Chain doesn't wrap around lower pulley when it's on the lowest gear on the
#76
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It's not necessarily that simple: straighter chain line but with greater rotation of each chain link as it leaves and joins the smaller sprockets under load, at lower speed and greater load because chain tension is proportionally higher running 39/21 than it is running 52/28 although the ratio and force at the crank are the same. I wonder how that all weighs up.
You are overthinking this. If there is more tension because of greater rotation then at the same time the sum of the aggregate would be lower because of less rollers contacting the cog.
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#77
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Chain tension is on the return or slack side of the loop not the drive or power side. The tension applied on the drive side between the rear cog and the front chain rig is the same regardless of tooth count of either. Force required will be the same if the ratio is the same.
If there is more tension because of greater rotation then at the same time the sum of the aggregate would be lower because of less rollers contacting the cog.
Friction advantages of larger sprockets have been known for well over a century (see the discussion on chain gearing in Bicycles and Tricycles by Archibald Sharp, 1896), and it's confirmed by modern drivetrain power loss testing (see page 9 in this report).
#78
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No. The chainring is basically a lever. If your power and rpm is the same but the ring is bigger, there's more chain speed and lower chain force.
Rollers contacting the cog isn't the problem. It's when things articulate and when they rub. Although frequency of these interactions is lower in the smaller-cogs case, both the size and the force of the interactions if higher, and this combines as a net drawback.
Friction advantages of larger sprockets have been known for well over a century (see the discussion on chain gearing in Bicycles and Tricycles by Archibald Sharp, 1896), and it's confirmed by modern drivetrain power loss testing (see page 9 in this report).
Rollers contacting the cog isn't the problem. It's when things articulate and when they rub. Although frequency of these interactions is lower in the smaller-cogs case, both the size and the force of the interactions if higher, and this combines as a net drawback.
Friction advantages of larger sprockets have been known for well over a century (see the discussion on chain gearing in Bicycles and Tricycles by Archibald Sharp, 1896), and it's confirmed by modern drivetrain power loss testing (see page 9 in this report).
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#79
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Ya might want to review the document you linked to. Page 3, item 3 in bold says that I am correct with regards to big ring and lowest three cogs is less efficient than the same ratio of small ring. So after all the exercises to measure such things my intuition prevails. Granted that I may be in error as to the why that I am right. Thanks for the link by the way.
I agree that low gears while in the small ring is usually mechanically better-running than big-big crosschain, at least within the scope of typical road drivetrains.
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Force applied at the pedal will be the same if you ignore the issue I raised i.e. losses caused by factors affecting drivetrain efficiency including but not limited to "cross chaining". But assuming all these losses are negligible then yes, the force required at the pedal to ride at a certain speed remains the same if the sprocket ratio remains the same.
"Fewer". I was playing devil's advocate - I don't know the answer nor do I have any particular desire to investigate further; I was simply pointing out that it is potentially more complex than just "more straight chainline always better than less straight chainline". But I think we have pretty much agreed that it doesn't really matter unless you're going for the hour record.
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#82
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If you don’t understand by now that the biggest cog in back is the easiest, and therefore slowest gear, while the large chainring is the hardest, but fastest gear, and that using them at the same time is dumb just for that reason, then I really can’t help you.
Best of luck in your cross-chained journeys.
Last edited by smd4; 07-28-23 at 04:13 PM.
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#83
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SNIP
"Fewer". I was playing devil's advocate - I don't know the answer nor do I have any particular desire to investigate further; I was simply pointing out that it is potentially more complex than just "more straight chainline always better than less straight chainline". But I think we have pretty much agreed that it doesn't really matter unless you're going for the hour record.
"Fewer". I was playing devil's advocate - I don't know the answer nor do I have any particular desire to investigate further; I was simply pointing out that it is potentially more complex than just "more straight chainline always better than less straight chainline". But I think we have pretty much agreed that it doesn't really matter unless you're going for the hour record.
My answer didn't consider mechanical advantage. You win on that one.
I was thinking of the tension that the derailleur added, you were thinking of the tension the crank applies under force... guess we were both confused as to what each other was referring.
Sorry replying with a different order than your objections.
Further the linked document conclude that what @smd4 and others have been saying is factual. Cross chaining is to be avoided for several reasons.
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Last edited by Black wallnut; 07-28-23 at 03:59 PM.
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In a Tour de France video from around 2005, the riders are on a slight rise just before the stage finish. A motorcycle cameraman zooms in on Lance Armstrong's drivetrain, showing that the chain is on the large cassette sprocket and the large chainring and prompting Phil Liggett to exclaim, "He's in the correct gear." He goes on to explain that under those circumstances, shifting down the cassette to get to his sprint gear is a more reliable move than shifting to the larger chainring from the smaller chainring.
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#85
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The bickering about cross chaining is hilarious. Regardless, this drivetrain shouldn't do that in this gear if everything is well adjusted.
I'd suspect hanger alignment(checked), bent derailleur or excessive pivot play, excessive play in guide pulley(replaced), poor match of chain/pulley wear, and/or incorrect chainline.
I'd suspect hanger alignment(checked), bent derailleur or excessive pivot play, excessive play in guide pulley(replaced), poor match of chain/pulley wear, and/or incorrect chainline.
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Yep. But some people prefer to drag up worn out arguments rather than to contribute something useful (likely because they have nothing useful to contribute).
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Not really. I'm a big "don't cross chain" person, but it's not dumb to use the big/big combo every once in a while. Personally I don't make a habit of it, having "grown up" when cross chaining was taboo, but use it when the situation warrants - several of which have been described. No harm, sometimes expedient, not dumb.
Last edited by Camilo; 08-02-23 at 12:39 AM.
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#88
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and it's confirmed by modern drivetrain power loss testing (see page 9 in this report).
People have to understand the simple thing: all that mythology about purported "disadvantages of big-big" actually originates from marketing departments of bicycle drivetrain manufacturers. It all dates back to the initial transitional period from friction-based shifters to indexed ones. While no one can deny the advantages of the latter, the manufacturers still had to combat the uproar of disapproval from the cycling community, caused by the fact that they effectively blocked big-big when it was well within reach. While these companies frantically worked on their big-big solutions (which gave us "trim" feature in indexed systems, as I mentioned previously), their marketing branches generated massive amounts of "you don't need big-big, because..." propaganda to persuade people into buying their initial big-big-incapable offerings. And when trim became a thing in indexed shifters, it took some time to trickle from TOL groupsets to more mere-mortal-oriented ones.
What we are fighting today, with our excellent big-big educational effort here, is not mechanics. It is the residual effect of that massive brainwashing campaign that managed to take hold in some feeble minds.
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"Trim" existed in index shifting systems starting in 1985. As I mentioned previously. It's not "new." It didn't "trickle down." Some feeble minds who have been brainwashed still don't understand this.
#90
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People have to understand the simple thing: all that mythology about purported "disadvantages of big-big" actually originates from marketing departments of bicycle drivetrain manufacturers. It all dates back to the initial transitional period from friction-based shifters to indexed ones. While no one can deny the advantages of the latter, the manufacturers still had to combat the uproar of disapproval from the cycling community, caused by the fact that they effectively blocked big-big when it was well within reach.
accompanying progress in chain construction, which effectively eliminated the issue of excessive wear in cross-chained gear combinations. By the time 10-speed (or, perhaps, 9) drivetrains went into mainstream, the matter of wear, as well as chainline stability issues became ancient history. Skewed gear combinations no longer had any appreciable effect on the wear of the components or drivetrain stability.
At any rate, your new argument is false, as evidenced by admonitions toward cross-chaining from prior to that period. For example, here's a page from a 1978 guide by Huret on derailleur usage, strongly recommending users against riding "with a crossed chain."
Last edited by HTupolev; 08-02-23 at 07:06 PM.