spring rate & motion ratio

[Lanie]

would changing the spring rate of a chasis affect the motion ratio?

[Chucky]

No.

[Martinmechanix]

Chucky is right to a certain point. Motion ratio curve is defined by the suspension geometry and changing spring rate will not change the motion ratio curve. But if your motion ratio curve is not linear, the static (or dynamic) damper length should also be taken into account. Generally speaking race car has raising rate motion ratio curve path (at the front as an example). This means that when the damper length is shorter the motion ratio is higher and by the same way wheel rate. So by using softer spring and not resetting the damper length to the previous one by preloading the spring you will end up with more static deflection, shorter static damper length and higher static motion ratio. But you should remember that your overall curve shape (and motion ratio value according to damper length)remains the same and you only change the stating position on that curve.

[Chucky]

I thought rising rate went out of fashion with GE skirts and bell bottoms.

[Martinmechanix]

The last two formula cars I have been working on (Swift Toyota Atlantic and Formula Renault 2000) have rasing rate. The Swift has a raising rate at the front while the rear is linear. The formule Renault 2000 has a raising rate at both end. Both cars generate downforce form their underwing. The designers probably decided to use a raising rate to reduce the aerodynamics sensitivity to the pitch angle. So the use of raising rate may still be use on race car having an under wing.

[Lanie]

Have you ever worked with a formula car with aero mounted into the suspension?

[Martinmechanix]

No Lanie