I have recently spent a lot of time with some great suspension guys and have spent lots of hours talking about spring rates, preload, valving, ride height, and such. What have I walked away with?

On almost every thread that I see on this site as well as others I see and hear lots of talk about preload and how it will affect ride height but I never hear about how it affects the harshness of the ride. I implore all of you to read this link, especially the sections about "Race Sag and Spring Rates" as well as "All About Preload". brucessuspension.net

I have bought and installed new springs to only use 1/2" of preload.(I have only compressed the springs 1/2" from free length) Then I measure static sag, race sag, and total sag. For my 2006 KLX250S, my numbers are spot on....using 30% to 33% of front and rear suspension travel. Using the stock spring I had to induce way more than 1/2" preload to get the correct sag numbers, but in doing so I was adding lots and lots of stored energy in the compressed springs, which made the ride much more harsh. Going up in spring rate made a big difference and a much better ride.

"What does all this mean? Lets say your bike is equipped with a 280 lb/sq inch spring and you had to turn the preload up to 3/4 inch to achieve proper race sag, you would now have 210 pounds of stored energy. If you would install instead a 290 lb/sq inch spring and were able to drop the preload to 1/2 inch, you would now have 145 pounds of stored energy. That 290 lb/sq inch spring, preloaded to 1/2 inch, would require less force to begin movement of the rear of the bike (i.e., on a smaller bump), than would the 280 lb/sq inch spring preloaded to 3/4 inch. That 290 lb/sq inch spring would require 870 pounds of force to bottom (3 inch shock travel) compared to 840 pounds of force for the 280 lb/sq inch spring. So the heavier spring (the correct spring in this example because it achieves the proper race sag) is more progressive than the spring that was only one step too light. The correct spring will move over the small bumps better and resist bottoming better. If you require more than one step difference in spring rate, the results be much more dramatic". Bruce Triplett

 

Because I weigh 136 pounds and only ride asphalt, I set the rear shock lockrings so there is no preload and installed lowering links so the rear swingarm is parallel to the ground. I live in the middle a Canyon so no matter which direction I ride, it's on twisted roads so riding a bike with a low center of gravity is an advantage.

 

I agree with Bruce.

 

Bruce died a short while back, but it's great someone picked up his site and is carrying the info forward. He's done as good a job at describing suspension setup and components as just about anyone I've seen in a way that most average people can understand. He's been a highly regarded and mentioned source on this and other sites for some time.