3rd Spring relative to normal springs

[kensaundm31]

You can say that there is are definite reasons to set the front springs harder than the rear. (rear traction, kerb-riding, minimising braking pitch).

So, my not-even-basic 'understanding': the 3rd spring allows you to have softer 'normal' springs.

So are the 3rd springs generally set at a higher n/mm or less or around the same as the 'normal' springs?

Do the 3rd springs also mirror the stiffer at the front, softer at the rear?

I thought also the 3rd springs are taking the pressure of the downforce so as there is more d/f at the back they might be stiffer at the rear.

[Jersey Tom]

3rd spring is there to give extra stiffness in axle or overall chassis ride while maintaining some amount of single wheel bump travel (though you can't completely decouple the 3rd spring effect). Generally this is used on high-DF vehicles to prevent the chassis some bottoming out under high aero load... or extreme braking to control pitch.. though not always. I believe the Lola champcars only ran 2 springs.

Regarding stiffness, that depends. You don't ALWAYS want the front ride frequency higher than the rear. Sometimes you want the opposite if you want the rear to catch up to the front quickly and you're focusing on ride. But for 3rd spring it depends on relative amounts of front and rear downforce, and if you want to do any tricks with the car setup. For example you might be able to run the front significantly stiffer than the rear, or throw a bump rubber in there, to get the car to pitch under braking without bottoming the front, to get extra DF out of the diffuser by increasing chassis rake.

The relative stiffness front to rear will determine how the chassis attitude changes under high aero load.. if you want it to stay flat, or the rear to squat down more than the front, or vice versa. Maybe another benefit of a soft rear spring would be to get the car to squat a bit in the rear at high speed, decrease the AoA of the wings and diffuser and shed some drag? Highly dependent on car's aero map.