Centre of Gravity/ Roll Inertia

[Tony]

The centre of gravity is dependent on height relative to the wheel track, this determines the load transfer from side to side causing the body to lean. Centrifugal force acts at the centre to lean the car toward the outside of the curve, increasing lateral force acting on outside of the tyres.

As seen here

 

The centre of gravity height, relative to the wheel base, determines load transfer between the front and rear. The cars momentum acts at its centre to twist the car forward or backward, respectively during braking or accelerating. Since it's only the downward force that changes and not the location of the centre of gravity, the effect on over/under steer is opposite to that of an actual change in the centre of gravity.

 

The effect is controllable by the use of the springs/ anti-roll bars or the roll centre height but with careful consideration to the roll angular inertia.

 

Rearward weight bias is preferred due to the enhanced effects during the transition from the straight-ahead to cornering. During corner entry the front tyres are generating part of the lateral force required to accelerate the cars centre of mass into the turn. However the lateral force being generated by the rear tyres is acting in the opposite direction trying to rotate the car out of the turn. For this reason a car with 50/50 weight distribution will under-steer on initial corner entry.

 

To avoid this most racing cars have a 45/55 or even a 40/60 weight distribution, this gives the front tyres the advantage of avoiding the cars moment of inertia reducing corner-entry under-steer.

 

Questions welcomed.....

[jon]

I'm not sure if this is valid for this level of discussion but the angle of the roll center / roll axis of the car is also very important, as is how the roll center moves during suspension travel. McPherson struts are notorious for this due to as the car rolls the roll center falls and moves into the corner meaning the car rolls even more.

 

Explains why almost all 'sports' cars with 'struts have ARBs.

[Tony]

I'm not sure if this is valid for this level of discussion but the angle of the roll center / roll axis of the car is also very important, as is how the roll center moves during suspension travel. McPherson struts are notorious for this due to as the car rolls the roll center falls and moves into the corner meaning the car rolls even more.

 

Explains why almost all 'sports' cars with 'struts have ARBs.

Indeed a subject close to your current needs. give me a trigger in this area to expand on and i will develop it..

 

Despite the introduction which needs to be expanded as i said.... the actual geometry was not mentioned.... this is in addition to the description.... pretty big this geometry lark don't you think!

 

Center of gravity and roll centre, yaw and polar inertia add to the maths....

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