Singlespeed Front Cog Ratio Discussion

[Pearl]

I always thought I had a 32 on the front of my rig until I folded it in half and realized it was a 33. Just now read that ChrisG runs a 34. I remember Jay saying that "34 is going to be the standard" or something like that. Can anyone shed some light on this?

Besides a smaller tooth for a rear cog, does running a bigger cog up front make a difference in performance?


I've heard the example of "one tooth up front equals two in the back", so:
33 x 19 is the same gear ratio as 32x17?
34 x 20 = 33 x 17?

Entertain me

 

[Norm]

IMO bigger is better until you start smashing it into rocks and break stuff. If it were practical I'd run a 42t in the front.

 

[clarkenstein]

you need to go to sheldon brown's website. lots of ratio/gear inches speak there.

 

[ChrisG]

you need to go to sheldon brown's website. lots of ratio/gear inches speak there.

+1 on this, there is a really good gear calculator on there which will let you see the comparative ratios.

A larger ring has a little more "chain wrap" so will tend to last longer, and I certainly can feel the smidge of added smoothness it provides.

 

[Pearl]

you need to go to sheldon brown's website. lots of ratio/gear inches speak there.

I've skimmed through it and used it before, but I realize it only helps me to get closer to a certain ratio over another. 34x20 is .1 shorter than 33x19. Not sure how big .1 is in singlespeedin', besides trying to dial in your gear choice.

+1 on this, there is a really good gear calculator on there which will let you see the comparative ratios.

A larger ring has a little more "chain wrap" so will tend to last longer, and I certainly can feel the smidge of added smoothness it provides.

I'm all about dat smoothness.

 

[Norm]

More teeth engagement translates to higher efficiency. More chain tension does as well. So run a 52-26 with the tightest chain you can and beat all your enemies up the hill.

.1 is negligible.

 

[ChrisG]

I've skimmed through it and used it before, but I realize it only helps me to get closer to a certain ratio over another. 34x20 is .1 shorter than 33x19. Not sure how big .1 is in singlespeedin', besides trying to dial in your gear choice.

View the ratios as "gear inches" to get a better basis for comparison/contrast.

33x19 is essentially the middle ground between 34x19 and 34x20.

 

[BiknBen]

More teeth engagement translates to higher efficiency. More chain tension does as well.

Huh? Where is this coming from? More teeth engagement is more efficient? You are gonna have to explain that to me.

And I'm just plain calling you out on the Higher chain tension suggestion. Excessive chain tension will efficiently destroy your chain, rings, and bearings.

Simple test. Put the bike in a stand and set the tension to whatever you wish. Turn the crank backwards. Any binding you feel or crackling you hear is the bearing of your freewheel or cassette being squeezed against their races. That is bad. This will shorten the life of the chain. If left that way long enough, you will wear the rings as well.

Quotes from Sheldon himself:
"If the chain is too tight, the drive train will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding."

"make the chain as tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible."

 

[Norm]

http://members.shaw.ca/bicyclescience/drivetrain.PDF

"the highest efficiency values occurred at highest chain tensions"

It stands to reason that I wasn't suggesting you tighten the chain to failure. Sheldon Brown says the same thing, specifically to tighten it as much as you can without damaging it. This is to address the debate of a tighter versus looser chain.

I can't find the other study which cites that more teeth engagement provides higher efficiency. I did run the idea by Woody and Utah (both mechanical engineers) and they agreed it made sense.

I believe the study also cited that chain lubrication had zero impact on the efficiency of the drivetrain.