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=== | ===[[Pedal]]e=== | ||
[[Bicycle pedal]]s are left-threaded on the left-hand [[Crankset#Cranks|crank]] so that precession tightens the pedal rather than loosening it. This may seem counter-intuitive, but the torque exerted due to the precession is several orders of magnitude greater than that caused by a jammed pedal bearing. | [[Bicycle pedal]]s are left-threaded on the left-hand [[Crankset#Cranks|crank]] so that precession tightens the pedal rather than loosening it. This may seem counter-intuitive, but the torque exerted due to the precession is several orders of magnitude greater than that caused by a jammed pedal bearing. | ||
Shimano SPD axle units, which can be unscrewed from the pedal body for servicing, have a left-hand thread where the axle unit screws into the right-hand pedal; the opposite case to the pedal-crank interface. Otherwise precession of the pedal body around the axle would tend to unscrew one from the other. | Shimano SPD axle units, which can be unscrewed from the pedal body for servicing, have a left-hand thread where the axle unit screws into the right-hand pedal; the opposite case to the pedal-crank interface. Otherwise precession of the pedal body around the axle would tend to unscrew one from the other. | ||
=== | ===[[Innenlager]]=== | ||
English threaded bicycle [[bottom bracket]]s are left-threaded on the right-hand (usually drive) side into the [[Bicycle frame#Bottom bracket shell|bottom bracket shell]]. This is the opposite of pedals into cranks because the sense of the relative motion between the parts is opposite. (Italian and French threaded bottom brackets have right-hand threading on both sides.) | English threaded bicycle [[bottom bracket]]s are left-threaded on the right-hand (usually drive) side into the [[Bicycle frame#Bottom bracket shell|bottom bracket shell]]. This is the opposite of pedals into cranks because the sense of the relative motion between the parts is opposite. (Italian and French threaded bottom brackets have right-hand threading on both sides.) | ||
=== | ===[[Ritzel]]=== | ||
Splined sprockets precess against any lockring which is screwed into the freehub. [[Shimano]] uses a lockring with detents to hold cassette sprockets in place, and this resists precession. [[Sturmey-Archer]] once used 12-splined sprockets for 2- and 3-speed racing hubs, and these were secured with a left-threaded lockring for the same reason. ([[Fixed gear bicycles]] also use a left-threaded lockring but this is not because of precession; it is merely to ensure that the lockring tends to tighten, should the sprocket begin to unscrew.) | Splined sprockets precess against any lockring which is screwed into the freehub. [[Shimano]] uses a lockring with detents to hold cassette sprockets in place, and this resists precession. [[Sturmey-Archer]] once used 12-splined sprockets for 2- and 3-speed racing hubs, and these were secured with a left-threaded lockring for the same reason. ([[Fixed gear bicycles]] also use a left-threaded lockring but this is not because of precession; it is merely to ensure that the lockring tends to tighten, should the sprocket begin to unscrew.) | ||
=== | ===Lager in [[Nabenschaltung]]en=== | ||
A bearing supported gear in a [[Manual transmission#Maintenance|manual transmission]] rotates synchronously with its shaft due to the dog-gear engagement. In this case, the small diametrical clearance in the bearing will induce precession of the roller group relative to the gear mitigating any fretting that occurs if the same bearing rollers always push against the same spot on the gear. Typically the 4th and 5th gears will have precession inducing features, while 1st through 3rd gears might not since cars spend less time in those gears. Transmission failure due to lack of precession is possible in gear boxes when low gears are engaged for long periods of time. | A bearing supported gear in a [[Manual transmission#Maintenance|manual transmission]] rotates synchronously with its shaft due to the dog-gear engagement. In this case, the small diametrical clearance in the bearing will induce precession of the roller group relative to the gear mitigating any fretting that occurs if the same bearing rollers always push against the same spot on the gear. Typically the 4th and 5th gears will have precession inducing features, while 1st through 3rd gears might not since cars spend less time in those gears. Transmission failure due to lack of precession is possible in gear boxes when low gears are engaged for long periods of time. | ||
== Siehe auch == | == Siehe auch == | ||