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chain rub..

Old 01-26-13, 11:57 PM
  #1  
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chain rub..

recently, i took on the advice of fellow BF members and changed my crank to 50/34 with my 11/34 combo. my knees loves you guys!! especially on climbs too!!

well, i noticed something weird and i think i may have the answer, but not 100% sure.

before i had 53/39 and my RD is a long cage. when i swapped it over to ultegra compact 50/34, i didn't resize the chain. when my bike is on the service stand, i can shift through all the rear cogs and no rubbing noise would be heard. but after 50 miles of riding, i started to hear some chain rub noise, specifically on 34/11, 13, 15t.

when it's 34/11, the RD cage is up, but not so high to the point it will hit the rear cassette.

i'm currently running the chain with a masterlink to connect to it.

so here are my questions.. in my setup, what would be the proper way to size the chain? i've seen some where you loop to the largest in front and largest in the back and add 1 extra link.

but on youtube, i've seen some where they loop the chain all the way through into the RD cage and shift to the largest in front and smallest in rear.

finally, i'm using a deore chain with my setup, is that chain directional? i've seen some ppl said some chains needs to face a certain direction.

sorry for the long post.. and thank for your help!
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Old 01-27-13, 12:28 AM
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your chain is probably hitting the back of the big ring when you're on the smaller rear cogs.

simple answer is, just don't USE those gears. you NEVER should use 34-11, use 50-16 instead (or whatever you have close to that)

with a 50-34 and 34-11, I'd use the 50T until I was in #2 in back THEN drop onto the small ring and use the lower 3-4 only.

also, is this a 10 speed rear with a 10 speed chain? those compact doubles are setup for 10-sp systems. if you're running a 8 or 9 speed rear, you can add a 0.5-1.0 mm spacers between the little ring and the spider to increase the spacing.
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Old 01-27-13, 12:47 AM
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I would get the chain length correct.

http://www.parktool.com/blog/repair-...-length-sizing

Then it still may rub in the little-little combination. Personally I'd ignore it and just ride.
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Old 01-27-13, 03:32 AM
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ah... my 11/34 is for a 9 speed... so could that be an issue as well? but i think also it's chain sizing issue as well. i'll check it out tomorrow. thanks~
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Old 01-27-13, 04:21 AM
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yeah, 9 speed uses a wider chain than 10 speed that the 50/34 stuff is intended for, albeit not as wide as the 7-8 speed stuff. I'd suggest mostly just only using the front 34 with the rear 1-2-3-4-5 gears and not 6-7-8-9

by the time you get to 5th, you can shift to the big ring and step back up to like 2nd or 3rd in back and be just fine. When I ran a 50-34 crank with a 8 speed rear, I stayed in the 50T and treated it like a 8 speed, and only used the 34 front as a granny gear. I still added those 0.5mm spacers to the 34. I also intentionally used a slightly too short BB so my 50T was in the middle of the chainline just like it was a 8-speed, which is kind of cheating, but it worked pretty nicely with that bike (a hjybrid made from recycled mixed up parts).
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Old 01-27-13, 09:08 AM
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Originally Posted by ruirui View Post
ah... my 11/34 is for a 9 speed... so could that be an issue as well? but i think also it's chain sizing issue as well. i'll check it out tomorrow. thanks~
Spacing out the chainwheels will help, sizing the chain will not.

You should not ride the 34/11, period. The 11 tooth cog wears very quickly so should be used as little as possible, and there is quite a bit of chain deflection in that combo as well. As already suggested use a combo with the large chainring that is close in gear ratio (front teeth/rear teeth) to the 11/34. Doing so will wear both the cogs and the chain at a lower rate and produce less noise.

There's no logical reason for the chain length to affect rubbing on the chainwheel, which is affected only by the angle between chain and chainwheel. The only functional reason a chain needs to be shorter is to keep the pulleys under tension and in better position for shifting performance.
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Old 01-27-13, 09:19 AM
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Originally Posted by cny-bikeman View Post
There's no logical reason for the chain length to affect rubbing on the chainwheel, which is affected only by the angle between chain and chainwheel. The only functional reason a chain needs to be shorter is to keep the pulleys nder tension and in better position
If the chain was originally sized to allow a 53/34 big-big combination it could indeed go completely slack in a 34/11 or 34/12 combination.
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Old 01-27-13, 01:30 PM
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Chain rub on the outer ring when headed to the inner from the outer cassette is a matter of chain line, chainring size, chainring separation and and chainstay length. It's simple geometry, the chain is coming from outside the outer chainring, and has to pass it on the way to the inner. If the angle is too great, the rings too close together, and if it meets the outer too far from the inner, it'll rub.

This was never a problem when freewheels were narrower, and chainring separation greater, but is very common on modern bicycles. You can improve it by moving the chainrings outboard a bit, but often not without going to extremes.

Sometimes there may be rub on the lower loop even when there isn't on the upper. This can be because the RD isn't quite vertical and the lower pulley is outboard of the sprockets.

Rub on 3 sprockets is above average, so consider moving the chainline out a bit if possible, otherwise accept is as an idiosyncracy of your bike and live with it.
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Old 01-27-13, 01:37 PM
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Electronic Di2 is said to self correct with chain rub detectors .. never seen one in person.


Currently Shimano rubs in the cross chain situations, that, a rider paying attention to what they are doing, will avoid.
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Old 01-28-13, 12:57 PM
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Originally Posted by HillRider View Post
If the chain was originally sized to allow a 53/34 big-big combination it could indeed go completely slack in a 34/11 or 34/12 combination.
Ooh, you could be onto something, Could be the slack chain rubbing on the heel of the front derailleur cage.

What say you, OP. is the chain rubbing on the side of the cage, the bottom of the cage, the inside of the big chain ring, or itself as it passes through the rear pulleys? We are slowly arriving at the need for accurate details in order to correctly diagnose problems and offer cures.
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Old 01-28-13, 01:05 PM
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Instead of us guessing, maybe the OP could take a look at his bike in the problem combinations and tell us where it's rubbing.

top of chainrings
bottom of chainrings
RD idler cage (top or bottom)
FD cage, either side
or someplace else.

Some rubs are easily curably, others less so, and some not curable without causing other issues. But either way, knowing the exact problem is the only way to find a solution.
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Old 01-28-13, 01:12 PM
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Originally Posted by pierce View Post
your chain is probably hitting the back of the big ring when you're on the smaller rear cogs.

simple answer is, just don't USE those gears. you NEVER should use 34-11, use 50-16 instead (or whatever you have close to that)
I like this answer the best. If the crankset is inboard enough that the chain rubs on the bigger ring when in the 34/15 combo, that means you should get good chainlines in the 50/23, 50/20, and 50/17 combos, and you'll have longer-lasting sprockets as a result.
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Old 01-28-13, 01:24 PM
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Check to see if there is any slack in the chain when it is on the smallest chainring (34) and smallest cassette cog (11). The rear derailleur should not "bottom out", that is it should not be at its maximum rearward position. The derailleur's spring should always have some tension on the chain.
As others have already pointed out, you should not be riding in the small to small combination (cross-chaining).
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Old 01-28-13, 01:36 PM
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in general, larger chain wheels/cogs give you less resistance and longer gear+chain wear. instead of 34/16, use 50/24, its the same ratio
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Old 01-28-13, 02:50 PM
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Originally Posted by HillRider View Post
If the chain was originally sized to allow a 53/34 big-big combination it could indeed go completely slack in a 34/11 or 34/12 combination.
Yes, but my comment still applies. A long chain would not cause rubbing on either the chainwheel or front derailleur cage (unless you count slapping against the outboard chainwheel from swinging back and forth). The only noise in such a case tends to be a rattling sound from pulleys. Again, we need the OP's observations regarding where/how the rubbing is occurring.
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Old 01-28-13, 05:40 PM
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Originally Posted by fietsbob View Post
Electronic Di2 is said to self correct with chain rub detectors .. never seen one in person.
Apparently not. DI2 corrects for front derailleur cage rubbing. It can't do anything about the chain rubbing on the inside of the large chainring when in the small chainring and cross chained.
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