Biopace
Biopace was a registered trademark of the Japanese company Shimano from 1983 to 1993 and designated chainrings for bicycles with derailleur gears that are not circular but oval .
principle
With the non-round shape of the chainring, it should be taken into account that the introduction of force via the crank occurs periodically over one revolution of the chainring. The course of the application of force to the crank is called the pedal cycle . The maximum force is applied in the front quadrant of the step circle. Measurement data show that the maximum effective propulsive force is actually applied before the 3 o'clock position and directed downwards and forwards, and that this makes sense for physical reasons. Conversely, the driver only applies a comparatively small torque to the bottom bracket shaft when it is in the vertical position, that is to say in the top or bottom dead center (TDC or BDC).
With Biopace, a reduced pitch circle diameter is effective in the 3 o'clock position, so that you drive with a gear with a smaller gear ratio.
The shape of a Biopace chainring corresponds approximately to an ellipse , whereby in the assembled state the larger of the two main axes lies roughly in the direction of the crank. Shimano himself called the shape a "point-symmetrical egg-shaped curvature".
The non-round chainrings were offered for years on numerous new bikes and also individually or with cranks, but ultimately could not prevail. They were discontinued by Shimano in the early 1990s.
Versions
There have been different versions of Biopace chainrings over the years. All of them were made of steel (matt chrome or black) or aluminum alloy (undyed, later also gray, brown, silver and black), depending on the quality of the crankset.
- Biopace: "original" Biopace, first generation
- Biopace II: second generation, was designed a little more "round" after cycling professionals and enthusiasts criticized poor efficiency at high cadence ("jumping on the seat")
- Biopace HP ( High Performance ): Shape slightly rounder than Biopace II
- Biopace SG ( Super Glide ): was developed for narrower chains, there were also changes to the chainrings in favor of smoother shifting (2 ramps on the large ring and modified teeth on the smaller chainrings)
Back then, Shimano recommended choosing the 44-50T and 38-48T combination of the middle and outer chainring for optimal shifting. The manufacturer also advised against using oval (Biopace) and round chainrings on the same crankset.
Trademark law
The BIOPACE brand was registered by Shimano at the German Patent and Trademark Office on June 7, 1983 for class 12 (bicycles and their parts) and on August 9, 1983 for class 28 (gymnastics and sports equipment). Both brands are no longer in force.
Similar / current concepts and further developments
The idea of oval sprockets already existed in the early 1920s, it was taken up again and again, but could not prevail. It was not until Biopace that it became widely used. The concept of variable diameter chainrings was continued by other manufacturers in the 1990s and 2000s. They differ from Biopace, among other things. a. in that with the greatest power development, d. H. The maximum chainring diameter becomes effective when the pedal is in a horizontal position, as it is exactly perpendicular to the crank arm and not offset as with Biopace. Asymmetrical chainrings are currently also used in triathlon and professional cycling.
- Stronglight has been producing oval chainrings since the 1990s, currently under the name O.SYMETRIC . The z. For example , chainrings with 54 teeth used in the time trial by Bradley Wiggins have a diameter that fluctuates between the equivalent of 58 teeth in the horizontal pedal position and 50 teeth in the vertical pedal position. Due to the even greater deviation from the circular shape compared to Biopace, this causes an audible noise development when driving.
- The so-called Q-Rings chainrings from ROTOR are structurally similar to Osymetric, i. H. the maximum diameter is perpendicular to the pedal axis. The degree of "ovality" is not fixed, but can be adjusted in three stages by means of an assembly offset by a hole. In the middle setting, a chainring with 53 teeth has an equivalent diameter of 56 teeth in the horizontal pedal position and 51 teeth in the vertical pedal position. They are used by Bobby Julich , among others .
- The French manufacturer of drive components, Spécialités TA, also has non-round chainrings in its range.
- The Cyfly drive ( spelling of the brand cyfly ) is an oval multi-jointed crank made by Möve Bikes , which has been installed in their bikes since 2017.
Web links
- DE3405791C2 - German patent application from 1984
Individual evidence
- ↑ The “round step” when cycling - myth or reality. Retrieved May 16, 2019 .
- ↑ Excerpt from the original Shimano Biopace outer packaging
- ↑ of registration of the trade mark 1061314
- ↑ Register excerpt of the brand 1061499
- ↑ Osymetric.com: OSYMETRIC trails are nor oval nor elliptical this is a TwinCam ( Memento of the original from July 14, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ rouesartisanales.com: Rotor Q-Rings (May 7, 2008)
- ↑ specialites-ta.com: Ovalution chainring (April 4, 2016) ( Memento of the original from April 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ SPS: The first Cyfly bike is here. Focus Online, August 18, 2017, accessed on August 18, 2017 (German).
