RE: Bend Assessment

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 doesn’t actual physically move, it’s 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.  It’s 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 ‘false reading.’

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 ‘balanced’ 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 can’t 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 can’t 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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Author
Discussion

DustyC

Original Poster:

12,820 posts

253 months

Thursday 16th October 2003
quotequote all
A very interesting read.
Can a ride-drive course help with sportscar insurance?
If not already then it should.

robp

5,769 posts

263 months

Thursday 16th October 2003
quotequote all
Interesting stuff.

Don

28,377 posts

283 months

Thursday 16th October 2003
quotequote all
Nice explanation! I regularly need to explain this stuff to my IAM Associates...

Now I can point them at this article as well!

Plotloss

67,280 posts

269 months

Thursday 16th October 2003
quotequote all
Nicely written piece.

Muncher83

12,219 posts

248 months

Thursday 16th October 2003
quotequote all
Good article, it's precisely what the IAM says.

tvrman

359 posts

283 months

Thursday 16th October 2003
quotequote all
This is what I was told on a course and it has kept me on the black stuff. It's all about keeping the car flat and stable and having a nice margin for error, or others causing a problem.

Ian

metcalfer

27 posts

283 months

Thursday 16th October 2003
quotequote all
Those who are interested in further reading might find this book useful:

www.amazon.co.uk/exec/obidos/ASIN/0113408587

The advice given in the article is covered here, plus more of the same.

pies

13,116 posts

255 months

Thursday 16th October 2003
quotequote all
Read this a while back and put into practice.Found it difficult to do at first but once i got the nack of it i found i could drive much smoother and faster if i wished

todiddly

33 posts

248 months

Thursday 16th October 2003
quotequote all
Nice article Boss, any chance of a payrise?

MEMSDesign

1,100 posts

269 months

Friday 17th October 2003
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Good article, but I disagree (mildly) with the first part "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.".

I've definitely heard it before, during the time I was learning to drive. I think I probably read it in Roadcraft or similar?

It's a useful deliberate methodology, but isn't it just a description of what your brain does all by itself when you're actually concentrating on your driving (addmitedly something I don't always do very well)?

77-84

77 posts

253 months

Friday 17th October 2003
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Excellent stuff.

ben789

126 posts

262 months

Monday 20th October 2003
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Help, I don’t get it

Surely point C will always move at the same speed as you when your going through a constant radius (i.e. it'll change is speed as you enter and exit the corner, but will always be the same speed as you through it and wont relay any info about going too fast)

e.g. a roundabout

a) as you approach the roundabout the point seems stationary

b) as you enter the roundabout the points moves away from you

c) you speed up the point speeds up, you slow down the point slows down (i.e. how do you know your going too fast?)

d) you exit the roundabout the point speeds away from you.


So how will this make me be able to take a corner faster? I just don’t get it, all it tells me is when to accelerate out of the corner, and maybe the turn in point?

uriel

3,244 posts

250 months

Tuesday 21st October 2003
quotequote all
Ben789 said:
Help, I don’t get it


Me neither...

But my car is off the road so I haven't had a chance to try it out.

Tripps

5,814 posts

271 months

Monday 27th October 2003
quotequote all
Having done a Ride Drive course last week and had this technique explained while hooning around the country lanes in southern (with the supervision of a police officer) it makes far more sense and you really need to see it happening rather than just picture it.

Along with the other techniques taught in that half-day it is amazing how much faster you can travel through roads while driving in a safer manner than before.

GreenV8S

30,149 posts

283 months

Monday 27th October 2003
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The explanation in the article isn't absolutely clear, but the principle is that if the 'vanishing point' is moving towards you, the bend is tightening up. If it stays at a constant distance, the bend is a constant radius and if it moves away the bend is opening up. You can make the same judgement intuitively once you can see enough of the road to make out the shape of the curve, but the vanishing point technique tells you what is happening right at the limit of vision which gives you a couple of seconds head start on the situation. Very un-intuitive, and a bl**dy useful technique to have.

haggishead

8,470 posts

251 months

Monday 27th October 2003
quotequote all
I agree - if you have it shown to you on the road by somebody who knows their stuff, the penny will drop. Once it clicks, you'll always use it - it makes a huge difference to driving along twisty roads that you don't know.