Information AboutCrankset |
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PARTS Cranks Deore right crankset, showing crank arm, spider, three chainrings and chainring guard]] The two ''cranks'', one on each side and usually mounted 180° out of phase, connect the bottom bracket axle to the pedals. Sizes .]] Cranks can vary in length from 150 mm to 185 mm to accommodate different sized riders,lengths for adult riders range from 165 mm to 177.5 mm. People with a shorter inseam (inside leg measurement) usually use shorter cranks, while those with longer inseams use longer cranks. Various formulae exist to calculate appropriate crank length for various riders, however, the length an individual cyclist feels most comfortable with may vary from this. Most major manufacturers offer crank lengths from 165mm to 180mm in 2.5 mm increments. Materials Cranks are constructed of either an Aluminum Alloy , Titanium , Carbon Fiber , Chromoly Steel , or some less expensive Steel . Tubular steel cranks (such as Tioga's Revolver) can be light and very strong, but are expensive to manufacture and rarely seen nowadays. Aluminium cranks may be cast, hot forged or cold forged ("cold" in this context means the billet from which the crank is to be made is heated to a specified temperature well below the melting point, not room temperature). Cold forging gives the metal additional stength, and the cranks can therefore be made lighter without increasing the risk of breakage. Shimano "Hollowtech" aluminium cranks are made by forging the main arms around a hard steel insert which is then withdrawn, leaving an internal void to save weight. They are then welded up before final machining. Attachments =To the bottom bracket There are a variety of methods used to attach the crank to the Bottom Bracket axle or Spindle .
:and are held in place by a bolt installed into the axle of the bottom bracket.
See the Bottom Bracket article for more details. =To the pedals Crank arms have a threaded hole (or "eye") at their outboard end to accommodate the pedal spindle. Adult or multi-piece cranks have a 9/16 inch hole with 20 TPI (a combination that appears to be unique to this application). One-piece or children's cranks use a 1/2 inch hole. Some crank on children's bikes have more than one pedal hole so that the pedal can be moved to accommodate growth. The right-side (usually the chain side) hole is right-hand threaded, and the left-side hole is left-hand (reverse) threaded to help prevent it from becoming unthreaded by an effect called Precession . Pedal spindles are hard steel, and gradually fret and erode the crankarm where the two meet. This can eventually be a cause of crank breakage, which commonly occurs at the pedal eye. Some manufacturers advise the use of a thin steel washer between the pedal and crank, but this is ineffective because the hard washer frets against the crank instead. A solution, suggested by Jobst Brandt, is to use a 45 degree taper at the surface where crank and pedal meet, as this would eliminate precession-induced fretting and loosening (it is already done for most automobile Lug Nut s for the latter reason). However, this would require manufacturers to change a well-established standard which currently allows most pedals to be fitted to most cranks. Spider On older styles the ''spider''—the multi-armed piece that connects the chainring to the bottom bracket axle—was a separate piece from the crank arm. The most common modern cranks have an integrated spider on the drive-side crank arm. However, Middleburn, TA, and Surly currently produce cranks with separate detachable spiders, enabling a wide variety of chainring patterns to be used with the same cranks. |
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