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Shifting and Chain Flex, What is "Normal Effects"

Old 08-01-20, 04:14 PM
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Digger Goreman
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Shifting and Chain Flex, What is "Normal Effects"

Spending a LOT of time musing on the effects of shifting a chain and running it off the most straight chain line. Obviously, one has to shift at least one cog just to shift. Mechanically, what are the stresses the chain is undergoing and, more importantly to my musings, what stresses are magnified by shifting and running the chain one, two, or more cogs off the straight line?

Example: I run a 9 speed Shimano and standard KMC chain. I almost exclusively stay within two cogs of straight (2/5/8) but do a lot of all round pedaling in the middle chainring and 7th cog (two cogs off of straight). In reality (and or theory), what am I doing to the normal wear and tear on the chain? Is two, three, four, or more cogs off the straight line increasing problems for the chain or other parts. When does "off the straight line" become cross chaining?

Thanks for all constructive instruction!
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Old 08-01-20, 04:42 PM
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Originally Posted by Digger Goreman View Post
Spending a LOT of time musing on the effects of shifting a chain and running it off the most straight chain line. Obviously, one has to shift at least one cog just to shift. Mechanically, what are the stresses the chain is undergoing and, more importantly to my musings, what stresses are magnified by shifting and running the chain one, two, or more cogs off the straight line?

Example: I run a 9 speed Shimano and standard KMC chain. I almost exclusively stay within two cogs of straight (2/5/8) but do a lot of all round pedaling in the middle chainring and 7th cog (two cogs off of straight). In reality (and or theory), what am I doing to the normal wear and tear on the chain? Is two, three, four, or more cogs off the straight line increasing problems for the chain or other parts. When does "off the straight line" become cross chaining?

Thanks for all constructive instruction!
multispeed chains have lateral flex baked in. There really isn’t a magic “flex point” beyond which bad stuff happens. The greater the deflection, the lower efficiency and greater wear due to friction, but it’s incremental and likely not noticeable. Even the horrors of cross chaining (riding on a big-big or small-small combination) have been largely debunked as a cycling old wives tale (although I have to commend the old wives for getting out there and putting in the miles. Chapeau, Ladies) - although I avoid cross-chaining like the plague for no logical reason except years of conditioning. At the end of the day, drivetrain components are wear items, and chain/cassette wear is the small price you pay for having all of those great gear options at the back - I suspect that if you dedicated yourself to maximum deflection and as much cross-chaining as possible, you might find yourself replacing the chain at, say, 3500 miles rather than 4000 miles. A small price to pay for not worrying about chain deflection and wear

Last edited by Litespud; 08-01-20 at 04:46 PM.
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Old 08-01-20, 05:10 PM
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Musing less and riding more will relieve a lot of the stress; on you at least.
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Old 08-01-20, 05:11 PM
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The inefficiencies from tension being at an angle to the cogs or rings tend to behave like (1-cosine(angle)). For small angles relative to straight on they are completely irrelevant.
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Old 08-01-20, 06:20 PM
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You might ask about chain life in the single speed section and compare it to your own.
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Old 08-01-20, 06:28 PM
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Next time you have your chain off the bike take hold of a section with two hands wide apart and twist into an 'S' shape. It's amazing how much flex is build into it for the exact purpose of crossing chain lines.
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Old 08-01-20, 06:29 PM
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I was thinking about how I'd measure that. A power meter of some kind and a speedometer maybe? You could measure how much power was necessary to maintain the same speed in various gearing combinations. I kind of suspect background noise, like wind differences and measuring errors are going to drown out whatever data you'd get.
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Old 08-01-20, 08:27 PM
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There is this paper: "Effects of Frictional Loss on Bicycle Chain Drive Efficiency", Spicer et al, J. Mech. Des. 123 (2001) 598, https://doi.org/10.1115/1.1412848, that claims that losses due to imperfect chainline are lower than other factors that matter, with the dominant being ring-sprocket size combination.
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Old 08-02-20, 01:12 AM
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I briefly stop pedaling to shift and then "ghost pedal" (pedal without load) for half a turn to engage the next gear.

One gear at a time. I'm running a dirt cheap Chinese drivetrain so gotta be very careful!! So many chainlinks littering the road!

DON"T shift under load unless you're being paid to do it!

AND I probably wouldn't pedal hard off the saddle (standing up) if the chain is not in the biggest chainring. Pedaling hard standing up in the smaller chainrings puts a bigger strain on the chains, may not be an issue if you're light.
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Old 08-02-20, 07:18 AM
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Originally Posted by 2_i View Post
There is this paper: "Effects of Frictional Loss on Bicycle Chain Drive Efficiency", Spicer et al, J. Mech. Des. 123 (2001) 598, https://doi.org/10.1115/1.1412848, that claims that losses due to imperfect chainline are lower than other factors that matter, with the dominant being ring-sprocket size combination.
Went from this link to a search for the free article. Excellent info, but didn't address flexing. However, that led me to check through the Sheldon site (still no flex info) that led me to this https://pardo.net/bike/pic/fail-006/000.html
A few paragraphs in, concerns about flex are addressed, but admits no studies exist. Unfortunately beyond my mental and physical pay grades....
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Old 08-02-20, 09:45 AM
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Now all derailleur chains are of a 'bushingless' design.

In making the inner link plate, the steel from punching the hole, is formed into part of the bushing for the roller edges.
No longer a sleeve piece under the full width of the roller ... that used to be separate (& different steel)

a smaller contact surface on the ends , means it wears a bit sooner..

that is where your lateral flex comes from . the way rollers, pins and the partial bushing-flange interact.

Sedisport chains were the earliest adopters of this design, I think.. now it's universal.
3/32" full bushing chains are what's rare.








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Old 08-02-20, 10:50 AM
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This area of concern could be called "chain-weenieism".

I wonder if those with earbuds are less prone because of something to listen to during long hours riding.

I've gone through a number of 'weenieisms" for example contemplating airfoil shapes to stick on the backside of cable housings.


AFAS cross chaining, IMO adequate lubrication is a much bigger factor for both friction and wear. I spend plenty of time in big/big (10 speed).
If you have a triple, and use the whole cassette with the middle ring, it will make no difference in chain life., but it's fun to theorize.
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Old 08-02-20, 02:15 PM
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Could be, could be... and I'm hoping it inadvertently is... nothing to worry about and nothing worth doing about it if it is... i.e., as mentioned earlier, just a normal wear situation.
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