What is roll stiffness?

What is roll stiffness?

Roll stiffness is defined as the resistance moment generated per unit of roll angle of the sprung mass, and it has SI units of Nm/rad. On independent suspension vehicles, roll stiffness is a function of the vertical stiffness of the suspension (ride rate, which includes tyre stiffness) and track width.

How does roll stiffness affect understeer?

Our general understanding is that Increasing roll stiffness at the front will increase steady state understeer and therefore the response of the car will be less. The car will be less agile.

How do you calculate wheel rate and chassis roll stiffness?

With the wheel rates for the coil springs and the anti-roll bars calculated we can now look at calculating our chassis roll stiffness….

1. Kwheel = Wheel Rate.
2. K = Anti-Roll Bar Spring Rate.
3. IR = Anti-Roll Bar Installation Ratio.
4. Φ = Drop link Angle from Vertical (shown in the image below)

What is ride frequency?

A ride frequency is the undamped natural frequency of the body in ride. The higher the frequency, the stiffer the ride. So, this parameter can be viewed as normalized ride stiffness. In Figure 1, we can see the undamped vertical motion of the chassis with the front ride frequency higher than the rear.

What is roll stiffness distribution?

There are two roll centers on a race car, one at the front suspension and one at the rear suspension. The ratio of the front suspension roll stiffness to the rear suspension roll stiffness is called the roll stiffness distribution; when worked to include the roll centers it is referred to as roll couple distribution.

Which is better soft or stiff suspension?

The purpose of a suspension is to keep your tires on the ground. A softer suspension will offer more mechanical grip as it will do a better job of keeping the tires on the ground vs a stiff suspension when it comes to depressions, bumps, and surface irregularities in the road.

Is cornering stiffness constant?

slip angle The proportionality constant Cα is known as the cornering stiffness, and is defined as the slope of the curve for Fy versus α at α = 0.

What is camber stiffness?

Camber stiffness is a parameter used to describe the camber thrust generated by a tire and it is influenced by inflation pressure and normal load. The orientation of this torque is such that it tends to steer a tire towards the direction that it is leaned.

What does roll stiffness on a car mean?

This resistance to chassis roll offered by the springs is called roll stiffness. In addition to the roll stiffness, the front and rear roll center heights also determine how each of the suspensions transfer the cornering forces, the weight transfer and how much roll the chassis takes on during cornering.

How are wheel rates and chassis roll stiffness calculated?

With the wheel rates for the coil springs and the anti-roll bars calculated we can now look at calculating our chassis roll stiffness. When a car corners, the sprung mass rotates about a roll axis between the axles and rolls.

How is the stiffness of a roll bar determined?

An Adams model as shown in Fig. 8.59 can be used to determine the torsional stiffness required at the point in the anti-roll bar where the elastic compliance is provided. It is then a simple enough design problem to convert this into the dimensions of, for example, a torsion bar.

How is roll stiffness used in multibody systems?

Mike Blundell, Damian Harty, in The Multibody Systems Approach to Vehicle Dynamics (Second Edition), 2015 This model is developed from the equivalent roll stiffness mass model by using revolute joints to allow the suspensions for all four wheels to ‘swing’ relative to the vehicle body rather than considering using the suspensions linked on an axle.