The inverted telescopic fork system where the upper tubes (fixed fork tube) have a larger diameter than the lower (immersion or slider tubes) increases torsional stiffness while at the same time preventing torsion in the fork bridge.
Tube and fork bridge are made of aluminium ensuring the surfaces interlock perfectly under pressure. At the same time, unsprung masses are no lower than with a conventional fork. Although the interior immersion tubes have a smaller diameter than the usual immersion tubes with the upside-down system, they are in fact manufactured from heavy-duty steel. As a result the weight is virtually just as high and in some cases even higher than with conventional aluminium or even magnesium forks. The key benefit comes from the very long guidance of the immersion tube through the fixed fork tube.
An upside-down fork by Marzocchi with anodised aluminium fixed fork-tubes and manganese alloy steel tubes with a stable 45 mm fixed tube diameter for example provides the F800 GS by BMW Motorrad with sensitive response characteristics and maximum stability even under high loads. The fork bridges guide the more torsion-resistant outer tubes with the greater diameter since greater leverage forces act there, which are very useful for off-road riding. Neither the telescopic fork nor the upside-down fork are adjustable in the compression or rebound stage.
In the BMW Supersport model S 1000 RR, an upside-down fork with a lavish fixed pipe diameter of 46 mm guides the front wheel. This generous dimension offers significantly high braking stability compared to the conventional dimension of 43 mm and as well as clearer response characteristics. It is mounted in the steering head via a light, steering shaft tube guided in two large aluminium ball bearings and two weight-optimised fork bridges forged from aluminium.
To adapt the vehicle height in the front section area, the protrusion of the fork immersion tubes may be used. Using the total amount of 15 mm, the front section can be lowered by up to 5 mm and raised by up to 10 mm. The upside-down fork is fitted with what are known as cartridge inserts on the inside. This is a separate hydraulic piston cylinder system with adjustment options for preload and compression/rebound stages. The total spring travel is 120 mm, 75 mm of which is positive and 45 mm negative spring travel. For simple setting of spring preload and rebound/compression-stage damping, setting stages of 1 to 10 are available. This means there is no need to count the clicks as is the case elsewhere and the current setting applies at all times. Rebound and compression stage settings are also differentiated by colour.