Taken from Apriliaforum.com and writen by Chuck B

Suspension 101 – The Basic’s

Modern suspensions comprise of a spring, oil and a cartridge system to control damping. They offer a host of adjustments such as spring preload which can be accomplished both manually by turning an adjuster ring directly on the spring or hydraulically controlled. They can have compression and rebounding damping adjustment and adjustments to the length of a rear shock and let’s not forget that more and more shocks are now offering both a high speed and low speed damping adjustment. Add in different spring rates, oil heights and oil viscosity (weight) along with riders of different sizes and abilities and you have a receipt for potential disaster in the hands of the unknowledgeable. This will be a multi part article to help you wade through your suspension, help understand how it works and walk you through on how to set up your bikes suspension. Once initially setup you’ll need to spend time playing and tinkering with your suspension to help you understand how it works in real world applications. I do that by finding a stretch of road with variables in road surfaces and terrain that I know like the back of my hand. Using a note pad and taking copious notes while spending several hours going back n forth on this stretch of road will lead you to the ideal settings for you and your bike and hopefully understanding suspension well enough to know if you need a change of spring rate, oil height adjustment and/or the help of a professional suspension tuner.

While I do not consider myself an expert, I believe I have a pretty good understanding of suspension and how it works. I’ve spent more than my share of time running around a race track and in the early days often off the track trying to figure out what happened. More often then not it was purely rider error but the faster I got the more I realized that suspension was one of the key’s to going around quickly while keeping both tires in proper contact. Most of my knowledge is by trial and error and collecting every tidbit of info that I could find. Most often I’ve found that so called experienced riders were more often misinformed or misunderstood suspension. Fast guys at your local tracks understand suspension. Maybe not in the technical manner but they can express what they are experiencing to a suspension tuner and eliminate the suspension for irregular handling problems. Most can not or do not wish to relay their knowledge to the uninformed as there are just too many variables and often results in frustration for both. Unfortunately suspension is not a one size fits all. What works for one most likely will not work for another. In order for a suspension professional to help you you must first understand the basic’s so that you can speak the same language. I hope that this will be a step in the right direction for you and your enjoyment of performance motorcycle riding.

On the surface suspension seems pretty basic. Its primary job is to keep the tire in contact with the road surface. A motorcycle without suspension moves over a rough surface, the whole motorcycle must rise and fall over every bump. The faster the motorcycle moves, the more rapid becomes this up and down movement. Bumps hit at high speed can kick the motorcycle up pretty hard, but it can’t return any faster than gravity will allow. The faster you go the more control you need with this up and down movement. Without it your tire will end up spending more time in the air rather then on the road surface where you most need it. 

Placing a spring between the tire and motorcycle is the first step in suspension. Problem was controlling the spring after it was compressed. The spring will apply equal pressure but now in the opposite direction. What you end up with is an undamped oscillator and you’ll quickly find yourself bobbing up and down as you travel down the road. Likewise, in sudden maneuvers undamped suspension will cause the bike to wallow and dive. You need something to isolate this unwanted movement and help rid the spring of its pent up energy. This is where damping comes in and no it’s not called dampening. Dampening is the act of wetting a rag, nothing to do with suspension. 

Damping on a modern motorcycle suspension uses a system known as a cartridge system. Most have a separate circuit for the compression stroke and the rebound stroke. Company’s like Ohlins and Showa use a cartridge that consists of a piston that has a ring of holes through it. These holes are covered by a stacked set of shims that will vary in both size and width. As the suspension moves up and down oil is forced through the holes, deflecting the shims into a slight cone shape. The faster the piston moves, the more the shim stack deflects, increasing the amount of oil flowing past. By stacking the shims with the largest first, against the piston, then adding gradually smaller shims or shims of various thickness and/or spacers the oil can easily move the edges of the first shim(s). As the pressure increases the larger shims bend further coming into contact with the smaller shims giving more resistance or damping. This is exactly what you want; damping that is proportional to velocity. At low speeds suspension is fluid and moves easily. As speeds increase damping increases thus by bleeding off the energy in the spring and maintaining tire to road contact. Kayaba and Works Performance cover each hole with a ball backed by a spring. By choosing the rate and preload of these tiny springs, the ball valves can be made to open in proportion to oil forces, producing the right curve of damping versus piston velocity.

Previous to modern cartridge systems motorcycles used damping rods which had a fixed orifice drilled at specific points of the rod. With this system you could adjust the placement and size of the orifice to work pretty well at a specific rate of travel. The downside is this system is set and not adjustable. A damper system based on this system is useless because it becomes rigid in response to sharp quick movements in the suspension. Remember damping is exponential to rate of velocity. You could set it up for a race track but forget about low speed plush ness. Set it up for the average street rider and you won’t like how it reacts at racetrack speeds or quick movements of suspension like hitting a pot hole. It was a one size fits all and a compromise overall. Damping rod systems have a damping curve that curves upwardly at an alarming rate in response to velocity. Unfortunately many riders are still under the belief or assumption that “harder is better”. This is nonsense as any good tuner can adjust a cartridge system to work well in most any situation if given the right input. A good suspension is set to give good predictable motion control at low speeds, preventing wallowing. As the piston moves faster in response to higher suspension movements the washer stack begin to open up or deflect to allow more oil flow and take control of damping. Thus giving good control during almost all but the most extreme of conditions.

A suspension tuner adjusts this stack of shims to not only the spring rate but also to the rider’s preferences and abilities and remember that spring stiffness and damping force must exist in proportion. Too much damping overcomes the spring, slowing suspension response, making the ride too firm and reducing the wheels ability to maintain contact and grip. Too little damping is overcome by the spring, and the motorcycle oscillates, or wallows after every disturbances. Rider A who weights 185lbs and can turn 2:10 laps at a local track may find his suspension perfect. Rider B, on the same motorcycle, who also weights 185lbs but can turn 2:05 may find that the suspension does some funny things that result in a lack of confidence in his suspension. Add or subtract a little damping and rider B’s suspension may dial right in. Take rider C who is 220lbs and runs 2:12 is told he needs heavier springs. Once installed, rider C still lacks confidence in the suspension. Unfortunately the damping is unable to hold the motorcycle in a stable manner. It now has to correctly absorb not only the additional weight of the rider but the increased energy of the suspension. Manufactures set up suspensions to fit under conditions the bike was designed to operate in, this includes riders size and ability. While cartridge systems offer adjustability unmatched in previous systems there are limits of adjustability and quality.

So what is the clicker for? Most suspensions have adjustment for both compression and rebound. This clicker serves to adjust low speed motion control, and acts as a trimmer or fine-adjustment on higher speed damping. Think of it as an adjuster that can slightly raise or lower the whole damping curve. This adjuster CANNOT change the shape of the curve. If the curve is wrong or the problem lies outside the clicker’s range of adjustability then only the help from a suspension tuner can help. Some shocks are now coming with high speed and low speed damping adjustments. As it sounds this allows fine adjustment to each circuit. What is low speed? What is high speed? Low speed would be when you press down on the suspension. When pressing down your feeling the tension of the spring and compression damping. When released the bike moves upward. The rate of movement is governed by the rebound damping circuit in relation to the energy being expelled by the spring. High speed would be when you hit a pot hole at speed or in many cases dips or sharp rises in the road surface. A motorcycle moving along at 25mph and hits a dip it may be classified as a low speed movement but raise the motorcycles speed and its now a high speed damping movement. Just remember that the clickers will only vary the damping slightly. 

Another thing to realize is that the quality and adjustable range can vary greatly by manufacture. Take a GSXR750 which has 4 turns of adjustability. From a closed position (fully clockwise) to 1 turn out there is quite of bit adjustment of damping. However, to get the same amount of adjustment you would need to turn the adjuster from 1 turn to 3 turns out. The rate of this adjustment is variable on many manufactures suspension systems. Moving just ? turn between closed and 1 turn out may be all that’s needed whereas a turn from 2 ? to 3 ? may be required. Ohlins on the other hand may offer 25+ clicks of adjustment and in most cases one click to another offers similar adjustment to damping throughout the clickers range. Tuners will often replace pistons to make the clicker more effective or offer a better more linear range of motion. So how does the clicker work? Typically the compression clicker presses an aluminum rod that has a hole drilled through it. This rod goes through an oil passage that bypasses the piston. Turning in reduces the amount of oil passing through the hole thus making it more resistant to movement. Rebound typically moves a long aluminum rod in and out of a orifice on the piston, again, controlling the amount of oil passing through. Neither effect the shim stack itself nor its function of controlling damping.


Suspension 101...part II 
Springs are another topic of long debate among riders. With few exceptions springs are helical wound, round wire metal with the front springs composed of two relatively long flimsy springs and the rear made short and stiff. Front springs must be able to support not only the weight of the rider and bike but also resist bottoming during hard braking. At the same time they must be soft enough to give good compliance during acceleration, when the weight transfers to the rear and the front is left skimming the road surface all the while fitting inside the fork tube. To meet these goals the springs must be long with abundant coils. Usually front springs are progressively wound. A simple progressive spring has its coils wound at two different pitches i.e. a coil every 3/4” versus’ a coil every 1”. In light loads all the coils are in use and the spring is soft. At heavier loads the closely wound coils bottom, becomes a solid cylinder, and the remaining larger spaced coils are left to handle the load. A spring’s tension rate, in inch lbs per inch, is inversely proportional to the number of coils being used. The fewer the coils the stiffer the spring rate. One way to think of this is it’s easier to bend a piece of rebar that’s 6ft long versus’ one 2ft long. Now you understand why when your 18yr old neighbor kid cut his springs to drop his car lower the car now bounces down the highway. The spring rate has been increased due to less coils but the damping rate remained the same. The springs are now overpowering the damping circuits. 

Most manufactures use a progressive rate spring up front. Does it matter which way the spring’s sits in the fork tube? Only as it pertains to fitment but not to function. A spring doesn’t care one way or the other. In the aftermarket world most suspension tuners prefer straight rate springs. They are not trying to be all to everyone like a manufacture. They can better tailor the damping circuits to a straight rate spring with lower viscosity oil to achieve a better and more consistent response. More about oil later.

Rear springs are short and to my knowledge all straight rate and very stiff. The rear spring carries its load through the linkage. The linkage multiplies the force at the axle by 2-3X. The design of the linkage can alter the rising rate at the spring. While not the first, dirt bike company ATK and later KTM, began to use rear shocks with no linkage. They found, like suspension tuners, they could target a specific user and tailor the spring rate and damping to better meet the needs of their customer. Having a much smaller and lighter spring helps too.

On modern suspensions both front and rear have preload adjustments. While many believe this makes the suspension stiffer (100% false) its primary purpose is to raise or lower the bike, simply affecting the attitude of the bike as well as placing the bike in the proper portion of the suspension travel when weighted down by the rider and gear. Preload can be negative, neutral or positive – that is the spring is slightly compressed at full extension. You can also adjust bike attitude in the front by raising or lowering the forks in the triple clamps. In the rear many shocks are now coming with a threaded length adjuster on one end of the shock. Changing this allows the shocks “eye to eye” length to be changed without altering the suspension travel length or preload. Remember there are parameters for not only the shock min/max length but also chassis geometry. Adjusting ride height front and/ or rear to extremes can bring along many handling problems. Small changes can make big changes to rake and trail. Use small adjustments only….less than 5mm at a time.

As oils heat up, they lose viscosity. This change in viscosity can cause damping to fade when hot. Modern suspensions are now all using lighter viscosity oils then previously used (some as low at 2.5wt). Lighter is better as it has less viscosity to loose thus more consistent damping despite the temperature increases. On the Aprilia’s many often wonder about the rear shocks close location to the exhaust pipe. Don’t fret. Those shocks have special heat conductors that help remove heat keeping damping consistent. Damping can also fade due to cavitation. Picture a prop on a boat going through the water. On one side of the prop is the high pressure point where water is being compressed and forced to the rear. On the other side is the low pressure side. Air bubbles form on this side due to the low pressure from the turning prop. Those air bubbles were already present but now that there is little pressure they expand like a balloon. The water surrounding the prop acts much like damping; maintaining a consistent load on the prop. Cavitation appears when air bubbles form in the oil and are passed through the piston. Air is much easier to squeeze through then is oil. Take the boat example. If you turn the boat sharply enough that its prop runs back through the air bubbles the engine suddenly increases in rpm. It’s much easier for the blade to cut through air rather than water. How do those air bubbles form inside the forks and or rear shock? Two ways primarily, one is due to the fork and shock design. An emulsion style shock is one that the oil and air is not separated; as is the case with forks. This mixture of the two forms an “emulisified” mixture thus creating tiny air bubbles in the oil which then pass through the piston cartridge. Just like the boat, damping can suddenly go away or be inconsistent. A de-Carbon style shock, which the Aprilia has on the rear, contains a remote reservoir filled with pressurized gas allowing for the expansion of the heated moving oil caused by the internal pistons movement. Key point…The oil is separated from this pressurized gas by way of a sealed rubber bladder. All shocks are pressurized, around 200psi, with nitrogen. Why nitrogen? Nitrogen will not support combustion. Remember oil is a combustible product. Also understand that not every remote reservoir equipped shock is a de-carbon style. Why the difference in price between a $900 brand versus’ a $500 brand X shock? You now know. Like most things you get what you paid for. Now that’s not to say that emulsion styled shocks are bad. I think they are better than plain forks. Shocks can be pressurized thus reducing cavitation. The higher the pressure the tinier the bubbles. I’ve often wondered why manufactures continue to use forks with internal damping rather than shocks up front. A shock in many ways is far superior. Take a modern BMW motorcycle as an example….not that I’m biased. For its size, weight and design its front tele-lever works very well. Until everyone see’s the light we are left with unpressurized, cavitation prone old world fork technologies.

This leads to oil height adjustment as found in front forks. Because front forks are sealed you get another kind of support, similar to a spring, by way of compressed air above the oil level. This kind of air spring is quite progressive and very linear, which is good because that’s just what the forks must deliver. In previous years manufactures used forks that you adjust by way of adding air pressure through the forks cap. This was to help the forks as they were limited by their damping rod design. Later, bleed valves were installed to bleed off pressure that built up due to heat increases in the oil. Today manufactures have all but abandoned increased air pressures and bleed valves. (for street applications anyways) Manufactures give specifications for oil quantity or better yet oil height. If you raise the oil too high you’ve decreased the amount of air space available. This decrease in air space can have a significant impact on the last portions (10-15%) of fork travel. Quantity versus’ oil height? When you drain your forks there is still a significant amount of oil still left in the fork tubes. Much of which is in the cartridge which can be pumped to drain and clinging to metal parts through out the inside of the fork. If you refill based on quantity rather than height you may be decreasing air capacity leading to what you believe is fork bottoming or often fork chatter. Ideally you want to end up with a front end that can carry 100% load plus braking load without bottoming, yet still be soft and compliant enough to hook up near zero loads during acceleration. Use a zip tie but first you must know when your forks actually bottom. Many think it’s when the outer wiper meets the lower fork stanchion. Not always the case. Much too often the fork bottoms internally well before the wiper meets the stanchion. Determine by manufactures stated length of travel or disassemble your forks, remove springs and reassemble to test manually. Understand that preload may affect total value.


Suspension 101...part III 
Talk to people about suspension and what they want and you’ll get a multitude of answers. Most will be happy simply to make their bikes comfortable and predictable. Modern suspensions with adjustable preload and damping will provide this. As a rider’s skills improve, and he pushes his bike and tires harder, all suspension variables become more sensitive and crucial to get right. At this point the rider is beyond ride quality. What they need is balanced grip front and rear. At this level of riding questions of bike attitude and damping come to the forefront where as previously (quality first) they had very little influence to the rider. If there is one thing I’ve learned it’s the rider (skill) who makes the difference not the bike. As the skills increase suspension plays an ever important role in the riders expectations.

With that said lets get into the nuts and bolts of suspension set up. Without spending the next three pages going over all the things that can upset and cause poor suspension performance I will go over the most common. These are things that must be checked/corrected before attempting to properly setting up a motorcycles suspension. While these all seem very basic be reassured they can have a tremendous negative impact on your suspension and your ability to figure out what’s wrong. 

•Chain Tension – It goes without saying that a properly adjusted chain is critical. As a chain wears you will get tight spots on the chain. Be sure and adjust the chain at the tightest point along is length. A few years ago I was invited to listen to a suspension seminar put together by a SoCal dealership. Participating was a suspension specialist who worked with the Honda AMA team. One interesting topic he discussed at length was the chain, pivot point and the forces that play with suspension during acceleration. He explained that when a bike accelerates the chain force tries to extend the rear suspension. Auto’s are just the opposite. Hit the gas and the rear immediately squats mostly due to weight transfer to the rear. On the bike that is not the case. The tension in the chain, acting at a slight angle to the swing arm pivot, exerts a downward force that will extend the suspension. This is most noticeable in the lower gears where torque has a greater influence. Watch a bike on a dyno or coming out of a slow corner and hitting second gear. He went on to explain this is why race bikes have adjustable pivot points. More angle more lift, less angle and less lift. As he explained it when a bike is in a corner the suspension is loaded which reduces swing arm angle. As you accelerate weight transfers to the rear. Chain forces begin when throttle is applied which would negate the weight transfer to the rear but because of the increased travel of the compressed suspension (less angle) the chain forces are too weak to overcome the bike wanting to squat. With the rear now squatting the front will lift more than normal which results in the front end pushing to the outside of the corner. The other extreme can occur as well. If the angle is such that chain forces exert enough force to lift the suspension so much so that the rear tire may kick out. Once it steps out the suspension unloads further. You see where this will lead you. While this is very technical I thought it was very interesting. Something to keep in mind if you are making gearing changes and find your bike wanting to run wide or the rear tire is breaking loose coming out of the corners or in most cases the pre-load was never set properly. Setting pre-load is coming up shortly.

•Tire pressures correct

•Tire wear…not excessive

•Rear wheel lateral alignment. (Don’t trust the marks on your rear axle for axle alignment!) I prefer the method of measuring from the rear axle to the swing arm pivot point. I have short steel bars that fit into the rear axle and the pivot arm which I then measure to be sure they are even on each side. The steel bars are long enough so that other parts of the bike (pipes) don’t interfere with the measurement. The other method is using a string around the front tire back to the rear tire.

•Leaky fork seals. Fork oil level must be correct.

•Steering head bearings. Just because your bike is new doesn’t mean it’s correct. 

•Rear suspension linkage and pivot free to move. Pull the rear shock and move the suspension up and down. Check for any side deflection. Most wobbles and weaves are the result of steering head bearings or rear suspension problems.

The next step is to set ride height. Ride height determines how much suspension stroke will be available for absorbing bumps that push the wheels up, and how much will be reserved to allow the wheels to extend for such things as dips in the road. Suspension travel is determined from the point where the suspension is topped out (tire off the ground) to full compression. The distance from full extension to ride height is called sag. This measurement is with the rider on board, fully geared up and in the normal riding position for the bike i.e. feet up, also known as rider sag. Sag (rider sag) is generally 25 to 30% of the amount of TOTAL suspension travel. Your owners manual will give total suspension travel (in mm generally) or you can check this manually by removing the springs and measuring the movement. As an example, on the Ohlins R&T forks travel is 120mm, sag should be between 30-40mm. This will leave an available travel of 80-90mm for compression. I often hear so called experienced riders tell others to set sag to 35mm front and 25mm rear but when questioned they don’t know how they arrived at those numbers other than that’s what they were told to set it at. While 25-30% is a general rule it works for any type of motorcycle….dirt, cruiser, short track etc. The 25-30% is to ensure a reserve for the suspension to extend. Different bikes require different sag amounts depending on the amount of total travel for that bike. The percentage stays the same. Often you’ll hear that for the track you want less sag. This is may be true. Having a little more suspension travel available for such things as braking and increased forces applied during cornering may be better. You can generally get away with it on a track because you are continually running the same stretch of pavement. Most tracks don’t have dips or situations that would require as much of a reserve of suspension movement upward as required for street riding to be safe. Remember, if the suspension tops out and the bike continues to move upward the tire will lift off the pavement. No amount of skill or praying will help you at that point. 

The process of setting sag is pretty simple. Rather than re-invent the wheel I’m going to paste Paul Thede’s, owner of Race Tech, procedure for setting this important setting. Paul has this posted to his website, www.racetech.com While he goes the further step of adjusting for suspension stiction I would recommend you NOT take this parameter into account until later once you have set sag and comfortable in the process. 

Measure where the bike naturally sits with the rider on board. Stiction with the front forks is more important to adjust/take into account then rear suspension. As long as the rear suspension is in good shape you’ll have very little stiction. Front forks can have a large amount of stiction, from the suspension is still new to bad bushings to that’s just the way the stock forks work. In my experiences Showa’s tend to be very “sticky.”

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REAR END 
Step 1: Extend the suspension completely by getting the wheel off the ground. It helps to have a few friends around. On bikes with sidestands the bike can usually be carefully rocked up on the stand to unload the suspension. Most race stands will not work because the suspension will still be loaded by resting on the swingarm rather than the wheel. Measure the distance from the axle vertically to some point on the chassis (metric figures are easiest and more precise; Figure 1). Mark this reference point because you'll need to refer to it again. This measurement is L1. If the measurement is not exactly vertical the sag numbers will be inaccurate (too low). 

Step 2: Take the bike off the stand and put the rider on board in riding position. Have a third person balance the bike from the front. If accuracy is important to you, you must take friction of the linkage into account. This is where our procedure is different: We take two additional measurements. First, push down on the rear end about 25mm (1") and let it extend very slowly. 
Where it stops, measure the distance between the axle and the mark on chassis again. If there were no drag in the linkage the bike would come up a little further. It's important that you do not bounce! This measurement is L2. 

Step 3: Have your assistant lift up on the rear of the bike about 25mm and let it down very slowly. Where it stops, measure it. If there were no drag it would drop a little further. Remember, don't bounce! This measurement it L3. 

Step 4: The spring sag is in the middle of these two measurements. In fact, if there were no drag in the linkage, L2 and L3 would be the same. To get the actual sag figure you find the midpoint by averaging the two numbers and subtracting them from the fully extended measurement L1: static spring sag = L1 -[(L2 + L3) / 2]. 

Step 5: Adjust the preload with whatever method applies to your bike. Spring collars are common, and some benefit from the use of special tools. In a pinch you can use a blunt chisel to unlock the collars and turn the main adjusting collar. If you have too much sag you need more preload; if you have too little sag you need less preload. For road race bikes, rear sag is typically 25 to 30mm. Street riders usually use 30 to 35mm. Bikes set up for the track are compromise when ridden on the street. The firmer settings commonly used on the tract are generally not recommended (or desirable) for road work. 
You might notice the Sag Master measuring tool (available from Race Tech) in the pictures. It's a special tool made to assist you in measuring sag by allowing you to read sag directly without subtracting. It can also be used as a standard tape measure. 
Measuring front-end sag is very similar to the rear. However, it' much more critical to take seal drag into account on the front end because it is more pronounced. 

FRONT END 
Step 1: Extend the fork completely and measure from the wiper (the dust seal atop the slider) to the bottom of the triple clamp (or lower fork casting on inverted forks; Figure 2). This measurement is L1. 

Step 2: Take the bike off the sidestand, and put the rider on board in riding position. Get and assistant to balance the bike from the rear, then push down on the front end and let it extend very slowly. 

Where it stops, measure the distance between the wiper and the bottom of the triple clamp again. Do not bounce. This measurement is L2. 

Step 3: Lift up on the front end and let it drop very slowly. Where it stops, measure again. Don't bounce. This measurement is L3. Once again, L2 and L3 are different due to stiction or drag in the seals and bushings, which is particularly high for telescopic front ends. 

Step 4: Just as with the front, halfway between L2 and L3 is where the sag would be with no drag or stiction. Therefore L2 and L3 must be averaged and subtracted from L1 to calculate true spring sag: static spring sag = L1 - [l2 + l3) / 2]. 

Step 5: To adjust sag use the preload adjusters, if available, or vary the length of the preload spaces inside the fork. 
Street bikes run between 25 and 33 percent of their total travel, which equates to 30 to 35mm. Roadrace bikes usually run between 25 and 30mm. 

This method of checking sag and taking stiction into account also allows you to check the drag of the linkage and seals. It follows that the greater the difference between the measurements (pushing down and pulling up), the worse the stiction. A good linkage (rear sag) has less than 3mm (0.12") difference, and a bad one has more than 10mm (0.39"). Good forks have less than 15mm difference, and we've seen forks with more than 50mm. (Gee, I wonder why they're harsh?) 
It's important to stress that there is no magic number. If you like the feel of the bike with less or more sag than these guidelines, great. Your personal sag and front-to-rear sag bias will depend on chassis geometry, track or road conditions, tire selection and rider weight and riding preference. 

Using different sag front and rear will have huge effect on steering characteristics. More sag on the front or less sag on the rear will make the bike turn more slowly. Increasing sag will also decrease bottoming resistance, though spring rate has a bigger effect than sag. Racers often use less sag to keep the bike clearance, and since roadraces work greater than we see on the street, they require a stiffer setup. Of course, setting spring sag is only first step of dialing in your suspension, so stay tuned for future articles on spring rates and damping. 

-Paul Thede 

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You’ll often hear that there is a certain amount the bike should sag under its own weight, known as bike sag. You’ll hear amounts like 0-5mm on the rear and 5-10mm on the front. I’ve found this to be erroneous and often leads to confusion. Often, in order to get the correct rider sag the bike sag won’t be close. If you set bike sag then you can’t get rider sag correct. At that point you would be told that your springs are too stiff or too soft. 

Here is what I found to work well to determine when/if you need stiffer or softer springs. Now that you’ve properly set sag you simply go back and measure how much preload was applied. Yes, most modern suspensions have a bit of preload even when preload has been set to its softest settings. This measurement works based on the amount of preload applied from the softest settings while using stock components and potential internal preload spacers inside the forks. 

Actual rear shock spring “pre-load” measured amount, required to achieve proper Sag:
*0-1/8” – Spring rate TOO STIFF for rider/bike combined weight
*1/4”- 3/4” – Spring rate CORRECT for rider/bike combined weight
*>1” – Spring rate TOO SOFT for rider/bike combined weight

Actual front fork spring “pre-load” measured amount, required to achieve proper Sag:
*0-3/8” – Spring rate TOO STIFF for rider/bike combined weight
*1/2”-1” – Spring rate CORRECT for rider/bike combined weight
*>1 ?” – Spring rate TOO SOFT for rider/bike combined weight