Today’s motorist is spoilt for choice. Front or rear wheel drive, constant or on-demand four wheel drive, dual range etc.etc., are all available from many makers.
It all started with rear wheels being the ones that transmitted the power to the road. Then Citroen, always a lateral thinker, introduced a front wheel drive car in the 1930’s. Four wheel drive cars do, in fact, date back even further – to 1899! But they weren’t really recognized until the Jeep of the Second World War, and from then on this multiple choice became commonplace. So, if you buy a new car today we can be thoroughly confused by choice, and that means we need to be informed, so let’s look at what the differences are and what could be best for you.
The vast majority of cars are driven by two wheels only, and that should be more than adequate for the vast majority of uses. But there is still a choice – the front two wheels driving the car, or the rear two wheels doing likewise. Most cars now are front wheel drive- and for good reasons. They cost less to make, save space in the passenger cabin (there’s no need to provide room for a hefty drive shaft to go from the front engine to the rear wheels) and they offer weight savings, which give marginally more economical (but crucial to marketing) fuel consumption. They also handle better – or, at least, more predictably, with less likelihood of wheel spin and loss of traction. This is less important today as most cars come equipped with some form of traction control. There are some drawbacks, however. When you test drive a front wheel drive car you need to test it under hard acceleration to see if it suffers from ‘torque steer’, which is where the car is less likely to respond to your steering input under heavy acceleration. This was an early problem, but, again, traction control has had a curative effect. You’ll also notice a difference under hard cornering, but you need to be driving pretty enthusiastically to notice this difference! The more traditional rear wheel drive still rules the roost with the larger saloons, where the front end engine weight can reduce the driver control of front wheel drive cars. It’s also favoured by sports car driving types who like to control cornering with the steering wheel. If you are towing a lot then rear wheel is also preferable to front wheel (but both are eclipsed here by four wheel drive).
So what’s the difference between four wheel and all wheel drive? Officially nothing. History tells us they mean the same thing, but some manufacturers have tried to create a difference for marketing reasons. In their eyes four wheel drive vehicles are those that are driven by all four wheels, often with an ability to switch to two wheels or low range four wheel drive, whereas all wheel drive vehicles are seen as those that are constant four wheel drive. But just to complicate things, others say that all wheel drive is reserved for those vehicles- mainly military, that have more than four all driven wheels! But then other countries will define four wheel and all wheel drive differences differently again!. So we’ll ignore the different definitions and look at the different types.
Some passenger cars have permanent four wheel drive, such as Subaru and Audi Quattro. All four wheels are being powered all the time, irrespective of conditions. They have a big advantage in difficult road conditions such as rain, snow and ice as they are less susceptible to wheel spin and loss of control. That’s because power, and therefore too much power (which causes wheelspin), is spread amongst four wheels, not just two. This provides quicker, smoother and safer acceleration and braking, though again, with modern traction control and anti slip sensors, the advantages over two wheel drive cars are reduced. On the other hand, they are more expensive to make, are more complicated, and suffer somewhat in the fuel consumption stakes.
The old idea of ‘on demand” was when the driver wanted to switch from 2 wheel drive to 4 wheel drive he’d press a switch- and often that would mean getting out of the car and changing a couple of lock nuts on the front wheels. Things have progressed since then, to a point now, where, with some vehicles, the computer takes complete control. Sensors can detect the ‘slip potential’ and bring in extra drive to wheels not currently employed, so that slip or skidding is avoided. This means that the vehicle can automatically switch from 2 to 4 wheel drive as driving conditions change. Generally 4 wheel drive is less fuel efficient, so such a switching feature helps improve fuel consumption.
Here we’re talking about the more specialist ‘off road’ vehicles that are specifically designed for challenging terrains. Most are also quite capable of normal tarmac travel, but, if you want to go off the highway, these are the vehicle most suited. Again they can be constant all wheel drive, and then be equipped with ‘low range’ which is an additional gearbox that allows the vehicle to tackle extreme conditions that you won’t be confronted with on main road travel.
The benefits and drawbacks of all of these traction systems are now being muddied by the advances in traction control and corner sensors. Some more sophisticated systems are already moving power from corner to corner, side to side and front to back to ensure both maximum grip and maximum economy, and it will only be a matter of time before these systems, currently the domain of expensive all (or four) wheels drives filter down the line.