Whether you’re a weekend warrior or full-time racer, improving the overall handling of your bike will no doubt make you a better rider. So if we told you that there’s a quick and easy method for achieving exactly that, would you be interested? Adjusting the ride-height, or “sag, is the simplest, most overlooked adjustment that one can make to improve the overall handling of a bike. And coincidentally, it’s also the most important. In addition to drastically improving handling, setting your sag to within the ideal range for your bike can also help you determine if you’re riding on the proper rated springs to begin with.
WHAT IS SAG?
There are a couple different sag settings that are often taken into consideration when setting up a bike, and the two of most importance are commonly known as “rider sag and “free sag. Rider sag is the distance that the rear end of the bike settles when on the ground and under the load of the rider’s weight. Free sag is the distance that the rear end of the bike settles when on the ground, but only under the load of its own weight (no rider).
THE IMPROPER SAG EFFECT
By setting the rider sag to within an appropriate measurement range, the bike will be positioned so that the front and rear of the bike are loaded correctly. When the balance of a bike is biased one way or the other, it may adversely affect both ends.
TOO MUCH: Having too much sag (the bike sits high in the front and squats in the rear) can reduce the front end’s ability to absorb bumps. Light and less compliant, the front end will simply ricochet around and deflect off of obstacles, and can actually make the rear end feel harsher, as it will be settling deeper into the travel. In addition, too much sag will adversely affect the steering of your bike. With the rear end riding too low, the front end will ride high, thus not settling into corners and ruts like it’s capable of.
TOO LITTLE: Not enough sag (the bike sits too high in the rear) will greatly affect its high-speed stability. With too much preload (tension) on the spring, the rear end will not settle and will kick its way through braking bumps and off of jump faces. Overall traction may also be sacrificed.
REQUIRED TOOLS: Metric tape measure, hammer, punch or sturdy flat head, and the bike’s pilot.
Note: Before checking your sag, make sure that your chain is adjusted properly and that your linkage and swingarm bearings are in good working condition. You may get a false reading if there’s binding and/or negative tension from any of these components. In addition, top off the bike with fuel, and make sure the rider is geared up.
Start with your bike on a stand, ensuring that the rear wheel is off the ground and that no part of the linkage is touching the stand. Next, locate the points you’ll be measuring between. On our team bikes, we run a longer bolt through the rear fender and subframe to use as a stable marker, and measure down to the corner of the swingarm. You may also choose a measuring point on the rear fender, which gives you the advantage of locating a spot that will give you a nice round number for easier math. With your initial measurement recorded (photo A), take the bike off the stand and roll it onto level ground. Next, have the rider sit on the bike so that he or she is positioned on the cradle of the seat with their legs dangling even with or in front of the foot pegs. Make sure that the rear shock settles properly by pushing down on the rear of the seat to allow it to settle back up into position. Also, be sure that the rider is not applying the front brake, as this will place an unwanted load on the suspension. Measure again between your two reference points, and subtract the difference to obtain your rider sag (ex. 600 mm. extended -- 500 mm. under load = 100 mm. sag).
Note: There’s not really a maagic number for sag, but a target range between 100-105mms is pretty close for most of today’s bikes.
To increase or decrease the amount of rider sag, first put the bike back onto the stand. From the right-hand side of the bike, using a hammer and punch, tap the top locking collar on the front side of the shock to break it loose (photo B). If you need to put more sag into your shock, you’ll have to loosen your spring. Using your hand, spin the spring counterclockwise so that its collar moves up the shock shaft--reducing tension (photo C). If you have too much sag, you’ll need to tighten the spring with your hand by spinning it clockwise so that its collar moves down the shock shaft--compressing the spring and increasing tension. Now, follow the same procedures for measuring the extended measurement (on the stand) and the loaded measurement (on level ground with rider’s weight), and recalculate your sag. Continue this procedure until the desired sag is met. Using your hammer and punch, tap the top locking collar from the backside of the shock to tighten it.
FREE SAG--ARE YOU ON THE RIGHT SPRINGS?
Now that you’ve obtained your rider sag, it’s time to measure your free sag to determine if the springs on your bike are right for you. Place the bike in the same level spot on the ground and measure between your two reference points without the rider on the bike. The difference between your extended measurement (on the stand) and this new one will represent your free sag.
TOO SOFT: If your free sag measurement is 20mm or less, I recommend going to a stiffer spring rate. A spring that’s too soft forces you to add excess preload to get the desired rider sag, and as a result the rear end is raised, which can cause it to unload too much in the air and top out as the travel rebounds, resulting in a harsh feel.
TOO STIFF: If your free sag measurement is 35mm or more, I recommend dropping to a softer spring rate. A spring that is too stiff will not allow for maximum traction under acceleration, and thus you’ll feel every bump on the track.
Note: If you determine that a stiffer spring is required on the rear end of your bike, then more than likely you’ll also require a stiffer set of springs in your forks, as well.