What to look for and WHY: Coilovers

MaysEffect

100% agree! None the less, we go out and buy "recommended" parts without getting all the information about what exactly we are buying and how to set it up. In most cases we have to rely on professionals to help us with these unknowns. Professionals generally don't do work for free though.

949racing are indeed very helpful from my experience with the group. But information and proper setup are two different things. Shops like 949racing can setup your car with alignment specifications with accuracy up to .01 of a degree across an axle if you have all the right parts. They can also probably setup a near perfect corner balance. But you still have to start with the right parts and you still have to pay for their service if you want them to do it right. Or pay for it one way or another (publicity work, street cred?,sponsorship, exchange services(prostitution?)).

Speaking of 949, those guys also provide excellent information with regards to the products they offer and how and why one kit may be better than another. But they are a specialty group dealing exclusively in Miata's.

direct pull from there ND Xida kit - ND Xida coilovers Miata
So not only do they offer coilover kits in several variations, but they also have recommended TESTED primary spring rates that would work best for the particular driving situation and the TIRE that can induce a high corner load. The tire specification being a important reference irrespective to the dampers and springs abilities to control wheel travel. If a tire can only support a maximum of 1000ibs of force but you have a corner load of 1050ibs at a simulated .96g from CG, the tire is beyond its limit of traction, in most cases you are sliding off the road into a pole or a tire stack if you persist at this simulated level of force. And if for whatever reason you haven't slid off the road and still have grip, you are working in a range of stiction, this principle is where road racing tires generate its cornering grip. It's also the reason slick tires have a uncanny ability to lose control of traction at unreasonable levels.

Most companies are not going to take the time to test several spring rates to counter the corner load double its static weight. For one, any potential tire capable of supporting the weight won't likely fit without major modifications. Secondly in order to produce such a load you'd have to be going uncharacteristically fast for public roads.

At most you'd hope a company did basic calculations to come up with a spring rate based on the corner weight in relation to its motion ratio while taking the potential wheel travel into consideration. Things immediately start becoming more complicated when you have to assume how much force passed this a tire is capable of accepting all while keeping the car from bottoming out or hitting something under the wheelwell. OEM specifications don't take lateral forces over 1g into consideration at all. The primary focus is to keep the car from bottoming out under normal driving conditions and weight restrictions. Thus the GVWR. Most aftermaket companies simply try to replicate this load rating in relation to the static ride height change you hope to achieve.