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 and damage themselves or worse yet their bike.
Problem 1: The right spring rate depends on more than the rider's weight. It's also about the bike, the sort of trails the rider rides, the weight of the stuff the rider brings along, and riding style.
Problem 2: Springs only come in big intervals...typically every 25 or 50 lb/in. Let's say you know your current 450 lb/in coil is too stiff because you know you're not getting full travel during a ride. What spring rate should you buy next? If you buy a 400, you might find it's still too stiff. If you buy a 350, you might bottom out. So you end up having bought 2 springs and the best you can do is ride the 400, which is still too stiff.
Problem 3: The ideal spring rate for a rider is different depending on the trail. A trail with big drops would require a stiffer spring rate than one with smaller drops. If your spring rate is right for the first trail, it's wrong for the second. Some riders actually switch out their coils for certain rides or races to try to solve this, but this is a big hassle and the spring rate change is big.
Problem 4: Many shock springs have spring rates dramatically different from claims. The problem is so significant, that sometimes a "weaker" spring is stronger than a "stronger" spring. For example, we have measured (major brand) claimed "400" springs that are actually 375 lb/in and claimed "350" springs that are actually 380 lb/in.
Problem 5 Spring rate is NOT the same thing as preload. They are unrelated. Preloading a spring that is too soft might correct the sag amount, but would not compensate for shock travel or prevent bottom-out. Preloading causes the coil to partially compressed, which requires a higher initial force to start coil movement but very little affect on force at full stroke. Preload does not increase spring rate. Too much preload causes:
Solution: Sprindex. Our system allows you to easily adjust your spring rate by hand and without tools. Sprindex spring rates can be adjusted through a range of 30 to 60 lb/in, depending on the coil model. Spring rate can be adjusted to any rate between the min and max, and there's a gauge that shows you your adjusted spring rate. Also, it is important to us that our spring rates are accurate.
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.