|Setting Sag on Street Bikes
Setting the amount of sag your suspension has is an important step in optimizing both the handling and the comfort of your bike. Unfortunately, there's a lot of confusion on the subject, so we'll try to keep things as simple and straightforward as possible.
First off, what is sag, and why does it matter? Sag is the amount of suspension travel that is used up with the bike sitting still, with the rider and any luggage or passenger on the bike also. It matters because it governs how much of the available travel is used for bump absorption and how much extension is there to "fill in" as the bike travels over dips or pot holes. Having the right balance between these two is critical to performance, safety and comfort.
To measure sag you'll need at least one assistant, preferably two. First, measure the exposed section of the fork tube with the suspension fully extended. For standard forks this is the distance between the top of the wiper or dust seal and the bottom of the lower triple clamp. For inverted forks, measure from the seal to a convenient point on the tube. Write this number down.
Next take the bike off the stands (This is important!! Do not measure sag with the bike on the stands!) and get on it. If you have a second assistant have him hold the bike upright while you assume your normal riding position. If not, hold the bike as vertical as possible with one foot, keeping as much weight as you can on the bike. Have the first assistant push down on the front end a little and slooooowly let the bike rise until it stops. Measure the exposed fork tube length and write it down. Now have him extend the front a bit and let it settle back down slooooowly. Measure the exposed fork tube length and write it down.
Now average last two numbers and subtract them from the first, this is your total sag. An example:
First measurement: 5 ½"
Second measurement: 4"
Third measurement: 4 ½"
Average of second and third is 4 ¼", subtracting that from 5 ½" gives 1 ¼", or approximately 32mm of total sag.
This is right in our recommended range of 30-35mm for street bikes.
If you have too much sag, add some pre-load. If too little, take some pre-load out.