Motorcycle Suspension Setup 101

[lamar]

I got this from some where else but good info so I am sharing it.

Suspension setup basics:
- Static (Rider) Sag: The amount of suspension travel used by the combined weight of the machine and rider, measured from topped out.
- Free Sag: The amount of suspension travel used by the weight of the machine alone, again, measured from topped out.
- Damping: Damping is simply the components ability to dampen the oscillating energies that the suspension will be exposed to.
- Compression: The damping that controls the downward stroke of the suspension. At the bottom of the forks and the top of the shock (typically).
- Rebound: The damping that controls the upward (return) stroke of the suspension. At the top of the forks and the bottom of the shock absorber (typically).
- Stiction: This is the drag placed on suspension components due to friction, drag, linkage and other moving parts of the suspension. DO NOT be surprised if this is a large amount as in the Kayaba forks used in the YZF-R1 and ZX10R. This is normal, and these forks are capable of performing extremely well.
- Rake: the angle of the steering head relative to a line perpendicular to the ground.
- Trail: the distance from the point axis intersects with the ground to the tires contact patch directly below the axle.
Tools needed - Generally, simple hand tools that come with the motorcycles tool kit are mostly all that are needed, but as with anything, better tools will make the job go smoothly, and include:
- Flat screwdriver
- Various box end wrenches (preferably six point)
- Various sockets (preferably six point)
- Spanner wrench for rear shock preload
- Tape measure or ruler (metric)
- Zip ties
- Stands (the Baxley type is GREAT for this)
- Assistant(s)
- Notebook or data sheets similar to those by Dave Moss at http://www.feelthetrack.com/

[lamar]

Part I Setting Sag

The first step to setting any suspension is to set the sag. Simply stated, sag is the distance the spring compresses from fully topped out. Race Tech and others have information on the different methods used to measure this on their websites etc, but I'm going to stick with explaining the method used by Race Tech due to the high amount of stiction found in the Kayaba forks.

Rear: When taking your measurements at the rear of the machine, you will need to measure from the center of the axle to a point directly above the axle.

Step 1: You will need to fully extend the rear suspension. You can do this with jacks, some really strong friends to dead lift the bike, or carefully pull it over onto the kickstand. Just remember the R1 has an aluminum kickstand, and it can snap pretty easily. Measure from the axle to the point directly above the axle on the frame.

This measurement is L1.

Step 2: With an extra person holding the bike balanced from the front, have the rider get on the machine in all normal riding gear and get into a the normal position they ride in. Yes, it does make a small difference. Firmly push down on the rear of the machine about 1 inch and VERY SLOWLY release the pressure. Again, measure from the axle to the point directly above on the frame.

This measurement is L2.

Step 3: Next, lift up on the rear of the machine about 1 inch, and again VERY SLOWLY let the rear end down. Again, measure from the axle to the point directly above on the frame.

This measurement is L3.

Step 4: Because of stiction, you should have a difference between L2 and L3. So the average of the two would be where the static sag is. To calculate do the following:

L1 - ((L2+L3) / 2)

Or in English, add L2 and L3 together, divide by two, then subtract from L1.

This number is your sag and should be between 25 - 30 mm (track) and 30 - 35 mm (street).

Once you have the measurement made, you will likely need to adjust to get to these numbers. If the measured sag is too large, you will need to increase the preload on the fork. Too small, you will need to decrease the preload.

After you have the static (rider) sag set to a good starting point, you can use the same method to determine the amount of free sag available. Record this number in your notebook or settings sheet. If your springs are in the correct weight range, this should be from 0-5 mm for street and road race sportbikes.

Front: There are a couple of ways to do this, but I'm going to explain the Race Tech method. Thing to note about measuring the front is there will be a minor difference in measuring conventional and inverted cartridge forks. Aside from that, it's all the same. I like to put a zip tie on a fork tube to help with measuring, and as an indicator of how much total travel I'm using of the suspension.

Step 1: Using assistants or a front stand that lifts from the triple clamp, fully extend the front suspension. Again, the kickstand can be used CAREFULLY. Measure from the dust seal to the bottom of the triple clamp (conventional) or from the dust seal to where the inner fork tube meets the lower casting (inverted cartridge).
This measurement is L1.

Step 2: Using an assistant to steady the rear of the machine, have the rider get on the machine in all normal riding gear and get into the normal position they ride in. Firmly push down on the front of the machine about 1 inch and VERY SLOWLY release the pressure. Again, measure from the dust seal to the bottom of the triple clamp (conventional) or from the dust seal to where the inner fork tube meets the lower casting (inverted cartridge).
This measurement is L2.

Step 3: With the rider still on the machine lift up on the front end about 1 inch and VERY SLOWLY release the pressure. Again, measure from the dust seal to the bottom of the triple clamp (conventional) or from the dust seal to where the inner fork tube meets the lower casting (inverted cartridge).
This measurement is L3.

Step 4: Because of stiction, you should have a difference between L2 and L3. So the average of the two would be where the static sag is. To calculate do the following:

L1 - ((L2+L3) / 2)

Or in English, add L2 and L3 together, divide by two, then subtract from L1.

This number is your sag and should be between 25 and 30 mm (track) and 30 and 35 mm (street).

Once you have the measurement made, you will likely need to adjust to get to these numbers. If the measured sag is too large, you will need to increase the preload on the fork. Too small, you will need to decrease the preload.

Do NOT be surprised by large differences between L2 and L3. There is notably a large amount of stiction in the Kayaba forks, and this is normal.

If you are able to get to the baseline numbers listed above for the riding you will do, you are at a good starting point. If not, you will likely need to re-spring the motorcycle. There are several options to choose from that can be less expensive than ordering new forks or shocks (significantly less in most cases).

After you have the static (rider) sag set to a good starting point, you can use the same method to determine the amount of free sag available. Record this number in your notebook or settings sheet. If your springs are in the correct weight range, this should be from 0-5 mm for street and road race sportbikes.

Once you have gotten the sag adjusted to your preference and recorded your results you will be ready to move on to the next part.

[lamar]

Part II Setting Rebound

Now that your sag is set for your weight, and you have a decent basis for further adjustments, it's time to discuss the most important damping setting. The rebound damping on your suspension ensures the wheel at the end of the suspension is able to stay in contact with the road without excessive oscillation.

The goal here will be to be able to push downward, very firmly and quickly on the suspension and allow it to rebound up. The suspension should smoothly reach the top of its travel and settle, without beginning a second down stroke.

Before setting a starting point it's good to be sure that your valving can accommodate what you are doing. To do this you will "bounce" the machine firmly down and allow it to return. I do this with the rebound adjuster full out, and then full in, to determine how adjustable it is. Then adjusting your damping whether it is rebound or compression, it is VERY IMPORTANT that you take care not to force the adjusting screws. Forcing the screws will likely damage the components and require replacement. Lightly seat the screws in each direction. With the rebound full open, the machine will bounce several times before dissipating the energy of the bounce. Conversely, with the rebound fully closed the machine will bounce partially back up, and either stop or "creep" to the top of the stroke. If it behaves other than this, your components may need servicing or replacement parts.

Once you know the total number of clicks from full open to full closed, you can start at about 1/3 of the clicks out from full stiff to start testing.

With the rebound adjustment at about 1/3 of the clicks out from full stiff, hold the front brake and push down on the bars firmly and quickly. While doing this it?s good to watch the nose fairing and the background to see movement. What you want here is to have the front return to the top of the travel range and settle smoothly. It should not begin a second down stroke nor "creep" to the top of it's range. If it is too fast and begins a second bounce, add a few clicks of rebound damping (clockwise, closing the valve). If it creeps or is slow to get to the top, remove a few clicks (counter clockwise, opening the valve).

The rebound damping is especially important in that it will help control the wheel?s ability to stay in contact with the pavement while traveling over bumps. Too much rebound damping and the wheel may lose contact with the pavement over bumps. Too little, and the front end will be constantly oscillating, sort of like a pogo stick.

With all things considered, the rebound damping is arguably the most important suspension setting. You will always want to recheck the rebound damping as conditions change.

[lamar]

Part III Setting Compression (low speed)

With the sag and rebound damping set, we are ready to begin addressing the low speed compression damping. More and more suspension components are equipped with high and low speed compression adjustments. The terms "high" and "low" DO NOT refer to the speed that you are traveling. They refer to suspension travel speeds. The primary adjustment will be to the low speed compression adjusters. The high speed compression adjusters will help you adjust for sharp edge type imperfections. While it may seem possible to set the compression damping similar to how we set the rebound, it isn't at all practical to do so. Because of factors such as unsprung weight, pavement surface, ambient temperatures etc, you will need to choose a starting point and adjust from there.

While adjusting the compression settings it's a good idea to determine how much damping you have available. To do this you can adjust the compression full stiff, by turning the screws full clockwise. Be sure to do so until they are LIGHTLY seated, and count the clicks in. If you push firmly on the suspension at this point you should see that the suspension is very stiff, and you are not able to go through much travel. Then you can adjust the compression full soft, by turning the screws full counter (anti) clockwise, counting the total number of clicks. Again be sure to do so until they are LIGHTLY seated. Pushing on the suspension at this point you will see much more travel and a plush feel. Return the screws to their original settings, the manufacturer suggested starting point, or about 1/3 the total number of clicks out from full stiff. Record this setting on your notepad or data sheet.

The majority of your compression tuning will be done from on track or on the road observations, so you will need to keep track of how the bike feels over single and repeated bumps or rough pavement. Remember the zip tie? Now is one of the times it will come in handy. After you run a session or stretch of road, you will look at the zip tie to see how much suspension travel you've used. Typically there should be between 5 - 15 mm of travel left. This will vary from manufacturer to manufacturer as many forks will typically bottom out internally before the zip tie hits bottom. Keep note of how far the zip tie is from the stops. You can adjust the total travel by adjusting the low speed compression damping.

I've heard of tuners putting a small zip tie on the shock shaft as well, although I've never done it or discussed it with anyone. But the principle is the same.

Again, your notebook is your best tool, and the more information you keep track of, the easier it will become to make positive adjustments.

[lamar]

Part IV Geometry: Ride height, rake, and trail.

As we make adjustments to the suspension, we have been ultimately affecting the chassis geometry. While the steering head is welded in place, setting the rake at a constant, it is possible to change this angle slightly via suspension adjustments/motion. For instance, raising the rear ride height can effectively make the rake angle more steep. Also, lowering the front by pulling the fork tubes up in the triple clamps will not only change the rake angle, but it will decrease the amount of trail. Generally speaking, the change in trail will be approximately 1 mm for every 4 mm of ride height change.

Increased rake will allow more relaxed steering and greater straight line stability. Conversely, decreasing the rake will provide quicker steering, and less stability in a straight line.

Increasing and decreasing trail is a little bit less subtle, and large changes, as with everything, should be avoided.

As the discussion continues, we may discuss other factors as necessary, but if you've read to this point, you have the basics.

Part V Balance

Although the topic of balance comes up at different points in discussion by different tuners, I've chosen to address it at the end. While we've been going through the suspension components making various adjustments, we've been doing so to either the front or the rear suspension. In balancing the chassis, we will want to be sure that the front and rear are moving at roughly the same rates of travel. This will help us to ensure the front and the rear will respond similarly to the same pavement inputs. And that is what it will take to help keep the chassis geometry as consistent as possible.

To check the balance of the motorcycle, using either a Baxley type front wheel stand/chock or an assistant to help keep the motorcycle upright, you will want to push down on both ends of the suspension with even force. You should push from about the gas cap (where your sternum would be in a race tuck) and the rear portion of the rider's seat. What you will want to see during this is that the forks and shock descend and rise at the same rate. If the front or rear descends quickly, add a click or two compression damping to the component that is quicker. Conversely you can remove a click or two to the opposite end making that end faster. In either case you will want to get the front and rear moving at the same rate.

Once that is done, you will want to push down on both ends again, this time observing the rate of rise. If the front or the rear rises too quickly you will want to add rebound damping to the faster end, or remove some rebound damping from the slower end. Again, the goal here is to attain a rising rate that is similar front and rear.

[lamar]

Handling is arguably one of the most important aspects of motorcycling. The entire time you are on the motorcycle, you are using it's handling capabilities. Understanding the principles of chassis setup will better equip you to maximize the ability to tune your motorcycle for the conditions you ride in and your riding style.

Thanks for reading. Please provide feedback or impressions you may have as well as any questions we can help one another with.

Good sources for further information

While preparing this thread I have gone through pages and hours of information from reputable sources. Most notable for me have been:

-Sportbike Suspension Tuning by Andrew Trevitt - This book has been the most helpful tool for me in understanding suspension setup and characteristics. I recommend Andrew Trevitt's book to anyone wanting to learn more about sport bike suspension setup and tuning.

-Twiddling the Knobs and Introduction to Suspension with Dave Moss from Dave Moss of Catalyst Reaction. These DVDs are available from Catalyst Reaction and are great for in depth explanations. The case studies are superb, and well, the way Dave Moss says "chassis" is just cool.


-Tuning Guide on Catalyst Reaction's website - http://www.feelthetrack.com/ - There are several articles done by Dave Moss on suspension tuning, as well as some outstanding data sheets for recording suspension settings for track days or race setups

- Motorcycle Trackday Handbookby Kent Larson, Pat Hahn, Jason Bishop and Max McAllister. This book is an excellent read for those planning track days, and contains a very good section on suspension setup.

-Suspension Tuning Guide by Dave Hodges. This is a useful guide in quickly troubleshooting motorcycle suspension that I've used a lot over the years.

- And of course, the FAQ and other information by Paul Thede of Race Tech at www.racetech.com. Not only do I personally prefer the parts offered by Race Tech, I frequent the website for troubleshooting and information. While preparing this thread I've noticed that many authors/tuners reference Paul Thede's methods, such as the sag setup exclusively.

Handling is arguably one of the most important aspects of motorcycling. The entire time you are on the motorcycle, you are using it's handling capabilities. Understanding the principles of chassis setup will better equip you to maximize the ability to tune your motorcycle for the conditions you ride in.

Thanks for reading. Please provide feedback or impressions you may have as well as any questions we can help one another with.

[lamar]

If you live in the Tacoma, Wa area go to FLUID SUSPENSION SCIENCE. CONTACT HIGHSIDE284@GMAIL.COM

He is awesome and knows his stuff.

[lamar]

http://www.youtube.com/user/Catalyst...?feature=watch

[jstyled]

WOW! That was alot. UMMMM... I may need a little professional help with this. But I am interested in trying it out.

[06blackpearl]

Originally Posted by jstyled

WOW! That was alot. UMMMM... I may need a little professional help with this. But I am interested in trying it out.

All that above is in this book with pictures.. i just picked it up monday..

http://www.amazon.com/gp/redirect.ht...&creative=9325