Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

Rear Derailleur doesn't shift well with 50/34t compact crankset.

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

Rear Derailleur doesn't shift well with 50/34t compact crankset.

Old 07-30-18, 05:12 AM
  #1  
zmalwo
Junior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Rear Derailleur doesn't shift well with 50/34t compact crankset.

Hi all, thanks for reading my post first of all. This is my first post ever on bike forums. So i'm using a 2014 Campagnolo Athena groupset with Chorus shifters for ultrashift capability., running 11 - 25t on the rear and 50/34t on the front. Derailleur cage is short. chain is correctly sized. Rear derailleur shifting is very bad around 3/4th and 7/8th rear cog area. won't go up and won't go down sometimes, shifts to 1st and 11th cog up and down with no problem at all. Problem only occurs while on 50t chainring and both cassette and chain are brand new. However when i switch to 52/39t crankset shifting resume normal. Ofc i switch to a longer chain too. What could be the problem? I tried to eliminate every problem I can but still can't figure out why rear derailleur shifting is so crappy with compact crankset. Is it a common problem?

Last edited by zmalwo; 07-30-18 at 12:02 PM.
zmalwo is offline  
Old 07-30-18, 06:42 AM
  #2  
gazza1286
Newbie
 
Join Date: Jun 2018
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Sounds like a possible meshing issue with the shorter chain. Is there any evidence of wear on the chain?

There's no reason why larger chainrings would have any impact on the operation of the rear derailleur. Does the behaviour occur in both the 50/34 rings?

Is it a new cassette? It could be on the cusp of moving to excess wear on a couple of cogs.
gazza1286 is offline  
Old 07-30-18, 08:49 AM
  #3  
wgscott
Occam's Rotor
 
wgscott's Avatar
 
Join Date: Jul 2013
Location: The Timbers of Fennario (CL77)
Posts: 4,778

Bikes: Steel

Mentioned: 61 Post(s)
Tagged: 0 Thread(s)
Quoted: 2366 Post(s)
Liked 151 Times in 89 Posts
Is the derailleur hanger straight?
wgscott is offline  
Old 07-30-18, 12:01 PM
  #4  
zmalwo
Junior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
No both the chain and the cassette are braind new. problem only occurs while on 50t, shifts good while on 34t.
zmalwo is offline  
Old 07-30-18, 12:02 PM
  #5  
zmalwo
Junior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
yeah I used a derailleur alignment tool from park tool and it was straight, only have shifting problem while on big chainring.
zmalwo is offline  
Old 07-30-18, 12:02 PM
  #6  
Colnago Mixte
Senior Member
 
Join Date: Sep 2017
Location: Center of Central CA
Posts: 1,685
Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 897 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
One stiff chain link, possibly?
Colnago Mixte is offline  
Old 07-30-18, 12:03 PM
  #7  
zmalwo
Junior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I just checked the chain and it was smooth on all links.
zmalwo is offline  
Old 07-30-18, 12:45 PM
  #8  
Aubergine 
Bad example
 
Join Date: Nov 2015
Location: Seattle and Reims
Posts: 2,948
Mentioned: 33 Post(s)
Tagged: 0 Thread(s)
Quoted: 771 Post(s)
Liked 16 Times in 13 Posts
Have you been able to put the bike in a stand and pedal it manually? I would want to watch what was happening before I could even begin to offer a suggestion.
__________________
Keeping Seattle’s bike shops in business since 1978
Aubergine is offline  
Old 07-31-18, 12:40 PM
  #9  
zmalwo
Junior Member
Thread Starter
 
Join Date: Jul 2018
Posts: 21
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
it seems like shifting got a little better after I bent the rear derailleur hanger out of alignment, is it possible a perfectly aligned hanger can cause shifting problem?
zmalwo is offline  
Old 07-31-18, 03:57 PM
  #10  
speedevil 
I never finish anyth
 
speedevil's Avatar
 
Join Date: Jul 2010
Location: Western KY
Posts: 971

Bikes: 2008 Merckx LXM, 2003 Giant XTC mtb, 2001 Lemond Alpe d'Huez, 1997 Lemond Zurich, 1989 Cannondale ST, 198? Masi Nuovo Strada, 1984 Pinarello Turismo

Mentioned: 40 Post(s)
Tagged: 0 Thread(s)
Quoted: 230 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by zmalwo View Post
it seems like shifting got a little better after I bent the rear derailleur hanger out of alignment, is it possible a perfectly aligned hanger can cause shifting problem?
I wouldn't think so - RDs are pretty much designed so that they work best when the cage is parallel to the wheel. I guess it's possible, but that would seem to be an outlier.

Having said that, adjusting the B screw to set the proper distance between the top guide wheel and the cassette cogs will definitely change shifting performance.
__________________
Dale, NL4T
speedevil is offline  
Old 07-31-18, 04:56 PM
  #11  
rm -rf
don't try this at home.
 
rm -rf's Avatar
 
Join Date: Jan 2006
Location: N. KY
Posts: 5,048
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 611 Post(s)
Likes: 0
Liked 3 Times in 2 Posts
My Athena triple doesn't shift well at all on older cables. The cable drag must be critical. But that doesn't really explain your all-new system.

More info needed:
The difference in diameter of a 52 chainring to a 50 chainring is about 8mm. So the extra chain length wrapped around half the circle is only about 12mm, or about one extra chain link.
How much longer is your 52's chain?
Have you tried that on the 50 chainring?

Did you just swap chainrings, or use a different crankset?
rm -rf is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.