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

Front derailleur middle crank position

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.

Front derailleur middle crank position

Old 04-23-19, 06:13 PM
  #1  
El Gato27
Senior Member
Thread Starter
 
Join Date: Dec 2014
Location: Texas
Posts: 213

Bikes: '88 Peugot 12 spd road bike, Nishiki hybrid, JC Penney 10 spd

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 45 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Front derailleur middle crank position

What affects the positioning of the front derailleur when in the middle crank?
When the derailleur is in the middle crank I experience chain rub and would like to shift the position of the derailleur.
Do I do this with cable tension or with the limit screws?
I'm am under the believe that the limit screws are to position the derailleur to prevent chain drop.
Thank you.
El Gato27 is offline  
Old 04-23-19, 07:14 PM
  #2  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,441

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1672 Post(s)
Likes: 0
Liked 5 Times in 5 Posts
Limit screws only effect the ends of the cage's travel. Typically when the chain is on the middle ring it's also between the two limits so the screws usually don't deal with that middle ground.

Ft der positioning has a few dimensions/axis of note. Height as in how close to the large ring's teeth tops is the cages outer plate. Rotation as in how the cage's plates or their centerline is relating to the ring's plane. Generally the cage centerline is fairly parallel to the rings planes. Limits of cage travel in and out is next. How much travel per cable movement (actuation ratio) is critical to indexing working as intended. And of course compatibility among the various parts is needed for indexing to work well.

But since we don't know which parts are at play in this thread we can't offer more specific help, and know we are on the right path. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 04-23-19, 07:44 PM
  #3  
JohnDThompson 
Old fart
 
JohnDThompson's Avatar
 
Join Date: Nov 2004
Location: Appleton WI
Posts: 20,222

Bikes: Several, mostly not name brands.

Mentioned: 103 Post(s)
Tagged: 0 Thread(s)
Quoted: 1614 Post(s)
Liked 9 Times in 8 Posts
Originally Posted by El Gato27 View Post
What affects the positioning of the front derailleur when in the middle crank?
When the derailleur is in the middle crank I experience chain rub and would like to shift the position of the derailleur.
Do I do this with cable tension or with the limit screws?
I'm am under the believe that the limit screws are to position the derailleur to prevent chain drop.
Thank you.
I assume that "middle crank" refers to the middle chainring on a triple crank?

Traditionally, chain rub with the front derailleur is dealt with by moving the shift lever slightly until the rubbing stops. But this assumes a friction-shifting set-up. If you have indexed front shifting, eliminating rub can be a problem. Sometimes cable tension can be tweaked to fix it, or changing the angle of the derailleur or height of the derailleur over the rings slightly. But sometimes you just have to put up with it.
JohnDThompson is offline  
Old 04-23-19, 09:04 PM
  #4  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,441

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1672 Post(s)
Likes: 0
Liked 5 Times in 5 Posts
Originally Posted by JohnDThompson View Post
I assume that "middle crank" refers to the middle chainring on a triple crank?

Traditionally, chain rub with the front derailleur is dealt with by moving the shift lever slightly until the rubbing stops. But this assumes a friction-shifting set-up. If you have indexed front shifting, eliminating rub can be a problem. Sometimes cable tension can be tweaked to fix it, or changing the angle of the derailleur or height of the derailleur over the rings slightly. But sometimes you just have to put up with it.
This! Shimano once had a small printed doc to be included with a new bike's manual. Well they have a lot of these but this one was about chain rub. It has a pictorial description of a triple crankset with the cog/ring combos that were "acceptable" if they had chain rub. It was as though god (small g intended) had spoken and decades of expectations were moot. One part of me was happy that Shimano had finally acknowledged some chain rub, given indexing's inability to really fine tune cage position at all price levels. The other was saying that now Shimano had little reason to do more to allow for fine trimming.

I have mentioned this small printed "instruction" over the years and few remember it. Tossing out the fine print is so easy... Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 04-24-19, 09:29 AM
  #5  
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 40,848

Bikes: 8

Mentioned: 182 Post(s)
Tagged: 0 Thread(s)
Quoted: 6533 Post(s)
Likes: 0
Liked 50 Times in 46 Posts
Shimano's index front shifting re designed the.. cage shape, so it will stay out of the way , on the middle chainring

until you go to the chain angles to the rear on the extreme ends of the cog stack 1 st & last..

on a triple the gear ratios overlap there..

so rather than cross chain middle to biggest rear cog ,

go to granny & a middle cog * , then down shift on the rear from there..

* being about the same gear ratio ..

Likewise on the front , middle cog & big chainring,

rather than middle chainring and small cog & chain dragging on the FD cage..










...

Last edited by fietsbob; 04-24-19 at 09:33 AM.
fietsbob is offline  
Old 04-24-19, 10:58 AM
  #6  
hokiefyd
Senior Member
 
Join Date: Feb 2017
Location: Northern Shenandoah Valley
Posts: 2,077

Bikes: 2018 Redline Zander, 2018 Giant Roam 2, 2015 Trek Verve 3, 1997 Trek 750, 1969 Peugeot PO-18

Mentioned: 24 Post(s)
Tagged: 0 Thread(s)
Quoted: 704 Post(s)
Liked 13 Times in 13 Posts
I have a few modern bikes with modern front derailleurs (both with triples in the front), and the cages are designed so that there is pretty much no chain drag in any combination. On both bikes, I can use any of the nine sprockets in the rear in the middle ring in front without drag. I think one of the bikes will drag very slightly in the small/small combination. But really, modern cages have made front index shifting very nice.

To the OP, I would start at the basics. Search YouTube for Park Tool's front derailleur adjustment video. They show you how to go from the very beginning -- unclamp the cable, get your limit screws set, and then clamp the cable and get cable tension set. It could be that your cable is too slack when the derailleur is in the small ring. If this is the case, then it may not be moving the derailleur far enough to the right in the middle ring for the chain to clear the cage in all combinations. It can be difficult to tune, so it's often best to start at the beginning and reset the whole system (following Park Tool's nice instructional video).
hokiefyd is offline  
Old 04-24-19, 11:16 AM
  #7  
El Gato27
Senior Member
Thread Starter
 
Join Date: Dec 2014
Location: Texas
Posts: 213

Bikes: '88 Peugot 12 spd road bike, Nishiki hybrid, JC Penney 10 spd

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 45 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Thank you all for the input, I have gone through the Park tutorial. I'll just live with it.
I normally prefer to leave the derailleur in the middle front chainring and just shift across the rear, but sometimes I'll get chain rub on hills.
I know I can shift to the smaller chainring but involves a small amount of mental anguish (JOKE).
El Gato27 is offline  
Old 04-24-19, 01:24 PM
  #8  
hokiefyd
Senior Member
 
Join Date: Feb 2017
Location: Northern Shenandoah Valley
Posts: 2,077

Bikes: 2018 Redline Zander, 2018 Giant Roam 2, 2015 Trek Verve 3, 1997 Trek 750, 1969 Peugeot PO-18

Mentioned: 24 Post(s)
Tagged: 0 Thread(s)
Quoted: 704 Post(s)
Liked 13 Times in 13 Posts
Originally Posted by El Gato27 View Post
I normally prefer to leave the derailleur in the middle front chainring and just shift across the rear, but sometimes I'll get chain rub on hills.
I take this to mean you have chain drag on the inner cage plate, when the chain is in the middle ring in the front and the largest one or two sprockets in the back? If this is true, then it could mean that the derailleur is slightly farther to the right than it might ideally be. You could turn the barrel adjuster on the shifter in (tightening it) a full turn or so, then re-check. In a perfect world, this would slacken the cable just enough to let the derailleur fall just slightly left, while still providing good shifting performance. If you go too far left, you'll get strong downshifts but upshifts might be less crisp. There may be a nice balance where you like the shifting and get no drag.

Of course, you certainly can leave it alone if it's slight or not bothersome to you. But this is BikeForums, where it's law to strive for perfection, right? :-)
hokiefyd is offline  
Old 04-24-19, 04:59 PM
  #9  
mitchmellow62
Senior Member
 
Join Date: Aug 2014
Posts: 80
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
Likes: 0
Liked 1 Time in 1 Post
At least some of the shimano brifters have a "half step" adjustment for front derailleur cage position to eliminate chain rub on the side plates when over the middle ring of a triple. My experience is with early 2000's 9 speed/triple Tiagra and Dura Ace. In both cases the derailleur could be pulled to a partial "half step", eliminating the rub.
mitchmellow62 is offline  
Old 04-24-19, 08:27 PM
  #10  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,441

Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Raleigh Pro, Trek Cycle Cross, Mongoose tomac ATB, GT Bravado ATB, JCP Folder

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1672 Post(s)
Likes: 0
Liked 5 Times in 5 Posts
Originally Posted by mitchmellow62 View Post
At least some of the shimano brifters have a "half step" adjustment for front derailleur cage position to eliminate chain rub on the side plates when over the middle ring of a triple. My experience is with early 2000's 9 speed/triple Tiagra and Dura Ace. In both cases the derailleur could be pulled to a partial "half step", eliminating the rub.
But we still don't know what kind of der, shifter or even bike the OP is referencing. So the Op might have friction shifters for all we know. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 04-24-19, 09:32 PM
  #11  
mitchmellow62
Senior Member
 
Join Date: Aug 2014
Posts: 80
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 21 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Originally Posted by Andrew R Stewart View Post
But we still don't know what kind of der, shifter or even bike the OP is referencing. So the Op might have friction shifters for all we know. Andy
I didn't mean to imply that the OP has brifters. The OP seems inexperienced. I can remember being very inexperienced. I didn't realize the left Tiagra shifter had the ability to trim the front derailleur until I had owned the bike for some time. I was only attempting to point out that some shifters have a feature to "trim" the front derailleur and my experience happens to have been with two 9 speed brifters. Wouldn't it be terrible for the OP to play with cable length if his shifters have that? Friction? Do you really think the OP would be asking how to change the position of the front derailleur while over the middle chain ring if he has a friction shifter? It also seems a little presumptuous to tell him to live with it without knowing more.
mitchmellow62 is offline  
Old 04-25-19, 12:09 AM
  #12  
Cycle Tourist
Senior Member
 
Join Date: Jan 2017
Posts: 139
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 30 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
I usually try to set the middle chain ring with the adjuster nut so it doesn't rub over the whole motion through all the back gears. Provided you've set the hight and angle of the FD correctly that should be doable. Then set the stops for the big and small chain rings so they quickly shift but no further than necessary to get a clean shift.

If that doesn't work I've got a nice friction shifter for your triple that I'll sell you.😁
Cycle Tourist is offline  
Old 04-25-19, 05:56 PM
  #13  
El Gato27
Senior Member
Thread Starter
 
Join Date: Dec 2014
Location: Texas
Posts: 213

Bikes: '88 Peugot 12 spd road bike, Nishiki hybrid, JC Penney 10 spd

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 45 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
The bike is a 2008 Fuji Absolute 3.0 with Alivio index trigger shifters and derailleurs.No trim, only one of my bikes has the trim feature. I understand the concept of chain rub and dropping to the small chainring to avoid chain rub as that would have improved parallelism. I have experienced this on other bikes as well.

I'm willing to accept chain rub from the small and large chainrings on the extreme opposite cogs. I just think a derailleur should be able to shift to all the cogs without chain rub from the middle chainring.

Maybe that is optimistic thinking.
El Gato27 is offline  
Old 04-25-19, 06:06 PM
  #14  
hokiefyd
Senior Member
 
Join Date: Feb 2017
Location: Northern Shenandoah Valley
Posts: 2,077

Bikes: 2018 Redline Zander, 2018 Giant Roam 2, 2015 Trek Verve 3, 1997 Trek 750, 1969 Peugeot PO-18

Mentioned: 24 Post(s)
Tagged: 0 Thread(s)
Quoted: 704 Post(s)
Liked 13 Times in 13 Posts
Originally Posted by El Gato27 View Post
I just think a derailleur should be able to shift to all the cogs without chain rub from the middle chainring.
In many cases, it can. I think yours is just an issue of very fine tuning one way or the other. I think most all of my triples will shift the entire rear cassette from the middle ring.

Else, you can adjust your derailleur so you get your chain rub in the middle/small combo rather than the middle/large combo, if you can't quite get it perfect on both ends. You're probably more likely to want to run middle/larger than middle/small.
hokiefyd 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.