Antriebssysteme ohne Umwerfer: Unterschied zwischen den Versionen

[[Fixed Gear]] Fahrräder, Fahrräder mit [[Rücktrittbremse]] und [[Singlespeed]] sind üblicherweise mit einem [[Mutternabstand]] von 110 mm verfügbar. 1970er [[Rahmen]], die mit Fünfgang [[Freilauf|Freiläufen]] gebaut wurden, hatten 120 mm. Nabenschaltungsnaben gibt es in Varianten von 110 mm bis zu 135 mm. Im Artikel [[Kettenlinie und Mutternabstand bei Fahrrädern mit Nabenschaltungsnaben]] werden die meisten aufgelistet. Die Abstände zwischen den Ausfallenden lassen sich nur bei Rahmen aus [[Stahl]] verändern, jedoch hat sich auf der anderen Seite auch der Abstand zwischen den Ausfallenden von Fahrrädern mit Kettenschaltung erhöht (Früher war 126mm Standard inzwischen sind 135 oder bei [[Mountainbike]]s bereits 142 mm Standard). Daher können oft mit zusätzlichen [[Unterlegscheibe]]n auf der Achse oder einer längeren Achse, die Naben für den Rahmen passend gemacht werden. Möglicherweise will man sowieso die Achse tauschen, weil im Allgemeinen Fixed Gear-Naben mit einer [[Vollachse]] statt einem [[Schnellspanner]]system geliefert werden.

===Klassische Dreigang-Fahrräder===

Ältere Dreigangfahrräder - [[Wartung englischer Drei-Gang-Fahrräder|insbesondere englische]] - ermöglichen recht zufriedenstellende Fixed-Gear- und [[Singlespeed]]fahrräder. Das hintere Rahmendreieck ist geradezu perfekt geeignet für [[Bahnnabe]]n, weil sie üblicherweise eine Einbauweite von 110 mm haben. Neuere Nabenschaltungsnaben erfordern, dass man diesen Abstand nachträglich vergrößert. Die besseren englischen Dreigang-Fahrräder hatten sehr nette fahrbare Rahmen und können für kleines Geld zu sehr erfreulichen Fahrrädern umgebaut werden.

|align=center|[[Datei:Dropf-camp.png|center]]<br>Horizonatels Ausfallende<br>Campagnolo 1010

|align=center|[[Datei:Dropf-short.png|center]]<br>Horizonatles Ausfallende<br>kurz

As the chain wears, it lengthens, and to keep it from falling off the sprockets, it should be adjusted a couple of times before it needs to be replaced. The limited range of adjustment possible with the kludge solutions may require replacement of a chain sooner than otherwise.

Eric House has prepared a whole web site devoted to the problem of finding sprocket combinations that will work with vertical dropouts. He has developed charts and Java applets that show the options available for particular chainstay lengths.

If you're converting a '90s mountain bike to singlespeed or an internal-gear hub, chances are that it has vertical dropouts, and you'll most likely need a chain tensioner of some sort. There are two different sorts of chain tensioners that you can use.

 

Adjustable tensioners are set for the particular chain length/sprocket combination you will be using, and then tightened up to hold the pulley in the correct position. These are mainly intended for use on (yuck!) downhill bikes, and are designed to supplement a derailer to keep increase the chain tension, reducing the risk of accidental derailment.

Some, such as the no-longer-available Tektro unit shown above, are also useful for singlespeeds. If you have a pure singlespeed, without a flip-flop hub, this type is adequate, and may even be very slightly more efficient, because there is no spring loading on the chain. I (Sheldon) used to like the Tektro unit, but it proved a bit too delicate in practice, and clamping onto the chainstay isn't all that secure. A tensioner which clamps to the chainstay is not suitable for a bicycle with rear suspension and will very likely damage a carbon-fiber chainstay. I now prefer units that attach to the derailer hanger.

 

Do we have to say this again? Well, maybe. Chain tensioners are only usable with freewheeling hubs. They must not be used with fixed gears or coaster brakes, because these tension the lower run of chain when you backpedal. No chain tensioner is built to withstand this force. The upper run of chain hangs loose, so the chain is at risk of coming off

===1/8 Zoll oder 3/32 Zoll Ketten?===

Many bicycles with a non-derailer drivetrain use a wider chain than is common on multi-speed bicycles. Derailer-type chain (up through 9-speed) has a nominal internal width of 3/32". Non-derailer bicycles, including most track bicycles, use the wider 1/8" size. You can buy sprockets in either width.

(Some people mistakenly refer to the width as "pitch", speaking of "road pitch" or "track pitch". This is a malapropism. The pitch is the distance between the rollers, and all modern bicycle chain has the same pitch, 1/2"/12.7 mm.)

The 1/8" size is slightly heavier, but doesn't seem to perform any better in our experience. Your choice may be dictated by the width of the rear sprocket, and a 1/8" rear sprocket will usually wear longer. A master link for 1/8" chain can be removed and replaced without loosening the rear wheel, making it easier to remove the chain for cleaning; not so with a master link for derailer chain.

For the true retro fixed-gear fan, another option is 1" x 3/16" chain. This used to be common on track bikes. This requires special sprockets with only half as many teeth as standard 1/2" pitch sprockets. Serious old-time trackies used "block" chain, which had no rollers. This is no longer available. Roller chain is still sometimes findable in this size.

Derailer bikes can work fairly well even with the chain running at a considerable angle, but this should not be done with a derailerless setup. It is quite important to get the chainline just right.

You can check the chainline by installing the hub in the bike, with no chain installed. By placing your head just in front of the chainwheel, you can sight along the chainwheel and see back to the rear hub, to see if the chainwheel lines up exactly with the rear sprocket. If it doesn't, re-arrange spacers or change the bottom bracket axle as necessary. You might also hold a yardstick or other straightedge against the side of the chainwheel, reaching back to the sprockets.

Usually, on a bike that came with double chainwheels, the inner chainwheel will be more in line with the rear sprocket. For a neat appearance with a single chainwheel, you can buy a set of shorter "stack bolts" (the 5 bolts that hold the chainwheel(s) to the crank spider). You may find it easier to locate these in a shop that deals in BMX bikes.

Most older one-speed hubs, such as BMX, fixed-gear and coaster-brake hubs have a chainline of about 40-42 mm (centerline of the frame/hub to center of the sprocket.)

The wider chainstays on mountain bikes often don't let you place a medium-sized chainwheel that close to the centerline of the bike, so there is a secondary de-facto standard chainline of about 52 mm for singlespeed mountain bikes. Stock MTB triple cranks usually have the outer chainring at around 52-57 mm; the middle is normally 47.5-50 mm.

When your install the rear wheel on any bicycle which has only a chainwheel and sprocket, no additional pulleys, there are basically three things you need to adjust simultaneously:

 

*   The wheel needs to be straight.

*    This basically means that the tire needs to be centered between the frame's chainstays. If it is properly dished, and you get it centered between the chainstays, it is properly aligned.

*    The chain slack needs to be minimized.

*    The axle nuts or quick release skewer need to be tight.

The chain slack on a bicycle without a rear derailer or chain tensioner is quite critical, and is regulated by moving the rear axle back and forth in the forkends. If the chain is too tight, the drivetrain will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). The chain should be tight as it can be without binding. If the chain is too loose, it can fall off, so there is no braking through the pedals with a fixed gear or coaster brake. The chain also might jam. (A bicycle should have a front-wheel handbrake in case of these dangerous problems!)

A rear sprocket intended for use without a derailer has long teeth, to allow the chain to loosen more with wear before it is at risk of falling off. Chainrings and sprockets for use with derailers have shorter teeth, to make shifting easier, but also making adjustment more critical. Lightweight ("track") aluminum chainwheels with long teeth are sold in the 1/8" width but are rare in the narrower widths. Generally, older 3/32" chainwheels have somewhat longer teeth than newer models optimized for smoother shifting.

When adjusting the chain, you need to be able to turn the cranks. With a fixed gear or coaster brake, the rear wheel has to be off the ground. Keep your fingers away from the sprockets: the momentum of the rear wheel can crush a finger caught between a sprocket and the chain.

Start by installing the wheel at approximately the correct position and tightening the axle nuts. They don't need to be super tight at this stage, but should more than finger tight. Check the chain tension and wheel alignment.

Most likely, the chain will be a bit loose, but perhaps the wheel is correctly aligned. Loosen the right-side axle nut and push the tire to the side so that the right end of the axle moves to the rear, then tighten the axle nut.

Now the chain should have less slack, but the wheel is no longer centered between the chainstays. Loosen the left-side axle nut and re-center the wheel in the frame. This will tighten the chain a little bit more. Repeat as needed. The key is to keep one or the other of the axle nuts tight at all times, and "walk" the wheel forward and back. This takes a bit of practice and getting used to how much axle movement is needed to adjust a given amount of chain droop, but it isn't really hard as long as you keep one side secured at all times.

The chain should droop as little as possible without your feeling increased resistance as you turn the crank. If you get the chain a bit too tight, tighten the right-side axle nut partway. Tap the middle of the top run of the chain with the wrench to move the rear wheel forward just the tiny bit needed to make the chain run smoothly. The wheel will then be skewed, and you need to readjust the left end of the axle.

Note, this technique doesn't work with a quick-release hub, but those are generally easier anyway. Stand on the left side of the bicycle and hold the rear wheel centered between the chainstays with your left hand, pushing it back until the chain is nearly taut; then tighten the quick release. If the bicycle is on a workstand or hanging with the rear wheel downward, gravity pulls the wheel back, making adjustment easier. With the rubber side down, if you grab the rear wheel with a rim brake and try to roll the bicycle forward, the wheel will slide back in the dropouts. You need to have a way to lock the rear brake (old toe strap, bicycle glove wadded under an open run of brake cable, a friend to lend a helping hand, etc.).

Once you have adjusted the chain slack, you will probably find that it doesn't remain constant as you turn the crank. The slack varies because the chainring and sprocket aren't perfectly centered. If you press the wrench down against the middle of the top run of chain, you can easily see how the amount of slack varies.

It is usually possible to center the chainring. Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Turn the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chainring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.

This takes a little bit of your hands' learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

Tighten up the stack bolts a bit and re-check. Tighten them in a regular pattern, like the lug nuts on a car wheel. Our standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row (well, not unless there are only 3 or 4 in all -- than you have no choice). You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.

Once you have the chainrings centered and secured, adjust the position of the rear axle again to make the chain as nearly tight as possible without binding. Notice how freely the drivetrain turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible.

Unfortunately, fixed-gear and singlespeed riding is somewhat of a fringe activity from a commercial point of view, and those who have not learned to love it tend to write fixed-gear fans off as nuts and fanatics. If you have a local bike shop that stocks fixed-gear stuff, you are in a lucky minority, and I urge you to patronize it.

Internal-gear hubs are common on conventional "city bikes" which usually are not designed for sporty performance. If you would like to install an internal-gear hub on a different type of bicycle, you may have to build a wheel or have one built.

 

* [[Kettenlinie und Mutternabstand bei Fahrrädern mit Nabenschaltungsnaben]]

* [[Grundlagen_der_Innenlagertechnik]]

Sheldon Brown's Fixed Gear and Singlespeed Articles

 

The Sturmey-Archer ASC Three-Speed Fixed-Gear Hub (and its successor, the S3X)

Converting a Sturmey-Archer AW to Fixed Gear