Friday, March 13, 2009

Shimano Chainrings are not Compatible with... Shimano

One of the things that drives me nuts about working on bikes, at least when I'm not getting some perverse enjoyment out of it, is that parts compatibility is a huge pain in the butt. Things don't fit with each other, pull the wrong amount of cable for each other, are threaded in odd ways, etc. etc.

My most recent project was to replace one of the chain rings on my mountain bike with one that isn't worn out.  I replaced the chain recently and stopped being able to shift from my middle chainring to my small one.  The way that bicycle drivetrains wear out means that if a chainring is worn out, it doesn't always effect shifting until a worn out chain is replaced.

So I need a new chain ring. I didn't do anything about the problem for a while except to use my heel to shift, which is not a very exact or reliable method, and then REI sent me a letter about how they're really cool and, by the way, I have an REI dividend of about $33. Sweet! I spent my dividend on a Shimano chainring with the same mounting pattern.  It's a Shimano crank, so I expected compatibility to be a complete non-issue.  When I tried to replace the ring, though, a five minute task turned into disaster.

As I was gently tightening the bolts holding the new chainring on, I heard a crunch. Uh-oh. I'd noticed that there was some gapping between the new chainring and the surface it sits on, but didn't think anything of it initially - there are a number of places on a bike where parts can't just be shoved into place, but have to be tightened down. Anyway, after the crunch, the gap was gone but instead of being circular, the chainring was shaped kind of like a wave or a flower or something. That happened just before nine o'clock last night, which is too late, even in New York, to buy hardware or bike parts.

So today I wandered down to REI with the violated crank in my backpack, to ask for some advice and see if I could talk them out of a part. The bike repair guy said he'd never seen anything like that, and yeah, Shimano has a ton of internal incompatibilities. He messed with it for a while, then mounted an FSA chainring in that position instead. I had my original receipt with me, so he did an exchange and didn't even charge me the difference - the FSA ring is slightly more expensive.  I kind of enjoy it that the three rings on my crankset are in three different visual styles.


I don't know what it is about me and funky drivetrains with parts from different eras, but somehow my bikes tend to end up with them.


Anyway, the true test is going to be seeing if I can shift from the fancy new middle ring into my skanky old small ring while I'm climbing a hill.  If I can, my bike is as functional as I need it to be to enjoy riding it and to go racing.  If not...  I'm kind of stuck until I can replace the whole crankset, I think.

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