Ritchey Cranks

RITCHEY LOGIC TANDEM CRANKS

The Logic Tandem cranks are a variation on the Logic Mountain cranks. This is a highly specialized crankset that has a number of unique threads on what appear to be common crank parts. First lets define terms, the person who rides on the front seat of a tandem bicycle is known as the "captain." The person on the rear seat is known as the "stoker." There are, in fact, two cranks in a tandem crankset, a front "captain's" crank and a rear "stoker's" crank. The captain's cranks are made of a right hand non-drive arm and a left arm that have a "middle" sized chainring. The captain's right arm looks like a normal left arm but (think about it) it has threads for a right hand pedal spindle. This is a particular and unique arm. The left crank arm is a drive arm, in the Ritchey case they have modified an original triple drive arm by milling away the inner triple bolt hole mountings before they were ever drilled and tapped. This left hand drive arm has a 38 tooth aluminum chainring bolted with five fixing bolts to the outer position of the arm. This left drive arm has the pedal threads tapped for a left hand pedal spindle, again unique. The stoker has a left arm that is exactly the same as the captain's, with the same 38 tooth middle bolted to the same modified arm.

The same size chainring is a must to achieve a one-to-one pedal revolution and cadence.

The stoker right crank arm is a drive arm with triple chainrings in sizes that approximate a Road crankset with an added small inner chainring to establish a very low gear for the two riders to be able to hill climb. The captain adds power to the front left crank arm that drives a chain on his left side back to the left hand arm of the stoker's cranks. The stoker's right hand drive arm receives power from the captain via its left arm, and adds to it the stoker's own efforts as it drives a chain on the right hand side of the bike around the rear hub's gearing.

The front derailleur, though controlled by the captain, is on the seat tube beneath the stoker. As mentioned the Ritchey Tandem set uses a 38 tooth aluminum chainring on both left arms. The stoker's right arm has 26-36-54 tooth gearing. Each of the three drive arms uses nickel plated steel fixing bolts and nuts. The stoker's inner chainring is held by nickel plated steel inner bolts. The Tandem set comes with four Chrome plastic press-in dust caps, (but no crank bolts). With tandem cranks, all four crank arms come in the same length. The Ritchey Tandem set is available in either a 170mm or a 175mm length. The chainring's have a standard mountain bike bolt pattern using 74mm BCD for the inner and 110mm for the middle and outer. We found the stoker's cranks had a Bike-Pro Q measurement of 145mm, and the captain's had a Bike-Pro Q measurement of 144mm. The weight of the complete Ritchey Tandem crankset in the 170mm length is 1363 grams. Tandem cranks are the perfect application for a 60 tooth chainring.

	Length-70-75 / T      $ Price in Catalog

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