Kettenpflege: Unterschied zwischen den Versionen

==Ketten und Ritzelverschleiß==

Auf den folgenden Bildern wird die Kette im Uhrzeigersinn um das Ritzel geführt. Das heißt, dass die Kette auf der rechten Seite abwärts gezogen wird.

[[Bild:Kette_NKNR.gif|center|Neue Kette auf neuem Ritzel]]When a new chain meshes with a new sprocket, every roller that is in contact with the sprocket is pressing more-or-less equally against the corresponding tooth of the sprocket, so the load and stress are shared out equally, among 10-11 rollers/teeth, in this case. From the center of each roller to the center of the next is exactly 1/2" (12.7 mm). This dimension is known as the "pitch" of the chain. The sprocket teeth are made so that the center the curve that makes up each "valley" is 1/2" from the next. The diameter of the sprocket is determined by the pitch and the number of teeth.

[[Bild:Kette_VKVR.gif|center|Verschlissene Kette auf verschlissenem Ritzel]]This chain and sprocket have worn together. You can see daylight under the chain in some places. The worn chain has "stretched" so that it no longer matches the original pitch of the sprocket. The sprocket has worn so as to effectively increase its pitch to match the worn chain. [This photo shows a chain hanging from a sprocket. During pedaling, the top run of the chain is in tension while the lower run is nearly slack, and a chain that has worn along with the sprocket may ride high on the teeth all the way around. I have yet to check this -- John Allen]

[[Bild:Verschlissene Ritzelzähne.gif|center|Verschlissenen Ritzelzähne]]The illustration above shows two formerly identical sprockets, viewed from the right side. The one closest to us is badly worn. On a new sprocket tooth, the surface that the roller presses against is perpendicular to the pull of the chain. The worn teeth have become ramps, causing the chain to ride up under load.The rollers ride up on the sloped teeth until they reach a radius that corresponds to the longer pitch of the worn chain. The effective diameter (and thus, the effective pitch) of the sprocket has become larger, since the chain is no longer riding in the bottoms of the valleys.

[[Bild:Kette_NKVR.gif|center|Neue Kette auf verschlissenem Ritzel]]A new chain on a worn sprocket. Most of the driving is happening on the left side, where the chain first engages the sprocket. Due to the mismatch in pitch, the rollers in the part of the chain that is about to leave the sprocket are doing very little to push their teeth forward, instead, they are being forced upward by the slope of the teeth. Since the teeth/rollers on our left are doing most of the work the load is concentrated on them. In addition, as the roller follows its tooth around the sprocket it rolls up the "ramp," while under load. This promotes wear to the insides of the rollers and to the "bushings" they roll on. With a properly meshed chain, the roller only turns a tiny bit as it rolls onto and off of the chain. [Again, this is a photo of a hanging chain. The links could not ride higher and higher as they come around to the top and still engage the back of each tooth. I still need to check, but I think instead that the links must ride lower and lower as they come around to the top. Indeed, that is what the photo appears to show for the first few engaged links at the right side. If the last link at the bottom of the sprocket rides too high, it lands on top of a tooth, and the chain slips forward when that link comes around to the top. A chain held in place by rear axle position rather than a derailer or idler is forced into engagement with a worn sprocket, but then each link is heavily stressed as it engages. Modern sprockets designed for easy shifting have short teeth. Taller sprockets can develop a hooked shape. It is often possible to flip a worn sprocket over, or grind off the hooks to give it a new lease on life -- not possible though with specially shaped and ramped sprockets, and not recommended with a fixed gear or coaster brake, which pulls the chain in both directions. -- John Allen]

[[Bild:Kette_VKNR.gif|center|Verschlissene Kette auf neuem Ritzel]]A worn chain on a new sprocket. Due to the pitch mismatch, the load is only carried by the teeth/rollers on our right, the chain hangs slack on our left. The new sprocket will wear rapidly to match the pitch of the worn-out chain. [In this case, Sheldon is probably correct, though the chain also could "ride high" all the way around. Some sprockets in a cluster get more use than others, and so sometimes a chain will be running on a (nearly) new sprocket even on an old cluster -- John Allen]