Input gear

from Wikipedia, the free encyclopedia
typical single wheel
High bikes (here 1886) were single bikes with a rigid gear
Opel bicycle from 1935, at that time gearshifts were still extremely rare

The term single-speed bicycle (Engl. Single-speed) means a bike that does not gear shift has. In addition, if there is no freewheel, one speaks of a rigid gear . Colloquially, the buzz word fixie (from the English "fixed gear") is often used for this. In bicycles of this type, brakes are sometimes dispensed with; you brake by applying counter pressure on the pedals. In the downhill area, one speaks of a direct drive or single speed . What is special here is that the chain tensioner compensates for the deflection of the rear end, i.e. H. he must always have enough chain available when the bike is compressed without losing tension.

history

The history of the bicycle begins with the one-way wheel without a freewheel , which, in the 1860s, when drive via pedals and chain was invented, was just as unavailable as gear shifting . The gear shift in the rear wheel hub with freewheel was invented in 1902 and became widespread from 1924, so that the proportion of single-wheel gears has decreased significantly since then. Nevertheless, there are still bicycles without gears, mostly combined with a coaster hub. This type of construction remained dominant worldwide until a few decades ago, and it was only with the widespread appearance of affordable shift hubs that they were replaced. Today only a few types of bicycles have no gear shift. These include children's bikes and Dutch bikes . For several years, find their way bicycles but again become increasingly common, especially in big cities and head to the downhill ( DH ) in bike parks are among young people as a single speed become popular.

Reasons for not using a gear shift

  • Costs: Bicycles without gears are still the rule in many poorer countries, as such bikes are much cheaper to buy. In addition, the lack of a circuit makes it easier to build a bicycle from old bicycle parts. Even with factory bikes, gears are sometimes not used.
  • Special bicycles : One-way bicycles without freewheeling are common in cycling and artificial cycling , because they also ride backwards and the bicycle is held in position using the pedals. For safety reasons, a rigid gear is required for track bikes . Since these special bicycles are not used in public traffic areas, there is no brake. For more information, see the main article rigid gait .
  • In recent years, not using a gear shift has become more popular again. In big cities, single-speed bikes are part of hipster fashion . The lack of gears is part of the minimalist style of these bikes.

advantages

  • The bike is lighter.
  • There is no need for care, maintenance or repair of gear shift components.
  • no switching work

disadvantage

  • Limited flexibility as the gear ratio of the input gear is adapted to the rider and the environment and can only be changed by changing the sprocket or chainring
  • Unsuitable for touring bicycles , as a lot of luggage and varied terrain can only be managed over a long period of time by engaging the optimal gear
  • Unsuitable for mountainous terrain and mountain bikes , the extremely changeable driving load requires the spontaneous adjustment of the gear ratio (enduro bikes)
  • Increased chain wear or the need for massive chains if you are driving with a very small sprocket (<16 teeth)
  • not possible with all frame types (suitable dropouts, possibly external chain tensioners required)
  • If it is a fixie , there are other disadvantages.

translation

The ratio is determined by the number of teeth on the chainring and pinion. It must be long enough to allow a reasonable speed on a level stretch or downhill, but at the same time short enough to allow starting and climbing slopes.

In the mountain bike sector, 2: 1 is the standard ratio. This means that the front chainring has twice as many teeth as the rear sprocket. A lighter translation is often used for driving in alpine areas. Those who drive mainly on the flat choose a heavier gear. For racing bikes , the usual gear ratio is between 2.1: 1 (winter road training, e.g. 39/18) and around 3.3: 1 (e.g. 52/16, a widely used standard ratio), depending on the area of ​​use and power Six days ).

For comparison: the gear ratios driven in road racing on a flat route profile are between 3.2: 1 and almost 5: 1. However, even a translation of z. B. 53/11 in the final battle (at speeds up to 70 km / h) a cadence of about 115 / min, which underlines the importance of the cadence-oriented training - for example with the rigid gait  .

Chain tension

The prerequisite for trouble-free drive is a chain that is always sufficiently tensioned. The gradual elongation of the chain during operation requires regular retensioning. There are several methods for doing this:

Rear end of a mountain bike frame with horizontal dropouts
  • Special entrance frames - like many older bicycles and frames for hub gears - often have horizontal dropouts . The rear wheel can be moved forwards and backwards in order to tension the chain. The position of the rear wheel brake may also have to be adjusted. These horizontal dropouts make it easier for laypeople to re-tension the chain and fit the rear wheel correctly.
  • In the case of displaceable dropouts, a disc brake that may be present is moved with the wheel so that the position of the rear brake does not need to be corrected.
  • The position of the axle of the rear wheel can also be moved with an eccentric hub. This is possible in every bicycle frame.
  • With eccentric inner bearings, the position of the inner bearing can be changed so that the chain is tensioned over it. The disadvantage of this design is that the effective seat angle and the distance from the saddle to the pedal change slightly when the chain is tensioned. Because it is integrated into the bottom bracket shell, this is the most inconspicuous device for tensioning the chain. Since the rear wheel always has the same position, there is no need to correct the position of the rear wheel brake.
  • With the chain tensioner , the chain runs over a small roller, the position of which can be changed by spring force. There are also versions with multiple roles.
  • A so-called half-link chain can be shortened in smaller steps than a normal chain, so that a correspondingly smaller adjustment range between the chainring and the rear wheel is required. This can significantly simplify the adjustment work because, for example, it is not necessary to adjust the brake pad position.

Rigid corridor

For the rigid drive, rear hubs were manufactured until the 1950s, which had a rigid gear on one side and a triple sprocket with freewheel on the other.

The rear wheel hubs, which were used until the 1980s, could also be converted to a rigid gear without much effort because the freewheel was integrated into the ring gear. The ring gear together with the freewheel could easily be exchanged for a rigid pinion. If a fixed pinion is not secured by a lock nut on the right-hand fine thread of the hub, it can - especially if it is well greased but not tightened extremely firmly - screw loosely in the opposite direction when subjected to sudden loads. Then the ability to brake can be lost or the hub can jam in the frame.

With the advent of the hub integrated freewheel this simple possibility no longer exists. The use of the rigid gear is only possible with the use of suitable hubs, mostly track bike hubs.

literature

Individual evidence

  1. ↑ Regulations of the Federation of German Cyclists on the drive of track bikes (pdf file; 823 KB)