Alles über Rücktrittbremsen

Aus WikiPedalia

Die Rücktrittbremse ist eine spezielle Variante einer Hinterradnabe, die zwei Funktionen erfüllt:

  • Das Fahrrad kann vorwärts rollen, ohne dass die Pedale vorwärts angetrieben werden. Das ist die Freilauffunktion der Nabe (daher wird Sie im englischen Sprachraum auch "Coaster Brake" zu Deutsch "Freilaufbremse" genannt). Hier gibt es verschiedene Mechanismen, das zu erreichen.
  • Sie funktioniert als Bremse, die betätigt wird, indem man die Pedale rückwärts tritt.

Die Rücktrittbremse wurde in den 1890er Jahren erfunden und ist seitdem weiterhin in manchen Gegenden bis heute beliebt.

Die klassische einfache Rücktrittbremsennabe ist ohne Gangschaltung. Jedoch kann eine solche Nabe auch mit eine Rücktrittbremse ausgestattet sein.

Vor- und Nachteile

Vorteile Nachteile
Rücktrittbremsen funktionieren bei Regen genau so gut wie bei Trockenheit. Rücktrittbremsen machen das Anfahren etwas schwieriger und behindern die Nutzung von Klickpedalen und Pedalriemen, da es keinen einfachen Weg gibt, die Pedale in die richtige Startposition zu rotieren.
Rücktrittbremsen benötigen im allgemeinen weniger Wartungsaufwand als jeder andere Bremsentyp. Rücktrittbremsen neigen zum blockieren des Laufrads und zum Skidden, das zu erhöhtem Reifenverschleiß führt.
Vom Lenker aus verlaufen keine Züge zur Bremse. Dadurch wird der Gesamtaufbau des Fahrrads einfacher und aufgeräumter. Wenn Rücktrittbremsen versagen (normalerweise durch einen Kettenriss oder -abwurf), versagt die Bremse plötzlich und vollständig.
Das Fehlen von Zügen bei einer Rücktrittbremse ohne Schaltung oder mit Rücktritt-Zweigang-Schaltung ist insbesondere Vorteilhaft bei Falträdern oder zerlegbaren Fahrrädern. Rücktrittbremsen neigen in bergigem Terrain zum Überhitzen und Bremsschwund.
Rücktrittbremsen sind eine gute Alternative für Fahrer mit geringer Handkraft oder ohne Arme. Eine Rücktrittbremse in einer Nabenschaltung verkompliziert den Mechanismus und verkleinert die Möglichkeiten zur Schmierung.
Rücktrittbremsen sind normalerweise recht schmal. Ihre Einaubreite beträgt 110-114 mm und sie können auch mittels Unterlegscheiben an der Achse auf größere Einbauweiten angepasst werden. Mann kann eine Rücktrittbremse nicht mit einem Kettenspanner oder eine Kettenschaltung kombinieren.
Eine Nabenschaltungsnabe kann eine Rücktrittbremse beinhalten, so dass man zwei Funktionen in einer Naben zur Verfügung hat. Zu viele Fahrräder sind ausschließlich mit einer Rücktrittbremse ausgestattet, so dass man keine Ersatzbremse im falle eines Bremsversagens hat.
Ein Fahrrad mit nabenbremse kann rückwärts rollen, ohne dass sich die Pedale bewegen (nützlich bei Fahrradakrobatik) Aus Sicherheitsgründen soll jedes Fahrrad mit einer Vorderradbremse und irgendeiner Art Hinterradbremse ausgestattet sein. Das kann eine handbetriebene Bremse, eine Rücktrittbremse oder Fixed Gear sein.

The Reaction Arm

A wheel consists of rotating parts (tire, rim, spokes, hub shell) and stationary parts (axle, cones.) The braking action of a coaster brake basically consists of creating friction between the rotating and stationary parts.

As the brake is applied, this friction will cause a twisting force to be applied to the axle. The normal axle nuts by themselves can't resist this force, so all coaster brakes have a "reaction arm" which runs below the left chainstay.

The back end of the reaction arm is attached to the left cone of the hub, which is also connected to the brake shoes.

The front end of the reaction arm is clamped to the chainstay, either with a metal brand that wraps around the chainstay, or by a brazed-on fitting underneath the chainstay.

[Note: the metal band in the photo below is only looped loosely around the chainstay, a common error. If the brake is used to hold the bicycle from rolling backward (for example, when stopped facing uphill), the brake arm will rotate upward. Then when the brake is used to slow forward motion, the brake arm will rotate downward again. Repeated motion will loosen the bolt holding the metal band, or the axle nuts, leading to failure. The metal band has multiple holes to fit different-size chainstays. Cinch it tightly around the chainstay -- John Allen]

Drehmomentstütze

The attachment of the reaction arm to the chainstay is vitally important. One of the most common causes of coaster-brake malfunction is failure to properly secure the reaction arm after removing and re-installing the wheel.

If the bike is ridden without the reaction arm properly secured, the arm will rotate downward, effectively loosening the left cone. The result will be a shaky wheel, and an increase in the amount of reverse pedal travel required to activate the brake.

The reaction arm is usually the place where the make and model of the hub is embossed.

Tip

If you come upon a bike that has been ridden this way, you will see the reaction arm out of position, and may be inclined to remove the wheel to adjust it. This is often not only unnecessary, but sometimes nearly impossible!

As the disengaged reaction arm and left cone turn, they screw the left cone outward. This squeezes the forkend hard against the left axle nut. As a result, if you try to unscrew the left axle nut, you may find it impossible to turn because of the pressure of the cone. Bike shops frequently see bikes come in where the left axle nuts have been butchered by unsuccessful attempts to loosen them.

The trick is to treat the cause, not the symptom. Instead of immediately going for the axle nut, use a hammer to rotate the reaction arm back to its proper position. This will often bring everything back to proper adjustment with a minimum of trouble. At the very least, it will ease the binding of the axle nut, and allow you to adjust the bearing cones in the normal manner.

Disassembly and Rebuilding

Single-speed coaster brakes are pretty simple. To disassemble a coaster-brake hub, all you need to do is to unscrew everything from one end of the axle or the other. All of the parts will then come out of the left side of the hub shell.

Two-speed coaster-brake hubs may shift by means of a "kickback" mechanism which shifts when backpedaling, or automatically by means of centrifugal weights.

The brake mechanism of multi-speed coaster-brake hubs is similar to that of single-speed coaster brakes, but these hubs can be quite complicated. They are covered on this site on the Sturmey-Archer, Sachs/SRAM and Shimano internal-gear hub pages.

Links to parts lists and rebuilding information for almost every coaster-brake models are at the bottom of this page.

Operation-How A Coaster Brake Works

Though there are differences in detail, all coaster brakes are fundamentally similar. Different manufacturers use different names for some of the parts, I'll try to use terminology as generic as possible:

  • The chain sprocket is attached to the "driver" usually by a snap ring (though some older models used threaded sprockets with lockrings similar to those of a fixed-gear hub.)
  • The driver has a coarse thread which is screwed into the brake cone.
  • The brake cone fits loosely over the axle. It typically has conical projections at each end.
  • When the sprocket turns forward, normal pedaling, the driver's threads pull it to the right, where the conical projection on the right end of the brake cone jams into the narrow part of the hub shell, transferring the pedaling force to the hub shell, and thence to the rest of the wheel.
  • When the sprocket/driver turns backwards, the driver threads push the brake cone to the left, where the conical projection on its left side spreads the brake shoes, causing them to press against the inside of the hub shell.
  • The brake shoes are curved to match the curvature of the inside of the hub shell, and they have tapered inside edges. These tapered ends fit against the brake cone on the right, and the left side bearing cone on the left. The left bearing cone will have some sort of projection that will make it impossible for the brake shoes to rotate around it.
  • The retarder spring comes in many different forms for different brands of brakes, but it always serves the same purpose: it keeps the brake cone from spinning too freely with the driver. If there isn't something resisting motion of the brake cone, the driver threads wouldn't be able to move it back and forth...it would just rotate with the driver.
  • Failure or wear to the retarder spring is the major cause of erratic braking/driving of a coaster brake. Sometimes they can be tightened by bending, sometimes they just need to be replaced, if you can find one.

Lubrication

Single-speed coaster brakes are intended to be pretty much packed with grease. There is no part of a coaster brake that can be harmed by grease, so be generous in applying it. You should use a grease with tolerance for high temperatures, such as automotive brake grease, but even so, coaster brakes used in mountainous terrain can "cook" any common grease.

An internal-gear hub with a coaster brake may need more than one type of lubricant. Follow manufacturer's recommendations.


Adjustment

There's basically only one adjustment to be made on a single-speed coaster brake, the adjustment of the bearing cones. This adjustment can usually be made without even removing the wheel from the bike.

The left cone is attached to the reaction arm (the arm that runs below the left chainstay, and is secured to the chainstay by a clamp of some sort.)

If you loosen both axle nuts, and stick a cone wrench onto the right side cone, or its locknut, you can turn the whole axle. Since the left cone is immobilized by the reaction arm, turning the axle will adjust the cone.

If you get it too tight, the wheel will tend to bind up. Too loose, and the wheel will shake from side to side, and the brake will require a lot of pedal movement to engage. .

English Coaster Brake Adjustment:

Sturmey-Archer SC and most other English coaster brakes adjust differently from other coaster brake hubs. There's a square end on one end of the axle. The right cone is fixed to the axle; the left cone, as usual, is attached to the reaction arm.

To adjust the cones on an English coaster hub, you leave it in the bike, but loosen both axle nuts. Use an adjustable wrench to turn the whole axle, screwing it in or out of the left cone, then re-tighten the axle nuts once the cone adjustment is correct.

Any coaster brake that has a square end on the axle is intended to be adjusted this way.

Sprockets ("Cogs")

Ein Ritzel mit drei Nuten

3-lug sprocketMost newer single-speed coaster brakes use the same 3-splined sprockets as are used on internal-gear hubs. Such sprockets are available in sizes from 14-24 teeth. Changing the sprocket to customize the gearing is often very worthwhile.

These sprockets are held on by a snap ring, which you can pry off with a small flat-blade screwdriver. When you replace the sprocket, it is a good idea to use a hammer and punch to seat the snap ring into its groove so that the sprocket can't accidentally pop off, leaving the brake inoperative! Sprockets available here.

Older coaster brakes used threaded sprockets and lock rings, as with track hubs. Although they are the same in theory, they commonly used different threading, so they are not usually interchangeable with track sprockets. Threaded sprockets made for coaster brake use commonly had a radial slot at one point, to make it possible to replace a broken spoke without needing to remove the sprocket.

Note that with a coaster brake, the gear ratio affects both the forward pedaling and the brake operation!

  • Using a larger hub sprocket (lower gear) will permit faster acceleration, easier hill climbing and stronger braking.
  • However, a larger sprocket will limit your top speed, and will also require moving the pedals farther backward to cause the brake to engage.
  • Using a smaller hub sprocket (higher gear) will permit you to go faster without having to pedal faster (just harder!). It will also provide quicker brake engagement (you won't have to turn the cranks as far before the brake begins to grab.)
  • However, a smaller sprocket will make hill climbing more difficult, and will also require pushing harder on the pedals to get powerful braking.

Information and Diagrams for specific brands/models:

Sutherland's Handbook of Coaster Brake and Internal-Gear Hubs, now hosted on this site, covers many common models.

Note that sometimes these are "private labeled" or there might be "knockoffs" so you might find an unlisted model that is identical to the ones shown.

Axles and axle nuts are generally fairly generic.

Other, internal parts are generally not available for purchase, please don't waste our time by asking!

The list below links to information on single-speed and two-speed coaster brakes. Internal-gear coaster-brake hubs with three or more speeds are covered on our internal-gear hub pages.

Single-speed Coaster Brakes

  • Bendix (also covered in Sutherland's)
  • Centrix -- covered in Sutherland's
  • Hawthorne -- covered in Sutherland's
  • Karat -- covered in Sutherland's
  • J.C. Higgins
  • Mattatuck -- covered in Sutherland's
  • Morrow
  • Musselman
  • New Departure (also covered in Sutherland's)
  • NK -- covered in Sutherland's
  • Perry (also covered in Sutherland's)
  • Resilion
  • Sachs Torpedo Boy, Komet Super, Komet Super 161, Pixie, Jet -- covered in Sutherland's
  • Sachs older models back to 1905: on Jens Hansen's Web site (mostly in German)
  • Shimano A Type, B Type, Mighty Mite -- covered in Sutherland's
  • Shimano D Type (also covered in Sutherland's)
  • Shimano E Type (also covered in Sutherland's)
  • Shimano Mighty Mite -- covered in Sutherland's
  • Steyr -- covered in Sutherland's
  • Sturmey-Archer SC (also covered in Sutherland's)
  • Sturmey-Archer SC1 -- covered in Sutherland's
  • Sturmey-Archer older models: covered on Sturmey-Archer Heritage Web site and if the site throws errors, go to the archive on the Wayback Machine.
  • SunTour -- covered in Sutherland's
  • Torpedo (also covered in Sutherland's)

Two-speed Coaster Brakes

  • Bendix Red Band, Yellow Band, Blue Band Overdrive -- covered in Sutherland's -- also see Bendix page.
  • Sachs Automatic A2110, Duomatic R 2110, Duomatic 102 -- covered in Sutherland's
  • SRAM Automatix
  • Sturmey-Archer B2C Kick Shift (Click on "Technical" and then on link to PDF Manual.)
  • Sturmey-Archer S2 Kick Shift without brake
  • Sturmey-Archer S2C Kick Shift with coaster brake
  • Sturmey-Archer S2K Kick Shift with disk brake fitting
  • Sturmey-Archer T-S2C Kick Shift -- Gear box for tricycle, with coaster brake
  • There are several older Sturmey-Archer two-speeds -- see S-A hubs cribsheet.

If you have information/diagrams of other makes/models that you would like to share with others, please send them to us. We prefer scans of 200 DPI or better, or if you mail us the material we can scan it and return it to you.

Werbung:

Siehe auch

  • Coaster Brake Instructions from Park Tools
  • Coaster Brake Instructions from TroubleShooters.com

Quelle

Thanks to Steve Birmingham and Henry Brunelle for their assistance.

Quelle

Dieser Artikel basiert auf dem Artikel Bicycle Coaster Brakes von der Website Sheldon Browns. Originalautor des Artikels ist Sheldon Brown.


Abgerufen von „https://wikipedalia.com/index.php?title=Alles_über_Rücktrittbremsen&oldid=14363“