To determine if you need to change your shock spring based on your weight you need to set your rider sag first. For big bikes, when standing centered over the footpegs, your sag should range from 95-115mm depending on the bike and handling characteristic desired. To determine if your shock spring is correct for your weight you then measure the static or free sag using only the weight of the bike. The free sag should fall between 25-45mm after you have your correct rider sag. If your free sag is below 25mm you need a stiffer spring because you are running your spring too tight. If the free sag is above 45mm you need a softer spring because you are barely tightening the spring to get the correct sag.
To remove the shock, start by taking off the seat and right side number plate. Remove the muffler. On some bikes you will have to remove the head pipe or mid pipe if they run beside the shock body. Take off all the subframe bolts and the tank strap. Leave the airboot secured to the throttle body or carburetor.
If you are servicing your shock, measure the compressed shock spring length so you can reset it to the same length after you service it. It’s easiest to work on a shock by securing it upside down in a vice.
Loosen the top lockring with a hammer and punch and unscrew it to the top of your shock body. If the threads are dirty, they can be cleaned with a wire brush and lubricated so the lockrings turn easily. Unscrew the lockring that rests next to the shock spring so the spring becomes loose on the shock body. On Showa and WP shocks there is a retainer clip located under the spring seat at the bottom of the shock that secure it to the bumper seat. If there is dirt preventing you from separating the spring seat from the shock you can free it with some lubrication and a soft mallet. The spring and seat will come off straight over the bottom of the shock.
On KYB shocks the spring seat has a large cut out so you can remove it from the shock shaft after you move the bumper out of the way. Once you have removed the shock spring measure its free length and compare it to it preloaded length. Usually shocks are preloaded between 5 and 12mm.
To reinstall the shock in the bike start with the bottom shock bolt first so you have easy access to it. When attaching the top shock bolt hold the rear wheel up so it gets tightened in a compressed state. Push down on the back of the subframe when you retighten those bolts so they are in a compressed state too. Once everything is together, set your rider sag and check the free sag.
Want more Dr. Dirt Wrenching Tips? Check out the Dr. Dirt section of Dirt Rider magazine, or stay tuned to the website for future stories and info. To suggest a topic for an upcoming installment or to ask Dr. Dirt a tech question directly, send an email to email@example.com, subject line: Dr. Dirt.