Author Topic: A home made 42 tooth cog.  (Read 1791 times)

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Offline zerodish

A home made 42 tooth cog.
« on: February 15, 2016, 07:42:41 pm »
My set up also has no dish and enough chain take up to work in all gears. The back is 12 13 15 17 20 24 30 42 and the front is 20 36 42. Come on industry keep up. https://flic.kr/p/DVyyQJ

Offline RussSeaton

Re: A home made 42 tooth cog.
« Reply #1 on: February 16, 2016, 11:03:00 am »
Pretty pathetic gearing.  Unless you purposely planned and designed a worse gearing system, you could not get much worse than the one you listed.  First off it uses 8 speed, which is getting more rare every day.  Do bike shops sell 8 speed anymore?  As for having a 52 tooth chain wrap, doubtful unless you custom built a rear derailleur cage about 10 inches long.  On the Shimano website some of the rear derailleurs have 45 teeth as maximum wrap.  Your choice of middle and outer chain rings is baffling.  It results in excessive overlap.  You end up with almost the exact same gears on both of these chain rings.  Why even bother having two chain rings?  It looks like your crankset uses 110mm bcd outer and middle.  And 58mm bcd inner.  A fine choice on crank arms/spider.  I use similar on my touring crankset.  My low gear is 20x32, 16.6 gear inches.  Low enough.  I could get lower by using a 34 or 36 inner cassette cog.  15.6 or 14.7 gear inches.  More than low enough.  Your low gear of 20x42 results in a low of 12.6 gear inches.  Lower, yes, but not really much lower.  2 to 4 gear inches lower.  Not a big deal.  And by using an 8 speed cassette and bizarre overlapping chainrings, you end up with very few usable gears for riding.  OK for climbing the steep streets of San Francisco with a loaded touring bike.  But a hindrance for riding into and out of San Francisco and everywhere else in the US or Canada.

If you want to improve your gearing, do the following.  Nashbar has 9 speed cassettes in 11-34 and 12-36.  And 10 speed cassettes in 11-34 and 11-36.  Put some quality chain rings from TA on your crank.  I use 44-33-20 rings and recommend that combination.  You could go 42-33-20 since you would only need to replace the middle ring on your current crank.  With a new ring and a 9 or 10 speed cassette of 11-34, 12-36, or 11-36, you would have an almost perfect touring gearing.

Your rear wheel with no dish.  I just built a tandem rear wheel for a friend with zero dish.  Uses a Phil Wood tandem rear hub.  Phil puts the non drive side flange very close to the axle center to make zero dish.  The rear wheel had 48 spokes built on a Velocity Dyad rim.  4 cross using Sapim Strong 13/14 gauge spokes.  Possibly the strongest rear wheel every built in the history of the world.  Cannot remember if it is 130 or 135mm rear spacing on the tandem.  Its a somewhat old Cannondale tandem so not sure the 135mm rear mountain bike wheel spacing had even been invented when this bike was built.