Post by anon on Feb 17, 2007 12:54:04 GMT
From: Reaper-FZ1 Sent: 1/24/2005
Setting up suspension can and is very tricky, but also becomes subjective per the riders own requirements.
The springs allow the weight of the machine + rider to travel over unsmooth road surfaces without jarring the bike/rider. But on there own they would produce a pogoing effect.
So we need some kind of dampening effect to slow and smooth out the travel of the springs. This is achieved in the form of oil travelling through a valve. Now depending on the thickness/weight of the oil and the diameter of the hole in the valve/shim stack you can smooth out the rate at which the spring compress and unload the compression.
Most of the Yamaha range of motorcycles use something close to transmission fluid for there fork oil. This is very light and thin and like all moving new parts the forks bed in and metallic deposits are introduced into the oil. After around 6 to 12 months the forks should be bedded in and so the oil will need changing. If you do this you will notice the oil is very grey with metallic particles and smells awful. After the initial change they can then go for around 2 years between oil changes.
Most owners feel that the oil/dampening is to soft and go for a higher weight of oil. Now the original is around 5W so if you use 10W you will get a smoother rate of dampening with out the harshness that can come from using something like 15W.
On more modern bikes that have fully adjustable suspension you will have,
Fork preload - An adjuster on the top of the forks for pre loading the springs.
Dampening - An adjuster on the top of the forks again to alter the rate at which the forks dive.
Rebound - An adjuster at the bottom of the forks to adjust the rate at which the forks travel back up after compressing.
Before starting the following set all damping/rebound settings to factory standard as this is a good starting point.Also take of any preload.
Most motorcycles don't have much in the way of front suspension adjustments. The following will help you to adjust your static sag.
Put the bike on its center stand and/or use an engine jack to get the front wheel in the air. ½" is fine. (sitting someone on the pillion seat while on the stand will fully extend the front too)
Measure the distance from the bottom of your lower triple clamp to the top of your fork leg seal. If this is inconvenient, pick some other place on the lower fork leg, like one of the bolts on a disk caliper. Write down this number.
Take your bike off the center stand. Sit on the bike, grab the front brake, and work the forks up and down a bit.Get the forks to their resting place while holding up your weight.
Measure the distance from the bottom of your lower triple clamp to your fork leg seal, or the disk caliper bolt,or whatever you chose. Another way to do this is to use a cable tye around the fork leg, tight enough so that it can be moved but stays in place when moved. Then sit on the bike while the tye is touching the fork seal/dust seal. Subtract this distance from the unloaded distance you measured above. This is your static sag. An easy way to measure this is to tape a garden cane or length of dowel onto the forks, with the end of the cane/dowel exactly at the top of the top triple clamp when the front forks are unloaded. You can the mark the sag off the cane/dowel.
Your static sag should be ¼ of your total fork travel. If your fork travel is 200mm, your static sag should be about 50mm. If your fork travel is 120mm, your static sag should be 30mm. If your sag is wrong, change your fork preload adjusters to make up the difference.
If you have too much sag and your pre-load adjusters don't have enough travel or you don't have pre-load adjusters, you can still fix this problem. Place the bike back on the center stand.
Remove your fork caps. Measure the outside diameter of your fork springs.
Buy a couple of washers which are as close as you can get to this size. Get some PVC water pipe, whatever size is closest to your spring diameter. Cut two lengths of the PVC pipe which are the length you wish to raise your front end.
Place the washers on top of the fork springs, then the PVC pipe, then the fork caps. Seal up the forks, you're done.
If your forks are riding too high and you need more sag, you still have hope. Open up your forks and see if there's factory spacer on top of the springs. If there is, you can cut down this spacer, or replace it with a shorter one made of PVC.
If after setting the static sag you have damping and or rebound adjusters "you should have set them to the factory standard before setting static sag" then you can try adjusting them as follows.
The rear suspension setup follows along the same lines, but it would be easier with a second person to help using a tape measure.
Now to damping, a lot of this is down to personal preference, but you need to understand the principles of what rebound and compression damping each do. Lets start with compression damping.
Compression damping is the damping that is used when the forks take a hit and are 'compressed' the damping simply controls the speed of this. First the forks, it needs some experimentation to get this right for you, i would suggest trying the middle and then in small adjustments,say 1 click at a time increase the dampening ideally (for fast road riding) you want it to be as slow as you can without it failing to compress enough to absorb a bump. The slower you make the compression damping the harsher the ride will be, the faster you make it then you will find the front will dive under braking and can possibly run out of travel on a succession of bumps. The rear is the same principle, but i find you're usually better off run in it with slightly less compression damping (not for ultimate performance, but to save you getting kicked up the backside by the seat on every bump)
Now rebound damping, now this is the tricky one, this controls the speed at which the forks return to their normal (sagged) position after taking a hit. again i suggest trying the middle setting again (carefully here) so you know what they feel like. The ideal here is to get the forks to return to their normal position as quickly as possible without bouncing the front up so fast that it unweights the bike or 'pogo`s', either of which could cause a loss of front wheel grip, and we all know what that means. Its a compromise, but whereas you can run compression a little bit stiff, running rebound too stiff can cause real problems, at extremes it can prevent the wheel returning after each hit, after a few of these you'll be bottomed out, then if you hit a bump hard it'll like having no suspension and could easily go pear shaped. With the rear rebound damping you can get away with it being a bit slower i find, but its exactly the same principle here.
This is the way I set my suspension up for my stile of riding, but it can be used for any rider/bike combination.
Paul