Dotek 155mm Triple Chainring Cranks
I've tooled up to convert Dotek 155mm BMX cranks to touring triples, by adding inner bolt circles of 58mm or 74mm.
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Dotek 155mm Triple Chainring Cranks |
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More and more riders are discovering the advantages of using shorter crank arms on recumbents. However they have been stymied by the lack of reasonably priced, short cranks, capable of accepting small 3rd chainrings. (Of course shorter riders, on upright bicycles, can also benefit from short cranks. )
I've tooled up to convert Dotek 155mm BMX cranks to touring triples, by adding inner bolt circles of 58mm or 74mm.
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Don't send any money without checking to see if I have any left.
Salsa Rings in 24-34-44 with 58mm BCD. $148 (Click for larger image) |
Sugino Ramped & Pinned Rings in 26-36-46 with 74mm BCD. $ 158 (Click for larger image) |
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Prices, as of 5/13/2005, for some typical cranksets
With Plain Rings
With Ramped & Pinned Rings Other chainring combinations are available, see "Chainrings" page. |
These prices include crankarms, 3 chainrings, 1 set of spacers, and 2 sets of bolts, but not bottom brackets. Unfortunately, the economics of assembling a crankset from modified arms and individual parts, means you end up paying near Ultegra prices. |
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Do not send money, based on these prices. Due to worsening exchange rates, my parts costs can rise at any time. And, my suppliers are often out of at least some specific rings. Chainring prices vary widely, depending on brand and size. Contact me mark@bikesmithdesign.com or 612-824-2372, for a current quote and availability. |
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| If you have, or can find, a set of these arms, I can drill and tap them to accept a 3rd ring for $35 + $8 S&H. Last I heard, Dan's Compe had a few. The only length that I know for sure has the pads are the 155mm. The 140s definitely do not. | |
About the Dotek 155sTodd Sorlie ( Alpha Engineering & Manufacturing: 763-542-8860) CNC'd me a drilling guide plate, which centers holes accurately around a BB spindle. Then I made a tapping machine out of an old drill press, to ensure the threads are straight.
These aren't fancy cranks, unmodified arm sets retailed for only $30-$35. Finish is good on the outer surfaces, not so good where it doesn't show. However, they are plenty strong and stiff, lighter than 165mm Shimano 105 Hollowtech arms and do a good job of transferring power from pedals to chain.
BB spindle; Square taper. Length needed depends on the reach of the front derailleur. With most derailleurs, 110mm or 113mm spindles work best. But one person needed to use a 107mm. Conversely, many people have been able to use them with the 118mm spindle on Rockets and Tailwinds.
Q factor; 173mm with Shimano 110mm spindle. Wider than road cranks, but about average for a mountain bike crank. But at least ankle clearance is great due to the short spindle. Ideal for those who might need knee savers with other cranks.
Bolt Circle Diameter (BCD) The middle and outer ring are 110mm BCD, inner can be drilled to either 74mm or 58mm.
People often ask if they can use the 52-42-30 rings from their 130mm BCD road cranks. The answer is no, but unless you are very fast, or have a small drive wheel, a 52t chainring isn't much use at the higher cadences encouraged by short cranks. They usually end up keeping their old crankset intact, to sell or put on another bike, and buying smaller 110mm rings.
If you aren't sure which you have - Holes on a 110mm BCD crank are 64.7mm (2.55") between centers and holes on a 130mm BCD crank are 76.4mm (3.00") between centers.