Effectively, all the external preload adjuster does on a shock or forks does is change the initial amount of force to compress the shock.
It does not change the spring rate. Only a change of spring can do that.
For example, imagine a spring with rate of 10 lbs/in with a free length of 10 inches.
If you take a 10 lb weight and rest it on the spring, it will compress 1 inch.
If you add another 10 lbs (now 20 lbs), it will compress another 1 inch (now 2 inches), and so on for every additional weight added until the coils can compress no farther and enter coil bind.
If you preload the spring by 10 lbs (1 inch), and then rest a 10 lb weight on the spring, it will not move since it already has 10 lbs of force on it.
But if you add another 10 lbs of weight, the spring will then move at the same rate as it did before it was preloaded (another 1 inch).
So you can see that preloading a spring only affects the initial spring movement but not overall behavior, except that the spring has been compressed more initially (1 inch), the spring travel has been reduced (9 inches) and can become coil bound quicker if the suspension is compressed quite a bit.
Now if you substitute the 10 lb/in spring with a 20 lb/in spring, and with no preloading, you'll then note that a 10 lb weight will not budge the spring, but a 20 lb weight will now compress the spring (1 inch).
So in this situation, with 20 lbs of force applied the overall spring travel is less (1 inch) with the 20 lb/in spring than the 10 lb/in spring (2 inches) even with initial preloading.
The OEM rear spring rate is 9.8 Kg/mm, 96 N/mm, or 548 lb/in.
The recommended spring rate for your weight (220 lbs) is:
575 lbs/in (10.26 Kg/mm, 100 N/mm) to 600 lbs/in (10.7 Kg/mm, 104 N/mm).
Last edited by SubSailor; 12-11-2011 at 12:46 PM.