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School me on motorcycle suspension

  #1  
Old 04-10-2009, 02:49 PM
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Default School me on motorcycle suspension

What are the differences between the major manufactures (Kawi, Honda, Suz, Yam, Duc)?

What makes a good or bad suspension?

How has the suspensions improved over the last 15 years?
 
  #2  
Old 04-10-2009, 04:15 PM
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I found a great write up! It's kind of long, but I am glad I read it. Opinions anybody?


The Difference Between First and Tenth: An Introduction To Sport Bike Suspension Tuning

Aug 19 '00



In the last ten years Iíve helped seven people transform their street bikes into racers. The process always begins the same. The owner wants to start by getting more horsepower out of the engine, and I try to diplomatically steer them into investing in suspension upgrades and tuning. It can be a hard case to make for someone who has never been on a track before and is most accustomed to measuring their bikes performance in a straight line on a weekend ride. But in production racing, where engine modifications are closely regulated, suspension tuning is the one mechanical variable that often decides the difference between winning and finishing in the middle of the pack, or worse. On a tight track it can be worth 20 horsepower. And unlike engine mods, setting up the suspension will dramatically lower the learning curve for a novice racer, and make a weekend ride more enjoyable for the street rider.

Iíve written this aimed at road racers, but the tuning tips and techniques are the same for a street rider. The only difference is that for a street rider the improved handling and suspension performance should improve the enjoyment of the ride, while a racer will use this for lowering his or her lap times. The ends are different but the means for getting there are the same.

Suspension setup isnít difficult but it can easily seem overwhelming. With adjustments for ride height, spring preload, compression damping, rebound damping and tire pressure at the front and rear on most newer sport bikes, the possible combinations are nearly limitless and most will make the bike slower-if not totally unrideable. But if you understand what the parts do and take it on with a methodical mindset, soon the black art wonít seem mysterious at all.

Begin With The Obvious:
The first step is often the most overlooked. If the tires arenít in good condition and properly inflated the rest of your work will be in vain. You should begin with the recommended inflation level in your owners manual-not the number stamped on the side of the tire-and you want to set the tire pressures when the tires are cold. For racing or street riding, you should invest in a quality tire pressure gauge; the stick gauges sold at convenience stores are notoriously inaccurate. I also recommend having an old-style bicycle tire pump (the kind with a flexible hose that locks to the tire valve) to set the inflation. They are cheaper than a portable air tank and easier to use. (Aside note: I also recommend angled tire valve stems. On many bikes they are easier to access that the traditional straight stems fitted from the factory, and they are immune to centrifugal forces that can depress the valve and cause air to leak from the tire at high speeds.)

Sag Me Baby!
Setting the sag is the next step, and it is the first step in dialing in the bike to fit you. Sag is how far the suspension compresses with the weight of you and the bike forcing down on it. Because the suspension can unload (extend upwards) while you are riding you have to get the bike off the tires to determine the maximum extended travel. This-not the position of the shock and forks when the bike is at rest-is your baseline for measuring the sag. To measure the sag at the forks get the front tire off the ground, wrap a nylon zip tie around the stanchion, and slide it up against the slider tube. Lower the bike and, with a friend holding the rear to keep it from falling over, get on the bike gently (so you donít bounce it) and sit on it in a riding crouch so the bike is supporting your weight, as it will be when you are riding. Then get off the bike (gently, again) and jack the front tire off the ground again. The fork slider has pushed the zip tie down and the distance between these two points is the sag. You should aim for 30-33mm as a starting point. If your reading is greater than that increase the spring preload adjustment in the top of the forks and, conversely, backing off the preload will make the bike sink farther onto the suspension if you need more sag. Once you get it dialed in leave the zip tie in place, youíll need it later.

To adjust the sag at the rear you need to get the tire off the ground again. But the shock being surrounded by the spring makes it impossible to use a zip tie around the shock rod. Youíll need to attach a measuring devise to the swingarm and the easiest way is to use more zip ties to temporarily attach a long, draftsmanís quality, ruler to the swingarm near the rear axle, and make a pointer from a coat hanger and attach it to a static point on the seat cowl. Lift the rear tire off the ground (as easy as putting the bike on the centerstand if you have one, if not use a strong friend to lift the rear) and note the number on the ruler the pointer is on when the rear wheel is fully extended. With the ruler and pointer in place, lower the bike and get on board as you did and record the number the pointer is at now. The difference between the two is the sag for the rear and like the front you should aim for 30-33mm. The preload adjustor for the shock is at the top of the spring and either uses a cam that locks the preload in increments or a lock nut atop the adjustment nut to keep the adjustment in place. If your bike has the second type, it is essential to make sure it is snugged down to keep the adjustment nut from backing out. It is the only thing holding your spring in place and if it comes loose you will be in for a big and unpleasant surprise.

Sag is important for many reasons. If it is too high or too low you have greatly reduced the amount of room the suspension will have to work. Too little sag will cause severe traction problems and create a bone-jarring ride. Too much will make the bike wallow in corners and in the transitions of acceleration and braking. Sag isnít effected by temperature or track conditions so you can set it up in your garage before heading to the track, and it only has to be checked a couple of times a year if you are racing. (Once annually is enough for street use.)

If you are finding that you need to use most of the preload adjustment to achieve the correct level of sag, you will need stiffer springs. This is most common in forks, where the factories use a softer spring rate to create a smoother ride. Replacement springs are available from several sources, in both progressive and straight rate. The spring rate on progressive springs increases as they are compressed and straight rate springs maintain a constant compression rate throughout their travel. For street use I recommend progressive springs for their greater versatility. But for track-bound machines you should use a straight spring to ensure you arenít chasing a damping problem when the spring rate changes.

Get On Your Bad Motorscooter And Ride
To dial in everything else you have to get on the bike and ride. I advise starting with the damping adjustments set to the factory recommended street settings for riders making their first trips onto the track, or for more experienced riders getting to know a new bike. Your end results might end up close to the recommended sport or race settings, but there are so many individual variables to take into account it is better to start with the street settings and discover for yourself where the bike needs improvement.

Before you start adjusting the damping you need to get the tire pressure dialed in. Take a few laps to get the tires up to operating temperature and bring the bike in to check the pressure. As the tires get hot the air inside expands, raising the pressure. If you donít want to invest in a pyrometer to measure the temperature of the tires you can use the pressure difference to tell if the tires are running too hot or arenít getting up to temperature. If the pressure increases by 6-8 psi after a few laps your cold pressures are fine and the tires should maintain this temperature through the race. If the pressure difference is greater than 8 psi your cold air settings were too low and need to be bumped up slightly, and conversely if it was less than 6 psi the base settings were too high and the tires will have to work harder to get up to temperature. Make your adjustments in one psi increments until you have it in the 6-8 psi range. Write everything down and also make a note of the ambient air temperature and the track temperature. (You can use a meat thermometer for this.) Keeping an accurate record of conditions and settings will become an invaluable reference for future setups, and it will help you make sense of problems you run into later.

Damping Time
Now we get to play around with the compression and rebound damping adjustments. Before you start turning the small screws at the top and bottom of the forks and shock, it is important to understand what they do and-more importantly-what they donít. Damping is the use of oil inside the forks and shocks, routed through passages in a sealed piston, to resist and control the spring movement. Compression damping controls the movement of the suspension in its downward travel and rebound damping controls the upward movement of the springs. Damping can be adjusted with oil viscosity, the volume of oil in the fork tubes and, if your bike has them, through adjustors that change the port volume.

Damping does not affect wheel travel or how much effort is required to deflect the spring. It only determines how much time it will take the spring to reach the deflection for the amount of work placed on it. Increasing the damping makes the suspension feel stiffer, but if the load is held on the spring it will eventually get to where it wants to go.

This makes damping most important for the transitions of braking and acceleration, where you need to control how much the bike dives under braking or squats under acceleration. This is all-important in road racing, but if your bike bottoms out on banked corners (like at Daytona) or in long, high speed sweepers you need stiffer springs-not more damping. (The zip tie you left on your fork is there to see if you are nearing the limits of suspension travel-or not using enough of it-because of spring rate.)

Damping is about feel. You can use compression damping in the forks and rebound damping in the shock to limit the amount of brake dive while you are on the binders because you are increasing the amount of time it would otherwise take the spring to react to the load being placed on it. At the exit you can adjust the rebound damping in the forks and the compression damping in the shock to manage the amount of squat when you get on the gas and to keep the front tire in contact with the pavement. Remember that, unless you are getting airborne, these forces work in concert. As the forks are extending the rear shock is compressing and vice-versa.

The reason I advise starting with the recommended street settings is because dialing in the damping is the best way to make you feel comfortable on the bike. If you feel comfortable you will go faster from the beginning. As your abilities increase youíll find the original settings arenít cutting it anymore, you are braking harder and deeper so you need to increase the compression on the forks, for example. But it is essential that you work up to these points. Trying to ride a bike that is set up for abilities you donít yet have is frustrating and dangerous.

The Low Ri-der...AAAARGH!!!
The last variable in suspension setup is ride height. Only a few bikes have adjustable ride height at the rear but most sportbikes can have the front ride height adjusted by raising or lowering the forks in the triple clamps. Dropping the forks reduces the trail and makes the bike steer faster, but it also transfers weight to the front tire. That can reduce the limit of traction available at the front, and reduce the amount of traction you will have available at the rear tire when you get on the gas at the exit. If you have adjustable ride height at the rear the opposite is true-greater traction for slower turn-in. It is worth noting that every professional and nationally ranked racer Iíve known only makes minute adjustments in ride height, and approach changing it with extreme caution. Ride height should be set up as the best compromise between the different styles of corners on the track and the riderís skill level. When you have this setup the rider can make adjustments for specific corners by shifting his weight on the bike.

Again, take notes on all of the settings you try and have someone keep track of your lap times so you can see how the changes translate into speed. It will take some time, but as you progress as a racer this suspension diary will allow you to look at a new track and have a good idea what setup youíll need to be competitive.

Like The Daytona 200, Even This Comes To An End (Eventually...)
If youíve read some of my other motorcycle reviews, you already know I am a huge fan of aftermarket shocks from Penske, Fox, Ohlins and WP, and the fork tuning services and kits from Race Tech. Improving your suspension is the best investment you can make in your sport bike-period. But having the parts is only part of the answer. You have to know how to set them up to best suit you, and I hope this helped.

Thanks for reading.

-Brian Igo
 
  #3  
Old 04-13-2009, 04:18 AM
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I am slightly disappointed in peoples lack of interest in this subject. If somebody posts up a thread on gaining more HP, there are many responses. The second somebody mentions the word "suspension" everybody clams up. I think that people should take A LOT(!) more interest in there suspensions! I know I will!!

I have a friend who has a certification at MMI (AZ) and eight years of experience in multiple shops throughout the country. He claimed that adjusting the suspension to ones body weight and riding style is very easy and will improve both riding quality and track times. I will have him help me adjust my suspension and I will post pics with step by step instructions.
 
  #4  
Old 04-13-2009, 05:11 AM
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Good read. There is another article floating around that I'll try to post up. We had it on here years ago so it might take me a bit to find it.

But you're right ... post a thread titled "10HP gains with blah blah" and you'd have 50 posts the same day -- 20 who say it works / 20 who say it doesn't / 10 trying to stir the pot
 
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Old 04-13-2009, 02:46 PM
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There is another article floating around that I'll try to post up. We had it on here years ago so it might take me a bit to find it.
It would be greatly appreciated. I have been reading a lot about suspensions lately and any bit of info would help. Thanks!
 
  #6  
Old 04-13-2009, 03:56 PM
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We had copied and pasted but I see they added more stuff so here's a link to the Sport Rider page ... enjoy
 
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Old 04-13-2009, 08:03 PM
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Good Read(s)!! With me its more not knowing a thing about suspension lol, but those articles definately enlightened me
 
  #8  
Old 05-27-2009, 07:54 AM
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Great thread, thanks!
 
  #9  
Old 08-01-2009, 05:58 PM
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Default lift the bike's rear end

Can anyone post instructions on how to raise the rear of a HONDA F4? thanks.
 
  #10  
Old 10-26-2009, 11:01 PM
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Great article that more people should pay attention too. I purchased a 2003 CBR 954 a little over a week ago and since I mostly ride curvy mountain roads decided to check all suspension settings before taking the bike out yesterday for the first time. THANK GOD I DID!!! The settings were all over the place from the previous owner. One fork had preload set to almost full soft and other was a few turns from full hard. None of the others were at the factory setting and most were in wrong direction needed for improved handling. I used this site to find the link to the sport bike suspension settings article and used that setup for my 954. Needless to say I felt very comfortable my first time out on a new bike. All the horsepower in the world is not worth a crap unless you are drag racing or just like to brag. Come ride the mountains in TN and find out real quick about what is more important because I will never need all the power of my 954.

The more I read on this forum it seems to me that most people who try to gain HP end up spending even more $$$$$ to try and fix problems. My buddy has a 2000 CBR 929 with only a slip-on and 22k+ miles and has never done anything to it but change oil, air filter, battery, tires and brakes. Spark plugs are factory and bike still runs like new. This is why I found an almost stock 954 instead of buying a new bike. I know how dependable this bike will be if I just ride it. My first purchase will be a steering dampner before spring.
 

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