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a thorn in RBR's side
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116 Posts
Discussion Starter · #1 ·
... it may seem like a stupid question, but it seems that every year for the last decade I discover something on the bike that I wonder "why the hell is it there" about.

So today's question is, as it says in the subject line, whats the point of the rear deraillure pulley cage's tabs - you know, the little ears of the inside plate that are bent in, making it nearly impossible to thread your chain through. I think I may know, but figure I bring up this important topic.

I sort of know what the point of one is - the lower one by the bottom pulley - helps not make your thumb dirty when you put your wheel in in a hurry before a race. Sure.

But the other tab on the other side, that one that is by the upper pully close to the cogs. I don't know. It seems like a real waste of material (considering the huge weight savings that have been made in the bikes these days (sarcasm)). The way I see it, the only point to have it is if your chain is awfully long and in the small/small combo the chain is folded so close together as to rub by the upper pully. I guess the tab is there to prevent that???

If I were building a really light bike, I'd probably cut the upper pully cage tab off. Or maybe I forgot the reason why it is there? HELP.

please share your wonderful knowledge of bike engineering with the dog.

thanks,

woof.

P.S. if this is too technical for you, well maybe it is.
 

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Registered
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They are there for a reason. They ensure that the chain is properly seated on the pulley. You will get chain slap no matter what. The tabs will force the chain to sit on the pulley when chain is slapping. Without the tabs chain can jump off the pulley and sit on the side plate instead and you are unable to rotate the pedals because of that.
 

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Larry Lackapants
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698 Posts
Besides, dirty hands help identifying those who do their own bike wrenching :) Also they tell who hasn't been cleaning their chain lately :)
 

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a thorn in RBR's side
Joined
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116 Posts
Discussion Starter · #4 ·
re

thanx!

I once made the chain too short and in the big big combon, the chain came off pulley and I couldn't pedal. What an amateur mistake. Different sort of thing, but I guess if the chain slaps around, the tabs should help.
 
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