's Forum Archives - Components

Archive Home >> Components(1 2 3 4 5 6 7 8 9 10 )

Triple crank largest sprocket(5 posts)

Triple crank largest sprocketDan Ida
May 11, 2001 7:56 PM
Shimano makes or has made triple cranks that have only a 46 large sprocket. Most are 52. Are the small version "meant" to be used on cross bikes, mountain bikes or road bikes that don't have as high a top speed? What did they come standard on?

re: Triple crank largest sprocketJethro Notbodine
May 11, 2001 10:32 PM
Me thinks you are refrencing the older RSX cranksets of a few years ago that used a 110BCD and 46/36/26 rings.I'm not sure the large ring can be smaller than a 48 on the 130mm BCD cranksets. Stand corrected if wrong.The 46 tooth large ring cranks and RSX group was the low end 7 speed stuff several years ago.They were typically used with a 11/24 rear cogset.The idea did not aparently go over well, as when RSX became 8 speed,the cranks became 130 BCD with the standard 52/42/30 rings.
re: Triple crank largest sprocketDan Ida
May 12, 2001 9:50 AM
Using Langley's book of Bicycle repair(chart -p.320) it shows that a 46-11 gives a gear inch value of 112. Switching to the more modern 52-12, that gives a value of 114.8. PRETTY CLOSE. On the other end, the smaller 27 gear wuld give slightly better hill climbing numbers, depending on where the tooth count was for the largest rear gear. SO what would have been wrong with smaller gears. It seems to me that lees chain would be better, and smaller front sprockets would be stronger as well.

re: A possible answer?Granny
May 12, 2001 6:45 PM
I duno. Your numbers sound good to me. Not sure about the other theories. Maybe the anal stud roadies just 'Thought' the small ring cranksets were something only fat ladies and geezers with oxyogen bottles should be riding. Looks and style points are everything ya know....
re: Triple crank largest sprocketSteve Bailey
May 14, 2001 6:33 AM
The gear inch numbers are correct.

Shimano jumped on the compact drive bandwagon in the early 90's after Suntour came out with Microdrive for mountain bike components. The concept was smaller chainrings (22-32-42 as example) mated to cogsets that started at 12 or 11, as opposed to a 26/36/46 110BCD ring combo and a cogset starting at 13. There was (is) a significant weight savings, which was (is) important to racers. Only problem was faster wear on all the drive train components - chain, rings and cogs due to less metal to spread the stress. In the real world the faster wear hasn't seemed to be much of an issue, excpet possibly to long distance touring bikes.

As to Don's original post, the 46 ring was used on older 110BCD cranks. Shimano has since gone to 130/74 BCD triples for road and touring bikes, which typically are equipped with a 30/42/52 ring setup. Much criticism has been noted about the poor gearing choices on stock touring bikes with this crank, although the combo seems to be adequate for road sport bikes.

Shimano has also muddied the waters immensely by moving away from "standards" such as 94/58 BCD compact drive, 110/74 BCD standard mt. and 130 BCD or 135 BCD Campy road cranks. They now have all sorts of 4 arm cranks whose BCD I no longer keep track of.