[Higgy]

I'm fast approaching my first anniversary of ownership of my '93 900 SS. I have ridden it this entire year (approaching 12,000 miles on it already) without touching a thing on the suspension, leaving it as it was set up by the previous owner. I never actually met him, but it is becoming apparent he is much smaller than I am... I'm just over six feet, and a solid 240 pounds.

As my confidence and skills increase, I have had mounting suspicions that my suspension is probably way too soft. Then, last month I had the opportunity to take advantage of the free dyno day at Ducati of Seattle. The dyno tech, Marty, is about my size, if not a bit smaller. First thing he said when he sat on it was "wow, that's soft..." as he rocked it back and forth on the suspension. Suspicions confirmed...

The forks have been re-sprung and re-valved. The shock is a Fox unit. The preload collar on the Fox shock is only about 1/4 of the way from full soft to full preload. I assume the damping is set in a range useful for this preload setting, but also know that will go out the window when I increase the preload. I'm not sure where either is set in the fork, other than to assume it was also set to the previous rider's weight.

So, with that lack of information, where do I start? I'm thinking I can dial the damping adjustments to full soft, counting clicks, then to full hard, counting clicks. That will at least tell me where they are. Preload will be easy to adjust visually on the shock, obviously, but how is this quantified and matched to rider weight? Is there an accepted sag value that I should be shooting for? And, with the forks not as affected by rider weight, would there be a sag value for them as well?

How about matching damping to preload? Could it be as easy as setting both, say, in the middle of their respective ranges? Or, for a fat old man like me, say 3/4 hard on preload and 3/4 hard on damping? Or is it going to be a little more involved than that? I'm just looking for a firmer starting setting - something I can continue to tweak as I ride it. But I need a ballpark, at least as far as matching preload to damping.

Oh, and one last question. Are both bound and rebound adjustable on both ends of the bike? Or just rebound on one end or the other?

 

[944SS]

The first step is setting proper sag. Being that you are gravitationally well endowed, this is even more important. The result could be you are not running the right spring weight. Sounds like your hardware is good on the damping side so once sag is set, you can start fine tuning. I'd cut and pasted this little blurb on sag a while back, author unknown.

"Sag is always measured from the fully extended position. Lever the wheel off the ground, measure, sit on the bike and measure again: That's "Rider Sag." "Static Sag" is how much the bike sags all by itself. Putting a zip-tie around one of the fork legs simplifies measurement and can be left in place so you can see how much suspension you are using.

Since damping can/will effect your readings, you should set sag with the damping dialled to fully soft. Be sure and write down your settings so you can return to them when you are done.

For a streetbike, I've found that 40mm up front and 30mm in the rear is a good place to start. Track mavens would/should start around 30/20~25. Since it's the more important, set rider sag first, and then go back and check static sag - The bike *should* sag a little by itself: 5~10mm is good. If you have proper rider sag but no static sag, then you have to wind your springs too tight, and you should install heavier springs. More than 10mm static sag and you should think about going to a lighter spring."

 

[Muschi]

a great post from this board that i copied some
days ago, that should answer all your questions:



On the front fork, the slotted brass screws on the very top adjust rebound damping, the hex nuts just below those slotted screws adjust the preload and the compression damping is adjusted from the bottom of each fork leg, with a straight screwdriver. The owner's manual gives the standard factory settings as:
- On both the rebound/compression, start by turning the screws clockwise until they stop, then turn each counterclockwise, 7 clicks for rebound (14 clicks out total) and 11 clicks for compression (16 clicks total).
- Preload is adjusted by turning the top hex nuts (clockwise for more, the opposite for less).

You really should set "sag" first, then start with the factory settings. Sag....Distance a motorcycle compresses with weight on it. There are two types of sag we deal with. The first is "free" (static) sag, which is the amount the springs compress under the weight of the bike. The second is rider sag, which is the amount the springs compress with the rider on board.

Preload....This is the amount a spring is compressed with no weight on it at all.


BASELINE SETUP:
At this point, we're finally going to do some measuring and adjusting. We will use a known working baseline to set up your chassis. Then the next time you practice, you will be able to analyze how it works and fine tune it to work even better. All suspension adjustments made by pushing or bouncing on the bike should be made with the bike off the stands, on level ground, and with the bike in neutral.

Rear Shock....The first and most basic adjustment is to set the sag on the shock. When you make these measurements, accuracy is important. If at all possible, use a metric tape measure with millimeter increments. If you use an S.A.E. tape, then measure to the sixteenth of an inch (1" = 25.4mm). You need to pick two fixed points on the rear of your bike for this. One on the rear of the swingarm (like a stand spool or the axle), and one on the sub frame (like one of the bolts that holds the rear passenger pegs on. never use the bodywork since it can sag when the rider gets on). Before you can measure the sag, you must first find the fully extended measurement between your two points. Have a friend help you by pulling up on the footpegs to fully extend the rear suspension. Your bike may be fully extended already. If it is, this is not a problem. Record the distance at "full extension" on your log sheet. Now have your friend balance the bike for you and push down on the seat several times to settle the suspension. Now measure and record the distance between your two points again. This is your static sag. There should definitely be a little static sag on the rear shock. Most expert race bikes have 5-10mm static sag. Your next measurement is rider sag. Have a friend stand at the front of your bike and balance it by the ends of the handlebars. Sit on the bike like you would ride it and bounce down on it three times to settle the suspension. Now have another friend measure between your two points for you and log the measurement in the log. This is your rider sag. Next you need to subtract your rider sag measurement from your full extension measurement. This is your rear sag measurement. You should have 30mm of sag. This is your baseline setting and can be adjusted after your test ride. If your spring tops out the bike, you will need a stiffer spring.

Now we need to adjust the damping. The object is to get the suspension to respond as quickly as possible to irregularities in the pavement. Damping is required to control the movement of the wheel and the spring. Set your rebound damping adjuster first. It is difficult to explain how it should appear in words, but as you push on the seat, it should return quickly, but not instantaneously. It should take approximately one second for it to return to the top from a hard push. You should be able to watch the seat rise. If it just pops back up right away, you need to add rebound. If it drags up slowly, loosen it up. If you have a compression adjuster, sit it up in the middle. You can determine how to adjust it after your initial test ride, too hard loosen it up, and to soft add.


Front Forks....Start here by setting the sag on the fork the same way you did on the shock. First you need a fully extended measurement. Only way to get consistency is to have two guys pick up on the handlebars until the front wheel leaves the ground slightly. Measure the exposed area of the fork slider. On a conventional fork, this will be from the bottom of the lower triple tree to the top of the dust seal on the slider. For an inverted fork, this will be from the dust seal down to the top edge of the aluminum axle clamp. Record this measurement on your log sheet. Push down on the fork hard three times, to settle the suspension. Now measure the static sag. Finally, get on the bike and push down three more times, while a friend balances the bike. Have your friend with the tape take the final measurement. The measurement you are looking for on the front fork is 35mm. If your spring is of the correct rate, the free sag should be about 65 percent of the rider sag, or about 20mm. The front fork has to have a great deal of free sag so that the front wheel may move down into a hole as well as over a bump. If your fork has too much sag turn the preload adjuster in. If you don't have preload adjusters, then you will have to remove your fork spacers and cut longer preload spacers. Adjust in 10mm increments. When you get close, you can go to 5mm increments.

 

[944SS]

a great post from this board that i copied some
days ago, that should answer all your questions.......

A very nice "how to" description. Thanks for sharing that.

 

[Higgy]

Thanks guys - that is exactly what I was looking for. Sorry it took so long to get back with you, but I wanted to make the changes and get a few days in the saddle to form some impressions before I reported back.

So, every blasted setting on the bike was dialed all the way to "full soft". No wonder it felt so "familiar", so accomodating. Just like my Road King... Either the previous owner was some mal-nourished little waif of a man, or he liked it quite soft. Either way, it had over 60mm of sag with my svelte young frame perched aboard.

Fortunately, I was able to achieve the unladen and laden sag values without necessitating a spring change on either end. I set the compression and rebound per Muschi's spec's as a starting point. What a difference...

The bike feels much more taught and planted than it did before. I've spent a few days on my favorite back roads, that I've come to know intimately from the seat of a car or bike. I found myself effortlessly holding a pace that would have been far more "exciting" on the original set-up. The bike is now far more confidence inspiring to ride briskly.

So, from here, the next question would be: how do I determine when the damping is "right" at either end? I know how to do this on a race car or sports car, how to set them up "loose" or with a bit of a "push", but how does one do this on a bike? I simply can't see myself pushing it hard enough to find the limits of traction on either end, to get either end to slide. Short of that, how do I know it's right? As my son rather astutely observed, "dad, you don't get to spin a motorcycle..." I don't want to be picking grass out of my ears, thinking "it feels a little loose..."

 

[joepopp]

Really great post Muschi. Thanks!

 

[redgea4]

Really great post Muschi. Thanks!

+1

 

[944SS]

Always set rebound first. For the front, shove down while holding the brake and allow the bike to spring back on it's own - It should rise back up, but make no additional movement. If it does, add rebound. If it does not, take rebound away until it does, then add back just enough to stop the excess movement. Rear rebound: Shove down on the back of the bike, no brakes: It should take about 1 second to rise back up (pretty much as stated in Muschi's post)

Compression settings are a little less scientific in my opinion. I like enough up front to stop excess diving on the brakes. You'll have to ride to determine that - start at 1 turn from full soft and go from there. Once happy in front, try to get the rear to compress at the same rate, buddy system works best on that front.