Article by Michael Gougis extracted from Road Racing World magazine.
Its easy for the novice to sportbike riding to look at the knobs, dials, screws and threaded collars on the motorcycle's suspension and reach one of the three conclusions:
* They must have gotten it right at the factory; or
* Somewhere in the middle of the adjustment range must be close; or
* This knob goes to 11, so if I crank it all the way up, I'll be really going fast.
If you're new, how do you know what's good and what's bad, what's right and what's wrong. Where do you even start? If the bike is handling poorly, which of the six basic adjusters move? Which way do you turn them?
And of course, you're trying to figure out what the suspension is doing at a time when your'e kinda busy. You want the suspension to work while cranked over, knee down on the ground, feeding in the throttle and feeling for the limit of traction at the front and rear. On a litre bike, that means that while 150+ horsepower are trying to tear the rear wheel loose from the ground, you're trying to analyse suspension movements. Its not easy, even professional racers sometimes just throw up their hands and tell their crewchief, "I dunno, it just no good".
What you need is a systematic approach to setting up the suspension, trying new things, and working towards a baseline setting that works relatively well. Once established, you can experiment with different settings, knowing that you can always go back to what worked.
That baseline setting does not come by accident. There are 2 ways you can find it. The first is to take some else's suggestion for what works for them - not necessarily a bad approach, but one that denies you the opportunity to learn how to find out how to set a suspension up.
The other approach is to start from scratch, building up a knowledge of your bike, your suspension, your knowledge of how changes in the suspension affect your bike, and your vocabulary for describing changes. That vocabulary is critical not only for discussing changes and improvements with a tuner, but in crystallizing in your mind what the bike is doing.
Getting a suspension tuning guide from a reputable source in the business can help with this learning process. Ther are a few well-known suspension tuners who have put together guides for riders who want to try to sort their way through the adjustment maze on their own. Among them are Max McAllister, whose "Suspension for Mortals" handbook is available from Traxxion Dynamics and Paul Thede who has a collection of technical articles on the racetech.com website.
Another source aimed at the beginner, is "Twiddling Knobs" a DVD put out by Dave Moss of Catalyst Reaction Suspension Tuning. This 94 minute DVD walks the rider through the various types of suspension adjusters, what each does, and how to experiment with them on the track. This last bit is particularly valuable as it gives the new rider some idea of what kind of behaviour from the motorcycle is related to the adjusters.
Moss advice can be broken down into three main areas:
* Set the springs up properly.
* Use the rebound damping to get the chassis balanced.
* Ride the bike, feel what it does, and turn rebound and compression dampers to dial out the bad stuff. (Doing these things in order is critical)
"Don't be afraid to change settings and try things out. Bust most importantly get the bike set up to your weight and use that as a benchmark before you then try any hydraulic dampers" Moss says. (Note: hydraulic dampers = compression and damping rebound adjusters).
Settting Up Springs
There's an entire section on the DVD devoted to setting sag - the distance the suspension compresses when you sit on the bike. The suspension works best in the middle of its travel; sag is the way you get the suspension sitting right at the beginning of the optimal performance area of its travel.
Preload adjusts the tension on the springs and adjusts the amount of bike sag under the rider at a standstill. Front and rear preloads are two of the basic suspension adjustments. Preload typically is adjusted by a hex nut atop the forks a threaded or ramp collar at the rear. (Different manufacturers have different adjusters in different places on their motorcycles. Before you turn anything, look at your model-specific manual and know what you are turning.)
While making this adjustment has been gone over in great detail many times before in this magazine, Moss adds a couple of caveats"
* Be sure you are measuring the total sag. Most motorcycles will sag somewhat under their own weight. Lift the rear by the subframe, or the front by the handlebars and make sure that the suspension is in full extension before making your first measurement.
* Street settings are somewhat softer than race settings. In the rear, Moss looks for about 1.125 inch of sag - the distance from full extension that the bike compresses down when the rider sits on it - for racing. For the street, Moss sets the rear sag at 1.25 -1.50 inches. Up front, Moss sets the sag at 1.50-1.75 for the track and 2 inches for the street. Set the sag when the springs and suspension fluids are warm from riding.
On the DVD, Moss demonstrates how much difference a rider's weight makes in a suspension setup. He puts one rider on a bike and sets the rear sag at 1.125 inch, then puts another rider about 30 lbs lighter on to the bike, the bike sags only by 0.75 inch. Moss points out that in this scenario, there isn't enough preload adjustment left to dial in the increase sag to necessary to get the lighter rider into the proper suspension operating range. A change in springs is necessary.
When checking rear sag, make sure the chain has slack; otherwise, it will cause the rear to stop in its travel.
Rebound damping slow the reaction of the motorcycle to the compressed springs front and rear. It is caused by forcing oil through the orifices in the shock and fork legs. When the motorcycle hits a bump, the spring compresses, then tries to return to its original length. Without adequate damping, the fork or shock will over-extend, then compress again, then over extend again, with the cycles getting shorter and shorter until they stop. The more the rebound damping, the more slower the return, the less, the quicker.
Front and rear rebound damping are the second two of the basic six adjustments.
Too little damping allows the motorcycle to bounce up and down on the spring. This means that when the next bump comes along, the suspension component is likely not in the proper position to react optimally. The result is a wheel that is bouncing in an uncontrolled manner compromising grip and rider confidence.
To adjust damping at the front, Moss suggests grabbing the brakes and pushing the end down and releasing it. Note how many times the forks compress and rebound on their own. Add rebound damping (typically screw type adjuster atop of the forks) until the forks return to their original position and stay there, or until they rebound slightly past their original position and drop back immediately.This way, the forks are ready for the next input, waiting at the place you carefully set the sag for to allow them to work optimally.
The next step is to make sure both ends of the motorcycle are rebounding at an equal pace. To check this, grab a handlebar and something solid near the back of the bike. Push both down at the same time. They should rise back up at roughly the same pace. Having a friend along to help check your perception can be very useful during this stage. Since the front rebound damping is set, increase or decrease the rear damping rebound until the rear rises at nearly the same pace as the front.
Time to go riding.
This adjustment determines how rapidly the suspension will react to an input. Front and rear compression damping are the last two of the six basic adjustments. On the track or on the roads, Moss says, too little compression damping at the front will feel like sharp shocks through the handlebars, the handlebars will start to twitch. This is because there is little damping to slow the compression input. The fork may bottom and the front may wash away rather quickly. Too little at the rear and the bike will move up and down, as as the wheel weights and unweights, traction will be compromised and the rear will feel like it wants to come around.
Too much compression damping at the front feels different. Instead of the dramatic suspension movements and the occasional sharp jolt, every little bump will send a jolt straight up the rider's arms and shoulders. Its a miserable ride. Too much compression at the rear feels similar, with the rear not moving around as much, but delivering a constant stream of sharp jolts to the rider.
Too much rebound damping at either end can also deliver a painfully harsh ride, as the suspension does not have enough time to return to its optimal setting after an input. A series of inputs packs the suspension into a fraction of its travel and the ride quickly turns harsh.
Too much rebound damping at the rear can also make the bike run wide at the exit of a corner, as the rear squats and the rake therefore increases.
For the DVD, Moss has mounted a camera on the motorcycle, aimed at the wheels, and he does laps with the suspension set at various places. This allows the viewer to to actually see the differences that the changes in suspension settings make. Too little damping allows the wheel to move wildly, while too much kept the wheel stable in travel but the camera and the rest of the bike shakes from shocks of unabsorbed inputs.
It takes some effort to get it right. But when you do, what you wind up with is a motorcycle that feels smooth and planted solidly everywhere on the track. You the rider, aren't paying as much attention to the bike moving underneath you. You find yourself paying more attention to braking markers, turn in points, and screwing on the throttle earlier and harder with every lap.
This is Moss most basic introduction to suspension setup. Others do it different ways. Suspension setup is one of those areas where even at the MotoGP level, they don't always get it right. But if you, the track day rider, don't have a plan on how to set it up, the odds of stumbling onto the right combination are pretty slim.
Most suspension tuners suggest making big changes. Moss suggests you figure out how much range you have to play with (the total number of settings or clicks for a particular adjustment) and make changes that total about one third of the range of adjustment.
If your rebound damping is five clicks out from SOFT, and you have 15 clicks to choose from and you want to add more rebound, try adding 5 more clicks.
You want to make a change you can feel. If you have gone the wrong way, you will know very quickly.
Keep careful track of the changes you make and don't be afraid to undo something that feels worse. When you get lost, start over. Check the sag, set the rebound, and ride again. A little time spent setting the suspension at the beginning of the day pays dividends in the terms of comfort speed and fun for the rest of the ride.
PS - This was another marathon typing session for me.