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

Making a close ratio/corncob 8 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.

Making a close ratio/corncob 8 speed cassette

Old 02-01-22, 07:28 PM
  #1  
Marylander
Senior Member
Thread Starter
 
Join Date: Sep 2019
Location: Frederick County, MD
Posts: 299
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 111 Post(s)
Liked 94 Times in 69 Posts
Making a close ratio/corncob 8 speed cassette

My indoor bike has claris stuff on it. I'm doing power based workouts on the rollers now and the jumps between gears are too big to make reasonable power jumps (11-13-15-18-21-24-28-34). Of course I have the option of following a more complicated shifting scheme and possibly getting better gaps (which I have charted out and will consider) although I've been too lazy to do that in the past... I do have a 10spd and a couple 11 spd cassettes that I might be able to make a straight block with. Can I use these cassettes on the 8 spd body with the 8 spd spacers? I expect I'll have to disassemble the ganged cogs...
Marylander is offline  
Old 02-01-22, 07:40 PM
  #2  
Bill Kapaun
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,065

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 1486 Post(s)
Liked 744 Times in 546 Posts
How about a 12-23 or 12-26?
https://cambriabike.com/products/sra...kaAt0vEALw_wcB

Last edited by Bill Kapaun; 02-01-22 at 07:45 PM.
Bill Kapaun is offline  
Likes For Bill Kapaun:
Old 02-01-22, 07:47 PM
  #3  
FastJake
Constant tinkerer
 
FastJake's Avatar
 
Join Date: May 2010
Location: Wisconsin
Posts: 7,952
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 183 Post(s)
Liked 86 Times in 72 Posts
You could measure the cog thickness to make sure it's not narrower, but it's probably close enough.

Don't expect good or even decent shifting. Modern Hyperglide cassettes are meant to be matched, and mixing different cogs in the middle will usually result in lousy, slow shifting. You may have to overshift to get a larger cog to engage. Maybe not an issue for an indoor trainer though?

You could also get a closer ratio cassette as a starting point, if you can find one. I stocked up years ago when they were getting scarce. I'm not sure what's still out there.
FastJake is offline  
Likes For FastJake:
Old 02-01-22, 08:05 PM
  #4  
Marylander
Senior Member
Thread Starter
 
Join Date: Sep 2019
Location: Frederick County, MD
Posts: 299
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 111 Post(s)
Liked 94 Times in 69 Posts
Hmm, that sram 12-23 might be ok. I'll have to put it in the calculator and check it out. Thanks!

FastJake I'm not sure if slow shifting would be an issue for me on the rollers or not. I can be pretty uncoordinated, which I'm using the rollers to help with... I had forgotten about the fancy matching of all the cogs on modern cassettes. The last race bike I had, a fuji back in the 90s, had 8 spd ultegra with a 12-21. That would be ideal...
Marylander is offline  
Old 02-01-22, 08:17 PM
  #5  
CliffordK
Senior Member
 
CliffordK's Avatar
 
Join Date: Nov 2014
Location: Eugene, Oregon, USA
Posts: 26,887
Mentioned: 213 Post(s)
Tagged: 0 Thread(s)
Quoted: 15752 Post(s)
Liked 3,169 Times in 2,360 Posts
There is a lot of info about cassettes, pull ratios, etc, on this page.
https://en.wikibooks.org/wiki/Bicycl...ing_Dimensions

8 speed Shimano Cassettes have a 1.8mm sprocket thickness, and a 3.0mm spacer.
10 and 11 speed cassettes have a 1.6mm sprocket thickness.

7 speed has a 3.15mm spacer.

You'd probably do best by using the 7 speed spacers with the 10/11 sprockets to approximate the 8 speed spacing.



Here is a Sunrace 11/23, 8-speed cassette.
https://www.ebay.com/itm/254407801416

Sunlite 11-21
https://www.ebay.com/itm/284513923946

7 speed spacers (for use with thinner sprockets).
https://www.ebay.com/itm/274967957746
CliffordK is offline  
Likes For CliffordK:
Old 02-01-22, 08:27 PM
  #6  
Andrew R Stewart 
Senior Member
 
Andrew R Stewart's Avatar
 
Join Date: Feb 2012
Location: Rochester, NY
Posts: 16,272

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: 3427 Post(s)
Liked 2,128 Times in 1,390 Posts
A few comments- Cogs do have somewhat decreasing thicknesses as the cog count goes up. Likely not enough to bother if only a single different cog is at play. But if a few are mixed don't be surprised if the indexing over a number of cogs begins to suffer.

My understanding as to the importance of a cog set being made of "matched shift gate" cogs is to better allow shifting across a few cogs in one sweep. Larger, matched series, cogs have their shift gates staggered in a spiral pattern that is close to the path a chain makes during shifting across a number of cogs. This pattern is not in effect if shifting only one cog at a time (as my mother taught me to do)

One of the cool aspects of rollers is that they reinforce good form, smooth power application, and readily show poor form. The classic way to deal with wide gaps in the gear ratios is to develop a wider "working" cadence range. The cost is the highest we humans can suffer, we have to try and practice. Andy (who has pulled out his rollers but has avoided riding them yet)
__________________
AndrewRStewart
Andrew R Stewart is offline  
Old 02-01-22, 09:41 PM
  #7  
TPL
Senior Member
 
Join Date: Jul 2017
Posts: 248
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 142 Post(s)
Likes: 0
Liked 88 Times in 63 Posts
Sky's the limit if you unshackle yourself from index shifting and use the most versatile shift system ever devised = FRICTION !
TPL is offline  
Old 02-02-22, 09:19 AM
  #8  
Crankycrank
Senior Member
 
Join Date: Jan 2009
Location: San Diego, CA
Posts: 2,973
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 622 Post(s)
Liked 572 Times in 437 Posts
Originally Posted by Marylander View Post
I do have a 10spd and a couple 11 spd cassettes that I might be able to make a straight block with. Can I use these cassettes on the 8 spd body with the 8 spd spacers? I expect I'll have to disassemble the ganged cogs...
As mentioned, it's not likely using cogs from different speed cassettes will play together well since both the cogs and spacers have different thicknesses but since you have them already give it a try. Here's a list of sprocket and spacer thicknesses compliments of forum member BikeGremlin. Bicycle cassette (rear chainrings) standards | BikeGremlin Scroll a little past halfway down the page.

Last edited by Crankycrank; 02-02-22 at 09:28 AM.
Crankycrank is offline  
Old 02-02-22, 09:55 AM
  #9  
70sSanO
Senior Member
 
70sSanO's Avatar
 
Join Date: Feb 2015
Location: Mission Viejo
Posts: 4,866

Bikes: 1986 Cannondale SR400 (Flat bar commuter), 1988 Cannondale Criterium XTR, 1992 Serotta T-Max, 1995 Trek 970

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 1576 Post(s)
Liked 1,573 Times in 992 Posts
Originally Posted by Marylander View Post
I do have a 10spd and a couple 11 spd cassettes that I might be able to make a straight block with. Can I use these cassettes on the 8 spd body with the 8 spd spacers? I expect I'll have to disassemble the ganged cogs...
Sure. I mix cogs from different speeds and mfg.

There are two basic rules.

1) You should adjust the spacer thickness for cog thickness. Being close 7, 8, 9 isnít critical, but going to some 11 speed cog may need a 7 speed spacer sanded down to get the correct c-t-c spacing.

2). The number of ramps on a cog impacts shifting more than brands. I donít think going to 1 tooth gaps is a big deal to use 2+ gap cogs. Iíve never built a mix-n-match corncob cassette. But going to a 2+ gap with a one ramp single gap cog slows shifting.

John
70sSanO is offline  
Old 02-02-22, 11:26 AM
  #10  
Marylander
Senior Member
Thread Starter
 
Join Date: Sep 2019
Location: Frederick County, MD
Posts: 299
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 111 Post(s)
Liked 94 Times in 69 Posts
Phew, lots more to this than I realized. I've got some stuff to think about (including maybe just buying the Sunlite 11-21 from ebay, although it has a weird 11-13 jump). I need to take a look at the cassettes I've got and see if I even have the cogs to make a corncob out of them.

Thanks all!
Marylander is offline  
Old 02-02-22, 11:43 AM
  #11  
79pmooney
A Roadie Forever
 
79pmooney's Avatar
 
Join Date: Oct 2014
Location: Portland, OR
Posts: 10,428

Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

Mentioned: 113 Post(s)
Tagged: 0 Thread(s)
Quoted: 3412 Post(s)
Liked 2,168 Times in 1,408 Posts
Originally Posted by TPL View Post
Sky's the limit if you unshackle yourself from index shifting and use the most versatile shift system ever devised = FRICTION !
And with rollers, you get to up your skills riding one-handed while you shift down tube shifters. (There are bar ends shifters but I've never gone there.) For inspiration, find the DVD on Eddy Merckx. There's a scene of him spinning the pedals really fast in a (then) huge gear,
79pmooney is offline  
Old 02-02-22, 11:53 AM
  #12  
79pmooney
A Roadie Forever
 
79pmooney's Avatar
 
Join Date: Oct 2014
Location: Portland, OR
Posts: 10,428

Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

Mentioned: 113 Post(s)
Tagged: 0 Thread(s)
Quoted: 3412 Post(s)
Liked 2,168 Times in 1,408 Posts
Originally Posted by Marylander View Post
Phew, lots more to this than I realized. I've got some stuff to think about (including maybe just buying the Sunlite 11-21 from ebay, although it has a weird 11-13 jump). I need to take a look at the cassettes I've got and see if I even have the cogs to make a corncob out of them.

Thanks all!
11-13 jump. I ride the Portland hills some days, the flats others. My 9-speed cassettes are mostly set up 12-14,15 ,,, On the flat a 50 something-14 is just fine. (I do very little group riding.) That 2 tooth jump to have a big one for fast descents is very nice and it is sometime useful to have to quiet the bike. On rollers, maybe up to 13 will work for you and you could use the 11 as a slow RPM hill-like condition.
79pmooney is offline  
Old 02-02-22, 12:20 PM
  #13  
Marylander
Senior Member
Thread Starter
 
Join Date: Sep 2019
Location: Frederick County, MD
Posts: 299
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 111 Post(s)
Liked 94 Times in 69 Posts
Originally Posted by 79pmooney View Post
11-13 jump. I ride the Portland hills some days, the flats others. My 9-speed cassettes are mostly set up 12-14,15 ,,, On the flat a 50 something-14 is just fine. (I do very little group riding.) That 2 tooth jump to have a big one for fast descents is very nice and it is sometime useful to have to quiet the bike. On rollers, maybe up to 13 will work for you and you could use the 11 as a slow RPM hill-like condition.
Yeah, that definitely makes sense I just haven't seen a cassette set up that way before.

As for getting a hill-like condition on the rollers I've got fast (conti 4000 700x23) and slow (kenda kwick roller sport 700x32) tires for the rollers. A complete set of fast tires is almost twice as fast on the rollers as a complete set of slow tires at the same power output so I can create different resistance levels based on the tires I've got on there (and can at least swap the front tires quickly as I've got one wheel with a fast tire and one with a slow tire). On super easy recovery days I can have both fast tires on, put out less than 100 watts and still manage to stay upright even with my poor balance.
Marylander is offline  
Old 02-02-22, 12:21 PM
  #14  
Marylander
Senior Member
Thread Starter
 
Join Date: Sep 2019
Location: Frederick County, MD
Posts: 299
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 111 Post(s)
Liked 94 Times in 69 Posts
So, I was just cruising ebay and found a shimano 12-21 8spd cassette so I took the lazy route and clicked "buy now".
Marylander is offline  
Old 02-02-22, 12:50 PM
  #15  
79pmooney
A Roadie Forever
 
79pmooney's Avatar
 
Join Date: Oct 2014
Location: Portland, OR
Posts: 10,428

Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

Mentioned: 113 Post(s)
Tagged: 0 Thread(s)
Quoted: 3412 Post(s)
Liked 2,168 Times in 1,408 Posts
Originally Posted by Marylander View Post
So, I was just cruising ebay and found a shimano 12-21 8spd cassette so I took the lazy route and clicked "buy now".
If I saw that, I do the same. Re: those Sunlite 2 tooth top end jumps - I'm betting that's a money saver; that it allows them to use a cruder, less critical design that either requires lesser steel alloys or cheaper to machine parts. (Go small right at the hub bearing and the distances between bearing and that little cog get very small. The 11 would be outboard of the bearing so that's OK but that 12 over it? Shimano would do this and we'd pay more.

I had an earlier Sunlite 12, 14, 15, 17 ... 7-speed. I'm guessing same thing.
79pmooney is offline  
Old 02-02-22, 01:58 PM
  #16  
Bill Kapaun
Really Old Senior Member
 
Bill Kapaun's Avatar
 
Join Date: Feb 2007
Location: Mid Willamette Valley, Orygun
Posts: 13,065

Bikes: 87 RockHopper,2008 Specialized Globe. Both upgraded to 9 speeds.

Mentioned: 17 Post(s)
Tagged: 0 Thread(s)
Quoted: 1486 Post(s)
Liked 744 Times in 546 Posts
My first 8 speed cassette was made from a 12-28 & 13-26 seven speed cassette with thinned 7 speed spacers.
Tape down a piece of sandpaper/emery cloth to the bench.
AVOID power tools or have spare spacers. A belt sander "ate" my 1st one.

Slowly sand a bit off the spacers, trying to use the same amount of strokes/pressure/rotation etc.
Do X number of strokes to each piece.
Check with a caliper frequently in 3 spots to keep them even with each other AND avoid getting "lopsided"

Every once in awhile, assemble the cassette on the FH and see where you are at.
You want enough purchase on the lock ring so you don't strip anything.
It took me about 2 hours.
It was when I had MUCH more time than money and I also wanted a "custom" configuration.

If you are making a corncob, shifting won't be a problem.
When I got my 8 speed Globe w/ index shifters, I swapped it in and it shifted perfectly. made me smile.....
Bill Kapaun is offline  
Old 02-02-22, 02:26 PM
  #17  
Sy Reene
Advocatus Diaboli
 
Sy Reene's Avatar
 
Join Date: Feb 2015
Location: Wherever I am
Posts: 7,844

Bikes: Merlin Cyrene, Nashbar steel CX

Mentioned: 12 Post(s)
Tagged: 1 Thread(s)
Quoted: 4219 Post(s)
Liked 1,194 Times in 786 Posts
OTOH, depending on the type of training workout you're doing, can't larger tooth-count jumps in the rear lead to quicker power output changes (eg intervals) on a non-smart set of rollers?
Sy Reene is offline  
Old 02-02-22, 03:14 PM
  #18  
CliffordK
Senior Member
 
CliffordK's Avatar
 
Join Date: Nov 2014
Location: Eugene, Oregon, USA
Posts: 26,887
Mentioned: 213 Post(s)
Tagged: 0 Thread(s)
Quoted: 15752 Post(s)
Liked 3,169 Times in 2,360 Posts
Keep in mind that the higher quality cassettes (Ultegra/Dura Ace) tend to have common carriers for the larger sprockets. They make those sprockets harder to manipulate, although one can sometimes discard the whole carrier.

The cheaper cassettes are generally riveted, although many people have removed the rivets, without replacing them.

If you do choose to go with 11T for a vintage freehub, then make sure it has the 11T groove around the end.


Left supports 11T cassettes, Right does not.
https://www.sheldonbrown.com/k7.html

I'm glad you found a cassette that you like on E-Bay. I've found several barely-used cassettes on E-Bay. But, one has to take care and both read the description and look at the photos carefully.
CliffordK 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 © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.