Seat tube drive

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Gear motor with freewheel and bevel gear, acting on the crank shaft
The engine control is also housed in the seat post.

A seat tube drive is an electric drive used on bicycles , in which the motor and transmission are installed inconspicuously in the saddle or seat tube of the diamond bicycle frame . The diameter of the motor used is correspondingly small (about 31 mm). It acts on the crank shaft via an angular gear (see illustration).

functionality

With the Vivax-Assist drive, which is available as standard , the reduction gear connected downstream of a brushless DC motor , a freewheel and the circuit board with the motor control are also housed in the seat tube or the seat post . The technical substance of the bicycle used remains largely untouched, apart from a few minor measures. The relatively small lithium-ion battery can be hung under the saddle or placed in the bottle holder, for example. This drive effectively supports the cyclist with up to 200 watts. If necessary, it is switched on with the aid of a push button . The complete electric drive, including the battery, weighs only 1.8 kg and can also be retrofitted in many existing bicycles with diamond frames. The prerequisites for this are, among other things, a seat tube inner diameter of at least 30.9 mm and a Shimano Hollowtech II bottom bracket.

The Vivax seat tube motor basically works in a similar way to a normal e-bike drive, the user can be assisted while pedaling; When the engine is switched off, the bike works largely conventionally, as the electric drive is decoupled from the bottom bracket axle by the freewheel. However, the motor does not provide assistance during the entire journey, but only after activation via a button and only as long as the cadence remains within a certain window (approx. 45 to 75 or 90 / min). Therefore, the focus of this drive is the support during brisk, sporty driving; The drive is less useful as a starting aid or in stop-and-go traffic.

Suspected fraud in road cycling

In the spring of 2010, Fabian Cancellara was suspected of having used a seat tube drive in two races. However, this suspicion expressed in the press and on the Internet could not be confirmed.

Related construction methods

The FAZUA drive pursues a similar concept of an optically "slim" electric drive with an angle drive in the bottom bracket housing, but this is housed in the usually slightly thicker frame down tube instead of the seat tube and requires a specially manufactured frame.

Individual evidence

  1. ↑ Seat tube drive Vivax / Gruber Assist (manufacturer site)
  2. ↑ Seat tube drive Vivax / Gruber Assist (retrofit kit with pictures)
  3. ↑ Additional thrust from the seat tube? derStandard.at, accessed on April 18, 2012 .
  4. ↑ The drives of e-racing bikes in comparison. Tour Magazine, accessed June 29, 2020 .

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