As taken from the basic terms section:
Sag – most suspensions are designed for an initial travel amount in stationary position, which is caused by the weight of the vehicle and the rider. This has an optimal amount given in a percentage of the total travel, usually 15-25%.
Linkage features a pop-up window for optimal sag or spring rate calculation. This is located at the project window's toolbar.
This feature works in two ways:
- find the optimal spring rate / shock air pressure for your bike and weight
- find the current sag of the bike for the given rider weight and spring rate / shock air pressure
To use either function, the weight-distribution must be set regarding the two wheels of the bike. It is set to an initial value first, you may change it depending on riding style. Also set the desired sag percentages, front and rear.
Finding the optimal spring rate for your bike and weight
Enter rider weight and weight distribution, desired sag percentages then read the coil spring rate at the bottom. This rate is exactly what balances the bike's suspension to the desired sag. You may want to buy a spring close to this value to improve your bike's suspension performance.
Note - for air shocks this method is currently not implemented, because of the non-linear nature of this problem. But you can use the switches to easily change the pressure values and see the result sag. When you're satisfied with it, you have the right pressure. Though this pressure will be only an approximate value, to start with in real life.
Finding the current sag of the bike for the given rider weight and spring rate
Enter rider weight and weight distribution and spring rate or air pressure then read the resulting rear sag percentage at the bottom. This is the percentage of rear sag this setup yields. If it's too much for your riding style, you may consider buying a harder spring / pumping up the shock - and vica versa.
Note: rider weight should include the bike's sprung weight (ca. weight without wheels) too. Add this to the rider's body weight.