Platte Reifen
Aus was besteht mein Reifen?
Gewöhnlich glaubt man, dass Reifen aus Gummi sind. Das ist nachvollziehbar, da Gummi das Material ist, welches man als erstes wahrnimmt. Dies ist aber eine starke Vereinfachung.
Ein Reifen ist tatsächlich aus 3 Materialien hergestellt:
- Der Wulst besteht aus 2 starken Stahldrähten (manchmal auch Kevlar ®)
- Die Stränge, welche die äußere Formgebung des Reifens bestimmen, sind zwischen die Wülste verwoben.
- Das Gummi verdeckt die anderen Teile. Derjenige Teil des Reifens, der die Straße berührt ist dicker und wird Lauffläche genannt.
Ein Fahrradreifen ist nicht von selbst luftdicht, daher wird ein Schlauch benutzt, der in etwa einem Gummiballon in Doughnut-Form entspricht. Dieser innere Schlauch hat ein Ventil, welches es erlaubt, ihn aufzupumpen.
Ventile
Es gibt zwei weit verbreitete Arten von Ventilen für Fahrradreifen:
- Schraderventile sind die gleichen, die auch bei Autoreifen zum Einsatz kommen. Sie sind an weniger teuren Fahrrädern verbaut, vor allem an solchen mit breiten Felgen und Reifen. Schraderventile werden gerne als "Amerikanische" oder "Auto" Ventile bezeichnet. Schraderventile haben einen herausnehmbares Ventilkernstück, das mit einem speziellen Schraubenschlüssel, welcher auch in besseren Ventilkappen integriert sein kann, herausgedreht werden kann. Sie haben einen federgespannten Ventilmechanismus. Ein schmaler Stift in der Mitte des Ventils muss heruntergedrückt werden, um Luft hineinpumpen zu können (oder Luft abzulassen). Vor der Verbreitung der Zé HP Pumpe in den 70er Jahren des 20. Jahrhunderts existierte keine tragbare Pumpe, mit der man geschmeidig Reifen mit Schraderventilen unter hohem Druck aufpumpen konnte. Dies führte zur Popularität von:
- Presta oder "Französischen" Ventile haben einen kleineren Durchmesser als Schraderventile. Das macht sie etwas leichter und sie kommen mit einem kleinern Loch in der Felge aus (wünschenswert bei schmalen Felgen). Prestaventile werden in Hochleistungsfahrrädern und Schlauchreifen eingesetzt. Prestaventile haben keinen Federmechanismus, sondern sie haben eine festsitzende Rändelschraube, die den Raifen dicht hält. Vor dem Aufpumpen eines Prestaventils muss die Rändelschraube losgedreht werden. Zudem kann es ratsam sein, den mittig sitzenden Stift kurz anzutippen, um die Dichtung zu lösen. Diese sitzen manchmal fest. Nach dem Aufpumpen des Reifens, muss man die Ventilrändelschraube wieder festdrehen, um das entweiche der Luft zu verhindern.
Jede dieser beiden Ventiltypen benötigt einen anderen Pumpenaufsatz. Günstig sind Adapter, die es erlauben, eine Scharderpumpe mit Prestaventilen zu benutzen. Allegmeingebräuchlich sind inzwischen auch Pumpen, die auf beide Ventiltypen anwendbar sind.
Prestaschläuche können in Felgen mit Schraderventillöchern benutzt werden, jedoch ist das umgekehrt nicht möglich, da die Löcher für Prestaventile unwesentlich kleiner sind als Schraderventile. Prestabohrungen können jedoch leicht aufgebohrt werden, um sie für Scharderventile passend zu machen.
Hier Bilder Schrader Presta-closed Presta-open Presta-adaptor Schrader valve Presta valve closed Presta valve open Presta valve with adaptor
Es gibt noch einen dritten Type Ventile, welche recht selten zum Einsatz kommen. Diese haben eine Breite, die ähnlich zu Schraderventilen ist. Der Ventilhals kann ähnlich lang sein wie Prestaventile. Dies sind die Woods Ventile, welche früher auf den britischen Inseln und Asien beliebt waren. Manchmal spricht man auch von Dunlopventilen.
Ältere low-tech Woodsventile funktionierten mit Gummiummantelungen und Spucke. Neuere Ventile dieser Bauart arbeiten mit einem Federmechanismus.
Hier Bilder Woods Woods or Dunlop valve
Felgenbänder
Die innere Oberfläche der Felge hat häufig Grate, die die Schläuche beschädigen können. Auch können die Enden der Speichen zur Punktierung der Schläuche führen. Aus diesem Grund werden Felgenbänder benötigt, die die Schläuche schützen sollen. Manche Felgenbänder sind einfache Streifen aus Gummi, die demjenigen ähnlich sind, der für die Schläuche selbst verwendet wird. Diese sind für niedrige Druckverhältnisse adäquat, besset sind jedoch Felgenbänder aus haftendem Tuch oder Kunststoff.
Gründe für platte Reifen
Wenn der Reifen platt wird, bedeutet das, dass der Schlauch ein Loch bekommen hat. Das kann bedeuten, dass etwas mit dem Reifen nicht in Ordnung ist oder auch nicht.
Platte Reifen können grob in vier Gruppe unterschieden werden:
- Der schleichende Plattfuß oder kleine Lecks benötigen so viel Zeit, zum platt werden, dass das Fahrrad tatsächlich noch gefahren werden kann. Jedoch muss der Reifen häufiger aufgepumpt werden als nötig. Es ist völlig normal, dass ein Schlauch über mehrere Wochen Luft verliert. Falls Du Dein Fahrrad zu Beginn der Wintersaison einmottest und erst im Frühjahr wieder hervorholst, werden in den meisten Fällen die Reifen sehr weich oder platt sein.Das muss aber nicht bedeuten, dass etwas nicht mit den Reifen oder Schläuchen stimmt; sie müssen lediglich wieder aufgepumpt werden. Falls Du Hochdruckreifen benutzt, solltest Du den Luftdruck wenigstens ein mal pro Woche kontrollieren. Kleine Lecks benötigen meist mehr als eine Stunde, um den Reifen komplett zu entleeren und können meist nur durch einen Schlauchwechsel repariert werden, da die Löcher meist so klein sind, dass man sie kaum finden kann.
- Punktierungen oder Durchstiche werden durch das Überfahren von spitzen Gegenständen hervorgerufen, welche durch den Mantel und den Schlauch hindurch stechen. Sie können durch Glasscherben, Dornen, Nägel, Drahtstücke oder andere kleine spitze Gegenstände hervorgerufen werden. Der typische Durchstich erzeugt ein kleines Loch im Mantel, egal welches Material. Flicken oder Austauschen des Schlauchs behebt das Problem. Man sollte allerdings nicht vergessen, den spitzen Gegenstand aus dem Mantel zu entfernen, bevor man wieder Alles zusammenbaut und den Reifen wieder aufpumpt.
- Quetschrisse oder Snake Bites werden beim Auftreffen auf Steine, Bordsteine oder scharfen Kanten in Schlaglöchern erzeugt. Wenn der Reifen die scharfe Kante hart genug trifft, wird der Mantel mit dem Schlauch so stark komprimiert, dass der vollständig in die Felge gedrückt wird. Dabei wird der Schlauch zwischen Kante und Felge so eingequetscht, so dass zwei kleine Löcher links und rechts am Schlauch entstehen. Deswegen spricht man hier auch vom Snake Bite (zu Deutsch: Schlangenbiss), weil die beiden Löcher aussehen wie die Bissmale einer Schlange. Quetschrisse ruinieren manchmal Mantel und Schlauch zusammen, jedoch ist dies nicht die Regel. Die kinetische Energie, welche auf die Felge einwirkt, kann eine Delle oder eine Ping verursachen.
- Platzer sind plötzliche Druckverluste, die meist mit einem lauten Knall einhergehen. Der Schlauch ist nichts anderes als ein Gummiballon. Wenn man ihn außerhalb des Reifens weiter und weiter aufpumpt, wird er größer und gröer, bis er explodiert. Der Schlauch alleine hält nicht viel Druck aus, der umgebende Reifen und die Felge werde benötigt, um den Druck aufzunehmen, Wenn der Mantel den Schlauch nicht vollständig umfasst (Schlauch zwischen Mantel und Felge) oder nicht mehr halten (Risse oder Löscher im Mantel) kann, wird der Schlauch unweigerlich platzen.
Radausbau
Obwohl es manchmal möglich scheint, einen Platten ohne Demontage des Rads vom Fahrrad zu reparieren, ist es normalerweise einfacher, das Rad aus zu bauen. Löse die Bremse, falls Dein Fahhrad Handbremsn hat. Qualitativ hochwertige Straßenräder haben Caliper Bremsen mit einen schnell öffnenden (Quick-Release) Mechanismus, mit dem man die Bremsschuhe so weit auseinanderziehen kann, dass der Reifen hindurchpasst. Um einen platten Reifen hindurch zu bekommen ist das evtl. nicht nötig, vereinfacht aber die Sache. Entweder gibt es einen Knopf an Bremsgriff oder einen kleinen Hebel am Caliper (oder an der Kabelaufhängung), um die Bremse ein Stück zu öffnen. Cantilever Bremsen, wie sie meist an Mountainbikes, Hybridrädern oder Trekkingrädern verbaut sind, haben keinen solchen Mechanismus. Daher muss man die Bremse komplett still legen, indem man des Traverskabel aus einem der Bremsenarme aushängt.
Schraubachsen
Schraubachsen haben Muttern, die das Rad mit dem Rahmen verbinden. Sie werden an älteren oder günstigeren Fahrradmodellen verwendet. Um das Rad auszubauen, muss man die Muttern an beiden Seiten der Achse lösen. Normalerweise müssen diese Muttern nicht von der Achse komplett entfernt werden, es reicht, sie zu lösen und auf der Achse zu belassen. (Das bedeitet weniger Arbeit und reduziert die Gefahr, Mutten oder Unterlegscheiben zu verlieren.) Man benötigt einen Schraubenschlüssel für diese Arbeit. Die meisten Hinterachsen haben 15mm Muttern, Vorderräder sind meist mit 1/2" (12 3/4mm) oder 14mm Muttern bestückt. Wenn Du nicht die richtige Schraubenschlüsselgröße zur Hand hast, kannst Du auch einen verstellbaren Schraubenschlüssel benutzen. Die Muttern müssen gegen den Uhrezeigersinn gedreht werden, um sie zu lösen. Diese Aufagbe sollte man nicht mit einer Zange durfchführen. Selbst wenn Du es schaffst, die Muttren zu lösen, wirst Du die Muttern am Ende nicht wieder fest genug anziehen können. Zusätzlich können Zangen, die Muttern unnötig beschädigen, so dass der richtige Schraubenschlüssel möglicherweise nicht mehr passt. Zwischen Gabelende und der Mutter sollte eine Unterlegscheibe liegen. Diese werden bei moderneren Fahrrädern aus Kostengründen gerne weggelassen. Falls Dein Fahrrad mit Unterlegscheiben daherkommt, benutze sie. Sollten die Unterlegscheiben mit einer rauhen Seite ausgetstattet sein, sollten diese gegen das Gabelende drücken.
Schnellspannerachsen
Schnellspannerachsen sind innen hohl und ein dünner "Spieß" führt komplett durch die Achse. Eine Seite hat ein Gewinde auf dem ein eichelförmiges Endstück aufgeschraubt ist. Das andere Ende (meist euf der linken Seite des Fahrrads) hat einen Nockenmechanismus, um das Rad sicher am Platz zu halten. Der Nocken wird durch einen Griff bewegt, den man umlegen muss, um das Rad zu lösen. Zieh am Hebel senkrecht vom Rahem weg und lege ihn ganz um. Damit ist die Spannung des Schnellspanners gelöst, jedoch muss man möglicherweise den Mechnaismus noch ein wenig mehr öffnen, um das Rad aus dem Rahmen herauszubekommen. Um den Schnellspannerspieß komplett zu lösen, hälst Du mit der einen Hand das eichelförmige Ende fest und dreahst gegen den Uhrezeigersinn am Griff bis das Rad soweit frei ist, dass es herausfällt. Bitte versuche nicht, das eichelförmige Ende komplett herauszudrehen, da sich auf dem Spieß kleine Federn befinden, die sonst möglicherweise verloren gehen könnten. Falls Du den Schnellspennermechanismus nicht verstanden haben solltest, solltest Du jemanden fragen, der sich damit auskennt. Möglicherweise könntest Du Dich sonst verletzen.
Vorderradausbau
Vorderradausbau ist recht einfach: Hebe das Fahrrad am Lenker an und das Rad wird einfach herausfallen.
Hinterradausbau
Der Ausbau des Hinterrads ist ein wenig komplizierter, jedoch nicht zu kompliziert, wenn man sich an eine gewisse Vorgehensweise hält
Kettenschaltung mit Umwerfer
Man könnte meinen, dass Kettenschaltungen die Schwierigsten seien. Jedoch sind sie tatsächlich die einfachste Art von Hinterrad zum Aus- und Einbau. Der Trick besteht darin, auf das kleinste (äußerste) Ritzel zu schalten, bevor man irgendetwas löst. Damit wird der Umwerfer so weit wie möglich von allen anderen Teilen entfernt. Dabei ist es gleichgültig, in welcher Stellung sich der vordere Umwerfer befindet. Nachdem man die Achse gelöst hat:
- Stelle Dich auf die linke Seite des Hinterrads.
- Benutze die linke Hand, um das Fahrrad an der Sattelstütze anzuheben.
- Benutze die rechte Hand, um den oberen Teil des Umwerfers nach hinten zu ziehen, so dass das obere Rändelrad nach unten geschoben wird und hinter den Gesamtaufbau gezogen wird.
- Falls notwendig, drücke mit dem Knie gegen das Hinterrad und das Rad wird herausfallen
- Lege das Rad immer auf die linke Seite, so dass kein Gewicht auf den Umwerfer gelangt. Dieser Teil ist der empfindlichste am ganzen Fahhrad.
Nabenbremsen
Nabenbremsen, wie die mit den Füßen zu bedienenden Rücktritt- oder Coaster-bremsen oder die mit der Hand zu bedienenden Trommelbremsen, die in der Hinterradnabe eingebaut sind, haben einen flachen Metallarm (den so genannten reaction arm), der unterhalb der linken Kettenstrebe befestigt wird. Dieser muss gelöst werden, bevor man das Rad entfernen kann. In den meisten Fällen muss dafür der Bolzen entfernt werden, der das Ende des Arms mit einem Metallgurt oder einem Anlötteil mit der Kettenstrebe verbindet. Im Falle der handbetriebenen Trommelbremse muss zudem noch das Bremskabel entfernt werden, welches normalerweise einfach aus dem Beschlag ausgehängt wird.
Internal Gears
Indicator Chains
Sturmey-Archer internally-geared hubs (most commonly 3-speed) use a small chain called an "indicator spindle" which fits into the end of the axle. The gear cable attaches to this chain. The threaded fitting at the end of the cable must be unscrewed from the end of this little chain. This will require re-adjusting the gears when the wheel is re-installed. This procedure is explained in my Sturmey-Archer article.
Bell Cranks
Shimano 3-speed hubs (and some Sturmey-Archer 5-speeds) use a bell crank to translate a pull on the gear cable into a push on a loose fitting pushrod that fits into the axle. The Shimano 3-speed is adjusted in middle gear, so that the letter "N" is centered in the window of the bell crank. Sturmey-Archer S-5 bell cranks should be adjusted so that the cable is taut when the wide-range position is selected with the left shift lever.
Sachs Clickboxes
Sachs 5- and 7-speed hubs use a "Clickbox" which is held onto the axle by a thumbscrew. No adjustment is normally needed (or possible) to the Clickbox. Once the Clickbox is removed from the axle, take care that the pushrod(s) don't fall out and get lost. Sachs 3-speed (including the 3 X 7) use an indicator spindle similar to that of the Sturmey-Archer hubs.
Shimano Nexus
Shimano Nexus Hubs require the cable to be unhooked from the control ring. This is explained on my Nexus Mechanics Page. With Nexus hubs, it is often easier to open up one side of the tire and patch the tube on the bike, because this type of hub is the most difficult to remove.
Den Reifen abziehen
Before you remove the tire, take a quick look at it to see if the cause of the flat is obvious. There may be a nail sticking out, or a hole in the sidewall, or some other obvious problem. More often not, the cause will not be obvious from the outside, but a quick look can sometimes save time. To remove the tire, you need to pull the bead off the rim, one side at a time. The diameter of the bead is smaller than the outer diameter of the rim. As long as the tire is centered on the rim, it cannot come off. To remove one side of the tire, you need to put the bead off-center. One part of the bead needs to go down into the valley at the bottom of the rim, so that the opposite side of the bead can be pried over the edge of the rim. This can often be done by hand, but usually is much easier if you use tire levers (tire levers used to be called "tire irons", but nowadays, most of them are made of fibreglas or other plastics.) Most tire levers have a rounded end and a hooked end. Tire levers commonly come in sets of three, because three is the most you ever need. For a difficult tire, stick the rounded end of one tire lever under the bead (starting somewhere away from the valve--that only complicates matters.) Insert the lever right where one of the spokes lines up. Pry one side of the tire bead over the edge of the rim, then hook the end of the tire lever to the nearest spoke. Insert another tire lever two spokes away from the first, and repeat the process. The third lever goes two spokes away from either of the first two. When the third lever is in place, the middle one will fall out, and you can repeat the procedure. After some number of times, the tire will be loose enough that you can just run a tire lever around the rest of the rim to pull the whole side over. This is the procedure for tight-fitting tires, particularly for narrow tires. Most tires will come off with less trouble. After you have removed one side of the tire, reach in and pull out the inner tube. Remove the tube completely, while leaving the other side of the tire in place.
Den Schlauch inspizieren
Keep track of which way the tube was facing in the tire, and pump it up. You will usually be able to find the hole by the hissing sound as the air escapes. If you have a slow leak, it may not make enough noise to hear, unless you pump the tube up enough to stretch it out. Tubes can commonly be inflated to twice their normal thickness or more without risk of popping them, and, as the tube stretches, the hole also gets bigger, making it easier to find. For very slow leaks, as a last resort, you can immerse the inflated tube in water and look for bubbles. Don't do this unless you need to, though, because you can't patch a wet tube. When you find the hole, make note of where it is with respect to the valve hole, also whether it is on the inner or outer side of the tube.
- If the hole is on the outer side of the tube, check the inside of the tire especially carefully in the area where the tube was punctured. It is very frustrating to install a new or patched tube and forget to remove the pointy object that caused the original problem!
- If the hole is on the inner side of the tube, check the inside of the rim. Although the rim tape is supposed to protect the tube from rim imperfections, sometimes it is not properly placed, and sometimes spoke ends can actually poke through the tape. Burrs and other sharp edges inside the rim can easily puncture tubes.
- If you find two holes, one above another, you probably have what is commonly called a "snake bite," a pinch cut resulting from hitting a stone or pavement break and pinching the tube between the rim and the rock. This sort of failure is most often caused by insufficient tire pressure.
Den Reifen inspizieren
While you have the tire off the rim, examine the inside of it carefully. Thorns and glass slivers can hide, and may be difficult to remove. I find that pushing them back out through the tread, using a sharp instrument, is often helpful.
In addition to looking for sharp pointy things poking through, look also for broken cords or cuts in the fabric of the tire. If you find such cuts that run more than a millimeter or two, you should replace the tire when possible.
Den Reifen reparieren
If you're on the road and have a tire with a bad cut that could allow the tube to bulge through, you can make a temporary repair by installing a "boot" on the inside of the tire. This can be made of any flexible but non-stretchy material. The ideal thing is a piece cut from an old tire, because this will have the correct curved shape to begin with. I usually like to carry a strip 2-3 inches (50-75 mm) long, cut from an old tubular tire or a high-pressure road clincher. Mountain bikers sometimes use dollar bills folded over, or Mylar food wrappers.
One thing that is often tried, but doesn't work too well, is the rubber patches made for inner tubes...they are too stretchy.
A boot doesn't need to be glued in place, it will stay put just from the pressure of the inner tube against the tire.
Even the best of boots should only be considered a temporary repair. The tire will be less reliable, and you will feel a bump every time the tire goes around.
Den Schlauch Flicken
Inner tube patching is a very old, well established technology, and is quite reliable if done properly:
- Select a patch appropriate to the size of the hole(s).
- Use the sandpaper provided in the patch kit to buff the surface of the tube for an area a bit larger than the patch. You need to buff the tube so that it is no longer shiny. If there is a molding line running along the area where the patch is to be applied, you must sand it down completely, or it will provide an air channel.
Avoid touching the buffed area with your fingers.
- Apply a dab of rubber cement, then spread it into a thin coat, using your cleanest finger.
Work quickly. You want a thin, smooth coat of cement; if you keep fiddling with it as it begins to dry, you'll risk making it lumpy. The thinner the cement, the faster it will dry.
- Allow the cement to dry completely.
- Make sure the cement has dried completely!
- Peel the foil from the patch and press the patch onto the tube firmly.
- Squeeze the patch tightly onto the tube. You're done!
If you follow this procedure, and use good materials, your patched tube should be basically as good as new.
Patch failure generally results from one of two errors:
- Not buffing the tube sufficiently, or:
- Applying the patch before the cement has dried fully.
Den Reifen wieder aufziehen
Although you usually need tire levers or a similar tool to remove a tire from the rim, usually you should be able to re-install the tire with your bare hands.
If you try to pry the tire on using tools, you are very likely to wind up pinching the inner tube between the tool and the rim, puncturing it.
It is usually helpful to have a little bit of air in the tube just enough to make it sort of round rather than flat. With presta-valve tubes, I usually just blow air into the tube by mouth.
In the case of a brand new tube, it sometimes helps to stretch it out first. I do this by stepping into it and lifting away by hand.
Start by fitting the valve of the inner tube through the valve hole. Loosely secure the valve using a valve cap or retaining ring so it won't fall back through the hole. If your valve is threaded for a retaining ring, don't tighten it down very far yet, just thread it on far enough that the valve can't fall out of the rim.
With the tube dangling down along one side of the wheel, install one edge of the tire onto the rim, so that the tube is hanging out of the open side. This is usually pretty easy.
Next, tuck the tube into the tire. It is best to start at the valve, work your way one third of the way around the tire, then go back to the valve and work around in the opposite direction.
Once the tube is in place, you're ready to install the second edge of the tire. This is the hardest part of the whole process, and the hardest part of this is the very last segment.
You should start at the valve, so that the valve won't be a complicating factor when you are trying to lift the last bit of tire bead over the edge of the rim.
As you install the second edge of the tire, try to push it toward the middle of the rim channel, where the channel is deepest. This will give you more slack.
Make sure that the tire bead is not sitting on top of the base of the valve. If it is, push the valve almost back through the rim to raise the reinforced patch at the base of the valve, and push the tire down around it.
For the last few inches of tire bead, some considerable force may be needed to pop it over the edge of the rim. (Some rim/tire combinations are easier than others.) If it is giving you difficult, resist the urge to press the middle part over. Instead, work alternately from each end of the section you're trying to lift over. Going back and forth from side to side will usually get it.
Most folks do this by holding the wheel horizontally, with the open side up. Wrap your fingers around over the tire to press on the bottom of the rim, while you push the tire either with your thumbs or with the heels of your hands.
If you just can't get it by hand, here are some things to check:
- Make sure the tire bead isn't sitting on top of the tube anywhere.
- Make sure the tire bead you're working on is pushed as close to the middle of the rim channel as you can get it.
- The thinner the rim tape, the easier it is to mount the tire. If you have thick rim tape, consider replacing it.
Some tire/rim combinations are just too tight a fit, and you may need to use a tool. The best tool for this is the "Kool Stop bead jack" because this tool lifts the edge of the tire without going inside of it, so it is less likely to damage the inner tube than a conventional tire lever is.
Den Reifen aufpumpen
Once the tire is fully installed on the rim, you can inflate it, but it my not be as round as it should be. If it isn't, it is usualy because the tire needs to be "seated" so that it sits at the same depth in the rim all the way around.
You are less likely to have a problem seating your tire if you have the wheel off of the ground before you start. If the tire is completely flat and is sitting on the ground with the weight of the bike on it, the part that is at the bottom is likely to seat incorrectly.
Generally, if your bike has quick release brakes, it's best to inflate the tire before putting the wheel back on the bike. If you don't have quick release brakes, though, it's easier to install the wheel before pumping up the tire.
It's best to start by inflating the tire just enough that it takes shape, maybe 20-30 psi, and to check that it is seated properly before full inflation. Check the seating by spinning the wheel and watching the tire.
Once you're sure the tire is properly seated, inflate it to full pressure.
Den Reifen setzen
Once the tire is inflated, you may see that it is not as round as the rim is. Usually this will take the form of having most of the circumference of the tire in the correct place, but there will likely be one place where the tire either bulges out too far, or dips inward toward the rim. It may do this on only one side.
Most tires have a "witness line" moulded into each sidewall. This is a narrow ridge of rubber running around the side of the tire, just outside of the rim. Spinning the wheel and observing the witness line will help you locate the place where the seating might be off. Note, it could be OK on one side of the tire but not the other.
Setzen eines unwuchtigen Reifens
If one part of the tire bulges out farther than the rest, deflate it right away or it may explode with a loud bang! Manually re-arrange the tire to get it centered on the rim before re-inflating it. Make sure the tire bead isn't sitting on top of part of the inner tube. If the bulge is right at the valve, this usually indicates that the tire is sitting on the reinforcing patch at the base of the valve. Completely deflate the tire, and push the valve up into the tire with your thumb, while pressing the tire down around it, then pull the valve back down before inflating.
Seating a Tire that Dips Inward
If your tire dips inward at one spot, it is usually a sign of an unusually tight fit. This may make it a bit of a struggle to install the tire, but it also means that you can get away with considerable overinflation with no risk of blowing the tire off the rim. Indeed, the best way to seat a "dipping" tire is by temporariliy overinflating it until it "pops" into position.
In some cases it may be beneficial to lubricate the side of the tire. This can be done with soapy water, but I usually use spray window cleaner for this, because it doesn't leave a soapy residue on the braking surface of the rim.
Das Rad wieder einbauen
Re-installing the wheel is a critical task, and if you don't do it right, the wheel can fall out, leading to a serious crash. This is particularly important on the front wheel. If it falls out you will probably land on your face!
Quick-release Wheels
Hundreds of people suffer gruesome injuries every year as a result of improper use of front wheel quick releases, but if you understand their operation, they're quite safe and secure.
Twist or Flip?
The quick release handle can move two ways: it can twist around like a wing nut, or it can flip 180 degrees outward and back, like a hinge.
The twisting motion adjusts the operating range of the quick release. You may have to hold onto the cone-shaped nut at the other end of the axle. You can't get it tight enough by turning it.
The hinge-like flipping motion is the locking motion. In the "open" position, the quick release handle curves away from the bike. In the "locked" position, it curves toward the bike. Never, ever ride with the lever in the open position!
If the quick release is too loose, this flipping motion will be too easy, but it will not hold the wheel safely--flip it back, turn it clockwise some more, then try again.
If it is too hard to flip, and you cannot get it to flip far enough to lie flat, loosen the adjustment by turning the handle counterclockwise.
It should take a good firm push to get the handle to lie flat.
It is a good idea to set it so that the handle points toward the rear when it is closed. This reduces the chance of getting it snagged on something. Turn the handle and the cone-shaped nut together to align the handle once it has been adjusted.
It is customary to install the front wheel so that the quick release handle is on the bicycle's left side.
Nutted or "Bolt-on " Wheel
Bicycles that don't use quick-release hubs normally have axles with nuts and washers that tighten against the fork ends of the bicycle. It is vitally important that these be securely tightened with a wrench.
Newer bicycles mostly have "vertical drop outs" for the rear wheel, so the wheel can only go in one spot. No adjustment is required with vertical dropouts.
Check the Brakes!
Make sure to check the brakes after you have re-installed the wheel, especially if you disconnected it or used a quick release to help remove the wheel.
Prevention
Many flat tires are avoidable, but some are not. Some people seem particularly prone to them. This is often caused by poor road position: people who get an unusual number of flats often do so because they are riding in the gutter instead of the traffic lane.
The main travel lanes of most roads are kept fairly clear of glass and other dangerous debris by passing motor traffic. Cyclists who travel in the normal traffic areas of the roadway benefit from this.
Many cyclists, however, hug the curb out of timidity and an irrational fear of being struck from behind by a motorized vehicle. The area close to the curb is where all of the glass shards, sharp rocks and other junk winds up. If you ride too close to the curb, you greatly increase the risk of tire punctures.
Riding too close to the curb also, paradoxically, increases your risk of being hit by a car! By cowering in the gutter, you reduce your visibility. You also encourage motorists to pass you even when there is insufficient room to do so safely. You also reduce your maneuvering room, and may have nowhere to go if evasive action is required.
Pressure
Tire pressure is the hardness to which a tire is inflated. This is commonly measured in PSI (pounds per square inch), BAR, or kPa (kiloPascals.)
Tires commonly have a recommended inflation pressure range, or at least a maximum value moulded into the sidewall. These values are only very approximate, and experienced cyclists will rarely pay much attention to the rated pressure.
A major cause of "snake bite" flats is under-inflation. Under-inflated tires also have increased rolling resistance, making it harder to pedal.
Less well known is the downside of over-inflation; this causes a harsh ride and can also cause poor traction on bumpy surfaces (over-inflated tires tend to bounce, and a tire that is airborne, even for a moment, has no traction!)
A correctly-inflated tire will have a slight bulge where it is in contact with the road. The correct inflation pressure is determined by the weight load, the tire width, and, to some extent, the riding surface.
For details on optimal tire pressure, see the "Pressure" section of my Tires Article.
Airless tires
Of all the inventions that came out of the bicycle industry, probably none is as important and useful as Dr. Dunlop's pneumatic tire.
Airless tires have been obsolete for over a century, but crackpot "inventors" keep trying to bring them back. They are heavy, slow and give a harsh ride. They are also likely to cause wheel damage, due to their poor cushioning ability. A pneumatic tire uses all of the air in the whole tube as a shock absorber, while foam-type "airless" tires/tubes only use the air in the immediate area of impact.
Airless tire schemes have also been used by con artists to gull unsuspecting investors.
Tire Liners
Aftermarket tire liners, such as the well-known Mr. Tuffy, are not necessary for most cyclists. They make your wheels heavy and sluggish, and, if incorrectly installed, they can actually cause flats!
In some regions, notably the Southwestern U.S., cactus thorns are so common that such liners, or thornproof tubes, are a desirable option.
Kevlar ®
Kevlar ® is a very strong artificial fiber, used in bullet-proof vests and bicycle tires. Kevlar is used in tires two different ways, for two different purposes:
- Kevlar beads are used on some high performance tires. Replacing the normal wire bead with Kevlar ® saves about 50 grams per tire. Kevlar-bead tires have the additional advantage of being foldable, making them popular as emergency spare tires with touring cyclists. Kevlar-bead tires are somewhat harder to mount on a rim, and are more likely to blow off than wire-bead tires. They work best on "hook edge" rims.
- Kevlar-belted tires have a layer of kevlar under the tread surface, with the purpose of making the tire more resistant to punctures caused by small sharp objects, such as thorns and glass slivers. Kevlar-belted tires have slightly higher rolling resistance, price and weight than corresponding tires without the belt.
Thornproof Tubes
In some regions, notably the Southwestern U.S., cactus thorns are so common that special "thornproof" inner tubes are needed. These tubes are very thick on their outer circumference, so that a short thorn (or a small glass sliver) may be embedded in the tube without being able to reach in far enough to let the air out.
Thornproof tubes are heavy, and add to rolling resistance, so they are a poor choice for cyclists who don't ride in conditions that require them. See also tire liners.
Tire Savers
Some punctures are caused by glass slivers or thorns gradually working their way through the tire tread. What can happen is that a small sharp object may be picked up by the tire, then gradually work its way in over the course of several tire revolutions. The pointy thing is driven in like a nail into wood by repeated blows against the pavement. A formerly popular device called a "tire saver" or "flint snatcher" used a loosely spring piece of wire (generally made from a bicycle spoke) to constantly brush the tire tread in hope of dislodging glass slivers and the like before they could penetrate all the way to the inner tube.
These are of dubious value in practice, but may be of help in backward areas where throwaway beverage bottles are still legal, and glass slivers are a major problem.
Spoke Divider
Tools CO2 Cartridges | Compressors | Patch Kits | Pressure Gauges | Pumps | Tire Levers | Wrenches | Valve Adaptors Pressure Gauges
Pressure gauges come in 3 types:
* "Pencil" gauges are the simplest and cheapest. They look like a pencil, with a fitting at one end that you can press against the valve. When you do so, a rod slides out of the other end. This rod is calibrated like a thermometer, and slides out farther the more pressure is in the tire. This type is most commonly used for Schrader valves (though Presta versions are also available.) Note that "pencil" gauges come in automotive and bicycle types. The difference is the pressure range they measure. Automotive pencil gauges commonly only read up to 50 PSI, while those intended for bicycle use run up to 120 PSI.
* "Dial" gauges are a bit more expensive, but are easier to read and may be a bit more accurate. Some dial gauges have double fittings, allowing the same gauge to work with both Schrader and Presta valves. Less expensive dial gauges must be read while they are on the valve, but better ones have a "memory" feature, and will hold their readings after being removed from the valve, until the "reset" button is pressed.
* "Digital" gauges have a liquid-crystal readout, and an electronic sensor. They are probably the most accurate, though real-world accuracy of any type of gauge is limited by the fact that a small amount of air is lost as the gauge is removed from the valve.
Valve Adaptors
If you have Presta valves, it is a good idea to carry a Schrader/Presta adpator
Pumps
You have 7 possible choices of tools to inflate your tires:
CO2 Cartridges | Compressors | Floor Pumps | Foot Pumps | Frame Pumps | Mini Pumps | Track Pumps CO2 Cartridges
CO2 cartridges are small cylinders of carbon dioxide, originally made for seltzer siphons. With a suitable adaptor, they can be used for inflation of bicycle tires. When everything goes well, this is the fastest way to inflate a tire. They're also the lightest and most portable inflation device available, so they're fairly popular among competitive cyclists.
The down sides of CO2 cartridges are that they are expensive and wasteful, and that each cartridge is normally only good for inflating one tire one time. While a few of the cartridge systems do permit controlled release of CO2, most of them are "all or nothing" designs, so you can't use them for topping off a slightly soft tire. If you carry only one cartridge and get two flats on the same ride, you may be in for a long walk. I advise against relying on CO2 cartridges except in competition.
Compressors
Compressors are a popular alternative, when available. Most gas stations will have a compressor available, either for free or coin operated. While these are convenient, they can also be dangerous. If you use a gas-station compressor, be sure to use a separate, hand-held pressure gauge, because if you rely on the gauge built into the compressor outlet, you risk blowing the tire off the rim.
The typical gas-station compressor has a head with a crank on it. You turn the crank to set the display to the desired pressure value in PSI. As air flows into the tire a bell rings. Each time the bell rings, the gauge checks to see if the pressure in the tire is more or less than the desired pressure. If it is more, the flow is stopped.
The problem with using these gauges for bicycle tires is that the volume of a bicycle tire is so much smaller than that of a car tire that the difference from one "ding" to the next can be 20 psi or so. If you set the dial to 100, the air will go "ding...ding...ding..." then there's, say, 99 psi in the tire. This is under 100, so it'll give it another blast and check again, and your tire could well be close to 120 psi. This assumes that the gauge is accurately calibrated for pressures in this range, which is a big assumption. The bottom line is that you really can't trust these gauges for bicycle tires. Instead, you should use a separate, hand-held gauge.
Floor ("Track") Pumps
The most effective human-powered inflation tool is the "floor" or "track" pump. This has a long vertical cylinder, with a "T"-shaped handle that you raise and lower with both hands. This type of pump has some sort of footrest to keep the bottom held in place, and a hose that connects to the valve. Floor pumps get most of their action from the user's back, and with an assist from gravity, as the actuall pumping occurs on the down stroke.
The better floor pumps have built-in gauges and holding tanks, so you can see just how much pressure you've got, while you're pumping. This makes them very fast and convenient to use.
Foot Pumps
An less-common type of pump, similar to a floor pump, also sits on the ground, but is operated by pressing with the foot. These are fast, but mechanically complex due to the extra linkages required. They also tend to be designed more for delivering volume than for pressure, so they don't generally pump up to high enough pressure for narrow road-type tires.
Frame Pumps
"Frame" pumps are portable pumps designed to be carried on the bicycle's frame. They are typically about as long as one of the frame tubes, and have a spring-loaded handle that holds the pump in place along one of the frame tubes. Older bikes often had two brazed-on "pump pegs" to secure the ends of a frame pump. Many newer bikes have a single peg just below the top tube on the back of the head tube, for a pump running below the top tube.
Frame pumps are the best thing to carry on the bike for emergency, on-the-road use. They take a fair amount of work to get up to full pressure, but it beats walking! They pump fairly easily at first, but they can require a fair amount of strength as the pressure gets high.
Frame Pump Techinque As you pump your tire up closer and closer to full inflation, the pump gets harder and harder to push. This is particularly an issue with narrow tires that need to be pumped up to high pressures.
Your arms may not be strong enough by themselves to get such a tire up to adequate pressure. Assuming you're right handed, it can help to brace your left hand or the pump head. If there's a convenient tree, I'll often lean the pump head against the tree, so my left arm doesn't actually need to do any work. If there's no suitable tree or other solid object handy, or if I'm topping off a tire without removing the wheel from the bike, I'll kneel on my right knee and brace my left wrist against the indside of my left knee.
As I approach full inflation, and the pump gets harder to push full stroke, I will start each stroke with my right arm free, then brace my right wrist against my chest for the final, hard part of the stroke, and use my back to complete the stroke.
With any type of pump, it is very important that the pump be pushed all the way to the end of its travel on each stroke, otherwise you're wasting most of your effort. One Is Not Enough A frame pump is not a substitute for a good floor pump; the well-equipped cyclist will own both. The floor pump is for routine pressure topping off at home, and the frame pump is for fixing flats that occur while you're out riding...they're too hard to use for non-emergencies.
Mini Pumps
The most popular type of pump these days is the "mini" pump, a pocket-sized version of a frame pump. People like them because they're small and easy to carry, but they take much longer to use than full-sized frame pumps. I generally advise against buying a mini pump unless you have particular issues with theft, because they are so inefficient. Their main advantage is that they are small enough to be carried in a bike bag that you can remove when parking in high-risk locations.
Tire Levers
Traditional tire levers, a.k.a. "tire irons" came in sets of 3, with a rounded business end, and a bent, hooked end for hooking onto a spoke. Newer ones are fibreglass or similar materials. I have an assortment of them for different tires. For very tight fitting tires, you need tire levers with thin ends, able to get underneath tight beads.
For less difficult tires, a single tire lever with a rounded, grooved end can be faster. I particularly like the "Quick Stick."
A similar unit, the Crank Brothers "Speed Lever" incorporates a telescoping extension that snaps onto the axle. This works very much like the power tools used in garages for mounting/dismounting automobile tires. This doesn't work too well on very tight tires, but on average tires, it is quite fast and easy to use.
The Kool Stop "bead jack" is an articulated tool for installing really tight tires. It has a comfortable handle and two ends, one of which is on a hinge. The rigid end uses the edge of the rim as a fulcrum, while the hinged end lifts the bead up and over the opposite edge of the rim. This is a very nice tool for dealing with really difficult tires.
Kool Stop Bead Jack
Patch Kits
Patch kits are available in any bike shop. A patch kit is usually a small plastic box containing a few patches, a tube of rubber cememnt, and a bit of sandpaper or a metal scraper for preparing the tube surface. The best patch kit is the Rema "Tip Top" from Germany.
Make sure to follow the instructions.
Glueless Patches
Glueless (peel & stick) patches are avaialble, and they are slightly more convenient than conventional patches. Unfortunately, they don't have a very good reliability record, and I can't recommend them--you're much better off with a standard patch kit.
Wrenches Unless your wheels have quick release hubs, you'll need a wrench or two to remove the wheels. (The term "wrench" is not common in British usage, where the term "spanner" or "key" is generally preferred.)
Wrenches are divided into two families:
# Fixed Wrenches are made of a single piece of metal, and only fit specific sizes of fasteners. Types of fixed wrenches include:
* Box wrenches have a complete loop that surrounds the fastener. They are substantially stronger than open-end wrenches, and are the best use for high torque applications, both because the wrench is stronger, and because it can contact more than two corners of the fastener.
* Open-end wrenches have ends shaped like a two-tined fork. They normally have two parallel surfaces which bear against two of the sides of a fastener. Open-end wrenches are faster to put on to fasteners, and are the only kind that can be used where there is not clearance to slip a box wrench over the end of the fastener.
Open-end wrenches don't get as good a grip as a box wrench, since they only engage two of the 6 corners of the nut. If you over-stress an open-end wrench, the jaws can spread, ruining the wrench.
* Combination wrenches are double-ended wrenches with an open end and a box end, usually for the same size on each end. This is the most useful and most common general-purpose wrench style.
# Adjustable Wrenches can be adjusted to fit different sized fasteners, usually by the use of a thumb screw. They don't fit as well as the correct size fixed wrench, so good, well equipped mechanics only use them as a last resort. See my Tool Tips article on Adjustable Wrenches.
Wrenches are sometimes confused with pliers, and naive users sometimes try to use pliers for jobs that really require a wrench. This usually results in damage to the nut or bolt so abused. It can also cause failure due to undertightening the part involved.
Quellen
- Dieser Artikel basiert auf dem Artikel What Every Cyclist Should Know About Flat Tires von der Website Sheldon Browns. Der Originalautor des Artikels ist Sheldon Brown.