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

Rule of thumb? Add this many teeth and add this many chain links?

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.

Rule of thumb? Add this many teeth and add this many chain links?

Old 06-10-19, 11:27 PM
  #1  
pennpaul
Senior Member
Thread Starter
 
Join Date: Sep 2017
Location: Jerusalem
Posts: 137

Bikes: Diamondback Haanjo Trail

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked 8 Times in 6 Posts
Rule of thumb? Add this many teeth and add this many chain links?

I ride a gravel bike but it's pretty much just a road bike now since the "gravel" here is beyond my abilities.

Anyway, I have a 46/36 in the front and an 11-40 in the back. I decided to get a compact crank (50/34), but realized I probably need a longer chain now since I'm adding 4 teeth.

Is there a rule of thumb that I can use to determine how many links I need to add? When I setup the 11-40, I used the whole length of KMC chain I bought. Of course, now I'm worried that the chain is too long since I lost 2 teeth on the smaller ring.

Last edited by pennpaul; 06-12-19 at 01:17 AM.
pennpaul is offline  
Old 06-11-19, 03:13 AM
  #2  
krecik
Senior Member
 
krecik's Avatar
 
Join Date: Jun 2018
Location: Tredegar, Wales
Posts: 191

Bikes: coastie

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 60 Post(s)
Liked 21 Times in 13 Posts
Originally Posted by pennpaul View Post
Is there a rule of thumb that I can use to determine how many links I need to add? When I setup the 11-42, I used the whole length of KMC chain I bought. Of course, now I'm worried that the chain is too long since I lost 2 teeth on the smaller ring.
I'm not sure myself. The rule that works in my case is add 3 teeth on the back cog, add 1 half link. Add 6 teeth, add 2 normal links. This might be different in your case since I ride a single speed bike and our chainstay lenghts may be different.

I don't know how the size of the cog changes with the increase in number of teeth. If it's proportional then that should work in your case too. Anyway, I'd try that as an estimate. Chain length isn't that vital with derailleurs from my experience since it's loosely tensioned by the derailleur anyway.

Kret
krecik is offline  
Old 06-11-19, 06:54 AM
  #3  
DiabloScott
It's MY mountain
 
DiabloScott's Avatar
 
Join Date: Sep 2006
Location: Mt.Diablo
Posts: 8,602

Bikes: Klein, Merckx, Trek

Mentioned: 57 Post(s)
Tagged: 0 Thread(s)
Quoted: 2198 Post(s)
Liked 35 Times in 21 Posts
You want a thumbrule based on experience?

"Probably zero, might be one... maaaaaaybe two."

If your derailleur is REALLY tight in the big big, you'll probably need a new, longer chain. Else just wait and see.
DiabloScott is offline  
Old 06-11-19, 08:17 AM
  #4  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 11,611

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: 1734 Post(s)
Liked 47 Times in 34 Posts
Since I don't assume that the bikes I work on have had their chains set up lengthwise for the best shifting (as opposed to the least cost, after 112 bikes the company has a "free" chain if they shorten each chain by one link/pair) I CAREFULLY test before I do anything. But I agree with DiabloScott. Andy
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 06-11-19, 08:17 AM
  #5  
HillRider 
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 31,468

Bikes: '''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!

Mentioned: 32 Post(s)
Tagged: 0 Thread(s)
Quoted: 1143 Post(s)
Likes: 0
Liked 25 Times in 22 Posts
The "rule of thumb" for changing total teeth count is add or subtract 1/2 of the tooth difference. For example, going from a 46T to a 50T chainring you should add 4/2=2 half-links. If the difference is an odd number go to the next even number since you can't add 1/2 of a link. The reason for adding only 1/2 of the difference is that the chain only wraps around 1/2 of the chainring or cog.

Before anyone says anything, yes, there are 1/2-links available but they are unusual and not commonly used.
HillRider is offline  
Old 06-11-19, 09:32 AM
  #6  
HerrKaLeun
Senior Member
 
Join Date: Mar 2017
Location: Madison, WI
Posts: 1,376

Bikes: Giant Toughroad SLR1 and Motobecane Sturgis NX

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 667 Post(s)
Likes: 0
Liked 26 Times in 22 Posts
To do it right, don't rely on the original chain being correct.

Read the RD manual on chainsizing and verify if the chain is the correct length. Typically it is big-big + 2 or 4 links.... but that differs for SRAM and Shimano and for FS bikes there is even more to consider. RTFM.
HerrKaLeun is offline  
Old 06-11-19, 10:36 AM
  #7  
squirtdad
Senior Member
 
squirtdad's Avatar
 
Join Date: Jul 2006
Location: San Jose (Willow Glen) Ca
Posts: 6,123

Bikes: 90/91 De Rosa, '84 Team Miyata, '82 nishiski,

Mentioned: 55 Post(s)
Tagged: 0 Thread(s)
Quoted: 810 Post(s)
Liked 43 Times in 32 Posts
I used big big +2 for years, but am now of the opinion that small/small works better ....this is what my LBS guy recommends and is what shimano recommends

__________________
Looking for Team Miyata F&F 58cm
squirtdad is offline  
Old 06-11-19, 10:45 AM
  #8  
3alarmer
******
 
3alarmer's Avatar
 
Join Date: Nov 2010
Location: The Big Tomato
Posts: 17,269

Bikes: old ones

Mentioned: 227 Post(s)
Tagged: 0 Thread(s)
Quoted: 14569 Post(s)
Liked 76 Times in 65 Posts
Originally Posted by pennpaul View Post
I ride a gravel bike but it's pretty much just a road bike now since the "gravel" here is beyond my abilities.

Anyway, I have a 46/36 in the front and an 11-42 in the back. I decided to get a compact crank (50/34), but realized I probably need a longer chain now since I'm adding 4 teeth.

Is there a rule of thumb that I can use to determine how many links I need to add? When I setup the 11-42, I used the whole length of KMC chain I bought. Of course, now I'm worried that the chain is too long since I lost 2 teeth on the smaller ring.
...if your goal is to gear up a little for road use versus gravel, have you considered running a smaller cluster in the back ? You can usually do this easily and relatively cheaply. But I guess I don't really understand the goal here.
3alarmer is online now  
Old 06-11-19, 11:13 AM
  #9  
Retro Grouch 
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 29,269

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

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1164 Post(s)
Liked 34 Times in 26 Posts
Originally Posted by 3alarmer View Post
...if your goal is to gear up a little for road use versus gravel, have you considered running a smaller cluster in the back ? You can usually do this easily and relatively cheaply. But I guess I don't really understand the goal here.
.

Smaller than 11t?
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.
Retro Grouch is offline  
Old 06-11-19, 11:17 AM
  #10  
Retro Grouch 
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 29,269

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

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 1164 Post(s)
Liked 34 Times in 26 Posts
To answer OP's original question, why guess? Since you're going to break the chain anyway just wrap it around the big/big combination and test it for sure.
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.
Retro Grouch is offline  
Old 06-11-19, 12:06 PM
  #11  
squirtdad
Senior Member
 
squirtdad's Avatar
 
Join Date: Jul 2006
Location: San Jose (Willow Glen) Ca
Posts: 6,123

Bikes: 90/91 De Rosa, '84 Team Miyata, '82 nishiski,

Mentioned: 55 Post(s)
Tagged: 0 Thread(s)
Quoted: 810 Post(s)
Liked 43 Times in 32 Posts
OP should also check what the wrap capacity of his rear derailler is, may not have the capacity for the change

currently he is at 41 wrap ((46-36) + (42-11) (10 + 31)

with a 50/34 the wrap is 45 (50-34) +(42-11) (14+31)
__________________
Looking for Team Miyata F&F 58cm
squirtdad is offline  
Old 06-11-19, 12:11 PM
  #12  
ThermionicScott 
hungry
 
ThermionicScott's Avatar
 
Join Date: Aug 2011
Location: CID
Posts: 18,424

Bikes: 1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX, 1980s Raleigh mixte (hers)

Mentioned: 68 Post(s)
Tagged: 0 Thread(s)
Quoted: 2029 Post(s)
Liked 99 Times in 82 Posts
Originally Posted by Retro Grouch View Post
To answer OP's original question, why guess? Since you're going to break the chain anyway just wrap it around the big/big combination and test it for sure.
+1. I almost never count links on my chain. I take a new chain out of the box, loop it around the big ring and big cog, add 1" for good luck, and cut it.
__________________
Originally Posted by chandltp View Post
There's no such thing as too far.. just lack of time
Originally Posted by noglider
People in this forum are not typical.
RUSA #7498
ThermionicScott is offline  
Likes For ThermionicScott:
Old 06-11-19, 01:31 PM
  #13  
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 41,398

Bikes: 8

Mentioned: 188 Post(s)
Tagged: 0 Thread(s)
Quoted: 6839 Post(s)
Likes: 0
Liked 217 Times in 180 Posts
bike chain is 1/2" pitch , a full link is 3 rollers, 2 on the inner and the 3rd one the 2nd pin into the next inner link
so an inch..
now you join 2 inner links with a quick link, functionally an outer link with pins fixed in it.. one on each side..









.....
fietsbob is offline  
Old 06-11-19, 01:52 PM
  #14  
caloso
Packfodding 3
 
caloso's Avatar
 
Join Date: Jul 2002
Location: Sacramento, California, USA
Posts: 38,035

Bikes: Ridley Excalibur, Gazelle Champion Mondial, On-One Pompino, Specialized Rock Hopper

Mentioned: 57 Post(s)
Tagged: 0 Thread(s)
Quoted: 1821 Post(s)
Liked 147 Times in 90 Posts
Originally Posted by ThermionicScott View Post
+1. I almost never count links on my chain. I take a new chain out of the box, loop it around the big ring and big cog, add 1" for good luck, and cut it.
Same. If it was good enough for Sheldon, it is good enough for me.
caloso is offline  
Likes For caloso:
Old 06-12-19, 01:22 AM
  #15  
pennpaul
Senior Member
Thread Starter
 
Join Date: Sep 2017
Location: Jerusalem
Posts: 137

Bikes: Diamondback Haanjo Trail

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked 8 Times in 6 Posts
Looks like I need to adjust my plans after a big Doh! moment. My current cassette is actually an 11-40, not 42. Not that that matters in the grand scheme because I was planning to use the original 11-32 on my spare rear wheel for Zwift. Of course, I'm not going to be swapping chains each time I want to Zwift, too.

Looks like I need to decide whether I want to stay with the 11-40 or go back to 11-32, and then buy another cassette to match. Doh.
pennpaul is offline  
Old 06-12-19, 01:32 AM
  #16  
HerrKaLeun
Senior Member
 
Join Date: Mar 2017
Location: Madison, WI
Posts: 1,376

Bikes: Giant Toughroad SLR1 and Motobecane Sturgis NX

Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 667 Post(s)
Likes: 0
Liked 26 Times in 22 Posts
Originally Posted by squirtdad View Post
I used big big +2 for years, but am now of the opinion that small/small works better ....this is what my LBS guy recommends and is what shimano recommends

https://www.youtube.com/watch?v=QuhHn7HaZcQ
SRAM recommends +4 on the 10 speed and higher. Shimano recommends +2. Probably works either way, but if I have a choice I do what the manufacturer recommends.
HerrKaLeun is offline  
Old 06-12-19, 09:20 AM
  #17  
Phil_gretz
Journeyman Bike Commuter
 
Phil_gretz's Avatar
 
Join Date: Aug 2009
Location: Alexandria, VA
Posts: 5,038

Bikes: '71 Jeunet 630, '79 Peugeot PXN10LE, '83 Fuji America, '88 Fuji Saratoga, '13 Motobecane Fantom29 HT, '16 Motobecane Turino Pro Disc, '16 Motobecane Gran Premio Elite, '18 Velobuild VB-R-022

Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 569 Post(s)
Liked 77 Times in 51 Posts
Originally Posted by Retro Grouch View Post
.

Smaller than 11t?
I think that he meant the 40T rear.
Phil_gretz is offline  
Old 06-12-19, 10:48 AM
  #18  
Iride01
Senior Member
 
Iride01's Avatar
 
Join Date: Jul 2017
Location: Mississippi
Posts: 2,305

Bikes: '91 Schwinn Paramount '78 Raleigh Competition GS

Mentioned: 19 Post(s)
Tagged: 0 Thread(s)
Quoted: 868 Post(s)
Liked 29 Times in 25 Posts
Shimano publishes the exact procedures to use for determining chain length. There are differences for things like 3x or 2x front. Long, medium or short rear DR and other things. Other mfr's probably publish how they want chains sized to their groupsets too.

Shimano Tech docs are here... https://si.shimano.com/#/

You need to find the DM's appropriate to your bikes groupset.
Iride01 is offline  
Old 06-18-19, 12:36 PM
  #19  
pennpaul
Senior Member
Thread Starter
 
Join Date: Sep 2017
Location: Jerusalem
Posts: 137

Bikes: Diamondback Haanjo Trail

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 54 Post(s)
Liked 8 Times in 6 Posts
The new crank is installed and it doesn't seem like I need to add or subtract any links.
pennpaul is offline  
Old 06-19-19, 05:47 PM
  #20  
squirtdad
Senior Member
 
squirtdad's Avatar
 
Join Date: Jul 2006
Location: San Jose (Willow Glen) Ca
Posts: 6,123

Bikes: 90/91 De Rosa, '84 Team Miyata, '82 nishiski,

Mentioned: 55 Post(s)
Tagged: 0 Thread(s)
Quoted: 810 Post(s)
Liked 43 Times in 32 Posts
Originally Posted by pennpaul View Post
The new crank is installed and it doesn't seem like I need to add or subtract any links.
just double check that big/big works.. it is not fun if it does not and you move into that at speed
__________________
Looking for Team Miyata F&F 58cm
squirtdad is offline  
Old 06-20-19, 06:46 AM
  #21  
Kapusta
Cyclochondriac
 
Join Date: Feb 2017
Posts: 2,151
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 908 Post(s)
Likes: 0
Liked 50 Times in 39 Posts
My rule of thumb is to measure it on the bike, thus taking out any guesswork or assumptions.

Big-big plus 2 or 4 (half links), depending on the application.
Kapusta is offline  
Old 06-20-19, 06:48 AM
  #22  
djb
Senior Member
 
Join Date: Jul 2010
Location: Montreal Canada
Posts: 8,856
Mentioned: 23 Post(s)
Tagged: 0 Thread(s)
Quoted: 1091 Post(s)
Likes: 0
Liked 38 Times in 30 Posts
Go to the park tools video series on chain sizing.
Clear, concise, no guess work from a reliable source.
djb 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.