Front suspension fork

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Front suspension fork
Kawasaki

Front suspension fork

Front suspension fork

Front suspension fork

Front suspension fork

12th pictures

Front suspension fork
Kawasaki

1/12
Current technical status: Kawasaki ZX 10R with 43 USD fork, Big Piston damping and relatively delicate triple trees.

Front suspension fork
Jahn

2/12
Beautiful, foldable MV Agusta clamp with very thin-walled but huge front wheel axle.

Front suspension fork
Artist

3/12
Hollow cast triple clamps up to 100 millimeters wide clamp the stanchions firmly in place. Often too tight.

Front suspension fork
Schermer, Franz Josef

4/12
1 spring with pre-tensioning sleeve and fork plug. 2 standpipe with plain bearing and Simmerring. 3 damper cartridge with damper rod and hydraulic stop piston. 4 Immersion tube with fork foot and central screw.

Front suspension fork
archive

5/12
At the beginning of the 90s, Yamaha pushed forward with the axle steering on the GTS 1000. Here, too, the high mechanical effort did not lead to the desired success.

Front suspension fork
Bildl, Andreas

6/12
Slotted upper triple clamps that are strongly retracted on the bars provide the necessary flexibility and improved feedback in road racing.

Front suspension fork
manufacturer

7/12
Elaborate and heavy: The Duolever front wheel suspension from BMW only dips a little when braking.

Front suspension fork
fact / Joachim / Dave / Schahl

8/12
Immersion tubes coated with carbon reduce the friction between plain bearings and Simmerrings.

Front suspension fork
gad

9/12
The end of an era: the 1989 Suzuki GSX-R 750 with a 43 mm telescopic fork. A year later the construction was replaced by a USD fork.

Front suspension fork
Schwab

10/12
Two massive, tension-free clamped pipe connections stabilized the Egli fork of the 70s and 80s.

Front suspension fork
fact, Joachim Schahl

11/12
Above you can see the big damper piston of a Big Piston fork that runs right in the dip tube. These include the small pistons of a conventional fork for rebound (right) and compression damping, which are housed in a common damper cylinder (cartridge).

Front suspension fork
archive

12/12

counselor

technology & future

Front suspension fork

PS-Technik series part 11
Front suspension: telescopic fork & Co.

Content of

Countless attempts to replace the telescopic fork with alternative wheel guides have so far failed. As a multifunctional talent, the telescopic suspension fork steers, brakes, springs and dampens without any dramatic weaknesses.

Werner Koch

02/19/2014

No amount of ingenious front wheel guidance can handle the wide range of tasks as perfectly as the telescopic fork. Even if the theory of a clear separation of wheel guidance, suspension and damping sees the alternative designs as an advantage, practice proves that the telescopic fork is unbeatable in the sum of its properties. Especially since the theoretical disadvantages are partially reversed in practice. When braking with the telescopic fork, regardless of whether it is upside down or conventional, the steering geometry changes dramatically in the direction of maneuverability, depending on the suspension travel.

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Front suspension fork

PS-Technik series part 11
Front suspension: telescopic fork & Co.

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Small example: By submerging the front and simultaneously rebounding the rear, the caster of a sports motorcycle is reduced from 100 to around 75 millimeters, while the steering head angle changes from 66 to 70 degrees and is extremely steep. Because the telescopic fork, due to the inclination (steering head angle), moves not only upwards but also backwards, the wheelbase is also shortened from 1450 to 1405 millimeters. The bottom line is that the motorcycle has a very manageable geometry during the braking phase, with the effect that the machine can be easily and quickly thrown into an inclined position on the brakes.

Front suspension fork

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The temporary solution of the 80s: the fork stabilizer

In the opposite case, i.e. when accelerating fully, the telescopic fork rebounds and the steering geometry becomes “more stable” because the steering head is flatter and the caster is greater. With which the geometric changes due to the compression and rebound of the
Adjust the telescopic fork almost perfectly to the respective driving situation.

In the 1970s and 1980s, attempts were made to get the problem of the strong torsion caused by the long telescopic construction under control with so-called fork stabilizers. In their need, the designers made do with drastically increased standpipe diameters before the whole system was turned upside down at the end of the 1980s. Upside-down, or USD for short, was the name of the trick that brought a few decisive advantages.

The extreme bending forces on the lower triple clamp are sustainably defused by the large diameter of the USD fork. In addition, during compression and the associated bending moment, the immersion tubes slide into the standpipes, which in many USD constructions contributes to further stability due to the increased overlapping of the bearing points. This fundamentally high stability of the upside-down forks is one of the reasons why their diameters have only changed for a few manufacturers in the last 20 years. Most large-scale machines currently only have 41, 43 or, in a few cases, 45 millimeter thick immersion tubes. Which is good for the weight and at the same time reduces friction.

The handicap of the undesirable high friction between the immersion tube and the standpipe was often the reason to replace the telescopic fork with low-friction front wheel guides. With the Telelever, BMW implemented a combination of telescopic fork and trailing arm. On the other hand, the BMW Duolever system was more radical, as the relevant components move in low-friction rolling bearings. There the wheel carriers are supported by massive trailing arms on the frame (photo above). An intermediate strut takes over the suspension and damping.

Due to the articulation points of the trailing arms, this construction hardly dived in when braking due to the so-called pitch compensation. Anyone who thought that BMW had thus sealed the end of the telescopic fork was taught better by the S 1000 RR. Because the Munich super sports car springs – after several attempts with the Duolever system – via a conventional USD fork from Sachs. 

Too much of a good thing: diameter and rigidity

A good 20 years ago, Yamaha tried to turn the world off its hinges with a stub axle steering on the GTS 1000 sports tourer (drawing above) and Bimota with the Tesi hub steering. But Yamaha’s sports tourer could not implement the theoretical advantages in practice and disappeared from the market after a 5-year construction period. The major disadvantages of both designs: expensive and time-consuming, too little steering angle for everyday motorcycles, indifferent steering force transmission. Countless prototypes in racing with alternative wheel guides have also proven that there was and still is no better solution for a racing or super sports motorcycle than the compact and inexpensive telescopic fork.

If you take a close look at the torsional stiffness of modern wheel guides in practice, it becomes clear that a certain flexibility can definitely be an advantage. Disturbances caused by the road surface, i.e. transverse grooves or bumps in rapid succession, are absorbed by a flexible system, while extremely stiff structures can initiate these impacts into the chassis and trigger knocking of the handlebars or chattering, i.e. high-frequency vibrations on the front wheel.

Low friction for perfect shock absorption

In addition, the so-called wheel elevation curve, i.e. the course of the wheel during compression due to bumps, is almost perfect with the telescopic fork. All other current systems, including the BMW Duolever design, partially spring against the direction of impact, which counteracts driving comfort on bumpy roads.

The triple clamps of some factory racing machines are an example of the specifically designed flexibility of a telescopic fork. At first glance, bizarre milled upper triple clamps hold the stanchions there and allow more or less large twisting due to the deep cuts. Which is why the extremely massive and often clamped lower triple clamps have almost always disappeared in racing and in series production. Only a few tuners still rely on such martial components for optical reasons.

Extremely large front axle diameters, such as those specially built into the MV Agusta-F models (photo above), ensure maximum torsional stiffness of the dip tubes. And here, too, the designers have pulled the brake and left it at a comparatively thin 30 to 35 millimeter clamping fist diameter.   

Over the years, the design-related disadvantages of the telescopic fork have been systematically eliminated. With low-friction surface coatings of the standpipes with titanium nitrite or carbon, the friction of the Teflon-coated plain bearings in connection with smooth-running Simmerrings was dramatically reduced.  

Creamy cushioning for crystal-clear feedback

The Japanese replaced the spatially limited damper cartridges in the slim immersion tubes with relatively small and difficult-to-adjust damper pistons with so-called big piston systems. These are hydraulic damper systems with large pistons that enable extremely sensitive and finely adjustable damping. Due to the larger diameter, the damping can be controlled in a more controlled manner, especially in the low and mid-speed range (approx. 10 to 150 mm / s). With which a delicate response behavior can be brought under one roof with the best stability and feedback.

In the so-called split systems, the damping is split up: compression damping in one, rebound damping in the other fork leg. The asymmetrical load distribution is not an issue, the rigidity is completely sufficient to prevent twisting during deep, fast compression. The next evolutionary step has already been established in racing: the gas pressure-assisted telescopic fork, known in technical jargon as a closed cartridge, has a small gas pressure shock absorber inside, which ensures constant damping force, as the oil can no longer mix with air to form an emulsion.

Adjust the fork correctly

Before assembly
Before turning the adjusting screws of the damping, it is essential to note down all original settings. To do this, turn the adjusting screws slowly click by click or in half turns clockwise. Make a note of these values.

Adjustment positions
In almost all cases, the setting values ​​on the fork are counted from the maximum closed position. The reason: The needle valves are completely closed in this position, while the minimum setting position (lowest damping, widest opening) can usually be changed during assembly.

Maximum cushioning
Once all the adjustment screws have been set to maximum, i.e. the hardest damping, push the machine into the suspension again. Do you feel a change? With an effective adjustment, the machine would have to compress and rebound more slowly. The adjustment range is designed differently depending on the fork manufacturer. Japanese manufacturers in particular work with a narrow range that usually does not allow extreme settings that can have a massive impact on driving behavior.

Minimal damping
Now turn all adjusting screws to the maximum (counterclockwise) and push the machine into the spring again. The machine now feels spongy and soft, and may even oscillate when it rebounds. By trying out different settings, you can get an impression of the effective range of the damping.

Basic setting
Now turn all adjusting screws to the original position (according to the manual or the tried and tested setting) and now start to correct the damping level as you think it is necessary .

Setting tip / street
Adjust the rebound damping of the fork so that the front section springs out a few millimeters above the starting position after rebounding and only then comes to a standstill.

Setting tip / racetrack
For sporty use, the damping is adjusted as described above, then turn the rebound stage in small steps until the fork no longer oscillates, i.e. it remains in its original position immediately after rebound. Caution: Only carry out one modification after the other in order to be able to clearly see the effects. Caution: Always change the setting on both fork legs equally.

Setting tip / pressure level
The compression damping can only be determined with great sensitivity. It is therefore determined while driving. As a starting point, select the setting recommended in the driver’s manual or a medium position and change this during the test drives towards comfort (soft) or sportiness (hard).

The test drive
Take a test drive and watch for changes. Better? Worse? Turn a few more clicks in the desired direction. If there is no improvement, go back to the initial value noted and try another option. 

Fork oil / air cushion
Another possibility to influence the suspension and progression in the telescopic fork is the air cushion that is created between the fork oil and the fork plug. This air cushion is compressed during compression and creates a pressure that supports the fork springs. The smaller this air cushion is chosen, the greater the spring effect and vice versa.

Spring progression
The air cushion depends on the standpipe diameter, the spring travel and the desired progression.

Filling process
In any case, the dimension is measured with the fork completely immersed, the damper rod immersed without the spring and preload sleeves. The values ​​can be varied continuously between the maximum and minimum values ​​as required. The difference in the air cushion between the two fork legs should not be greater than five millimeters. If the oil level is too high, suction to the required level with a small syringe and attached fuel hose.

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