No. The chain speed will depend on the rpm and the size of the chain ring. If your cadence is 90 rpm, the chain ring makes 1.5 revolutions per second. If the chainring has 52 teeth, the chain will move 52*1.5 = 76 teeth (=38 inches or 0.965 meters) per second. If the chainring has 42 teeth, the chain will move 63 teeth (31.5 inches or 0.800 meters) per second. A watt is a Nm/s, so if 300 watts is traveling through the chain, at 90 rpm with a 52-tooth ring the chain tension must be 311 N while at 90 rpm with a 42-tooth ring the chain tension must be 375 N.

This is how the old Polar S710 power meter worked. It measured chain speed and chain tension and multiplied them to get power.

Sure, but we didn't have an electric motor as a power source. What we had were a SRM and a PT. As has been pointed out elsewhere (including by Spicer himself), Spicer's findings were at odds with what had been observed in the mechanical engineering community for about a century: that efficiency increases with sprocket size. We weren't doing something de novo. Spicer's findings were the odd ones.

This is why we can't have nice things.

No, it's not. I believe this has been explained by several other posters, RChung giving the best explanation. Trying again, torque = force * distance. Obviously at the same GI and power, your crank torque is the same regardless of chainring. However distance of the chain from the BB varies, hence force on the chain also varies. Just look down at your rings as you pedal and visualize it.

Just two thoughts as a "for what it is worth":

In the 1980's, bushingless chain was introduced for bicycles. Essentially all modern geared bike chains are of this design. Bushingless chain shows higher friction losses in the loaded direction, and lower loss when side loaded. When people talk about chain efficiency being known for a century, I believe a variable was introduced in the 80's that modifies that conventional thought.

The Spicer write up linked, and a different Human Power article on efficiency of different shifting methods, all include a feature that the bicycle does not have. On page 5 of the link, the write up specifies that the output shaft could be moved to set distance, in a way that I read as longitudinally as well as laterally. This allows each chain ring to be set at its optimal center distance. A bicycle does not move center distance as it is used. Deviations from optimal CD have a direct impact on losses from chordal action.

I may be misreading. Just thoughts.

Chain pins and bushings wear when they move in relation to one another. This movement occurs as the chain rotates into its sprocket and again out of the sprocket. There is little wear as the chain straightens leaving its sprocket since there is little or no load. A chain being pulled might as well be a solid rod.

Small sprockets increase the rotational movement between pins and bushings. Large sprockets reduce the wear rate between pins and bushings, every thing else being the same.

Joe

Yes

See also post No.50, bottom of page 2 on this thread.

This.

FBinNY & Sixty Fiver:

Yes to both Y'all !! I just wanted to say it in isolation. Big sprockets are better for chain wear.

Joe

The most noticeable friction losses occur on modern cassettes with an 11-x... when you drop below 13 teeth the frictional losses become much greater than they do for similar changes at the low end.

My fixed gear bicycles (save for the winter bike) all run larger chainwheels and larger cogs to minimize friction and reduce wear on the chain and drive.

A 46/16 and 52/18 are the same gearing and with all things being equal, the 52/18 is smoother running and longer lasting.

In isolation this statement is true, but thats only part of the picture when talking about multispeed bikes. Look at the friction facts graph. 53x28 has higher friction losses(=increase wear) than 39x21 for ~ the same ratio. Side loading introduces its own wear patterns. Its also why many triathletes use larger chainrings, not because they can turn a 56x11, but so that their desired gear is in the middle of the cassette.

In the motorcycling world, 16 teeth is (or was) considered too small. Honda's 750 four had a rather high chain wear rate with its 16T front sprocket. The Brits typically used 20 or more and their chains lasted longer.

Joe

Hmm --- why would 52x28 wear faster than 39x21? What else is going on besides pin/bushing rotation wear?

Joe

Because you are cross chaining and putting a side load onto the chain. Just listen to your chain when you go to big/big.

The wear is from the outer ends of the captive links rubbing the captured links.

It starts debates when trying to quantify the extra wear, but friction = wear.

I know this from experience as I rode a Honda 750, the nice thing is that you can change the front sprocket.

I used to do a lot of long road trips and increasing the gear ratio made it less of a screamer at high speeds and improved the mileage... as my bike also had an 812 big bore kit and some other performance upgrades the bottom end was still rather excellent as the engine has excellent bottom end torque.

Does anyone really consider this burning issue when actually riding their bicycle?
I select the gearing combination that matches the terrain, wind conditions, cadence and level of effort I feel like putting out w/o agonizing over chain speed vs. wear and relative humidity.
Constant maximum cross-chaining on crud encrusted un-lubricated worn out chains and cogs is ill-advised, other than that........

What I find more interesting is how many riders have zero idea of what the actual gear range and progression of gearing is fitted to their machines, and how to effectively use it.

-Bandera

A lot of it is going to depend upon what's ahead of you.

If you see a big hill/incline ahead of you, use the smaller chainring/cog combo.

If you see a flat or downhill, use the bigger chainring/cog combo.

GH

I don't concern myself with it. It's interesting but trivial.

when splitting hairs it might pay dividends to pay more attention to decimal points, if the intention is to make convincing arguments, when comparing gear ratios.

and possibly (i haven't done the proofs yet ) prime numbers of teeth in cogs or chainrings should be avoided too, as well as irrational ratios.

Hehe, when they start pulling out the charts and references to white-coat lab studies and such.....it's just a euphemism for "There is no discernible difference in the real world". You'll see the same modus operandi in many subjects, such as:

Clipless vs. straps.
Elliptical chainrings.
Carbon vs. kryptonite.
23mm vs. 25mm tires.
15.2 lbs. vs. 16.07 lbs.
Red vs. black.
Dogs vs. cats..... (O-K that one' absurd- we all know that dogs rule!)