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Old 3rd May 2005, 12:27   #1
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Default Cornering force

I have a doubt regarding cornering force and self-rightening torque produced in for wheelers during cornering.I understood that when a car is taking a turn, a side thrust is produced
beacause of centrifugal force, then as i studied in an automotive book that beacuse of this
side thrust, the car wheels slip to a certain angle to counteract this side thurst and this
slip is caused due to distortion of the tyres.This is where i did not understand the concept
of tyre distortion and slip angle.morever it was mentioned that a cornering force will act on
the wheels, not at the center but at a distance from the center of the wheel causing a torque
to be produced called as self-rightening torque. Can you please explain how.And one final question,
the concept of under and over steering was explained based on the slip angles, so i need some
clarification of that is mentioned above.Thanks in advance
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Old 3rd May 2005, 12:48   #2
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Let me answer your second question.

Understeer : Centripetal Force, that is, the body continutes to move towards the centre of the circle along its radius. Usually caused in Front Wheel Drive and to some extent in Front engined vehicles

Oversteer : Centrifugal Force, that is, the body moves along the circumference of the circle. Similar to the fact that when you tie a stone to a string and circulate it by holding the end of the string. This is cauzed in Rear Wheel Drive cars, Rear / Mid engined cars.
Hope I was little clear.
Had this in my 12th standard Physics
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Old 3rd May 2005, 13:25   #3
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This self rightening torqu is produced because of the castor angle. This is similar to the wheels on the shopping cart wagons. No matter in which direction the wheels are pointed the moment you start pushing them, they all turn to the same direction in which you are pushing.

This is because they have a negative castor angle. The amount of castor angle determines how much self correcting torque is produced. So ideally a large angle would ensure that the steering corrects itself automatically immediately. But a large castor angle increases the steering effort. This can also be seen in the shopping cart wagons in some super market which are such a nuisance to push and turn into the aisles.

This self correcting torque is the force that holds the steering sraight and prevents the car from drifting when yuo are travelling on a plain road and let go off the steering wheel. Remember how people tell you every time your car pulls to a side you got to check the wheel alignment?

Coming to the cornering forces, its actually very complex that there is a separate course called advanced vehicle dynamics. But in a nutshell here is what happens, the forces acting on a car are

1. The weight acting on 4 wheels (may or maynot be equal depending on the weight distribution)
2. The cornering forces (centrifugal and centripetal)
3. The gyroscopic couple because of the rotation of the engine which causes the inner wheels to lift while the outer wheels are puched down.

The net effect of the forces on each of the wheels is algebric sum of the induvidual forces. In most cases when a front engine RWD car is taking a turn, the inner rear wheels are the one on which the least downward force is acting and under hard cornering, the inner rear wheel tends to lift.

Try reading some indian author's books first. They leave out the complicated stuff and give you the basic concept. Then read some other advanced books. Try Anglin and Crowse to get a clear picture. But if you need the matematics part of it then yuo should try some thing else.

PM me if you need some more info about vehicle dynamics. I'll try to get you some stuff.
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