Thursday 16th October 2003


BEND ASSESSMENT

Ride Drive's Julian Smith educates us in the art of making progress through corners

You may be surprised to hear that cornering is one of the aspects of motoring where drivers get into a great deal of difficulty. It's an area of driving where far too many cars simply end up falling off the road. 

Effective cornering is not something that we as drivers ever get to know about, unless we have taken part in some form of advanced driver training.  The way in which people drive around bends in very much based on their own personal experience, which they build up through their own individual experimentation and usually through observing others.  That is very much a trial and error method of doing things and is perhaps more than a little haphazard.

The Science

The art of successful cornering is not merely a case of just turning the steering wheel, but one that involves a whole range of other factors.  How do you take a bend properly, effectively and safely?  There are many forces acting on a car depending on road conditions and driver input and the subject of poise and balance become most important here.  As an ideal we do not brake or accelerate, because this, combined with the requirement to steer, would amount to an additional force being added to the lateral/centrifugal force induced by making the car travel in a curved path.

So as not to brake in a bend we have to first get the car travelling at the correct speed for that bend before we actually begin to apply any steering, and this means we have to accurately assess the severity of that bend before we get to it.  So, how do we know at what speed to be travelling at for any given bend before we are actually going through the process of negotiating that bend?  Well it has a lot to do with something called 'vanishing points' or 'convergence points.'

Vanishing Points

Vanishing Points The vanishing or convergence point is the last little bit of the road surface that you can see before it disappears out of the range of view, which can be the point where the road surface disappears around the corner.  So how does that help us?  Well it works like this.

Take you car out on the road, preferably to a rural environment, and find yourself a right-handed bend, for example.  Drive towards it and stop the car on the near side of the road at a distance of about 50 metres before the start of the bend.

As per the diagram, from your driving seat site an imaginary line from your head, passing through the last bit of visible offside verge to a point where your 'line' meets the near side verge.  By labelling these points A, B and C in the order of appearance we can see that C is the point where your line ends against the near side verge and is your vanishing point, B is the vanishing point of the offside verge and A is your eye.

Whilst keeping your eye fixed on point C, move the car forward towards the bend and watch what happens.  You should see that point C will 'move away' from point B or, to put it another way, the verge on the far side of point B will begin to unravel as you begin to see more and more of it.  It is rotating around point B.  When point C is moving at the same speed as your approach it means that your speed is appropriate for that particular bend and you should be able to negotiate that bend safely at that speed.  Of course the verge doesnít actual physically move, itís just that you begin to see more and more of it revealing itself.

In Motion

Now go back and approach your bend again, this time without stopping.  Watch for the movement of point C around point B. As you know the bend by now, drive it again and deliberately approach it too fast (within reason! ).  You will see that all the time that you are travelling at excessive speed for the corner, points B and C remain static relative to one another.  Itís a bit like driving at a brick wall.  Your brain will make a calculation as to the where the latest point is that you can apply your brakes in order to stop before hitting it.  Much in the same way you will want to reduce speed for the corner if you do not see the convergence points moving relative to your distance from that corner.

One word of warning here, once the points indicate that your speed is appropriate for the corner, don't take it for granted!  You have to keep watching as you will have to be wary of the bend that has a double apex!  Another warning here as well is to make sure you use the road-edge and not the hedges (refer back to diagram) because where the hedge line sits back from the edge of the road this will give a Ďfalse reading.í

Which Gear?

So, you have got your approach speed right so now what?  Having assessed your approach speed accurately prior to reaching the bend and you have adjusted your speed accordingly, you should now select the appropriate gear for that road speed.  This will be a responsive gear that is going to take you around the bend under full control.  Don't accelerate but keep your right foot in such a position that you are travelling on a 'balanced' or 'neutral' throttle setting, that is to say with the engine driving the car along but with no fluctuation in road speed.  Drive the car like this smoothly through the bend and wait until you are back on a straight, or near-straight path, on the exit side before you apply the power to accelerate.

If you think about this procedure you will realise what is happening in terms of the cars' balance. As you approach the corner, and you are either decelerating or braking, which means the weight shift within the vehicle is moving forward and it is doing so whilst you are travelling on a straight line.  Once your speed is adjusted correctly, and you have selected your appropriate gear, by applying a Ďbalancedí throttle the balance of the car returns to a point where its weight is evenly distributed, making the car as stable as possible before introducing any further forces, such as steering.

Practice

This is something that takes a while to become tuned into, but once you do get the hang of it you can drive along any piece of road and use this method at every twist and turn and find that you can make good progress, even if you have never driven that road before.  The method works just as well for left handers as well.

There is something else to bear in mind.  Many of you may have participated in the odd track day, or may even do a spot of competition work in a track environment.  If that is what you do then you probably are thinking that what you have been reading here does not have credibility?  Well, let us leave you with this thought.  On the track, how many vehicles are travelling in the opposite direction?

How important is it that you exit a corner on your own side of the road?

Track vs Road

Whilst travelling around a circuit for several laps you become familiar with every little ripple, stone and crack of the road surface.  Every damp patch or imperfection is indelibly printed on your brain and you are able to compensate for it.  This means that you can brake into corners and you can 'boot' the car out of the bend in a controlled power drift across the whole road-width quite comfortably.  But when you take a car down a public road can you say with confidence that you know every little ripple, crack and oily spot there is in that environment? 

Are you absolutely certain the local farmer hasn't just parked and left his tractor around the next bend - complete with plough attached?  There are so many variables on a public road you canít afford to take anything for granted.
 
The public road can change in character quite dramatically over a very short period of time.  You do not know what is there so drive accordingly and base your assessment on what can be seen, what canít be seen and what circumstances may reasonably be expected to develop.  Always be in a position to stop within the distance you can see to be clear ahead.  That means the distance between you and the 'Vanishing' point!

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