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

Why does my chain shift when I roll the bike backwards?

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.

Why does my chain shift when I roll the bike backwards?

Old 10-02-13, 07:10 PM
  #1  
2 wheeler
Ancient Clydesdale
Thread Starter
 
2 wheeler's Avatar
 
Join Date: Aug 2005
Location: Columbia River Gorge
Posts: 683

Bikes: Specialized Allez Elite

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked 1 Time in 1 Post
Why does my chain shift when I roll the bike backwards?

Just like the title says, why does my chain shift when I roll the bike backwards?

The bike is a mid 80s Stumpjumper, so it's got a triple in front and IIRC 8 speed in the back. I can't see any misalignment in the derailleur hanger, but suspect that might be an issue.

Any ideas?
2 wheeler is offline  
Old 10-02-13, 07:37 PM
  #2  
urbanescapee
Junior Member
 
urbanescapee's Avatar
 
Join Date: May 2013
Location: Salt Lake City, UT, USA
Posts: 196

Bikes: 2011 Raleigh Sojourn, 2012 Marin Four Corners, 2013 Soma Saga, 2014 Scott Spark 940, 2017 Brompton H6E, 2016 Trek FX 7.2

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Likes: 0
Liked 1 Time in 1 Post
If you look at the top of the cassette where the chain rolls off and goes back to the chainrings on the crank, if the chain-line is not straight (i.e. you have the front in lowest gear and the rear in the highest gear), you'll see that the chain comes off the cassette at an angle...not parallel with the gears of the cassette. When pedaling forwards, the chain is guided onto the cassette from the bottom side. The rear derailleur ensures that the chain is lined up for engagement with the cassette, that's its job. But when the system is run backwards, the chain advances onto the cassette from the top side where there is no guidance to keep it in one particular gear...so it naturally tries to shift to the gear which offers the straightest chain-line to the front chainring. To illustrate this better, try rolling the bike backwards in the hi/lo combination mentioned above (be careful, you could potentially damage your drive train) and then use the middle/middle combination. with a well adjusted drive train, the middle/middle gear combination should not cause the chain to shift when rolled backwards. This doesn't mean that there's anything wrong with your drive train...it's just not designed to operate in reverse. That's why there's no "R" on the shifter indicator, lol. Hope this helps your understanding.
urbanescapee is offline  
Old 10-02-13, 08:45 PM
  #3  
2 wheeler
Ancient Clydesdale
Thread Starter
 
2 wheeler's Avatar
 
Join Date: Aug 2005
Location: Columbia River Gorge
Posts: 683

Bikes: Specialized Allez Elite

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked 1 Time in 1 Post
I'm not often guilty of overlooking the obvious, but in this case, I am.

I've been riding derailleur equipped bikes since 1969 and I'm astounded that I haven't figured this out. An old dog can learn new things (and tricks).

Thanks for the great reply!
2 wheeler is offline  
Old 10-02-13, 10:42 PM
  #4  
supremekizzle
Senior Member
 
Join Date: Mar 2013
Location: Rochester, MN.
Posts: 81

Bikes: 2012 Diamondback Trace Comp

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Happened to me the other day. I was cross chained pretty bad and I went to peddle in reverse around a corner to get my pedal in position. Low and behold, my jockey wheel retracted all the way and I had no movement in the peddles. Didn't know what it was at the time, but I'm going to guess it was this. Thanks for the great explanation.
supremekizzle is offline  
Old 10-03-13, 12:11 AM
  #5  
urbanescapee
Junior Member
 
urbanescapee's Avatar
 
Join Date: May 2013
Location: Salt Lake City, UT, USA
Posts: 196

Bikes: 2011 Raleigh Sojourn, 2012 Marin Four Corners, 2013 Soma Saga, 2014 Scott Spark 940, 2017 Brompton H6E, 2016 Trek FX 7.2

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Yes. So the derailleur wants to keep the chain on the gear selected by the shifter on your handlbars. But when you pedal backwards, the chain will follow the tendency I mentioned above and the derailleur won't move with it. This can cause a pretty bad jam, as you mentioned, supremekizzle. And that is the point at which the drive train could become damaged if enough force is applied. You're welcome.
urbanescapee is offline  
Old 10-03-13, 07:20 AM
  #6  
rydabent
Senior Member
 
rydabent's Avatar
 
Join Date: Apr 2010
Location: Lincoln Ne
Posts: 9,716

Bikes: RANS Stratus TerraTrike Tour II

Mentioned: 43 Post(s)
Tagged: 0 Thread(s)
Quoted: 3114 Post(s)
Liked 960 Times in 576 Posts
Actually rolling backwards or turning the crank backward should not make the chain switch gears. There are several things that might be wrong. Bent RD, bent RD hanger, bent chain stays, and a bad chain line. I have always used the check of spinning the cranks backward as a check that the RD is properly adjusted, and that there are not the other problems I have listed.
rydabent is offline  
Old 10-03-13, 07:35 AM
  #7  
cny-bikeman
Mechanic/Tourist
 
Join Date: Apr 2007
Location: Syracuse, NY
Posts: 7,510

Bikes: 2008 Novara Randonee - love it. Previous bikes:Motobecane Mirage, 1972 Moto Grand Jubilee (my fave), Jackson Rake 16, 1983 C'dale ST500.

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 482 Post(s)
Likes: 0
Liked 10 Times in 10 Posts
As Urban very thoroughly explained there are some combos where one can do what you describe and some where it will not work. It depends mostly on how cross-chained one is (outside rear to inside front primarily). Yes, if the derailleur is not lined up that will also cause problems, but it happens at the bottom of the freewheel, not the top in that case. The problem due to cross-chain tends to happen more when rolling backward vs. spinning the cranks because the chain is under tension in the former situation, so it more easily catches on the next larger cog. All it takes is simple observation to see the how/why of it.

Last edited by cny-bikeman; 10-03-13 at 11:13 AM.
cny-bikeman is offline  
Old 10-03-13, 09:55 AM
  #8  
cxwrench
Senior Member
 
cxwrench's Avatar
 
Join Date: Jul 2013
Location: Nor-Cal
Posts: 3,767

Bikes: lots

Mentioned: 7 Post(s)
Tagged: 0 Thread(s)
Quoted: 1954 Post(s)
Liked 2,925 Times in 1,488 Posts
Originally Posted by rydabent View Post
Actually rolling backwards or turning the crank backward should not make the chain switch gears. There are several things that might be wrong. Bent RD, bent RD hanger, bent chain stays, and a bad chain line. I have always used the check of spinning the cranks backward as a check that the RD is properly adjusted, and that there are not the other problems I have listed.
Can you explain how a bent RD or hanger will cause a backwards moving chain to shift gears? Since the chain goes directly from the chainring to the cog, I'm thinking you're gonna have a helluva time telling us how this happens.
cxwrench is offline  
Old 10-03-13, 10:32 AM
  #9  
Homebrew01
Super Moderator
 
Homebrew01's Avatar
 
Join Date: Jul 2004
Location: Ffld Cnty Connecticut
Posts: 21,761

Bikes: Old Steelies I made, Old Cannondales

Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 1139 Post(s)
Liked 738 Times in 495 Posts
Originally Posted by rydabent View Post
Actually rolling backwards or turning the crank backward should not make the chain switch gears. There are several things that might be wrong. Bent RD, bent RD hanger, bent chain stays, and a bad chain line. I have always used the check of spinning the cranks backward as a check that the RD is properly adjusted, and that there are not the other problems I have listed.
Read post #2
__________________
Bikes: Old steel race bikes, old Cannondale race bikes, less old Cannondale race bike, crappy old mtn bike.

FYI: https://www.bikeforums.net/forum-sugg...ad-please.html
Homebrew01 is offline  
Old 10-03-13, 11:15 AM
  #10  
fietsbob
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,599

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,343 Times in 850 Posts
..or just the RD pulley is not dead on in line with the cog above it .



Bene Sugg: lock the rear brake , pull your bike to stand on the rear wheel, turn the bike 180,

and set it back down, facing the other way..
fietsbob is offline  
Old 10-03-13, 02:39 PM
  #11  
bobotech
Senior Member
 
Join Date: Jan 2012
Location: Spokane, WA
Posts: 2,255

Bikes: Specialized Sequoia Elite/Motobecane Fantom Cross Team Ti/'85 Trek 520

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
That is one of the mysteries of tuning that is always a pain to figure out. I did recently notice that my Giant TCX with a triple kept shifting when I tried to pedal backwards.

My shop manager at the co-op checked my derailleur hanger alignment and sure enough, it was way off. He straightened it and I can back pedal all day long now without the chain shifting.
bobotech is offline  
Old 10-03-13, 06:53 PM
  #12  
itsmoot
in cog neato
 
itsmoot's Avatar
 
Join Date: Mar 2008
Location: Missouri
Posts: 357
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by rydabent View Post
Actually rolling backwards or turning the crank backward should not make the chain switch gears. There are several things that might be wrong. Bent RD, bent RD hanger, bent chain stays, and a bad chain line. I have always used the check of spinning the cranks backward as a check that the RD is properly adjusted, and that there are not the other problems I have listed.
If you're basing your opinion on recumbents, most have a great enough distance between crank and cogset that chain angle doesn't get acute enough to cause the problem.
itsmoot is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
124Spider
Bicycle Mechanics
9
09-03-19 03:14 PM
TBerk
Bicycle Mechanics
8
08-31-19 11:52 AM
bikecommuter13
Bicycle Mechanics
17
07-02-17 03:09 PM
ausey00
Bicycle Mechanics
15
02-09-13 09:58 AM
itsthewoo
General Cycling Discussion
9
10-29-10 05:54 AM

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 or Share My Personal Information -

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.