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Discussion: Chain tension at certain gear ratios

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Discussion: Chain tension at certain gear ratios

Old 10-07-16, 08:06 PM
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jeffreng
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Discussion: Chain tension at certain gear ratios

Is there a certain gear ratio where the chain tension causes the chain to wear and tear at a much higher rate?
I assume the shorter the chain the higher the tension because there is less chain links to bear the weight of the tension.
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Old 10-07-16, 08:57 PM
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Let's start off on the right foot.

The right chain tension is ZERO tension. The lower loop should always have some slack. However when riding fixed, that slack allows backlash (free movement before engagement) when you reverse torque. Ideally you want minimal backlash, so the goal is to have the least slack greater than zero slack.

Since sprockets always have some eccentricity, you have to confirm minimal slack at the tightest position.

Now that we've established what correct chain tension is, we can go forward and say that for practical purposes sprocket size and chain length have no effect on chain life. However, larger sprockets, either front or rear or both reduce chain wear by virtue of lowering tension, but the difference is proportional to the change. Practical limits on sprocket size keep the usable sprockets so similar that we can forget about worrying about any difference in chain life.

Choose sprockets to give you the gearing you want, set the chain slack correctly, use decent chain lube (let's not discuss which), and you'll get the life you get, which will be good enough.
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Old 10-07-16, 09:02 PM
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Chain length has nothing to do with chain wear. All the links transfer the same tension force from link to link in series, regardless of the number of links in the chain. Now, it is true that smaller cogs wear out faster, since they have fewer teeth to carry the load.
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Old 10-07-16, 09:12 PM
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Originally Posted by TejanoTrackie View Post
Chain length has nothing to do with chain wear. All the links transfer the same tension force from link to link in series, regardless of the number of links in the chain. Now, it is true that smaller cogs wear out faster, since they have fewer teeth to carry the load.
You started out OK, but faded in the stretch.

Chain length doesn't matter because all the wear happens only as the chain bends off the top of the rear sprocket and onto the top of the front. The length of the straight section doesn't matter because nothing s moving there.

But your reason for faster wear on smaller sprockets is far off the mark. Like the case of the chain, the wear only happens on top where the chain is bending on or off. The chain is stationary (relative to the sprocket) as it comes around, so no wear happens there.

Also, the bulk of the load is taken by the top tooth, and progressively smaller amounts on the next few, so only the top few teeth see any load, however load doesn't cause wear without movement.

Smaller sprockets wear faster because they lack leverage, so the pressure on the engaging rollers is much higher, plus each tooth spends more time in the "wear zone" at the 12 o'clock position.
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Old 10-07-16, 09:25 PM
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This should be fun.
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Old 10-07-16, 10:51 PM
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Originally Posted by seau grateau View Post
This should be fun.
And simultaneously irrelevant.


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Old 10-08-16, 07:51 AM
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Chain tension will vary based on frame geometry + gearing pairing which may affect wear rate. For example my 44x15 gearing on vintage sport tourer trek is quite slack and set all the way back in the dropouts (adjustment screws removed). Removing links for tighter fit = having too move it to far forward in dropouts. So I run it near the permissible end of slack, this does affect back pedaling slightly but have see zero evidence chain will dismount.

Conversely 48x17 gearing on racing trek 560 geometry equates to a slightly tighter chain set mid dropout (with adjustment screws set). This allows much tighter back pedal. Chain is still slack though which I think is the key for longer wear and smoother/quieter drivetrain. Over-tensioned chain will wear faster regardless of gearing.
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Old 10-08-16, 10:36 AM
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Originally Posted by dailycommute View Post
Chain tension will vary based on frame geometry
Chain slack is adjustable. Why wouldn't you adjust it adjust it to the correct amount on all frames, regardless of their geometry?
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Old 10-08-16, 02:39 PM
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Old 10-08-16, 07:16 PM
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Originally Posted by SquidPuppet View Post
Chain slack is adjustable. Why wouldn't you adjust it adjust it to the correct amount on all frames, regardless of their geometry?
+1. My FG, being an '80s MTB, has longer chainstays than the track-inspired bikes you see a lot of in SS/FG. But I'm still able to adjust it for a minimal but extant amount of chain slack that allows smooth running without being sloppy. Considering that removing (or adding) a chain link only moves the axle by 1/2", it should be possible to set up any SS/FG correctly if it has semi-horizontal or track dropouts.
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