Spring rate : Usually expressed in lbs/in, it�s the force required to compress a linear spring one inch. Linear springs have a constant spring rate. Progressive springs have progressive spring rate that rise has the spring load increase.

Corner weight: It�s the weight of the car applied to ground through the tire. It�s made of the sprung weight plus the unsprung weight.

 Unsprung weight: Weight of the part of the car that is not supported by the suspension. It�s made of the weight of the tire, the wheel hub, the brake and half the weight of the axle and suspension links.

 Sprung weight: Weight of the car that loads the suspension. Equal to the overall weight minus the unsprung weight.

 Spring mechanical advantage: It�s the ratio of the spring length over the wheel movement. Almost equal to one for McPherson struts.

 Wheel rate: Spring rate times the square of the spring mechanical advantage.

 Coil bind lenght: State of a spring were the coil touch each other's. The spring then becomes solid with a nearly infinite rate.

 Spring static deflection: The amount of deflection of a spring under the car sprung weight. For a linear spring, it�s equal to:

 To design a suspension, 3 factors must be taken into account : the wheel frequency, the roll force balance and the fore and aft pitching period.

 Wheel frequency : The wheel frequency of oscillation in cycle per second of a car without damper. It�s a function of the car sprung weight(W) and the wheel spring rate(K) :

Typical frequencies range from 1 cps for large soft sedan to 2.5 for a racecar without aerodynamic down force.

 Roll force balance: It the front to rear distribution of the roll force of the spring and anti-roll bar effect. It affects the over/understeer property of a car. Weight distribution and wheel geometry also affect car steer property.

 Pitching period: The pitching in the front and aft oscillation of a car on its suspension. It can be reduce to zero at a given speed by carefully using a slightly higher wheel frequency at the rear of the car. For a given wheel base and speed. Over a road bump, the rear suspension that it the bump after the front, will settle at the same moment than the front one. The speed V at which this phenomena occurs is:

Where L is the car wheel base in meters and f is the wheel frequency at the front and the rear. For streetcar, this speed is usually set to the usual highway speed and to the mean track speed for race cars.

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