Helpful Tools
In this column and the next I will describe three tools that you can make that will simplify checking and setting race sag on the rear shock.
First I will describe how to make and use a sag stick. Basically, you will be making a customized ruler to be used for your specific bike. You will need a piece of aluminum or steel 1/8 or1/4 inch thick, ½ to 1 inch wide, and approximately 28 inches long. Since bikes vary in their design around the rear axle/chain adjuster systems, you will need to choose from several options for configuring the bottom end of the sag stick.
Option 1: If your rear axle has a hole drilled in its center, you can drill a hole in the end of your sag stick the same size as the hole in the axle. Then install a bolt and nut in the hole of the sag stick with approximately ¾ to 1 inch of the bolt extending past the nut. This bolt will then fit into the hole in the axle - thereby allowing the sag stick to be supported with no up or down “slop”.
Option 2: If your axle is the type that is plugged or not drilled, then you will not be drilling a hole in the sag stick. Instead, you will need to bend the end of the sag stick at a 90 degree angle approximately ½ inch from the end. This will allow the sag stick to rest on top of the chain adjuster bolt.
Option 3: If your bike has the cam type chain adjusters, it will have a pin for the cam to push against. Just drill a hole in the end of the sag stick to fit over this pin. You may have to trim away some of the sag stick to allow the stick to extend up toward the rear fender at a 90 degree angle to the swingarm.
Now that you have the sag stick made to fit at the axle you are ready to calibrate the stick. Put the bike up on a stand so that the rear wheel is off the ground and can be turned without touching. Install the sag stick at the wheel. The top of the sag stick should be above the rear fender and at about a 90 degree angle to the top of the swingarm. Using a thin line permanent marker (such as a Sharpie), draw a horizontal line (which will be known as the extended line) on the sag stick where it intersects the bottom of the fender, and draw a vertical line on the fender along the leading edge of the sag stick.
Remove the sag stick from the bike and place it on a work bench/table. With a metric ruler, measure down from the extended line and draw a line at the distance of your ideal race sag (100mm on link type bikes and PDS KTM’s up to 2002, 115 mm on PDS 2003 & 2004, and 110mm on 2005). This is your race sag line. You will now need to draw two more lines – one 5mm above the race sag line and one 5mm below the race sag line. Then measure down from the extended line and draw a line for static sag (30mm for link systems, 35mm for PDS up to 2002, 40mm for PDS 2003-2005). To finish, draw two more lines – one 5mm above and one 5mm below this static sag line.
These 5mm above and below lines give you the maximum and minimum range of adjustment for both race sag and static sag.
Now, when you want to measure or adjust your race sag, put the bike up on a stand and check your extended length. It should always be the same unless you have bent your subframe or have tight or worn linkage/swingarm bearings. (If bearings are tight, the extended length will probably be too short and if bearings are loose or worn, the extended length will probably be too long.) Remove the bike from the stand, bounce it up and down and sit on the bike in the attack position and have an assistant install the sag stick at the wheel. Line up the vertical line on the fender with the leading edge of the stick. Have the assistant draw a pencil line on the sag stick where the bottom edge of the fender intersects the stick. Park the bike and measure down from your extended line to the pencil line. This is your race sag. Now, check your static sag. With the bike on the ground, push up and down on the rear fender and allow the suspension to settle. Install the sag stick and draw a pencil line where the bottom of the fender and the stick intersect. This is your static sag. If you have the proper spring for your weight, the race sag will be between the lines you created that were 5mm above and 5mm below your race sag line, and the static sag will be between the lines you created 5mm above and 5mm below your static sag line. If your measurement is ABOVE the 5mm line you made above the race sag line, the spring is too stiff (indicating a need for less preload or a softer spring.) Adjust preload to get proper race sag and check static sag. If static sag is proper, the spring is O.K. If race sag is BELOW the 5mm line you made below the race sag line the spring is too soft (indicating a need for more preload or a stiffer spring.) Adjust preload to get proper race sag and check static sag. If static sag is O.K, your spring rate is correct. A general rule of thumb: Once race sag is correct, if you have too much static sag this indicates that the spring is too stiff. If you have too little static sag this indicates that the spring is too soft. For reference, 1mm of preload is approximately 2mm of race sag.
Remember to always use proper safety precautions and equipment including eye protection when drilling or cutting metal.