Dropout
In the case of bicycles , the mounts for the axle of the bicycle hub that are attached to the bicycle frame and the bicycle fork are called dropouts . According to DIN EN 15 532 (2009), the dropout for the rear wheel is called the rear end dropout , for the front wheel it is called the fork dropout . In practice, only the term dropout is usually used.
Designs
- Inclined construction
- The downward sloping design is open to the front and allows the chain to be tensioned without a chain tensioner. These dropouts are now the most common standard for mountain bikes, racing and trekking bikes and designs similar to these types. Often a derailleur hanger is attached to the right dropout , with some manufacturers this is exchangeable. The combination of angled dropout and derailleur hanger has the advantage that corresponding bikes can be delivered with both chain and hub gears. If the dropouts run tangential to the braking point on the rim, they rarely require readjustment of the rim brakes after the axle has been moved , as the relative position between brake and rim remains constant and the brake does not move up and down as it does with horizontal fork ends. On racing bikes, there is often a set screw with a spring on the dropout , which enables the rear wheel to be installed precisely (in the middle). In addition, the screws can be used to adjust the distance between the upper pulley and the sprocket , because the wheel moves in relation to the rear derailleur. With today's rear derailleurs , which have an additional adjusting screw, this is no longer necessary, which is why more and more racing bikes and mountain bikes have very short angled or even vertical dropouts. Mountings for luggage racks and mudguards can also be located on the dropout. The disc brake is always mounted on the left side.
- Vertical construction
- Vertical dropouts are open at the bottom. Since there is a lot of effort involved in sprints on the track, special track frames with dropouts that were open at the bottom were used to prevent the axles from slipping. The high-strength clamping axles used today allow clamping forces that prevent this. Frames in which vertical dropouts are installed initially only allow chain gears, as the chain can only be tensioned using a chain tensioner. Thanks to an eccentric inner bearing , however, the chain can also be tensioned without a chain tensioner and the bike can be driven with or without gear shifting.
- Horizontal dropouts
- Horizontal dropouts are open to the rear. With the invention of the angled dropouts in the 1930s , this design was largely replaced on everyday bikes. They are still standard today for track bikes and are currently still used for Dutch bikes and some special designs. Recently, fork ends that are open towards the rear can be found again more frequently on so-called single wheels . The chain can be tensioned by pulling the wheel backwards. In addition, chain tensioners are sometimes used.
- Rohloff dropouts
- The Rohloff dropout is a mostly sliding, long vertical dropout. The hub is clamped vertically; H. the impeller is pushed into the actual dropout from below; the greater length is necessary to accommodate the torque support. In order to be able to tension the chain, there are usually elongated holes in the rear of the frame , the actual (vertical) dropout can be moved a few millimeters backwards. This combines the advantages of vertical and horizontal dropouts: the position of the rear wheel is only set once and is not adjusted by removing the wheel (which is inevitably the case with horizontal dropouts). If the Rohloff dropout is not designed to be slidable, the chain must be tensioned in some other way, for example using an eccentric bottom bracket
- Thru axles
- On mountain bikes, dropouts with thru axles are sometimes used. In the case of plug-in axle systems, the axle is not inserted from below, front or rear, but is inserted, locked and clamped through an opening provided for this purpose. Thru axles have a larger diameter than common quick release axles (usually 12 or 15 millimeters) and are screwed to the frame. Quick-release axles usually have the highest vertical support on the dropout (seen in the direction of travel) and can only withstand side forces with difficulty, as they are only relevant for clamping the rear wheel. Strictly speaking, thru axles are screwed directly to the frame and thus (also due to their diameter) ensure increased stability and less torsion in the rear triangle. In the past, rear axle axles were only used on downhill or freeride mountain bikes, today the majority of high-quality mountain bikes have quick-release axles. For the rear wheel, thru axles with 12 mm (installation width 135, 142, 150 or 165 mm) and 10 mm are used. There are also QR15 thru axles (up to 150 mm travel ) and 20 mm thru axles (for bikes, from 160 mm travel) on the market.
Installation width
The distance between the dropouts is known as the installation width. The width of the rear hub must be selected to match the installation width of the frame. Compressing or bending the rear triangle apart in order to be able to install a hub that does not fit exactly is possible, but not recommended, depending on the frame material, as this can damage the frame and the dropouts are no longer plane-parallel to each other. This can lead to problems when setting the circuit. Using special tools, it is possible to straighten the dropouts and derailleur hanger .
| Type of hub | Width in mm |
|---|---|
| BMX | 110 |
| Resignation without switching | 109-110 |
| Track bike | 120 (rarely 110) |
| 2-speed hubs | 112-114 |
| 3-speed hubs | 120-135 |
| 5-speed hubs | 122 |
| 5-speed hubs with drum brakes | 126 |
| 7-speed hubs | 127-130 |
| 8-speed hubs | 132-135 |
| 11-speed hubs | 135 |
| 14-speed Rohloff | 135 |
| 3–5 wreaths | 124 |
| 6–7 rings racing bike | 126 |
| 6-7 wreaths | 127 |
| 8–11 rings racing bike | 130 |
| 8–10 rings MTB | 135 |
| tandem | 135-160 |
| Fat bikes | 170 |
Footnotes
- ↑ MTB standard dimensions for wheel axles , bike-magazin.de
literature
- Michael Gressmann, Franz Beck, Rüdiger Bellersheim: specialist knowledge of bicycle technology. 1st edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 2006, ISBN 3-8085-2291-7
- Fritz Winkler, Siegfried Rauch: Bicycle technology repair, construction, production. 10th edition, BVA Bielefelder Verlagsanstalt GmbH & Co. KG, Bielefeld, 1999, ISBN 3-87073-131-1
Web links
Commons : Dropouts - collection of pictures, videos and audio files
