.
Sales figures underscore the popularity of these variants, despite the cost surcharge. The extra grip has become a big sales and profit generator for makers who offer the option.
There are detractors who dismiss FWD as a hype feature with no everyday benefit.
Not Arnulf Thiemel, who works for the ADAC motoring club. The German expert is adamant that powering all four wheels makes sense although it does depend on the type of driving a buyer has in mind.
Manufacturers do not always distinguish clearly between FWD and AWD. Classic four-wheel-drive means power from the drivetrain is split equally between the front and rear axles. AWD systems channel traction more individually to each wheel in low-grip situations.
They use differentials which regulate the torque or power being fed to the wheels.
"FWD or AWD ensure that engine power is transferred more evenly to the wheels," said Thiemel. The effect is the same on paved roads and loose surfaces such as trails and farm tracks.
A key advantage is that four wheels under power largely prevents slipping and wheel-spinning under acceleration, said Thiemel. Mated to traction control, it should keeping you moving when the going gets tough.
Compared to electronic stability control (ESP) and power delivered through a single axle, feeding power to all four wheels has advantages on sand and in ice and snow. The technology makes it easier to start on hills or when hauling loads such as a caravan, horsebox or trailer, said Thiemel.
The ADAC man also pointed to another reason for the run on FWD-fitted cars.
They have become lifestyle accessories which stand for individuality and yearning for the wild blue yonder. Most owners will however never venture off-road and may encounter nothing more stressful than a speed bump during most journeys.
FWD goes back to the early days of motoring. The pioneering Lohner-Porsche Mixte Hybrid which appeared in 1900 was a battery electric vehicle with two front-wheel hub-mounted motors. It was also offered with four-wheel drive to crawl along rutted tracks.
Off-road cars got FWD from the beginning, but the first car for asphalt offered with four-wheel drive was the two-door FF coupe from boutique maker Jensen in 1966. It was feted by engineers but did not achieve the popularity of the Quattro sports coupe from the Audi.
From 1980 onwards Audi offered the Quattro with permanent all-wheel-drive.
Audi is now moving away from fixed four-wheel-drive.
The new A4 Allroad uses the so-called "Ultra" system of on-demand traction technology. On normal trips the rear axle is uncoupled but engages in less than a second if on-board systems detect a need, said spokesman Josef Schlossmacher.
"These days this is all done using sensors," said Thomas Schuster of the KueS vehicle certification franchiseo. Chips are used to tell if the wheels are starting to spin and the power is then channeled to the wheels.
Other systems can predict and correct swerves or skids before traction is lost.
The ADAC man said buyers should be aware that four-wheel-drive inevitably leads to higher fuel consumption, owing to friction losses in the more complicated drivetrain.
Drivers may also be lulled into a false sense of security by the extra grip which will still not shorten the braking distance in an emergency. (DPA)