The Xida, being a long stroke damper, requires dual springs to make full use of the extra stroke available.
Spring stroke vs suspension articulation
A 2000 lb car with the motion ratio of just under 1.5:1 won't compress a short 700# spring far enough to allow meaningful droop travel with long stroke damper. To get the correct ride height, one must lower the preload collar until the springs have 25-60mm of free play. Without the secondary springs (helper), there is no spring stroke left to push the tire down to remain in contact with the road.
Weight
To get the correct spring rate for competition and high performance use while retaining enough spring stroke, would require a 9-11" long spring. Springs aren't light, particularly less expensive springs so that isn't a good solution. Hyperco and Swift generally have the lightest and most consistent rate springs on the market. We use Hyperco's because they cost about the same as Swifts and many of the sizes utilize their proprietary OBD (Optimum Body Diameter) design technology which further reduces weight and helps control distortion under compression.
Progressive rate
Beyond the spring weight issue, the Miata doesn't need 400-800lb springs when at full extension as the contact patch loading is almost nil then. A much lower rate will work better with that lightly loaded tire. What is called for is a progressive rate spring. Look at any purpose built race car that has more than about 75mm of damper stroke and you'll see dual springs. Off road and rally cars will often use three separate springs stacked up for a huge spring rate range.
Costs
If you start with the higher rate single spring setup then upgrade to duals later, the main springs may have to be swapped for a shorter set at the cost of about $150/pair. We offer the Xida Club Sport without the helpers for the Miata owner on a tight budget. The system will do everything better with the dual springs in place though. We tested the single spring Club Sports on our local bumpy road course on a Spec Miata with 9" wheels. They worked very well. Well enough for me to be comfortable offering the XCS without the helpers. Guys have been adding high spring rate Ground Control and other coilover sleeves to their Bilsteins and Koni Sports forever with good results so it's not like it doesn't work at all. It's just less than optimum. "Less that optimum" wasn't in the design criteria for the Xida's .
Without Helpers. Note the spring dangling free at full droop. Next image shows dual setup with coupler and Torrington bearings
Originally Posted by 949 Racing
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