Spindex behaves exactly like an ordinary progressive spring except the spring rate is adjustable.

Spring rate is different from preload.  Preload should only be used to remove play and NOT to compensate for a weak spring.  Coil shocks include a threaded ring for preloading the coil. Preloading is not the same as using a stiffer (higher spring rate) spring. Preloading does not change spring rate but preload does change the force to start moving the shock and high preload dramatically reduces shock performance over smaller bumps and makes for a more harsh ride and worse traction. Spring rate is the force required to move a certain distance whereas preload adds a fixed force across the whole stroke. Heavy preloading can add over 100 pounds (45kg) of force required to start shock movement whereas optimal shock performance comes from the lowest starting force possible. Heavy preload means those smaller bumps won't even move your suspension. Mountain bike shocks are designed for as little preload as is necessary to take play out of the system. Sprindex allows spring rate adjustment and also allows proper preload. 

Proper preload

Preloading more than the minimum to get rid of play is bad. For best shock performance, turn the preload ring until it contacts the spring and then another 1 to 2 turns. No more.

Too much preload

Excessively preloading your coil increases the force to start shock movement which causes poor small bump absorption resulting in a harsh ride and poor traction.  Heavy preload destroys shock performance, over-stresses the coil, and can reduce shock travel. Preloading is not the correct method to reduce sag or prevent bottom out. Instead, the correct way to adjust sag and bottom out is by adjusting spring rate.  Here's a link to a video with details on why preload is bad:  https://www.youtube.com/watch?v=uUGRbaWlH8M

Here's an overly preloaded shock on the left compared to a properly preloaded shock on the right. Notice how too much preload causes the bike to bounce. The only difference between the two is preload.

     Left coil overly preloaded 10 turns.            Right coil properly preloaded 1 turn. 

Instead of adjusting preload, the correct way to set up your suspension is to have the correct spring rate. Unfortunately, traditionally, this means replacing springs and even then, that means big intervals between available spring rate (typically 50 lb/in increments). Sprindex is the better solution because Sprindex allows you to easily finely adjust your spring rate. A Sprindex coil adjusted to any particular spring rate behaves exactly like a regular spring that was manufactured to that spring rate.

For example, Sprindex adjusted to 360 lb/in spring rate performs exactly the same as a custom made ordinary spring that has a 360 lb/in spring rate.   

For example, Sprindex adjusted to 380 lb/in spring rate performs exactly the same as a custom made ordinary spring that has a 380 lb/in 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?

Sprindex works by altering the number of active coils available for deflection. The spring's active coils are the coils that can flex as the spring is compressed. Fewer active coils makes for a stiffer spring and vice versa. Think of it like this:  the less wire there is to bend, the stiffer the spring. 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.  Sprindex is designed using high tensile steel to handle the stress at the highest adjusted setting.  

Most people ride the wrong spring rate. If too stiff, they don't get full travel, have poor small bump absorption, and diminished traction. If too soft, they bottom out on bigger hits. Sprindex solves this. The right spring rate dramatically improves your ride.

Sprindex allows you to easily adjust your coil's spring rate to any rate within a certain range, which can profoundly improve your bike's suspension. Just use your hands to twist the adjustment Dial. Adjustment is so easy and tool free that you may find yourself using different spring rates for different trails, depending on trail conditions and types. Or you may increase your spring rate for long climbs and decrease it for down hills.