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

8 speed cogs on 7 speed cassette?

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.

8 speed cogs on 7 speed cassette?

Old 02-09-17, 07:46 PM
  #1  
Senior Member
Thread Starter
 
due ruote's Avatar
 
Join Date: Dec 2006
Posts: 7,704
Mentioned: 30 Post(s)
Tagged: 0 Thread(s)
Quoted: 902 Post(s)
Liked 523 Times in 317 Posts
8 speed cogs on 7 speed cassette?

So I built a 7 speed cassette using the first 7 cogs from an 8 speed cassette and the spacers from a 7 speed. Is there anything about this that should cause problems with my 7 speed Deore thumbies? I am having some trouble getting the indexing right. My suspicion is I need to overhaul the shifters, but just thought I would check the brain trust here first.
due ruote is offline  
Old 02-09-17, 07:56 PM
  #2  
Senior Member
 
Join Date: Jan 2009
Location: San Diego, CA
Posts: 3,607
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 827 Post(s)
Liked 1,023 Times in 722 Posts
The 7 and 8 speed cogs are different thicknesses so that is probably why it won't index properly even with the 7sp spacers.
Crankycrank is offline  
Old 02-09-17, 09:55 PM
  #3  
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 5 Times in 5 Posts
For more information scroll to:
"Cassette /Freewheel Spacing"
on this page:
Sheldon Brown's Bicycle Frame and Cassette Spacing Crib Sheet

If the 7 speed cassette originally installed was a Shimano HG, it should work ok. If it was a Shimano IG - too much difference.
nfmisso is offline  
Old 02-10-17, 07:46 AM
  #4  
Junior Member
 
Join Date: Mar 2016
Location: Round Rock
Posts: 144
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 51 Post(s)
Liked 6 Times in 6 Posts
Originally Posted by nfmisso
For more information scroll to:
"Cassette /Freewheel Spacing"
on this page:
Sheldon Brown's Bicycle Frame and Cassette Spacing Crib Sheet

If the 7 speed cassette originally installed was a Shimano HG, it should work ok. If it was a Shimano IG - too much difference.

Using the numbers on the referenced web page, it seems that:

If the original cassette was HG, then use the original spacers - that would result in 4.95mm spacing versus the needed 7-speed 5.0mm spacing.

If the original cassette was IG, then use the 8-speed spacers - that would result in 4.80mm spacing versus the needed 7-speed 5.0mm spacing. The difference of 0.2mm might not be a problem if you set up your derailleur for perfect shifting on the middle cog ... you'd have to try it and see.
Jean_TX is offline  
Old 02-10-17, 08:14 AM
  #5  
Constant tinkerer
 
FastJake's Avatar
 
Join Date: May 2010
Location: Wisconsin
Posts: 7,954
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 184 Post(s)
Liked 92 Times in 75 Posts
I've done 7+1 cassettes before and 8-1 cassettes as well. But I try and keep the spacers with the cogs because as mentioned above, there are slight differences and mixing and matching too much can mess up the spacing in ways you might not expect.

Some people will say that 7/8 speed is close enough to mix and match shifters and cassettes. I've made it work in the past but given up on it lately and just use the correct shifter/cassette for the job.
FastJake is offline  
Old 02-10-17, 09:47 AM
  #6  
Full Member
 
Join Date: Jul 2015
Posts: 359
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 74 Post(s)
Liked 19 Times in 14 Posts
I have done the same conversion a number of times, most of the time it is fine but on the odd occasion shifting is average to poor. Try putting the 8 speed spacers back in I don't usually bother changing them out as long as the cassette is proud of the freehub there is usually no issue.
headasunder is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Spoonrobot
Bicycle Mechanics
10
03-21-17 11:39 AM
BenVoiles
Bicycle Mechanics
10
05-15-16 01:00 AM
Frum
Bicycle Mechanics
3
05-08-14 02:05 AM
TampaRaleigh
Bicycle Mechanics
5
02-04-13 11:26 AM
hauk
Bicycle Mechanics
11
10-05-10 06:50 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
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.