does any make a 23 tooth cog?
 

other than soma? if not I'm probably just gonna have to get a 22 tooth

I doubt it. Why not get the Soma?

And what the hell chainring do you have?

what's wrong with the soma? plus, 52t ring?

I've just been reading that the soma's aren't that good..I'm running 48/19 right now..just looking for something a little tougher.

A 23 tooth cog will not be tougher. Unless I'm not grasping what you mean by "tougher".

uh, if you want a tougher gear ratio, you need a smaller cog, not a bigger one.

doh, this guy beat me to it

maybe he's trying to develop a super-tough spin.

wouldn't lower gear inches make it easier to skid and what nots? I heard the guys from mash run 42/20 or something like that which gives them gear inches of 55.3..? right? I dunno?

lol.

Those MASH dudes run pretty big gears. You ever watch the parts where they just spin through traffic downhill? That's 75+ inches.

right. and you said you wanted your ride to be tougher.
how would being able to skid more easily equate to this?

I think he is referring to the quality of the cog folks.

You have nothing to worry about with Soma cogs. I've used about every brand of fixed cog available, and Soma's are basically just as good as EAI, Surly, Dura ace, and Miche cogs.

I've used a number of different cogs, too, with the exception of Phil Wood's cogs, and, to me, EAI cogs seem the best, by far, and Soma...well...I didn't like my Soma cog.

I have a thing about prime numbers, and in terms of cogs and chain rings, that means 13, 17, 19, 23, 43, 47, and 53 teeth.

This winter, I've also discovered the charm of riding at a much lower gear inch than I had ever anticipated.

I presently ride at 59 gear inches.

For those not familiar with gear inches, the typical factory fixie, with a 16t cog and a 48t ring, has about 78 gear inches.

I've ridden has high as 82 gear inches, and I need to ride at 72 gear inches or below in order to ride without a brake (I always ride with a front brake).

Further, I have always intuited that the greater the number of teeth in total, the more mechanical efficiency one experiences.
I couldn't prove this until just recently, when I picked up a book on mathematical proofs and the book addressed this very subject.

At any given gear inch, the more teeth one has, the more mechanical efficiency, or smoothness, if one wants to think of it this way.
At some point, though, the increased weight negates the increased smoothness/efficiency.

Anyway, I have 53 tooth chainring that I like, and I ride it with a 19 tooth cog.

How cool if I had a 23 tooth cog, for 60 gear inches and 23 skid patches (even though I don't skid).

can you explain the mathematics?

Let me find the book.

I have right here in plain view, somewhere. :)

Seems like more contact area with more teeth, but each link is bending fewer degrees as it travels around the cog.

Ken, your babble about prime numbers, gear inches, and tooth counts does not explain what was wrong with your Soma cog. A lot of people claim the EAI is better, but most people just repeat what they hear without actually perceiving any real differences. I can't honestly tell any difference between my Soma 17t cog and my EAI 17t cog*. Perhaps if I was on a smooth wooden track and had years and years of racing experience. But whatever minute differences that exist between these cogs don't matter on the road...all that really matters (aside from gear ratio obviously) is that the cog doesn't strip the hub, is reasonably quite, and doesn't wear too fast. They (EAI, Soma, Surly, etc.) all perform about the same on those terms.

edit: *I'm talking about the basic EAI cog, not the gold super($$)cog, which I have never used.

Mechanical efficiency with more teeth? Sorry, that doesn't make sense. If anything, the longer your chain the less efficient it is.

The bigger your cogs/chainrings the longer they will last.

sounds bout right...

Even if more a few more teeth (but with the same ratio) is more efficient in some way (less friction?), the effect of adding a few teeth to your chainring and cog would be so minor that it would be basically irrelevant.

I read about this somewhere (Sheldon Brown-ish no-bull**** place), that smaller chainrings and sprockets will cause more stress on the chain and as a result, higher friction losses.

Then there's that paper in "Human Power" that compared various gear systems - among them deraileur-equipped systems, and compared the transmission losses for various sprocket-chainring combinations. Even there, there was a trend to have higher efficiency (closer to 100%) with larger sprocket+chainring, although by no means a linear function.

Babble, eh?

How nice.

That kind of talk just endears me to people. :)

Maybe we could have dinner some time.

In any event, I had some reluctance to name the Soma cog, because I might have gotten a bad one, and it seems wrong to take away from someone's livelihood over a chance event...and a lot of people read this forum.

Anyway, I had an out of round cog from Soma.

How could that happen?

Certainly not because Soma doesn't try to market round cogs.

I think an anomaly somehow slipped through the process.

I would think a computer makes these things, and computers never make mistakes, right?

In any event, just handling the various makes of cogs, the EAI cogs feel and look like higher quality.

Subjective, I know, but very real to me.

I regularly handle high-end machined parts, and the EAI cogs have that look and feel.

=====

Now I'll get a letter from Soma's attorneys telling me to either produce the allegedly out-of-round cog or retract my statement.

Can I shortcut the process by retracting my statement before I make it?

Post Script: I'll find the book that had explanation of the efficiency of greater numbers of teeth; actually, combined radii.

Well, I couldn't find the book, so I did an Internet search.

I couldn't find one site that had the complete answer, but I'll just combine some of them.

I still haven't found the proof I want.

=====

For any given gear ratio, say 2:1, many different gear diameters and numbers of teeth will work, as long as they have a ratio of 2:1.

However, as the diameter of the gear pairs increase, the chain remains more straight as it reverses direction, and thus, each chain segment bends less.

As each chain segment bends less, the entire drive train system experiences less "chain segment bending loss."

One can further reduce chain segment bending loss, which involves not only the interaction between the pins and bushings, but the interaction between the pins and bushings and the faces of the gear teeth as well.

The straighter the chain stays, or the larger the "corner" it turns, the less chain segment bending loss.

Additionally, one can further reduce chain segment bending loss by replacing the bushings with bearings, so that the meeting surfaces between the gear teeth and the chain experience no friction.

The so-called bushings of high-end 1/8" track chains correspond to bearings rather than bushings.

At some point, the combined weight of the larger diameter gears and the more complex chain undoes the advantages of bearing surfaces between chain and gear teeth, and a straighter, less-bent chain.

Where do the two curves cross?

I don't know.

However, somewhere between a small chain ring and cog combo and a large chain ring and cog combo; and somewhere between the simplest lightest 3/32" bushingless chain, and the heaviest, most complex chain with bushings/bearings, lies the optimum in terms of minimal friction, bending loss, and weight.

I don't think they make a 23 (for 23 non skidding patches), but maybe you could get a (non prime) 24?!

Check out this site:

http://www.gizmology.net/sprockets.htm

It explains chain design and how the engineers design the profile of the teeth for a given size sprocket.

This site corrects a misconception I had about chain bushings:

http://chain-guide.com/applications/...cle-chain.html

Very good drawings.