Subject: Re: Crankset vs Cassette Posted by: Al on August 10, 2006 at 05:10:15: In Reply to: Re: Crankset vs Cassette posted by Christopher Krenz on August 09, 2006 at 15:35:56:

Message: >>>>>I own a 2001 Trek 4500 mountain bike. I have been making minor upgrades to better my ride, and just for the fun of it. I'm in the process of making a major change with my crankset. Most cranksets indicate they work with 9 speed cassettes. I have an 8 speed cassette and am not planning on making the upgrade to a 9 speed for a while. Will the 8 speed cassette cause problems with a new crankset? >>>>You should experience NO PROBLEMS using a crankset with 9-speed chainrings with your 8-speed drivetrain. >>> >>>Thanks. >>>Why then is this mentioned with so many cranksets? >>>-Chris >>MY OBSERVATION, and others may choose to disagree, the significant difference is in the chainrings ... >>An 8-speed chainring has a slightly raised band on its inside face ... >>Generally, a 9-speed chainring is ramped-and-pinned -- the ramps-and-pins facilitate shifting the chain from a smaller chainring onto the larger one next to it. >>And, a 10-speed chainring has thicker ramps-and-pins than a 9-speed chainring because the chain is narrower, but the plane of the respective chainring's teeth appears to remain a constant to one another. >>You CAN use 8-speed chainrings with a 9-speed chain + EITHER a 9-speed Shimano (okay) OR Campagnolo (better) shifter ... but, the shifting will be slightly better if the chainring matches the chain. >>The shifting might get too dodgy if you try to use an 8-speed chainring with a 10-speed chain, but maybe not. You should be able to use a 9-speed chainring with a 10-speed drivetrani, but the shiftig may be fractionally slower. >>You should be able to use EITHER a 9-speed OR a 10-speed ring with an 8-speed drivetrain; and similarly, a 10-speed chainring with a 9-speed drivetrain. >>MY OBSERVATION is that the chain should match the front derailleur (or, vice-versa) when using a Shimano drivetrain for efficient shifting ... and, the chain MUST match the front derailleur with a Shimano triple. There ARE some exceptions ... >> >Another question I have is...what is the importance of the crank length? I've seen 170mm to 175mm. What's the difference? >Thanks again, >CK A longer crankarm gives the rider more leverage ... Depending on a person's riding style, it may not make any difference ... BUT, depending on a person's riding style, it may make a big difference. Some people are locked into 170mm ... a traditional length for road bikes. Tradition is dying slowly, but many road riders are now using longer cranks (e.g., 172.5 & 175). Typically, longer cranks are recommended for taller riders ... and, shorter cranks for shorter riders. 170mm is the recent ROAD norm, and 175mm is the current MTB norm. I've seen some formulations which must be based on an incredibly small sampling of a homogeneous ethnic/family group whose proportions are all the same ... I think that one of those formulas indicated that I should be using a crank shorter than 160mm (they don't exist as an off the shelf item) ... and, I would guess that a person would probably have to be about 6'0", or taller, to use a 170mm crank. I prefer 175mm cranks (if only for the psychological benefit); but, just put a 172.5 on one bike that I am building up. The particular crank was "cheap" -- it uses an ISIS BB, BTW! Now, I am pretty sure that some of these formulas for crank length AND other notions were derived after observing Eddy Merckx -- the rider & his bike -- and, possibly, some other professional racers. What worked for Merckx/whomever isn't necessarily what is viable for anyone else ... is THAT stating the obvious? Sheldon Brown, FWIW, suggests that the gearing will compensate for the leverage benefit that a longer crank arm would provide; but, he clearly does NOT ride in the mountains. I know when I am using the LOWER gears on my bike (we ride on mountain roads) that the additional leverage does mean something. Leonard Zinn miscalculates the leverage advantage (at least, the one time I read something he wrote on the topic), BUT he is a big advocate of using longer cranks if you are a taller rider (he is well over 6' tall and apparently uses a ~200mm crank). The crank length WILL have a small effect on your riding position if your bike is properly set up for you ...