Originally Posted by nak3dsnake
Except the ZL1 front spring rates are almost identical to the SS front spring rates. And The rears are much stiffer to allow for hard launches and better control. Springs manage the weight of the car, a stiffer spring rate will allow you to handle better. Yes finding the right spring rate + dampening level is more optimal. Ford runs GT spring rates on V6 dampeners with the Performance package from the factory. With your logic no one should lower there cars with spring with much high rates than from the factory. There are aftermarket companies that use the same springs and rates for both V6 and V8 cars.
ZL1 front spring rate IS identical to SS. They are both 27 N/mm. The rears are different, SS is 66 N/mm and ZL1 is 70 N/mm. Higher spring rate doesn't mean better control. Control comes from matching dampers to the springs in compression, rebound, and travel. What higher spring rate will give you is less body movement (body roll, brake dive, and squat under acceleration). You will think the same damper can be used for SS and ZL1 springs but it isn't optimal because the travel is different. ZL1 suspension travel is lower compare to SS but it can get away with it because MRC can dial in more compression when it detects a big hit. SS structs are not as smart. If you compare v6 to SS springs, you will see that lower 25 N/mm spring rate of v6 is compensated by longer travel of 96 mm. 25 N/mm x 96 mm = 2400 Newton unit of force to bottom out. SS springs are 27 N/mm x 84 mm = 2268 N.
I don't know about Mustangs so I am not going to comment on them but I will say something about aftermarket lowering springs. It is MY OPINION that most lower the car's handling capacity. Lowering springs have too little travel, too low of spring rate, and factory dampers cannot control them well. It is basically a cosmestics modification at the expense of handling. I am not saying you cannot lower your car with higher rate springs. All I am saying is that you gotta match those springs to proper dampers. Pedders supercar coilovers have 8kg/mm springs up front. This is twice the factory spring rate but it rides and handles very well. Compare that H&R super sport lowering springs that has very close to factory rates and you'll quickly see the importance of matching springs to dampers.