29
ROLL CENTER
A “roll center” is a theoretical point around which the chassis rolls, and is
determined by the design of the suspension. Front and rear suspensions
normally have different roll centers. The “roll axis” is the imaginary line
between the front and rear roll centers.
The amount that a chassis rolls in a corner depends on the position of the
roll axis relative to the car’s center-of-gravity (CG). The closer the roll axis
is to the center of gravity, the less the chassis will roll in a corner. A lower
roll center will generally produce more grip due to the chassis rolling,
and the outer wheel “digging in” more.
Roll-centers have an immediate effect on a car’s handling, whereas
anti-roll bars, shocks and springs require the car to roll before they
produce an effect.
ROLL CENTER BASICS
Here are some basic facts about roll center (RC) and center-of-gravity
(CG):
• Roll center (RC) is the point around which the car rolls.
• Each end of the car (front and rear) has its own roll center.
• Center-of-gravity (CG) is where all cornering force is directed.
• RC and CG are (ideally) in the middle (left-right middle) of the car.
• RC is vertically below the CG in cars.
• More chassis roll equals more grip
CG Center-of-gravity
RC Roll center
ROLL CENTER IN ACTION
When cornering, centrifugal force is applied to the car’s CG, which tends to push the car to the outside of a corner. This causes the CG to rotate
around the RC. Since the RC is below the CG, cornering force causes the car to rotate AWAY from the force. Hence, the car rolls to the OUTSIDE
of the corner.
• When the RC is far away from CG (lower RC), when the car corners the CG has more leverage on the RC, so the car will roll more.
• When the RC is closer to CG (higher RC), when the car corners the CG has less leverage on the RC, so the car will roll less.
• If the RC was right on top of the CG, when the car corners the CG has no leverage on the RC, so the car would not roll at all.
• Depending on what the car is doing, you will want one end or the other to roll more or less. You change the height of the RC accordingly to make
it closer or further from the CG (which for all intents is a fi xed point).
roll
Cornering force
Cornering force
Lower RC - more roll
Lower RC - more roll
Higher RC - less roll
Higher RC - less roll
Cornering force
Cornering force
roll
roll
EFFECTS OF ROLL CENTER ADJUSTMENT
FRONT ROLL CENTER
Front roll center has most effect on on-throttle
steering during mid-corner and corner exit.
FRONT ROLL CENTER
EFFECT
Lower
• Increases on-throttle steering.
• Decreases car’s responsiveness.
• Decreases weight transfer at front of car, but increases grip.
• Increases chassis roll.
• Better on smooth, high-traction tracks with long fast corners.
Higher
• Decreases on-throttle steering.
• Increases car’s responsiveness.
• Increases weight transfer at front of car, but decreases grip.
• Decreases chassis roll.
• Use in high-grip conditions to avoid traction rolling.
• Better on tracks with quick direction changes (chicanes).
ROLL CENTER
Summary of Contents for NT1
Page 1: ......
