News Article

What maketh a good chariot then? Where do they come from? How do you recognise one? And how do you get the best from it? This is the question most often asked and is an ancient question challenging charioteers and manufacturers throughout history.

Over almost five millenia chariots changed little. At the beginning of the century the horseless carriage was hailed in New York as a saviour from pollution. Several thousand tons of dead horses and manure were apparently collected from the streest daily. And, today, chariot development continues across the industrial world - with many configurations tried and championed by chariot designers, makers, and drivers.

Make no mistake, there is nothing new on the chariot front, but charioteers leave no stone unturned in their quest for the competititve edge. Front drive was by far the most common type of chariot. The horse(s) at the front drag the vehicle along the road and off the straight and narrow corners as required by terrain or at the command of the charioteer.

They are relatively economical to construct, lightweight and keep the horses out of the passenter area. The Gauls in particular were exponents of this type of chariot.

Front wheel drive is the natural choice for the modern era, bent upon building mass produced cheap cars. Front wheel drive vehicles are relatively easy to produce, and tuned to be be safe in the hands of the masses. Type two chariots effectively put the cart before the horse. This on the face of it seems a silly idea but there are significant advantages. Most notable is more and better control of direction and, apparently, less need to communicate with the horses regarding directional changes. Such rear pushed chariots are also relatively simple to construct. It also offers good acceleration and generally less conflict when changing direction - achieved by altering the front wheel's direction.

Rear Wheel Drive

So what's the difference with rear wheel drive cars? Nothing is the answer - until the limit approaches. Rear wheel drive cars generally have superior steering systems that provide excellent front grip and feedback. The great advantage of well designed rear wheel drive cars is that the front wheels steer and the rear wheels drive. It is also possible to put more power through the driven wheels when you don't have to steer through them.

Modern computer modelled multi-link suspension systems have revolutionised rear wheel drive cars. These can now easily be designed and tuned to understeer and in combination with modern eletronic stability systems they have transformed limit handling anomalies of the past - making RWD 'safer' than it was.

The third design of chariot is a combination of the first two and involves pushing and pulling horses; 4WD.

All Wheel Drive

All (or four) wheel drive has the huge advantage of traction. In low grip situations this really shows in acceleration performance.

The huge potential difference in acceleration performance compared to two wheel drive often causes big problems for inexperienced drivers or those new to all wheel drive. The acceleration is so much better. But braking and turn-in are slightly less effective. The key point here is that all vehicles are 'no wheel drive' at optimum turn in. The AWD system forces more weight into the components that make the front suspension work, destroying optimum turn-in performance, unless modified.

Handling Characeristics

All cars in the modern era have to obey what has become termed the 'Natural Steering Model' (NSM). Turn the wheel more and the car turns more. It's not absolutely perfect but it's not a bad model. It's a natural friend of understeer. When the limit of grip is approached, the car simply becomes less responsive to steering inputs. Steering simply becomes less and less effective. People having a simple understanding notice the model becoming less effective and assign, quite correctly, they are going too fast. Crucially the NSM didn't disappear, it just became less effective.

The onset of understeer is often accompanied by a little voice in the head saying - 'Mummy it won't go round the corner'.

The secondary feature of the NSM is that the natural response of the driver tends to help them out near to the limit. As the driver notices the limit of adhesion they have several options: Steer more, Steer less, Get off the gas or Slow using brakes.

Steering more simply provides the driver with confirmation they are near, or over, the limit of adhesion. It also causes increased drag at the front; since the wheels are not pointing in the direction of travel and are sliding somewhat sideways to the direction of travel of the vehicle. This drag causes the vehicle to slow and forces the car in the direction of the steering resulting eventually in the car slowing down, finding grip and turning-in.

As long as there is enough room for this to take place, the situation is basically self-correcting. This is a good result, apart from increased tyre wear as a result of increased slip angles.

Steering less is the domain of the smart driver, who knows they have passed the optimum steering angle and that they will find slightly more grip with slightly less steering - especially if they are near the limit and have eased off the gas.

When the NSM causes the driver to slow down or stop accelerating, there is a change in the weight distribution, pushing mass over the front wheels. The load increase on the front tyres makes them more effective and the vehicle tends to turn in more. This naturally happens when lifting off or under modest braking.

In a front drive car, lifting off the gas causes the front tyres to engage in an attempt at steering and braking at the same time. Tyres are generally only good at doing one thing at once - preferring to go straight on rather than turn. One action is always preferable to both at once. The activities have to share out the capacity of the tyre to provide grip. It's physics see?

In low grip situations (icy roads) with even modest capacity engines it is possible to lose front wheel traction completely by lifting off the gas. Loss of steering results.

In rear wheel drive cars, lifting off the gas results in engine braking at the rear wheels, thus front grip increases as the weight shifts forward. This is an optimal situation because the front wheels are not braking and steering as with FWD and AWD cars. Front grip increases with load, as rear grip tends to reduce.

Depending on critical factors, the vehicle might turn-in better at the front and at the same time it may very well turn out at the rear. Less weight means less potential grip. In the extreme, we see motor cycles with their rear wheels in the air. No firm contact with the ground means no grip and the vehicle tends to spin - this is oversteer. At this point the Natural Steering Model fails completely, and it's up to the driver to control. But how?

An over-steering vehicle requires counter steering. This is outside the NSM. Oversteer correction is like that!

So what's the difference with rear wheel drive cars? Nothing is the answer - until the limit approaches. Rear wheel drive cars generally have superior steering systems that provide excellent front grip and feedback.

That said, all powerful rear drive cars which do not have ESP can be persuaded into oversteer very easily in poor grip situations. Power oversteer is assured when excess power results in loss of traction which means loss of lateral grip. Sideways.

So how do we drive these different cars on the limit? The fundamental advantage of a rear drive car is that we can control each end of the car independently. Front is controlled with steering and rear with throttle and steering. What this means is we don't necessarily have to turn the vehicle using the front wheels only. In fact we don't have to turn the front wheels very much at all, if we can get the rear to do some of the turning of the vehicle into the desired direction, using a bit of oversteer.

Both ends moving means less steering and less drag with a more effective change of direction. (All this happens at the limit of adhesion - the limit of possibility). And this means, if we can master oversteer, we can turn the vehicle quickly, getting on the gas early, giving fast exits from bends and speed on the straights.

Firstly, we need to optimise frontal grip to get the car to turn in. And for this we need the right amount of steering - carefully selected, and progressively added. We want this with the maximum weight on the front wheels. And to do this we will be decelerating off the throttle - just like with front wheel drive cars.

When the front is pointed where we want to go, we can start to reduce the quantity of steering and at the same time start to increase the degree of throttle applied. This is the holy grail.

The downside is this can be a bit scary at speed and needs more than a little skill and far more than average commitment.

It is rare indeed that a front wheel drive car out-performs a rear drive car and it's no coincidence that all F1 cars are rear drive vehicles. F1 dallied with AWD in the late '60s and it was eventually banned. No FWD car has ever been successful in F1. And neither has any AWD car really succeeded in anything, other than rallying.

All wheel drive is easy, because it generally follows the Natural Steering Model. Even at the limit of grip, AWD cars are tuned to understeer. When an AWD car slides in a drift, having lost traction at each corner, it is possible to change the direction that the vehicle faces by application of steering and a controlled, liberal dose of throttle. This is similar to a drifting front wheel drive car.

The applied steering gives direction. And applied throttle drags the front of the vehicle in the desired direction (i.e. the direction in which the front wheels point.) It is possible to recover from any body slip angle. Full throttle, full lock will bring these cars back from the dead, provided that we have enough room, and grunt.

Just watch the rally cars in action at flat chat on a special stage if you don't believe me. This is AWD in its element. The marketing machine tells us that all wheel drive is better, and most people take that for granted. But it's my belief that this only applies for relatively high power to grip situations.

In general, my view is that all wheel drive is an unnecessary gimmick of the marketers, who have taken advantage of the successful kudos that international rallying brings. In reality, there are very few occasions where all wheel drive is much of an improvement over an optimised rear wheel drive set-up. There I've said it! Nailing my colours to the mast, rear wheel drive is my preference, still.

Just remember, of the ancients, Walterious Rholious was legendary; whipping his horses into a frenzy before charming them with doughnuts. That's the spirit.