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What the heck is going on here?(10 posts)

What the heck is going on here?Crankist
Jun 7, 2002 7:19 AM
Sorry for that foul, sewage mouth language, but I gotta know: why, at approx. equivalent chain inches, does it just feel better to be on the big chainring? For example: my normal speed is 20.5 mph at around 95 cadence. Both 52/19 & 42/16 result in 72.15 +/- 1.25 chain inches and gets me to that speed/cadence, but the 52/19 feels like I'm smoother, stronger, and well, better! Que pasa?
chain line?DougSloan
Jun 7, 2002 7:30 AM
I'd guess that it's either a straighter chain line, or your imagination.

Try both with an HRM at a constant speed and see if there's a difference.
Jun 7, 2002 8:10 AM
a 52/19 is not a straighter chainline than a 42/16! on a 9 speed setup, the 42/16 is dead straight, and depending a what cassette you are runnng, the 52/19 has a nice angle to it. if you are running a 12/25, yea, it's pretty straight, but the 42/16 is still straighter. it's all in your head!
put on a 44 and there's not much need for the big ring unless you're going over 40kmh.
re: What the heck is going on here?biggiecycles
Jun 7, 2002 7:30 AM
I remember reading long ago....
in bicycling magazine or perhaps mountain bike action, that it was better to be in the larger chainring...

something about less friction or something ...but I never really understood it.. if you have the same gear inches, the chain is going around the same number or time per minute or whatever.... so it has to go through the same number of bends, the only real difference there is the curve around the larger ring is less drastic, but if your chain is in good shape it's basically a wet noodle anyway..

so, i too would love to hear some clarification on this phenomenon... (especially since in the above example, the chainline seems to be better in the smaller ring)
I remember the same story, I thinkcory
Jun 7, 2002 7:35 AM
At the time, I didn't care enough to pay much attention, but I think it was in Bicycling, and I remember about as much as you do--it was better to be in the big ring for some reason I didn't really understand.
Might not even be true, though. I remember a long discourse in Road & Track magazine years ago explaining why cars could never corner at greater than 1g. Sounded good at the time...but now they're pulling 3+.
Could it be...Shad
Jun 7, 2002 7:49 AM
The large ring and a larger cog size mean more teeth of the chain are being engaged during the crank revolution and less power is being lost in the loose part of the chain? Or perhaps this just makes it "feel" like things are rolling better/tighter. My fixie doesn't feel quite the same when the chain has too much slack.
Actuallythe dad
Jun 7, 2002 8:11 AM
Since you are using a bigger diameter chainring, it yields less leverage. To make up for that, the larger cog on the back has more leverage. The result is for equal power to the back wheel, there is less tension on the chain. That, theoretically, should cause it to wear less.

I can't answer why you would feel better in one gear than another equivlent gear. I'm pretty sure that tension differences on the chain aren't the reason.
My guesslaffeaux
Jun 7, 2002 8:17 AM
I've noticved the same thing.

My guess is that it has to do with the chain's relative position on the moment arm (i.e. the cranks). The cranks act as a lever that pull the chain around. The lever is constantly rotating around the BB, and the length of the lever remains constant. However in the larger chain ring, the point where the chain meets the cranks arms is closer to the end of the lever. My guess is that there is some mechanical advantage in this.

Any mechanical engineers care to confirm?
That was the whole idea behind Shimano's Biopace...Ken of Fresno
Jun 7, 2002 11:54 AM
Vary the distance of the chain to the lever arm at different places where more torque is needed/available. It failed misserably though.

re: I noticed that years ago and decided it was all in my mind.dzrider
Jun 7, 2002 9:37 AM
Look at me! I'm riding on the big ring. It was so much better for my morale. Older now and less concerned for appearances I frequently forget which ring I'm on and even wind up cross-chained which is far more embarassing than riding on the smallest chain ring.

On a more mechanical note, I find that one of the signs of a stretched chain is that it feels worst with the straightest chain lines. Perhaps the bend in the chain takes up more and more slack as the chain line worsens.