Proper suspension is critical to good performance. If your suspension is not setup correctly, it will likely hinder your performance capabilities, whether slightly or significantly. Admittedly, suspension experts such as Race Tech have their tricks and products to make your suspension awe inspiring, but you can still accomplish good adjustment within the limitations of your particular machine. Following some basic principles, you should be able to get your suspension working effectively.
Spring rates are the starting point of your setup. If you want to go fast, the springs have to match your riding weight. Every stock motorcycle suspension is designed for a target weight. Manufacturers typically include information on spring rate selection in their owner's manuals, although this information is often generic. Fortunately, there are resources available such as Race Tech. Race Tech is a well respected and knowledgeable suspension company and provides reference charts to help you find your correct spring rates. You can find information and suspension related products on their website at Racetech.com.
The purpose of the springs is to absorb energy and return the suspension back to the ride height after compression. Furthermore, the springs hold the bike at the correct ride height when loaded statically with you and your gear on the bike in the neutral riding position. Typically, the normal ride height is at a point where the suspension is sagging about 1/3 of its travel (check your manual). It is important to realize that your suspension not only has to absorb an impact, it must also extend when the wheels roll across low spots. Checking and adjusting the ride height is usually referred to as "the sag".
Many rear shock absorbers include a threaded preload adjustment ring so you can set the sag at the rear of the motorcycle. The ring can be turned to increase or decrease the amount of spring preload, thus altering the sag. It is important to note that you can adjust for correct static sag but have incorrect "free sag". Free sag is the amount of sag with no rider on the bike. When the static sag is correct but the free sag is not, the size of the spring is incorrect. For example, too little free sag indicates a spring that is too soft. This is because the spring preload has to be set too high to achieve the correct static sag. In this scenario, the rear suspension will kick upward on rebound because the spring never runs out of energy as the suspension tops out.
Front forks are typically less forgiving when adjusting the springs because there is often no means of adjustment. Regardless, the concept of setting sag is no different than for a rear shock. If forks sag is incorrect, adjustment may be possible with the use of preload washers. If there is too much sag, washers can be added to increase spring preload. In all probability however, the springs would need replaced with ones having a different spring rate. Of course, pneumatic spring forks are now available on some dirt bikes that make spring adjustments simple, using only a pump. However, there are tradeoffs with pneumatically sprung forks, but I do not intend discuss that here.
Damping controls the rate at which the suspension compresses and rebounds. Damping is achieved by controlling the flow of oil moving within the suspension as it is compressed or extended. As with spring rates, the amount of damping required depends on rider weight, rider ability and riding style. Damping adjustments are made to allow the suspension to move faster (also referred to as softer) or slower (also referred to as harder). Not all suspensions provide all means of damping adjustments, but most modern motocross bikes do. Additionally, it is important to realize that adjuster locations can vary across models of bikes. Always consult the owner's manual when in doubt. Typical adjusters are:
The slow speed adjusters, commonly referred to as the "clickers", are adjustable flow control valves. Turning the adjusting screw counter clockwise allows more oil to flow and turning the adjusting screw clockwise allows less oil to flow. The slow speed adjusters affect the damping feel of the suspension at all speeds, but they have no effect on the main valving itself. These adjusters can be thought of as fine tuning adjustments. The amount of available damping adjustment is therefore limited.
High speed adjusters are sometimes provided in addition to slow speed adjusters. The high speed adjusters do not affect the main valving, but have a much more pronounced effect than the slow speed adjusters. For example, a single adjustment position on a high speed adjuster may represent a full range adjustment of a slow speed adjuster. Of course, suspension designs vary.
Damping can adjusted beyond the provided external adjusters, but this kind of adjustment requires suspension service and is what is referred to as revalving. If a rider's ability and weight fall within the target design for a particular motorcycle, revalving is generally not needed.
Discussion here assumes a rider is skilled enough that the motorcycle is being ridden correctly with the proper techniques and body position.
Always start by referring to your owner's manual, making sure the adjustments are at the recommended starting position. If you do not have access to an owner's manual, set all of the adjusters to the middle position. Do this by turning adjusters all the way out (seated lightly), then count the clicks (or number of rotations) it takes to fully seat the adjusters all the way in (lightly). Set the adjusters to the middle of the count. Do this for any high speed adjusters also. Generally, there are a few different ways to approach suspension adjustment. In the end, the best result will be a compromise between big hits, rough terrain and cornering. In all cases, there must be good damping balance between the front and the rear.
It is highly advisable you keep a log of the adjustments you make and the effects those results had. It can be a painstaking process but if you are competing seriously, for example, a properly working suspension can make the difference in endurance and speed. Besides, it only makes sense to have a suspension that works correctly.
Test and adjust for big impacts
Carefully ride the bike when testing the adjustments. You must be careful because you don't know what to expect from the suspension's behavior. After getting a feel for the suspension action, start testing impacts. In the end, you need the suspension to perform correctly on the biggest impacts you intend on taking. Do not just go out and mindlessly hit some huge jump! Start small and work up, adjusting the compression adjusters one position at a time until the overall stiffness is satisfactory to your biggest landings or impacts. For your biggest acceptable impacts, the suspension should use the full stroke but not bottom hard. Focus not only on stiffness, but also on the balance between the forks and shock. Pay careful attention to how the bike springs up on rebound. During the testing of your compression, note if the bike has a pogo effect on rebound (front or back). A pogo action is when the suspension accelerates upward on rebound rather than rebounding controllably. If the bike does spring up, turn the appropriate rebound adjuster in one click at a time until the pogo action stops. Note: Typically, the rebound dampening should be as fast as possible, but with good linear control. If you are unable to get the compression stiff enough (or soft enough), you will have to revalve, assuming there are no mechanical problems with your suspension. In the case where there is a high speed adjustment, always adjust the slow speed adjuster first. If the slow speed adjuster must be adjusted all the way in (or out) to get good results, put the slow speed adjuster back to the starting point and adjust the high speed adjuster one increment. Resume testing using the slow speed adjuster.
Test and adjust for cornering
Choose a corner that requires you to use all of the basic cornering skills: Braking coming in, transitioning through the apex and accelerating out. Ride the corner giving careful attention to the attitude of the bike. As you brake coming into the corner, the bike should pitch forward smoothly at a controllable rate. Transitioning through the corner, the front tire should be planted firmly to the ground. As you accelerate out of the corner, the bike should pitch back to it's normal balance without losing front wheel traction. If the bike does not pitch forward when braking into the corner, the balance is not correct between the front and rear suspension, assuming that you are riding the motorcycle correctly. Make adjustments where needed, one click at a time, until the proper cornering manners are achieved. Testing each single adjustment will help to determine if what you are changing is the correct approach. Strive for the best possible balance.
Adjust for bumps, whoops and holes
To adjust for bumps, whoops and holes, you will need to find an appropriate area where you can test your settings. As with adjusting for big hits, the goal is to adjust to the most extreme conditions you intend on riding. Furthermore, you should experiment in different ways such as accelerating out of bumps, braking through bumps and blitzing whoops. You'll need to test this way because you'll find the need to compromise adjustments so the suspension can work the best in all conditions you intend to ride.
Things to keep in mind
Your strategy for tuning the suspension should be based primarily on your ability and riding style. If you ride only trails for example, cornering manners and bump absorption may be your only concerns. On the flip side, if you are a freestyle rider or supercross rider, you may be more concerned about taking big hits. Regardless, keep in mind that damping adjustments are all about controlling the speed of the suspension. Riding very fast across bumpy terrain, for example, would require faster rebound than riding slow across bumpy terrain. The reason is so the wheels can keep contact with the ground as much as possible, but in a controlled manner. If we are to consider jump landings, a harsh landing will require a slower compression setting than a jump landing where there is very little impact. The bigger the hit, the faster the suspension tends to compress. As the hits get bigger, the amount of compression damping required needs to increase.
As I already indicated, damping adjustments are for controlling the speed of the suspension. Clockwise adjustments make the suspension slower. Counterclockwise adjustments make the suspension faster. Softer compression is the same as faster compression which means the suspension compresses in a shorter amount of time for a particular compressive hit. Harder compression is the same as slower compression which means the suspension takes longer to compresses for a given compressive hit. Softer rebound is the same as faster rebound which means the suspension will rebound more quickly. Harder rebound is the same as slower rebound which means it will take longer for the suspension to rebound.
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