SPRINDEX ALLOWS FOR TOOL-FREE, EASY ADJUSTMENT OF YOUR COIL'S SPRING RATE. Adjusting your shock's spring rate can profoundly improve your bike's handling and suspension. In fact, you may find yourself using different spring rates for different trails, depending on the conditions and type of trail. Or you may increase your spring rate for long climbs and decrease it for down hills. No expense was spared on the materials or manufacturing processed used. The coil itself is made of super high tensile spring steel similar to "lightweight" springs (which is why Sprindex is lighter than regular springs) in order to handle the stress of the system when adjusted to its highest spring rate setting, as well as reduce coil mass. The Sprindex assembly is made of glass reinforced polymer. The 5 included adapters are made of slippery Delrin. Spring rate is the force required to move a spring a given distance and independent of preload. For example, a "400 lb/in" spring requires 400 pounds to move the spring 1 inch and 800 pounds to move a spring 2 inches. Preload is how much force is required to start moving the spring. Sprindex is patent pending in many countries. Follow your shock manufacturer's instructions for preload amount and sag and other shock adjustments. Do not preload your Sprindex more than 3 turns and 1 to 2 turns is preferred. Your Sprindex coil behaves like a regular coil that has a spring rate the same as your adjusted Sprindex spring rate. Adjusting your Sprindex does not change the length of the coil and so does not change your preload. Preload is adjusted normally and with the threaded ring that came with your shock. HOW DOES SPRINDEX ADJUST SPRING RATE? The spring rate of a spring is the amount of force it takes to deflect the spring a certain distance (typically pounds per inch or Newtons per mm). Spring rate is a function of 4 characteristics: wire diameter, coil diameter, material, and number of active coils. More active coils causes a lower spring rate and fewer active coils causes a higher spring rate. Think of it like this: the less wire there is to bend, the stiffer the spring. By twisting the Dial, Sprindex works by altering the number of active coils available for deflection. The adjusted spring rate is displayed through a window in the Dial. COIL SHOCKS VERSUS AIR SHOCKS Most agree that coil shocks outperform air shocks, assuming the right spring rate for the particular rider. Air shocks have significant "stiction" which is friction that resists the shock's initial movement. Coil shocks have much less stiction. Coil shocks soak up small bumps much better, better tire contact with the ground, give better traction, better ride quality, and make a rider measurably faster. So why are air shocks more common? The answer is lack of adjustability for coils and weight. Traditional coils have a fixed spring rate and spring rate has a dramatic effect on riding performance and feel. Most people ride the wrong spring rate because springs are typically only available in wide increments. Spring rate has a profound effect on bike performance. Coil shocks also weigh more than air shocks, but when using the right spring rate, the small weight penalty is easily worth it. Besides, Sprindex is lighter than ordinary shock springs. SPRING RATE IS DIFFERENT FROM PRELOAD Coil shocks include a threaded ring for preloading the coil. However, preloading is not the same as using a stiffer (higher spring rate) spring. Sprindex Preload A sprindex coil behaves exactly like a regular coil of the selected spring rate. For example, Sprindex adjusted to 435 lb/in behaves just like a custom made 435 lb/in standard coil. Poor small bump absorption resulting in a harsh ride and poor traction because it increases force to start coil movement. Either reduces shock travel and/or over-stresses spring. Improper SAG. SAG must be achieved by spring rate, not preload. Doesn't change coil spring rate. If you bottom out with a spring, heavy preloading may not solve this and will mess up the rest of the stroke. Mountain bike shocks are designed for as little preload as is necessary to take play out of the system. Any more preload than this harms ride performance. SPRINDEX IS PROGRESSIVE Besides having an adjustable spring rate, Sprindex is also progressive. Sprindex is specifically designed to have a progressive spring rate for the last 20% of stroke for big hit support and for bikes with a linear linkage design. Coil versus Air: A coil is usually very linear, whereas an air shock starts out Regressive (a reducing spring rate), and then turns progressive (an increasing spring rate). See the chart below. One of the disadvantages to using an Air shock is that its regressiveness mean less small bump sensitivity and traction. This is partly why Air shocks are not as plush as Coil. Regardless of your bike's suspension design, Sprindex being linear between about 0-80% stroke and progressive between about 80% and 100% stroke works great because it provides unbeatable sensitivity and traction through all the small and medium movement and it provides progressive support for big hits. Most importantly, Sprindex also provides spring rate adjustment in order to fine tune the perfect spring rate so that you maximize your suspension performance. Performance Adapters Performance Adapters are included. Sprindex coils fit a wide variety of shocks, but you must use the Performance Adapters for most of them. Our Performance Adapters both improve the fit between the coil and your shock and are made of low friction Delrin to improve shock performance by allowing the spring to twist during high deflection. Also, the Performance Adapters help prevent the preload ring from self-adjusting due to coil windup. See bottom of Performance Adapter for instruction of which Performance Adapter you should use. For Rockshox, no Performance Adapter is required but we recommend you use the Performance Washer adapter for shock performance and to help prevent preload self-adjustment.