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

Help with cassette compatibility 8spd-9spd

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.

Help with cassette compatibility 8spd-9spd

Old 04-07-20, 05:47 PM
  #1  
bikebikebike
Senior Member
Thread Starter
 
Join Date: Jul 2006
Location: TX
Posts: 232

Bikes: Downtube IX NS&FS, Dahon Speed8Pro/Matrix/Curve, Brom S2L,Montague Para, ICE-XL w/Rollie/Schlumpf, Trident Spike, ebikes, BFSatRDay

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Liked 26 Times in 24 Posts
Help with cassette compatibility 8spd-9spd

I need my logic reviewed on this, as my search got lots of fragments and in no concise answer.
I have been tuning up some older eight and nine speed bikes and wanted to play around with different cassette configurations.
I understand that going with the same speed and same brand makes for smoother and better wearing set ups,
but I just want to see if I can get a basic testbed by playing around with less than a complete set of every type of cassette.
My understanding is that you can put a nine speed cassette on a bike with an eight speed chain and shift mechanism and get eight speeds out of it.
Likewise a 9speed set up would accept an 8 speed cassette . Both would work ,just not as smoothly as could be.
My goal was just to run something long enough to get a feel for the gear spacing and range and make some kind of sense out of the charts that Sheldon's Gear Calculator provides.
I have been playing with a foldie with a SA 3x9 rear and it handles overlap such that the wide ratio cogs give some suboptimal ratios.

Thanks

Last edited by bikebikebike; 04-07-20 at 05:53 PM.
bikebikebike is offline  
Old 04-07-20, 06:10 PM
  #2  
bikeaddiction1
Senior Member
 
bikeaddiction1's Avatar
 
Join Date: Jan 2015
Location: Calgary Alberta
Posts: 229

Bikes: Many

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 74 Post(s)
Liked 29 Times in 24 Posts
Shimano 8 speed cassettes have a center to center gear spacing of 4.8 mm and 9 speed cassettes have a spacing of 4.34 mm. (ref: https://www.sheldonbrown.com/cribsheet-spacing.html). The 9 speed chain is correspondingly narrower. You might get it to work but it is not going to shift as well as using the correct cassette. when you ad the.46 mm difference up over 8 spaces things are now going to line up well.
bikeaddiction1 is offline  
Old 04-07-20, 06:12 PM
  #3  
Retro Grouch 
Senior Member
 
Retro Grouch's Avatar
 
Join Date: Feb 2004
Location: St Peters, Missouri
Posts: 29,771

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

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1395 Post(s)
Liked 262 Times in 164 Posts
Not really. It'll probably kind'a work but it definitely won't index right.

A 9-speed cassette puts 9 sprockets into the same amount of space where an 8-speed cassette only has 8. Somewhere it's going to skip one or require a double shift or do something else goofy.
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.
Retro Grouch is online now  
Old 04-07-20, 09:42 PM
  #4  
bikebikebike
Senior Member
Thread Starter
 
Join Date: Jul 2006
Location: TX
Posts: 232

Bikes: Downtube IX NS&FS, Dahon Speed8Pro/Matrix/Curve, Brom S2L,Montague Para, ICE-XL w/Rollie/Schlumpf, Trident Spike, ebikes, BFSatRDay

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Liked 26 Times in 24 Posts
Thanks.
Discussions I found weren't free from implying more compatibility than you're describing. Sheldon's crib sheet explains it well.
Better to just snag some used, and build a collection of cassettes if need be.
I'm older and do my best on narrower spaced ratios.
If the Nuvinci's weren't so heavy a 3x nuvi would do me well.
bikebikebike is offline  
Old 04-07-20, 10:05 PM
  #5  
Camilo
Senior Member
 
Join Date: Apr 2007
Posts: 4,694
Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 300 Post(s)
Liked 77 Times in 50 Posts
I seem to recall that read somewhere (Sheldon Brown? I'm not sure) that there is alternate cable routing at the rear derailleur that allows a 9 speed shifter to shift 8 speeds - with the derailleur stops set properly. In other words, the alternate cable routing changed the cable pull on the derailleur to match the 8 speed cassette spacing, even though it was being pulled by the 9 speed shifter.

I tried that with DuraAce 9 speed indexed bar end shifters and an 8 speed cassette once, but couldn't get it to index properly. I can't even remember why I was trying to do that.

I wonder if there's a JTek Shiftmate that would work for that? That's what they do - change the cable pull. Although, again, I don't know why you would because it's easiest and best just to match the cassette with the shifters. whether it's 10, 9 or 8 speeds, because they all will fit on the same hub with whatever spacers are needed.

Last edited by Camilo; 04-07-20 at 10:09 PM.
Camilo 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 - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.