Over, Under, Sideways
Sydney Morning Herald
Saturday September 8, 2001
Front- and rear-drive cars have distinct performance and packaging differences. Neither layout has outright superiority, says Peter McKay.
Is front drive more efficient than rear drive? The push or pull question is almost as old as the car itself.
Front drive is lighter, allows lower floor pans (thus lower seating and lower centre of gravity), frees up more room for passenger accommodation and luggage and is more stable in slippery conditions.
Rear drive is the preference of the enthusiastic and sporting driver, and those who tow boats and caravans.
Holden and Ford have done a heck of a job convincing Australians that rear-drive cars are right for them.
But Peter Evans, an engineer who worked in the product areas of Ford and Toyota and is now the marketing chief of Hyundai, suggests the vast majority of motorists wouldn't know the difference.
"I defy 90 per cent of customers to pick, blindfolded, which is rear-drive and which is front, even when towing," he says.
He believes Australians have deluded themselves into thinking they have an unshakable affection for rear-drive vehicles.
"Their love affair is not with rear-drive cars, but with big, wide, solid, spacious, torquey, cheap, locally built cars. I also defy 90 per cent of customers to be able to enunciate the pros and cons of each system except for old wives' tales and hoary myths!"
He even disputes that towing capability is one clear advantage of rear-drive cars. In his time at Toyota, he says, in-house towing tests showed Camry and Avalon enjoy clear superiority to the Commodore and a small advantage over the Falcon in the areas of stability and traction.
Mercedes now says that front drive makes sense for small cars with modest performance. As well as a low-cost, compact design, front drive simplifies the task of designing the luggage compartment (a simple and more compact rear end is possible because these wheels don't do the driving). The absence of an intrusive transmission hump allows a roomy interior.
As for driving, a front-drive car generally has better traction on slippery roads, when lightly laden and when driven at low speeds. In addition, such cars provide good directional stability on slippery roads.
However the front wheels have a dual role - to drive and steer simultaneously. This double stress on the front tyres can have a deleterious effect on handling.
Still, some exceptionally fine- handling cars on the market today are "pulled" by the front wheels - Alfa Romeo 147, Honda Integra Type-R, Toyota Celica, VW Golf, Hyundai Coupe.
Sports sedans are usually rear drive (BMW 3 Series, Lexus IS200), as are performance cars (Honda S2000, Porsche 911, Toyota MR-2). It features in luxury cars where sporty handling is required, where customers expect it, and where the space and weight trade-off is acceptable (Mercedes S Class, BMW 7 Series, Lexus LS430).
Of course, not all big cars and luxury sedans are rear drive. Audi has long had its whole range in front- or all-wheel-drive. Saab is 100 per cent front drive (with AWD coming).
For the unskilled or even average driver, front drive is considered "safer" because it produces a condition at the limit called understeer - when the front end "pushes" or shows a reluctance to obey the steering wheels. The natural reaction from the driver is to lift off the accelerator, which is the ideal response...
"From an engineering viewpoint," says Evans, "understeer is a 'stable' condition. And very intuitive."
Oversteer - the term used to describe the tail of the car sliding out and more common to rear-drive cars - is an "unstable condition", he suggests. "If the driver of an oversteering car freezes, or lifts off the accelerator, the condition can get progressively worse unless he or she has steered into the slide.
"Countersteer is not intuitive. [And] if you don't get it right, the oversteering can get worse!"
This downside to rear drive is a major reason for the prevalence of vehicle stability control and traction control in luxury (rear-drive) cars.
Rear drive is by far the better layout for race cars (and is enjoyed by race drivers). Given its packaging benefits - and the low skill levels and varying conditions facing the average driver - front drive suits conventional cars rather well.
PUSH OR PULL
Rear-drive characteristics
Natural oversteerer (tail out)
Better traction under acceleration
More sporting
Transmission tunnel compromises interior packaging
Front-drive characteristics
Natural understeerer (front pushes)
More predictable on slippery roads
Safer for the average driver
More efficient packaging,
less weight
© 2001 Sydney Morning Herald