BMW - Upside Down Forks


Featuring fixed tubes of larger diameter than the sliding tubes, the system with the upside down fork serves to raise torsional rigidity and at the same time cannot twist in the fork bridge. Both tube and fork bridge are made of aluminium whose surfaces practically intermesh under pressure. The unsprung masses, however, are not smaller than in a conventional fork. Although the sliding tubes running inside the upside down system have a smaller diameter than the usual designs, they are made of heavy steel. Accordingly, the weight is almost as much, and sometimes higher than the aluminium or even magnesium in the conventional forks. The crucial advantage is a result of the sliding tube's very long path through the fixed tube. For instance, an upside down Marzocchi brand fork with anodised aluminium fixed tubes and manganese steel alloy tubes with a stable 45 mm diameter is presented by the F 800 GS from BMW Motorrad for sensitive response and the maximum stability even under high loads. The fork bridges guide the torsionally more rigid outer tubes with the larger diameter because there greater lever forces take effect and these can be used for offroad riding for excellent results. Neither the telescopic fork nor the upside down fork can be configured in the rebound or compression stage. On the BMW supersports model S 1000 RR, an upside down fork with a generous 46 mm fixed tube diameter is responsible for the front wheel suspension. This generous measurement provides considerably greater braking stability and far better feedback than the customary measurement of 43 mm. The receiver in the steering head takes the form of a lightweight aluminium steering stem mounted in two large ball bearings and two weight optimised fork bridges of forged aluminium. The projection of the fork sliding tubes can be used to adjust the vehicle height in the front section. The total distance of 15 mm allows the front to be lowered by max 5 mm and raised by max 10 mm. The upside down fork is fitted on its inside with so called cartridge inserts, i.e. a separate hydraulic piston and cylinder system, and presents configuration options for the spring basis and the rebound and compression stages. The total spring travel is 120 mm, of which the positive travel takes up 75 mm and the negative 45 mm. Setting levels of 1–10 can be selected for the easy configuration of the spring preload and rebound and compression stages. The “clicks” used elsewhere therefore no longer need to be counted, and the current configuration is active at all times. Furthermore, the rebound and compression stages can be differentiated by their colour.