Tuesday Tip: Suspension 101

Setting sag is the first class you¿ll want to ace on the road to higher handling education. RG3¿S Rob Henricksen Shows You How.

Intro By Ryan Cooley
Photos By Garth Milan

¿The most overlooked adjustment on a motocross bike is sag,¿ says Rob Henricksen, President and Technical Director for RG3. ¿It¿s an easy adjustment and one that makes huge improvements to the handling of a bike.¿ Sounds too good to be true, right? It¿s not! So what is sag and why do we adjust it? There are a couple different sag settings that are often taken into consideration, but the one we¿re most concerned about in today¿s lesson is commonly known as ¿rider sag.¿ Rider sag is the distance that the rear end of the bike settles under the load of the rider¿s weight. Generally speaking, by setting the rider sag to an appropriate measurement, 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. For example, having too much sag can cause the front end of the bike to not absorb bumps properly. It will simply ricochet around and deflect off of obstacles, and can actually even make the rear end feel harsh as well because it will be settling into a deeper part of the travel.

Anyway, enough technical talk. By now you should get the point. Sag is important and the right amount is easy to achieve. As a suspension specialist who¿s trusted by some of the best in the business, we figured no one could better teach the class than Rob. Pay close attention¿ This is Suspension 101.

REQUIRED TOOLS: Metric tape measure, hammer, punch or sturdy flat head, and the bike¿s rider.

Start with the bike up on a stand, ensuring that at least the rear wheel is off the ground. Check to make sure that no part of the linkage is touching the stand. This could influence the expanded measurement, which we¿ll get to. Next, locate the points you¿ll be measuring between. My recommendation is to measure from the axle to a point on the side of the fender near the seat. Be sure to keep a finger on the end of the tape measure located in the axle hole so that it doesn¿t slip out or move around. Measuring to a point on the fender gives you the advantage to locate a spot that will give you a nice round number (ex. 600mm). This will make your math much quicker and easier. When you locate where this point will be on the fender, using the side of your tape measure, cut a locating mark into the fender to ensure that you won¿t lose your spot.

Note: Every time you check your sag you should always remeasure this reference point to ensure accuracy.

Now that you have located your two reference points you should know what your extended measurement is. Using your tape, double check that the distance between your two points measures what you were shooting for, and record the measurement somewhere so you don¿t forget it.

With your initial measurement recorded, lift the bike by the rear wheel and put it on the ground (no stand). It is very important that you find level ground for this sttep so that the weight bias will be balanced and accurate. Next, have the rider sit on the bike so that they are positioned on the cradle of the seat and his or her legs are dangling down, even with or in front of the foot pegs. The consistency of the rider¿s positioning during this step is important. To make sure that the rear shock settles properly, I always recommend 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 at this point, as it will place an unwanted load on the suspension. Now, take the measurement between your two reference points again. To calculate the rider sag, subtract the new measurement (under load) from the extended measurement (ex. 600mm extended ¿ 500mm under load = 100mm sag). 

Note: There¿s no real magic number for sag, but you¿re looking to obtain between 25-33% of wheel travel, which generally calculates to around 95-105mm of rider sag. A target of 100mm is pretty good 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. 

If you need to put more sag into your shock you¿ll have to loosen your spring. Using your hand, spin the spring so that its collar moves up the shock shaft (reducing tension). If you have too much sag (eg. sag desired is 100mm, but you¿ve got 105mm), you¿ll need to tighten the spring with your hand by spinning the spring 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. 

From the right-hand side of the bike, turn the locking collar down until it is snug against the shock collar. Using your hammer and punch, tap the top locking collar from the backside of the shock to tighten it. Try not to tap and move the shock collar (bottom ring), as this will change the tension on the spring.