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

Rear derailleur specs

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 specs

Old 09-30-16, 06:52 AM
  #1  
Senior Member
Thread Starter
 
Join Date: Dec 2010
Posts: 97
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Rear derailleur specs

How do I determine specs on rear derailleur? I have boxes of old parts and although I can look at length of derailleur and tell if it can handle mountain or road range, I am running into trouble figuring if a derailleur can handle 8 speed or 9 speed. Is there a way to figure that, such as length of parallelogram or such? I'm having trouble with a derailleur right now, in smaller cogs it's good, but seems stressed or not reliable in lower ranges. Maybe it's a 7 speed and I'm asking too much of it going to an 8 speed?
Thanks.
cajunpedaler is offline  
Old 09-30-16, 07:04 AM
  #2  
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 33,656

Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!

Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2026 Post(s)
Likes: 0
Liked 1,095 Times in 741 Posts
Nearly any even reasonably recent rear derailleur will have enough "swing" to handle 8/9/10-speed cassettes even if it was made in the 7-speed era. BTW, 8, 9 and 10-speed cassettes are almost identical in overall width so if the derailleur will work with 8-speed it will work with 9 and 10 too.
HillRider is offline  
Old 09-30-16, 07:10 AM
  #3  
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 30,225

Bikes: Catrike 559 I own some others but they don't get ridden very much.

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 1572 Post(s)
Liked 643 Times in 364 Posts
There are 3 significant specifications. Interestingly, in all but a very few cases, 8-speed vs. 9-speed isn't one of them.

The most obvious one is the derailleurs capability to take up chain slack as you shift from bigger to smaller cogs. With a minimum of experience you can estimate that simply by looking at the length of the derailleur's arm. As a rule of thumb, short arm = double crankset, long arm = triple crankset.

The second, which I can't tell by simply looking, is large cog capability. For years Shimano only rated their road group derailleurs to handle a 27t large rear cog. Consequently an Ultegra long arm derailleur might not work too well with a 34t mountain bike rear cog.

The last is cable pull. Your shifter, derailleur and cassette all have to be on the same page for the shifter to move the derailleur the precise right amount for an indexed shift. With a few exceptions, your shifter and your derailleur need to be from the same manufacturer.

Manufacturers tend to rate such capabilities on the conservative side so there's generally a little bit of "cheating room". My personal rule of thumb is, if I'm buying parts, especially for a customer bike, I'll always hold out for something that I know is supposed to work. If I already own parts I'll bolt them up and see if I can make them function well enough to meet my standards.
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.

Last edited by Retro Grouch; 09-30-16 at 07:14 AM.
Retro Grouch is offline  
Old 09-30-16, 07:36 AM
  #4  
Senior Member
Thread Starter
 
Join Date: Dec 2010
Posts: 97
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Thanks for the replies. I think that could also be one of my problems is that I am too many teeth on this cassette and thinking of going two more teeth larger. It's a vintage RSX
cajunpedaler is offline  
Old 09-30-16, 08:48 AM
  #5  
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,860

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds. 2019 Giant Explore E+3

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1787 Post(s)
Liked 1,264 Times in 872 Posts
VeloBase.com - Component: Shimano RD-A410 GS, RSX
Bill Kapaun is offline  
Old 09-30-16, 09:10 AM
  #6  
Senior Member
Thread Starter
 
Join Date: Dec 2010
Posts: 97
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Exactly my problem. Thanks. I have a cassette with 32 teeth. And thinking of going to a 34...will change derailleur. Thank you, thank you!
Perry
cajunpedaler is offline  
Old 09-30-16, 09:32 AM
  #7  
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,860

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds. 2019 Giant Explore E+3

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1787 Post(s)
Liked 1,264 Times in 872 Posts
Originally Posted by cajunpedaler
Exactly my problem. Thanks. I have a cassette with 32 teeth. And thinking of going to a 34...will change derailleur. Thank you, thank you!
Perry
Do you have the "B" Screw turned all the way in?
Chain long enough?

I think you probably may be exceeding the cog size limit, but some bikes are more forgiving, depending on RDER Hanger geometry etc.

Last edited by Bill Kapaun; 09-30-16 at 09:40 AM.
Bill Kapaun is offline  
Old 09-30-16, 09:43 AM
  #8  
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 30,225

Bikes: Catrike 559 I own some others but they don't get ridden very much.

Mentioned: 16 Post(s)
Tagged: 0 Thread(s)
Quoted: 1572 Post(s)
Liked 643 Times in 364 Posts
Originally Posted by Bill Kapaun
Do you have the "B" Screw turned all the way in?
Turning the "B" screw (near where the derailleur mounts to the frame) may help. It'll pull your derailleur back so that it doesn't rub the big cog. If your "B" screw isn't long enough, try taking it out and installing it backwards on your derailleur. After you do that, try shifting to your smallest rear cog to see how much chain wrap you have. That's never been a problem for me but I'm not the most powerful rider.
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.
Retro Grouch is offline  
Old 09-30-16, 10:07 AM
  #9  
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,355 Times in 862 Posts
to compile raw data ... Measure?

The lengths of the parallelogram sides and the actuating arm affect how far the inward motion is

relative to amount of cable pulled..

the C&V Campg moves inward with relatively short cable pull from a relatively small diameter wrap
around the drum of the shift lever..

more modern slant pantograph seem to require a bit more cable pull for inward motion so drum of shift lever wrapping up the other end increased.






./.
fietsbob is offline  
Old 09-30-16, 10:22 AM
  #10  
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,860

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds. 2019 Giant Explore E+3

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1787 Post(s)
Liked 1,264 Times in 872 Posts
Originally Posted by retro grouch
turning the "b" screw (near where the derailleur mounts to the frame) may help. It'll pull your derailleur back so that it doesn't rub the big cog. If your "b" screw isn't long enough, try taking it out and installing it backwards on your derailleur. after you do that, try shifting to your smallest rear cog to see how much chain wrap you have. That's never been a problem for me but i'm not the most powerful rider.
Huh?
You were going good there and then the water got muddy fast.
(although not as muddy as the post below it)

Last edited by Bill Kapaun; 09-30-16 at 10:28 AM.
Bill Kapaun is offline  
Old 09-30-16, 11:33 AM
  #11  
Senior Member
Thread Starter
 
Join Date: Dec 2010
Posts: 97
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 24 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
I am positive I am greatly exceeding what this rear derailleur is willing to give. The specs say a max of 28 teeth, I have screwed in the b screw and presently I can get 80% success rate shifting up to the 32t cog. I plan on touring with this bike and I am trying to weed out potential problems. Some things I'm willing to putz with and make it work, this...not so much.
This has been a good discussion. I learned a good bit.
Perry
cajunpedaler is offline  
Old 09-30-16, 12:09 PM
  #12  
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Mentioned: 197 Post(s)
Tagged: 0 Thread(s)
Quoted: 7607 Post(s)
Liked 1,355 Times in 862 Posts
Back in the DIY days .. a frame dropout distance drop could be chosen so RD sits Lower

It is another way to increase the Low Gear Cog size.. in design of frames .



I think you will be looking at fitting a Mountain Bike rear derailleur.. that is a typical solution..

long cage for the Triple chainrings chain wrap take-up, or a wide difference between 2.

Think Gear Ratios not Speeds you can have a corncob rear cluster with the increase of just 1 tooth larger ..

have lots of gears close together , but a narrow gear ratio range.






./.

Last edited by fietsbob; 09-30-16 at 12:13 PM.
fietsbob is offline  
Old 09-30-16, 12:12 PM
  #13  
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,860

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds. 2019 Giant Explore E+3

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1787 Post(s)
Liked 1,264 Times in 872 Posts
Probably an Altus or Acera would serve you well.
Higher levels and you are getting into 9 and more speeds.
No sense getting something that would likely be a bit more finicky with 8 speed chain vs the slightly narrower chains of the 9+.
Bill Kapaun is offline  
Old 09-30-16, 02:40 PM
  #14  
Nigel
 
nfmisso's Avatar
 
Join Date: Mar 2011
Location: San Jose, CA
Posts: 2,991

Bikes: 1980s and 1990s steel: CyclePro, Nishiki, Schwinn, SR, Trek........

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 384 Post(s)
Likes: 0
Liked 6 Times in 6 Posts
Originally Posted by cajunpedaler
I am positive I am greatly exceeding what this rear derailleur is willing to give. The specs say a max of 28 teeth, I have screwed in the b screw and presently I can get 80% success rate shifting up to the 32t cog. I plan on touring with this bike and I am trying to weed out potential problems. Some things I'm willing to putz with and make it work, this...not so much.
This has been a good discussion. I learned a good bit.
Perry
My go to RD is Shimano's M592; with will work with indexed 9 speed and fewer (6, 7, 8) Shimano MTB shifters and 10 speed and fewer Shimano Road Shifters. It also works fine with friction shifters. It is rated for up to 36T in the largest rear cog. I am running one on my every day commuter with a custom 14-32 8 speed cassette and Sunrace friction thumb shifters.

I am running a KMC X8.93 chain through the M592 with no issues.
nfmisso is offline  
Old 09-30-16, 03:00 PM
  #15  
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,860

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds. 2019 Giant Explore E+3

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 1787 Post(s)
Liked 1,264 Times in 872 Posts
Originally Posted by nfmisso
My go to RD is Shimano's M592; with will work with indexed 9 speed and fewer (6, 7, 8) Shimano MTB shifters and 10 speed and fewer Shimano Road Shifters. It also works fine with friction shifters. It is rated for up to 36T in the largest rear cog. I am running one on my every day commuter with a custom 14-32 8 speed cassette and Sunrace friction thumb shifters.

I am running a KMC X8.93 chain through the M592 with no issues.
ANYTHING will work with friction shifters.
I was running a 9 speed/Tourney with friction shifters.

As far as availability of a 36T cog 8 speed**********????

It might be helpful if the poster specified their max-min chain ring and cassette tooth counts.
One can maybe recommend a more appropriate RDER based on how much they want to spend and "perceived" functionality.
The 592 you strongly urge to be used has a recommended smallest cog range of 11/12, whereas some are more "lenient" at 11/14. You might not have the same "pristine" results if you were using an indexed shifter, although in general, RDER's are pretty "lenient".

The OP probably has an 11T smallest cog, rendering things pretty moot.
Bill Kapaun is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
chans
Mountain Biking
1
12-09-17 08:52 PM
tarwheel
Bicycle Mechanics
12
04-05-16 01:13 PM
tronnyjenkins
Classic & Vintage
30
01-27-16 10:48 AM
Candlesticks
Bicycle Mechanics
6
02-20-13 07:39 PM
skn_g
Bicycle Mechanics
2
11-22-10 05:07 PM

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

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

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.