# Even vs. Odd # of Teeth on Freewheel/Cog



## Wrex Everything (Oct 29, 2006)

Has anyone else heard any "naysaying" regarding the use of an odd # of teeth on your rear cog? I want to run a 32:21 set up on a new 29er (Tahoe rides primarily), but seems like I heard someone dissing on using an odd numbered amount of teeth on your rear cog while running an even number of teeth up front at the chainring.


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## ionsmuse (Jul 14, 2005)

****.

I better go take the 37x15 off my fixie right now.


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## Schmucker (Aug 23, 2007)

Sheldon Brown talks about this. Basically when you run an odd number on one or both it results in even wear on every tooth throughout the life of the chain. If you use even number and always put the chain on the same teeth you can wear out half the teeth at a time.


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## dashSC (Jan 27, 2008)

Schmucker said:


> Sheldon Brown talks about this. Basically when you run an odd number on one or both it results in even wear on every tooth throughout the life of the chain. If you use even number and always put the chain on the same teeth you can wear out half the teeth at a time.


Hmm, never thought about that. Good thing to keep in mind, especially since my 32:20 is a bit too spinny for around here. Maybe I'll step up one. 

Also, I know it makes a difference when riding a fixie, as the number of 'skid patches' [also on Sheldon's site]. Even numbered cogs on front and back lead to fewer skid patches in general.


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## DanD (Jan 15, 2004)

dashSC said:


> Hmm, never thought about that. Good thing to keep in mind, especially since my 32:20 is a bit too spinny for around here. Maybe I'll step up one.
> 
> Also, I know it makes a difference when riding a fixie, as the number of 'skid patches' [also on Sheldon's site]. Even numbered cogs on front and back lead to fewer skid patches in general.


I learned the fixie thing the hard way, some even:even gear ratios can really destroy a tire. I think number of skid patches is equal to the lowest common denominator of the cog and chainring. When I was running 48:16 it took no time to wear the tire bald in the 3 spots.


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## Cygnus (Jan 7, 2004)

*prime numbers*

i'm running a 19 tooth eno freewheel. i like prime numbers on my freewheels.

SS math.


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## Wrex Everything (Oct 29, 2006)

Schmucker said:


> Sheldon Brown talks about this. Basically when you run an odd number on one or both it results in even wear on every tooth throughout the life of the chain. If you use even number and always put the chain on the same teeth you can wear out half the teeth at a time.


Sooo, if anything, am I hearing that it's _actually a good idea_ to go odd-numbered on your cog/freewheel?


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## Velobike (Jun 23, 2007)

I like prime numbers too. 

Prime numbers mean the wear gets spread better and not localised.

But if it means I can't get up the hill I am prepared to compromise my principles


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## Kalgrm (Sep 22, 2005)

Velobike said:


> Prime numbers mean the wear gets spread better and not localised.


Sorry, I'm calling BS. Freewheels coast when you aren't pedalling, so you spread the wear anyway.

It would be different on a fixie.

Cheers,
Graeme


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## Velobike (Jun 23, 2007)

Kalgrm said:


> Sorry, I'm calling BS. Freewheels coast when you aren't pedalling, so you spread the wear anyway.
> 
> It would be different on a fixie.


The BS is in the mind of the beholder, methinks.

It isn't different on a fixie.

The coasting is done by the pawls in the freewheel. The cogs are girt by the chain and don't slip (on my bike anyway)


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## fat guy (Feb 19, 2005)

This is all nonsense, other than avoiding even-even on a fixed bike.
The low cost to replace the entire drivetrain on a MTB is not worth the concern of using an even-even setup.


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## chairthruster (Dec 17, 2004)

fat guy said:


> This is all nonsense, other than avoiding even-even on a fixed bike.
> The low cost to replace the entire drivetrain on a MTB is not worth the concern of using an even-even setup.


Sure, the effect might not be very significant, but nonsense? Why not extend the drivetrain life if possible. cog + chain + ring of good quality can approach $100.


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## Schmucker (Aug 23, 2007)

It actually makes no difference either way for most of us I'm sure. I pull my chain off frequently to clean it. Any time you drop a chain, or change a flat, the chain is no longer on that teeth. You have a 50/50 chance of putting it back on the same teeth as before unless you mark it. Odds are you're going to wear it all out evenly.


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## RSW42 (Aug 22, 2006)

If the bike is south of the equator, will the wear pattern be different, much like how toilets flush in the opposite direction?



.


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## serious (Jan 25, 2005)

*If you use even number and always put the chain on the same teeth you can wear out half the teeth at a time.*

I would like to understand how can one reach such a strange conclusion. The only thing that makes sense is to change the position of the chain on the ring and cog so that you avoid the same teeth being in the same position through the power phase of the pedal stroke.


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## fishcreek (Apr 10, 2007)

racerdave posted this calculator before and totally makes sense if you are running fixed. if you enter an odd numbered cog, notice the skid patch analysis and you will see that the skid position is evenly distributed on every pedal stroke unlike the even numbered cogs. this explains the tire wear for fixies. and i think, the same applies to a freewheeler on his drivetrain wear. odd numbered drive = even wear. odd/odd combo = best.


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## Velobike (Jun 23, 2007)

RSW42 said:


> If the bike is south of the equator, will the wear pattern be different, much like how toilets flush in the opposite direction?


Don't be silly. They're upside down there so it works the same way in an upside-downy fashion.


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## serious (Jan 25, 2005)

But that calculator is for *skid patches*. First you cannot translate skid patches to a freewheel for obvious reasons. You can barely translate it to a fixed cog, since the chain wrap will certainly distribute the force over many teeth (unlike the skid patch on the tire).

Common guys use some common sense. With 32:16 you get one skid patch. Is somebody going to theorize that 1 tooth will get worn on the cog? Common!


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## fishcreek (Apr 10, 2007)

fishcreek said:


> the same applies to a freewheeler on his drivetrain wear.


i never mentioned tire wear because i know.


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## fat guy (Feb 19, 2005)

chairthruster said:


> Sure, the effect might not be very significant, but nonsense? Why not extend the drivetrain life if possible. cog + chain + ring of good quality can approach $100.


I think you have quality confused with overpriced components, but that's another topic.

You only benefit from even-even if you plan on running your chain until it falls apart. Who wants to be out in the woods when pins start shearing off? :madman:


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## kdonks (May 27, 2005)

Just use a half link to make it an odd number of chain links........


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## fishcreek (Apr 10, 2007)

kdonks said:


> Just use a half link to make it an odd number of chain links........


true.


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## bd.sahib (Aug 17, 2005)

*3's*



Cygnus said:


> i'm running a 19 tooth eno freewheel. i like prime numbers on my freewheels.
> 
> SS math.


All choices should be multiples of three and add up to multiples of 3.

egg-sample: for a 6er (2x3), 33x15... 3+3=6 and 1+5=6
for a 9er use an 18t fw (1+8)

and sew on

Instead of using a half link, I just file the ends off my track drop outs. Prevents the recurring bald patch and enhanced my track stand. Saves wait too.


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## Cygnus (Jan 7, 2004)

*SS math*

part of the fun of riding SS is that it frees your mind from shifting (sheldon brown)

so, you have time to think about other things when you're riding, like gear ratios and gear inches for particular terrain, and how your chain links, chainring teeth, and cog teeth interact mathmatically.

but, obviously, don't take it too seriously.


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## itsdoable (Jan 6, 2004)

If you run a chain full of half links, odd # of teeth on the chain ring _and _cog, then it follows that your drivetrain will not ever wear out.


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