Bend Lines

Following last months edition of ‘Tip Offs’ which covered the reading of bends, in this months edition we are looking at bend lines themselves, that is to say the path along which you need to travel to get the car around the corner.

What we are trying to achieve when cornering in this way is for the vehicle to negotiate a curve efficiently and safely whilst keeping the forces acting upon that vehicle both to a minimum and singular.

If you have a conker on a string, and spin is around your head, the string remains taught and parallel to the ground.  This occurs because there is centrifugal force acting on the conker, which keeps tension on the string because the conker is pulling outward.

If we again spin the conker, but at a faster rate, the amount of centrifugal force increases resulting in a tighter string.  When we apply this analogy to a cornering vehicle there will come a point, as the speed is increased, where the speed at which it is travelling, and trying to corner at, will make the force become so great that the tyres are no able to cope and adhesion will be lost.  In other words the centrifugal force reaches a point where it exceeds the force that is keeping the car on the road – tyre grip. 

Every bend will have its own critical speed point depending upon severity, which means it has a physical speed limit up to which it will allow a vehicle to travel around it and stay on the road. However, that limit will become reduced if the curve is not taken on the optimum line and from the optimum position on the road and is not kept to a perfect arc.

That is one of the reasons we take the widest arc as this, amongst other things, reduces the centrifugal force acting upon the car, which means you are further away from the point of control loss.

With this in mind, and with the aid of diagrams, let us look at what the optimum line will be.

Dealing initially with a right-handed bend we see the correct approach position should be with the near side wheels as close to the near side edge of the carriageway as possible, having due regard to any potholes, broken or subsided edges, mud or gravel that may be present.  Now this is where the skill factor comes in.

In the diagram you will see that our driver has tucked the car well into the near side on the approach and then held that line as the car has driven through the curve keeping, as far as possible, to a constant arc.

Try to simulate that position as you travel around the curve and without submitting to the temptation to pull the car off-line towards the centre white line.

In fact, whilst bearing in mind what we said about conkers and string, by putting in more steering this means a driver is only making matters worse.  Remember, the corner you are entering may continue for longer than you think and if you come off-line too early you may eventually end up facing the near side kerb/verge at right-angles with no where left to go but ditch-bound!  This takes a great deal of practice to perfect and should initially be done at low speeds until the skill is mastered.

The advantages of cornering in this manner are many:

  • It allows you to assess the severity of the bend earlier enabling you to set the car up ready for the corner (speed, gear, etc.)
  • It allows you the maximum view into the bend so you can see further ahead.
  • A driver approaching from the opposite direction will see you earlier.
  • You are away from any potential conflict so that when Ronnie Rep comes a little too fast the other way drifting wide as he rushes to his next appointment you are in the safest, and therefore the most defensive position.
  • You negotiate that corner whilst keeping the centrifugal force acting upon the car to a minimum.

If we take the situation we see here in the second diagram, this time our driver has adopted the very awkward position of placing the car towards the crown of the road.  This now makes the curve very much tighter and also has the effect of pushing the car wide on the exit.  It is very difficult to maintain a perfect arc from this position and cornering in this way is a very common cause of cars falling off the road.  If you go in shallow you come out wide – remember it well!

Going back to our original drawing, once you can see the finish of the curve then your line may change as necessary, for example if the right-hander is immediately followed by a left - the position for which we will discuss next.

Much the same principles apply for left-hand bends. Obviously the most effective approach position for these is to put the car as far across to the offside of the road as possible.  The problem with this is that the right-hand side of the road tends to be used by traffic coming from the opposite direction and those drivers could perhaps become somewhat upset with you being a potential threat to their general state of well-being!

If the layout of the land is such that you are able to see around the curve to the opposite end, or you can get a good cross-view (this is a view you would get say across a field that has no hedges) and therefore be confident there was nothing coming you could, road markings permitting, move the car out over the road centre on the approach side before you get into the bend.

The advantages here are similar to that of the right-hander in that:

  • It allows you to assess the severity of the bend earlier enabling you to set the car up ready for the corner (speed, gear, etc.)
  • It allows you the maximum view into the bend so you can see further ahead.
  • A driver approaching from the opposite direction will see you earlier.
  • You negotiate that corner whilst keeping the centrifugal force acting upon the car to a minimum.
  • It takes a great deal of the ‘sting’ out of the curve and is therefore more comfortable and puts less stress on the car’s component parts.

Obviously if there is another road user approaching from the opposite direction then you would remain on your own side of the white lines.  All it means in this scenario is that you will have to reduce your speed and keep to a tighter line.  You have to remember also that the view into a bend will vary from one to another and from one day to the next so use the diagram as a guide only.  Each bend has to be judged upon its own merits.

You could also get the situation on the approach side where there would be a junction to the right.  Again this would be a potential area of conflict and use of the offside should be avoided.

The advanced driver should always be in a position where he is travelling at the correct speed with the correct gear engaged and be able to exit the curve whilst remaining on the correct side of the road.

The thing to remember here is that on either type of bend you have to assume the correct position well before you reach that bend, not as you are in the process of entering it.

The overriding factor in all of these techniques is that you never sacrifice safety for position and you MUST always be able to stop within the amount of tarmac you can see in front of you at any given time.  Don’t get territorial and always be prepared to give ground to someone else.

The Tuscan driver in the photograph  is positioned so as to obtain the best possible view through to the left hand bend coming up at the back of the picture.  Effective early approach line.

Comments (27) Join the discussion on the forum

  • billbob 05 Jan 2004

    I liked the "taking the bend" article. However, as a Physics teacher I have to remind the author and readers that there is no such thing as centrifugal force. It is an imaginary force that is actually the tendency for something to go straight -- that is unaccelerated in either direction or speed. That tendency to go straight is Newton's first law. A force has to be applied to accelerate (change direction) of the car in the bend (Newton's 2nd law). That force (called "Centripetal Force") is what keeps the car turning on an arc and centripetal force comes from the friction generated by the tires.

    If you lose traction completely (start sliding) you do NOT go in the opposite direction of the radius of the corner -- that is slide out. You go straight because there is no force acting on the car to turn (accelerate) it.

    Now while you may think this is a semantic difference, it is not. The reason the string on the "conker" (or whatever the example was -- it is a term we don't use on this side of the Atlantic) is tight is because there is a force acting to pull it inwards. Without the force pulling it would fly off straight at a tangent to the circle it was on. So would the car. We inherently know that because we believe in Newton's laws and have seen them work. But we also make up ideas like "centrifugal force" which doesn't exist in Newtonian mechanics, only in rejected earlier mechanics models.

    So... at the risk of sounding like an academic...... Just keep on obeying Newton's laws (F=ma -- Newton's 2nd law is a good one) and you can drive quickly indeed!


  • Graham.J 05 Jan 2004

    Blimey talk about lurkers

    Good article I thought and it's far too early in the morning for my brain to learn about centripetal forces as apposed to centrifugal forces

  • pdV6 05 Jan 2004

    Pedantic head on...

    The first diagram appears to be the same as the 2nd... which explains why it confused me so much on first reading!

  • PetrolTed 05 Jan 2004

    pdV6 said:
    Pedantic head on...

    The first diagram appears to be the same as the 2nd... which explains why it confused me so much on first reading!

    Ooops... Sorry, my fault. Teach me to edit in the early hours

    It's fixed now.

  • boltona 05 Jan 2004

    Good article, but I have a comment on the first right hand bend diagram: Any circuit driving book will tell you to clip the apex, which on the road means trying to touch the offside wheels of the car to the central white lines at the apex, and then move to the outside of the bend on the exit. It's somewhat counterintuitive, but if you actually draw this out, you will see that this results in an arc of larger radius than the outside arc of the bend and in theory allows greater speed around the bend than just hugging the outside. It also gives you a bit more room if the bend tightens unexpectedly, or puts you in a better position if an unexpected left hand bend occurs soon after the right hand one.

    HOWEVER, this obviously does result in reduced visibility around the bend, and makes you vulnerable to people coming the other way drifting towards/over the centreline. So I would suggest only doing this if you have reasonable visibility around the bend.


    >> Edited by boltona on Monday 5th January 11:19

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