Biopace

Biopace was registered from 1983 to 1993 mark the Japanese company Shimano chainrings and designated for bikes with derailleur that did not circular, but oval in shape.

Principle

With the non-circular shape of the chainring the invoice fact should be taken that the application of force is spread seen over the crank one revolution of the chainring unequal. The maximum force is initiated when the crank in the direction of travel and slightly pointing upwards. Conversely, only a comparatively small force is exerted on the crank if they do, is in the vertical position, ie in the top or bottom dead center (TDC or BDC) from the driver.

Biopace tried this imbalance offset by a reduced chainring diameter acts in the position of maximum power transfer, so that the feeling arises, it would take a transition with smaller translation. This should be included to make it easier to overcome the following dead center in this position enough momentum.

The shape of a Biopace chainring therefore approximates an ellipse, the larger of the two major axes is in the mounted state approximately in the direction of the pedal crank. Shimano himself described the cast as " point - symmetrical egg-shaped curve ."

Versions

Over the years there have been various versions of Biopace chainrings. All were - depending on the quality level of the crankset - steel (matt chrome or black ) or aluminum alloy ( uncolored, later gray, brown, silver and black ) manufactured.

• Biopace: "original" Biopace, first generation
• Biopace II: second generation, a bit "rounder" was conceived after by racing professionals and enthusiasts poor efficiency was criticized at high cadence ( " hopping on the seat " )
• Biopace HP ( High Performance): Form a little rounder than Biopace II
• Biopace SG ( Super Glide ) was developed for smaller chains, and there were changes to the chainrings in favor of slightly more common switching (2 ramps on the big ring and modified teeth on the smaller chainrings )

Shimano then recommended to choose for optimal switching following combination of the middle and outer chainring: 44 -50T and 38 -48T. In addition, Shimano, advised the oval ( Biopace ) and round chainrings use mixed on the same crankset.

Trademarks

The Biopace mark was registered by Shimano at the German Patent and Trademark Office on 7 June 1983 for class 12 (bikes and parts ) and on 9 August 1983 for class 28 ( gymnastic and sports equipment ). Both brands are now no longer in force.

Similar / Current concepts

The concept of chainrings with variable diameter was continued in the 1990s and 2000s of other manufacturers. From Biopace they differ, inter alia, by the fact that at maximum force development, ie, in a horizontal position, the maximum pedal chainring diameter is effective because this is exactly perpendicular to the crank arm and not offset as in Biopace. Asymmetric chainrings find current sporadically in triathlon and professional cycling use.

• OSYMETRIC produced since the 1990s oval chainrings. The chainrings for example, used in the time trial of Bradley Wiggins with 54 - teeth have a pedal in a horizontal position and 50 teeth varying in the vertical pedal position between converted 58 teeth diameter. By unlike Biopace even stronger deviation from the circular shape, this causes while driving produce audible noise.

• The so-called Q-Rings chainrings the company ROTOR are structurally similar to Osymetric, that is, the maximum diameter is perpendicular to the axis of the pedal. The degree of " roundness " is not fixed but can be adjusted by an offset to a hole assembly in three stages. In the central position has a chainring with 53 teeth diameter of an analog converted 56 teeth in the horizontal pedal position and 51 teeth in the vertical pedal position. They are used, among others, Bobby Julich.