Toothed belt drive (bicycle)

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Toothed belt drive on a bicycle
Belt on toothed pulley on the rear wheel of a bicycle

The toothed belt drive in bicycles is based on a toothed belt as the power transmission medium from crank to hub. It is an alternative to conventional chain drives for bikes with hub gears or single gears .

technology

Instead of a chain, belts made of mixed rubber fabric are pulled on and toothed pulleys are used instead of chain rings and sprockets.

The advantage of the toothed belt drive on bicycles is the lower wear compared to the bicycle chain and thus the longevity of the transmission medium. The belts require little maintenance and do not need to be lubricated. Belts are also significantly lighter than metal chains; At 70 to 90 g, they weigh only around a third compared to modern bicycle chains (approx. 300 g). A major disadvantage of endless belts is that they cannot be opened like conventional chains by pushing out a bolt with a chain rivet or opening a chain lock. This means that the length of the belt cannot be adjusted (as can be done by removing or inserting chain links), so a belt of a specific length is required for each wheel. Furthermore, a special construction is necessary for the frames so that the belts can be built into the rear end. As a rule, this fact is taken into account by a divisible right seat strut in order to obtain the necessary gap for "threading" the belt. The divisibility of the frame strut partially offsets the mass advantage.

To avoid cracks in the belt, the belt tension must be set very precisely during the first attempts. The belts are now reinforced with carbon fibers, which greatly increases their service life, but also makes the belts more expensive.

development

In the two-wheeler area of motorcycles, the technology of the toothed belt drive for power transmission to the rear wheel was tested earlier than in bicycle technology.

One reason for the more hesitant use in bicycles is the very strong fluctuations in pulling forces due to the nature of the pedal crank drive. Depending on the position of the crank in the pedaling cycle , the transmitted force varies due to the changing lever ratios. When stepping on the pedals, the torque and thus the force acting on the toothed belt varies greatly, which leads to high stress. The pulleys must also be precisely aligned even when the frame is flexing in order to avoid misalignment and the resulting increased wear or damage to the belt. Frames for belt drives must therefore have an increased degree of rear structure rigidity .

The belt pulleys used were initially made of aluminum and steel, as is common with sprockets. Stainless steel washers were introduced from 2012 to provide better protection against corrosion and less wear on the pulleys and belts.

Belt drives are increasingly being used today (2019) in the higher- priced hub gear segment and bottom bracket gear systems. Several bicycle manufacturers are currently producing toothed belt drives with different toothing. A uniform system has not yet established itself.

In 2018, Continental had to completely recall the belt it had used and withdrew it from the market because it could tear. It was recommended to convert the delivered bicycles to a chain drive or to a belt system from the competition if the frame meets the technical requirements.

Manufacturer

belt

  • Carbon Drive from Gates Corporation from Denver (USA)
  • Former: Contitech Power Transmission Group (2013) from Continental , developed Benchmark Drives (manufacturer of pedelec drives), a drive system for bicycles, pedelecs and e-bikes, discontinued in 2018 and withdrawn from the market.

frame

Individual evidence

  1. ↑ a b Holger Dambeck: Bicycle with toothed belt drive: The silence of the asphalt. 2012 in Der Spiegel, accessed on January 11, 2016 [1]
  2. ↑ radlager.de Belt drive or chain on bicycles? Retrieved January 11, 2016 [2]
  3. ↑ Continental recalls bicycle straps. Retrieved October 31, 2019 .
  4. ↑ Announcement on the manufacturer's website. Retrieved November 1, 2019 .

Web links

Commons : Timing Belt Drive (Bicycle)  - Collection of Images