Suspension

Suspension:

This page is written to cover some basic of suspension tuning.

Metric to imperial spring rates. A quick and dirty method is dividing or multiplying by 56.

Example:

350 lb/in divide by 56 = 6.25 kg/mm

8kg/mm multiplied by 56 = 448 lbs/in

The exact conversion factor is a pain to work with and 56 is so close.

Terms used:

Understeer = Push = Plow = When, in a turn, the front wheels loose traction and the car fails to turn.

Oversteer = Fishtail = When, in a turn, the rear tires loose traction and the rear of the attempts to pass the front.

Snap Oversteer = A sudden violent loss of traction at the rear wheels.

Spring rate = The stiffness of a spring. Expressed in unit of force per unit length. Example kg/mm; lb/in ect.

Oversteer and Understeer:

Stock suspension usually understeers. The reason for this is so if a turn is taken slightly too fast the front slides out and the natural reaction to let off throttle gets you out of trouble. Letting go of the throttle slows the car and shift weight onto the slipping tires witch hopefully prevents an off road excursion. This is a good controllable set up for the average driver. However performance drivers and those who are more skilled prefer a balanced or even a slight oversteer set up. So how do you tune over and understeer?

Tuning Oversteer and Understeer: Finding your balance

Bellow shows the the basic idea of how to tune

If you have excessive...
understeer. Then...		oversteer. Then...
Stiffen Rear		Soften Rear

and or		and or

Soften Front		Stiffer Front

The easiest way I found to think about oversteer and under steer is as a ratio. They are interrelated. If you look at the picture above you'll see that if you have understeer you need to stiffen the rear suspension and or soften the front. Both of these increase oversteer. So one counteracts the other. Also you may have noticed the effected end of the car doesn't have to be what you work on. Just because it understeers doesn't mean you need to work only on the front suspension.

To make adjustments tire pressure, adjustable sway bars, larger sway bars and springs of different rates can be used.