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

Rear Derailleur Issue

Notices
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 Issue

Old 08-08-21, 11:53 AM
  #1  
paulcurtis
Junior Member
Thread Starter
 
Join Date: Aug 2021
Posts: 6
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Rear Derailleur Issue

Hi,

I wonder if someone can suggest what my issue is. I have eight gears on the rear sprocket. When I turn the pedals by hand, gears one to seven feel fine, very smooth. Gear 8, the smallest in the cassette, feels ... it's hard to describe. Lumpy is the best word I can think of. Like something is not aligned or engaged.

The 48T crank is new, the chain is new. The jockey wheel appears to be right over gear 8. Gear 8 looks to be in good condition. The chain appears to have tension.

Any suggestions on what I should check please? Thanks.
paulcurtis is offline  
Likes For paulcurtis:
Old 08-08-21, 12:11 PM
  #2  
andrewclaus
Senior Member
 
Join Date: Feb 2012
Location: Golden, CO and Tucson, AZ
Posts: 2,549

Bikes: 2016 Fuji Tread, 1983 Trek 520

Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 576 Post(s)
Liked 435 Times in 297 Posts
If you ride in that gear a lot, you've worn it out and need a new cog or cassette. This is very common with a new chain. If will commonly skip under load. The good news is the smallest cog is also the lock ring for the cassette and they're pretty easy to find salvaged at a bike co-op. But you may want to check the rest of the gears too, under load.

Is this an ebike by any chance?
andrewclaus is offline  
Old 08-08-21, 12:32 PM
  #3  
paulcurtis
Junior Member
Thread Starter
 
Join Date: Aug 2021
Posts: 6
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Hi Andrew, thanks for the quick reply.

The answer is yes, it is a standard bike that I just converted with a Bafang mid-mount. However, I have only done literally a couple of miles since the conversion, and I noticed this before I even rode it the first time. The odd thing is, that whilst the bike is a few years old, I hardly ever used Gear 8 conventionally.

So are you suggesting that there is something about the new Bafang crank that is causing the issue? As I say, the other gears are fine.
paulcurtis is offline  
Old 08-08-21, 12:53 PM
  #4  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 16,582

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Srewart 650B ATB

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3570 Post(s)
Liked 2,427 Times in 1,542 Posts
"the smallest cog is also the lock ring for the cassette" andrewclaus

Sure, if the cassette is a twist tooth UG type. But if that's the case good luck finding one as they've been out of production for years.

Sure the small cog can and might well be worn out. It doesn't take much wear on such a small cog to get skip with a new chain. But also make sure the lock ring is the correct size. If a 12+ tooth lock ring was used it could be preventing the chain from fully settling down into the small cog's teeth.

BTW an E motor that uses the chain for it's power assist means that the chain is seeing vastly more force going through it then when a human only is powering the bike. Both the chain and the teeth will wear faster then a non E bike's will. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 08-08-21, 12:57 PM
  #5  
shelbyfv
Expired Member
 
shelbyfv's Avatar
 
Join Date: Jun 2007
Location: TN
Posts: 10,099
Mentioned: 32 Post(s)
Tagged: 0 Thread(s)
Quoted: 2996 Post(s)
Liked 3,853 Times in 1,978 Posts
For an ebike, I wouldn't spend much time worrying with this. Since it doesn't much matter what gear you are in, just use a different one. That said, the smaller cogs can be noisier because the chain has to take a tighter path.
shelbyfv is offline  
Old 08-08-21, 01:04 PM
  #6  
paulcurtis
Junior Member
Thread Starter
 
Join Date: Aug 2021
Posts: 6
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Thanks Andrew R Stewart and shelbyv. Actually, replacement cassettes don't appear to be horrendously expensive. But as shelby suggests, I simply will avoid gear 8, and use one of the lower gears. For all I know, that will give better range anyway, plus, it will put less strain on the drive chain anyway.

It just BUGS me that gear 8 is not smooth. But unless it needs some adjustment I am unaware of, I will probably just work around it.
paulcurtis is offline  
Old 08-08-21, 01:32 PM
  #7  
alcjphil
Senior Member
 
alcjphil's Avatar
 
Join Date: Jun 2002
Location: Montreal, Quebec
Posts: 5,155
Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1455 Post(s)
Liked 1,101 Times in 662 Posts
The thing is that the smaller the cog, the less round it is. Cogs smaller than 13 teeth force the chain into a very tight turning path and don't engage the teeth of the cog as smoothly. Also, as noted earlier in this thread, small cogs wear much faster, 11 tooth cogs have fewer teeth engaging the chain than a 13 tooth small gog. This wears the chain faster as well. All this wear is further accelerated by a mid drive motor assist
The issue has nothing to do with the derailleur

Last edited by alcjphil; 08-08-21 at 01:41 PM.
alcjphil is offline  
Likes For alcjphil:
Old 08-08-21, 02:13 PM
  #8  
dsbrantjr
Senior Member
 
dsbrantjr's Avatar
 
Join Date: Sep 2010
Location: Roswell, GA
Posts: 8,280

Bikes: '93 Trek 750, '92 Schwinn Crisscross, '93 Mongoose Alta

Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 1420 Post(s)
Liked 1,038 Times in 695 Posts
Chordal Action: 2.2.1 Chordal Action
dsbrantjr is offline  
Likes For dsbrantjr:
Old 08-08-21, 02:18 PM
  #9  
elcraft
elcraft
 
Join Date: Sep 2008
Location: Greater Boston
Posts: 797
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 137 Post(s)
Liked 89 Times in 64 Posts
Sometimes there is a stiff link on the chain that causes problems on the smaller cogs. The chain works fine until it must go around the smaller radius of the smallest cog. If the chain was subjected to a splash of water on one particular section, the links can develop a spot where this partial stiffness can occur. Watch the chain as it travels through the derailleur pulleys and it might be more noticeable.
elcraft is offline  
Old 08-08-21, 02:39 PM
  #10  
paulcurtis
Junior Member
Thread Starter
 
Join Date: Aug 2021
Posts: 6
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by alcjphil View Post
The thing is that the smaller the cog, the less round it is. Cogs smaller than 13 teeth force the chain into a very tight turning path and don't engage the teeth of the cog as smoothly. Also, as noted earlier in this thread, small cogs wear much faster, 11 tooth cogs have fewer teeth engaging the chain than a 13 tooth small gog. This wears the chain faster as well. All this wear is further accelerated by a mid drive motor assist
The issue has nothing to do with the derailleur
That makes sense, thanks.
paulcurtis is offline  
Old 08-08-21, 02:41 PM
  #11  
paulcurtis
Junior Member
Thread Starter
 
Join Date: Aug 2021
Posts: 6
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by dsbrantjr View Post
Chordal Action
Thanks, but that doesn't link to a valid site.
paulcurtis is offline  
Old 08-09-21, 07:26 AM
  #12  
SJX426 
Senior Member
 
SJX426's Avatar
 
Join Date: May 2008
Location: Fredericksburg, Va
Posts: 8,706

Bikes: '73 Bottecchia Giro d'Italia, '83 Colnago Superissimo, '84 Trek 610, '84 Trek 760, '88 Pinarello Veneto, '88 De Rosa Pro, '89 Pinarello Montello, '94 Burley Duet, 97 Specialized RockHopper, 2010 Langster, Tern Link D8

Mentioned: 63 Post(s)
Tagged: 0 Thread(s)
Quoted: 1289 Post(s)
Liked 1,326 Times in 728 Posts
@paulcurtis - watch the lower jockey wheel. I had an issue with mine. I resolved it by twisting the cage ever so slightly. the issue was that the chain was derailing.
__________________
Bikes don't stand alone. They are two tired.
SJX426 is offline  
Old 08-09-21, 10:37 AM
  #13  
Litespud
Senior Member
 
Join Date: Oct 2017
Location: Chapel Hill NC
Posts: 1,683

Bikes: 2000 Litespeed Vortex Chorus 10, 1995 DeBernardi Cromor S/S

Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 644 Post(s)
Liked 790 Times in 443 Posts
Originally Posted by dsbrantjr View Post
Chordal Action: 2.2.1 Chordal Action
that’s great - I was trying to explain to someone a while back why the chain on the smallest sprocket “thrums” a bit, even when everything is set up correctly. I knew there was a specific term for this phenomenon, but I couldn’t remember it. Thanks!
Litespud is offline  
Old 08-10-21, 03:07 AM
  #14  
paulcurtis
Junior Member
Thread Starter
 
Join Date: Aug 2021
Posts: 6
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Thanks for all the replies, I think I have the measure of this now. ('Thrums' - yes, that's it exactly)
paulcurtis 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 - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.