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If you talk to people about suspension and what they want out of it 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 skill improves, 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’s needed is balanced grip in the 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, 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.

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* 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 why they don’t know how they arrived at those numbers other than that’s what they were told. 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 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 here. 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.”

Race Tech’s Instructions

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

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 ¼” – Spring rate TOO SOFT for rider/bike combined weight

The next installment will cover setting damping and reviewing some of the misconceptions of suspension travel as it pertains to damping.