G'day everyone,
tinkerbell, apologies if it was not entirely clear for you.
The optimum spring rate for a car is that which is enough to hold it up in place and to deal with the anticipated suspension travel (pitch, heave) and loading resulting from cornering (some portion of roll). No more, no less.
As the post discussed, warp modes arguably dictate "0" spring rate as an ideal to ensure the tyre to road contact patch is maximised. All suspension and chassis design is about maintaining articulation of the wheels over the road surface. We compromise warp functionality because we need spring rate for pitch and heave but excessive spring rate here will compromise warp even more.
And why is that such an issue? The simplest example is to imagine a car fully loaded into a corner, the outside front wheel suspension is compressed 50 mm or with a load of 500kg assuming a 10kg spring rate. That same wheel then hits a surface change like undulations or tarmac edge, the loaded wheel can no longer soak up or absorb the surface change hence passes this change directly to the chassis of the car. The chassis pulls away from the road and takes the wheel with it momentarily and, for a short but none the less significant time the tyre losses contact (or quality contact) with the road reducing available grip to that wheel which reduces available grip to that wheel pair etc etc.
This is where the tyres grip capacity come into the equation. The more grip the more cornering G's you can generate hence the need for more spring/roll rate to compensate and maintain suspension travel. Hence why a dedicated race car using slicks needs say 9kg and -4.0 camber to pre-empt the load but what would happen if you used these settings for a road car with road tyres on a track? The tyres would not generate sufficient grip to need the spring rate so the negative camber becomes a major liability when accelerating and braking and is not used when cornering. The excessive spring rate then leads to skidding under lateral load as the transferred weight can not be used by the tyre because it won't roll. And, the wheel wont compress to bring the camber back into neutral to maximise the contact patch.
I hope that makes it clearer.
DOHCVTEC, believe or not, weight or load transfer is to be avoided in setup as it constantly changes each tyres grip potential and it is affected by heavier springs. Swaybars don't actually affect weight transfer. Its a sometimes contradictory dance that is always a compromise unless you can use 3rd and 4th springs as in Formula 1. A lot of the oversteer and understeer you refer to is actually as a result of weight exceeding the capacity of the tyres grip potential, not loss of weight.
Its important to remember that any camber is a pre-emptive setting used to provide a relatively flat surface and optimised contact patch when cornering. Its a liability in almost every other occasion. Modern strut based cars also have problems with migrating roll centres which exacerbates roll during cornering where as double wishbones do not.
Cheers
Jim
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