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Motorcycle road holding qualities
All motorcycles are designed with a suspension geometry that includes height and fork angle. The changing of components can affect this and it is therefore essential that both the rear and the front ends match each other.
Changing to Öhlins suspension gives optimum performance only when both the front fork and the rear suspension interact properly. It is of great importance that the front and rear loaded heights are within the specified values.
Function
Fluid is forced through needle valves at a low rate of flow (Fig.3) and through a number of apertures in the piston (Fig.4) at a high rate of flow. The flow through these apertures is regulated by shims (thin steel washers, Fig.5) that at high pressure are deflected to open for the fluid. On most models the needle valves can be set individually.
By altering the size of the shims stack (i.e. number, thickness, diameter) the characteristics of the damping action can be varied (this should only be done by Öhlins authorized service workshops).
Compression damping
When movement of the motorcycle causes compression in the shock absorber, the fluid flows through the needle valve (combined compression and return valve) in the piston rod. If velocity of the piston is high, i.e. in the case of rapid compression, this will not be sufficient and consequently the shims underneath the piston will open to allow a greater rate of flow (Fig.6).
The fluid that is displaced by the volume of the piston rod is forced into the external fluid chamber via a separate compression valve. Even this valve is fitted with shims that open at high piston velocity. The separating piston is displaced, thus increasing the gas pressure.
Rebound damping
When the spring presses the shock absorber out again, the fluid flows back through the needle valve in the piston rod. The fluid flowing into the chamber is forced by the pressure of the gas back into the shock absorber via a separate non return valve.
If velocity of the piston is high, the shims on top of the piston will also open to allow the fluid to flow though (Fig.6).
Settings
Basic setting
Always ensure that the basic setting made by Öhlins is correct. It is adapted to the make and model (in its original state) and for a rider of average weight.
Spring pre-load
Pre-load on the spring/springs is very important because it affects the height of the motorcycle and the fork angle.
Everything must harmonize
In the recommendation table there are Öhlins front fork springs that are specifically adapted to the shock absorbers recommended for your motorcycle.
If none is noted in the table, then "intact" original springs are the right choice. Incorrect spring action can produce a fork angle that is too steep or too flat. This in turn will give a tendency for oversteering or understeering, which could seriously affect the handling characteristics of the motorcycle.
Setting the Spring pre-load
Measuring
Proceed as follows (it will be much easier if done by two persons):
NOTE!
- A) Place the motorcycle on a stand.
Raise the rear end of the vehicle so that the suspension is in a fully extended position.
- C) Measure the distance, e.g. from the lower edge of the rear mud guard or from a point marked by a piece of tape, immediately above the rear wheel axle, to the wheel axle. (R1)
- D) Make a similar measurement on the front axle, e.g. from the bottom of the upper fork crown to the front wheel axle. The fork must also be fully extended. (F1)
- E) Allow the motorcycle (without rider) to apply load on the springs and repeat the measuring procedure. (R2, F2)
- F) Then take the same measurements with the rider and equipment on the motorcycle. (R3, F3)
It is important that the rider has a correct riding posture, so that the weight is balanced on the front and rear wheel in the same way as when riding.
The measurements must not differ from the following sizes:
Without rider (static sag):
Rear: 10-20 mm (R1-R2)
Front: 15-30 mm (F1-F2)
With rider (ride height):
Rear: 25-40 mm (R1-R3)
Front: 35-50 mm (F1-F3)
Adjusting
Adjust the pre-load with the rings on the shock absorber or by hydraulic pre-loading. In the first case, hold the upper ring and adjust the lower one to the desired position (Fig.7A). Then lock with the upper ring.
For hydraulic pre-loading, increase by turning clockwise and reduce by turning counter clockwise (Fig.7
The original setting of the shock absorber, when delivered from Öhlins, should always be a base when the settings are changed by use of the adjustment devices.
Front fork springs
To optimize the road holding qualities of a motorcycle the front fork must match the rear suspension. Öhlins springs are available for a large number of motorcycles (Fig.8). These, in combination with Öhlins shock absorbers, contribute to superior road holding qualities. The original make of springs should be used if there are none of our springs in the recommendation table. However, they must be in good condition and not fatigued. Remember to change the fluid in the front fork at least once every year. We recommend Öhlins front fork oil.
Setting the Damping
The adjusting possibilities of Öhlins shock absorbers facilitate fine setting. You can optimize adjustments to suit your own weight and equipment, your individual way of riding and the condition of the road. To be able to improve the road holding qualities it is of the utmost importance that you fully understand the functioning of the shock absorbers. Then you can learn by trial and error how they affect the motorcycle.
Depending on the model there are adjustments for rebound damping, compression damping and adjustment of the length of the shock absorber. Damping is set with knobs and screws with a normal right-hand thread. By turning them clockwise the damping action is increased, and by turning them counter clockwise it is reduced. The knobs have definite positions with noticeable "clicks", making it is easy to count to the right setting.
Rebound damping action affects the characteristics of the motorcycle most. The setting knob is located at the bottom on the piston rod (Fig.9). It can be adjusted in about 40 steps.
The compression damping knob is located at the end of the external reservoir (Fig.10). This can be adjusted in about 25 steps.
Some models (PRX) have separate adjusters for high speed compression and low speed compression (Fig.11). The low speed compression is adjusted in 25 steps. Use a slotted head screw driver.
The high speed adjuster has a wide range within about 48 clicks. Use a 14 mm key.
Setting your Motorcycle
By utilizing the adjustment possibilities you can test by trial and error, and learn how they affect your motorcycle.
Always begin by test riding the motorcycle with all adjustments at their delivery setting. Choose a short run of varying character, i.e. long and sharp bends, hard and soft bumps. Keep to the same run and adjust only one setting at a time.
Start with the rebound damping (Fig.12):
If the motorcycle feels unstable, loose and rather bouncy then the rebound damping should be increased. Begin by turning the adjusting knob 4 steps (clicks) clockwise. Test run again and adjust two steps back if it felt too hard and bumpy.
If the motorcycle is hard and bumpy, especially over a series of bumps, then the rebound damping should be reduced. Turn counter clockwise 4 steps, test run and make any necessary correction to 2 steps.
Compression damping (Fig.13):
The low speed compression adjuster affects ride height, smoothness over small bumps and grip. The high speed compression adjuster affects stability, firmness in depressions and fast corners.
If the motorcycle has a low riding position, the low speed compression should be increased. Turn clockwise four steps and test run again. If this was too much then turn back two steps (counter clockwise). If it feels unsmooth over small continuous bumps or has bad grip, the low speed compression should be decreased. Turn counter clockwise four steps. Test run and make any necessary correction in two steps at the time.
If the motorcycle feels unstable in fast corners and has a tendency to bottom easily in depressions and chicanes, the high speed compression should be increased. Turn clockwise six steps and test run again. If this was too much then turn back three steps (counter clockwise). If it feels harsh and too rigid or has a tendency to hop during braking, the high speed compression should be decreased. Turn counter clockwise six steps. Test run and make any necessary correction in three steps at the time.
When you have sufficient feel of the motorcycle you can make further fine adjustments. It is feeling and experience that counts.
When you feel that you have achieved an improvement, go back to where you started and check once more. Be observant of other relevant factors such as tires, temperature, etc. Testrun to make sure whether further fine adjustment should be made.
Setting the shock absorber length
Sensitivity of the steering can be adjusted by altering the length of the shock absorber, without affecting other characteristics. The length is adjusted using two nuts down and the treaded clevis at the end of the piston rod (Fig.14). The shock absorber can be adjusted up to 12 mm.
Adjusting the shock absorber length
A long shock absorber results in steeper inclination of the front fork (steeper fork angle) and consequently sensitive, quicker steering. A short shock absorber gives a greater angle of the front fork (flat fork angle) and consequently slower and smoother steering. Each complete turn of the shock absorber gives one millimetre (Fig.15). The length may never be altered more than to where the groove (Fig.16) that is cut in the thread becomes just visible under the lower nut of the level brachet. Make small steps and testrun.
NOTE!
On shock absorbers that have mechanical type adjustment the position of the adjusting/pre-load rings can be adjusted. On a shock absorber that has hydraulic setting the basic position can be adjusted. Such changes should be attended to by an Öhlins authorized service workshop.
The spring pre-load affects the ride height, it does not affect the spring stiffness. Therefore, on models with a linkage to the shock absorber, the suspension may actually feel harder when you reduce the pre-load and the shock absorber gets into the harder range of the link system.
Older gear shaft drive driven motorcycles (not para lever shaft drive) usually raise the rear end during acceleration. We recommend that the the static sag (R1-R2) is extended to 15-20 mm and the ride height (R1-R3) to 35–45 mm on these motorcycles.
It is important that the recommendation table is followed for new front springs. If there are no recommended front springs you must ensure that the existing springs are in good condition. Neglecting to check the front springs could seriously affect the handling qualities of the motorcycle.
If no "click" is felt in the rebound adjuster, the shock absorber must be inspected by an authorized service workshop. It could be due to low gas pressure or lack of oil.
When making new adjustments it is easiest to go back to fully closed, and then count forward to the new setting. The adjusting device should not be turned too hard.
The hexagon of a two way compression valve is naturally anodized aluminum. The high speed adjuster has a key width of 14 mm and a range of 48 steps (clicks). The low speed adjuster (slotted head screw) has a range of 25 steps.
The one way compression adjuster is gold anodized. The adjuster (slotted head screw) has a range of 25 steps. Do not turn the hexagon as this will allow for the oil to spurt out of the shock absorber.
High and low speed refers to the shaft velocity of the shock absorber. It is not necessarily related to the speed of the vehicle.
Always begin with the basic settings recommended by Öhlins. Always make notes, adjust in small steps and make only one adjustment at a time. Adjustments should be made with two steps (clicks) at a time. Adjustments should not be more than four steps from the basic setting.
Ensure that the springs are properly pre-loaded before attempting to make any adjustments. A simple rule is that increased pre-load of the spring should be followed by an increase of rebound damping by two steps.
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Atlas Performance, dyna pumps, " your name goes here"
Originally Posted by arwon 
) can detect changes of 1mm to the trail of a bike. Changes in tyre circumference as per above can change the trail by around 2mm+ on some bikes the equivalent of dropping or raising the forks 8mm.
Make sure you record each change in MM! Both static and loaded that way you won't go round in circles. Ride height is VERY important. 
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