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Chainline fudging/nudging?

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Chainline fudging/nudging?

Old 01-07-18, 01:27 PM
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tyrion
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Chainline fudging/nudging?

I have a 3x10 with 48, 36, 22 chainrings. Let's assume I use the 48t 30% of the time, 36t 50%, and 22t 20%.

Would it make sense to remove one of the BB spacers on the drive side (or relocate the spacer to the other side), moving the chainrings inward a hair? The assumption is this will reduce cross chaining on average given that the small chainring is used infrequently.

(of course if this causes clearance issues that negates the idea, but it doesn't look like it will cause any clearance issues.)
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Old 01-07-18, 01:50 PM
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IMO, it wouldn’t make enough difference to be worth the effort.
I might consider it while replacing the BB though.
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Old 01-07-18, 02:00 PM
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To my mind, chainlines aren't sacred. (More so if you are running 1/8" chain and single cogs but still, a few mms make very little difference. On a geared setup, even more so. If fudging it a little to improve the chainlines you actually use and you can live with the extremes (either they are usable, just noisier, say or you just plain don't use them, go for it.

Now, this is my thought. I ride my bikes until they die. I have yet to sell a bike. I've recycled a few. So I am not concerned with what others think. It is just me riding it. And as I get older, I am starting to think of my knees as a bigger investment than my cogs (or even the paint on my chainstays).

Ben
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Old 01-07-18, 02:14 PM
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I tend to use the smaller cogs more, so I just use a slightly longer BB. (I use sq. taper)
Same idea as yours. I assume you are locked in to a specific BB because of your crank?
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Old 01-07-18, 02:28 PM
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Originally Posted by dabac View Post
IMO, it wouldn’t make enough difference to be worth the effort.
I might consider it while replacing the BB though.
Yes, I have a new BB on the way, so I was thinking about this. I know we're talking 1 or 2 mm and minimal returns.
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Old 01-07-18, 02:33 PM
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I don't think it makes sense

especially if it makes other gears in the drivetrain have problems for the odd times you do need them.


Rather, if you're gears usage is so biased
this is really just an indication that your cassette/sprockets are the wrong sizes for you.
I'd look into changing those around before messing with the BB and chainline.
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Old 01-07-18, 03:14 PM
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Originally Posted by xenologer View Post
I don't think it makes sense

especially if it makes other gears in the drivetrain have problems for the odd times you do need them.


Rather, if you're gears usage is so biased
this is really just an indication that your cassette/sprockets are the wrong sizes for you.
I'd look into changing those around before messing with the BB and chainline.
I don't think using some chainrings more than others indicates something is wrong.
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Old 01-07-18, 03:21 PM
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As an aside:

Funny thing is, I soaked my chain in solvent then lubed it with Triflow, and now I can really hear the chain. When it's aligned it's nearly silent, but when it gets angled I can hear it. The greater the angle, the louder it gets.

So I have chainline on my mind. It's kind of interesting to hear the cross chaining.

(new chain, cassette, and BB are on the way - I won't be able to hear the cross chaining when the new chain is installed.)
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Old 01-07-18, 03:43 PM
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Factory chainline works really well when you shift as intended. The people that complain about the way the drivetrain was designed are generally using it "wrong" and crosschaining when it would make more sense to shift the front derailleur.


If you solvent clean a chain you are unlikely to ever get the type of excellent lubricant that comes from the factory back into the rollers. Hence the extra noise.
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Old 01-07-18, 03:50 PM
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I learned a lot from this when I was looking trying to figure out the 142+ spacing on my Enduro.

I run a 1x setup, but I think it's applicable.


https://www.oneupcomponents.com/page...-and-non-boost
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Old 01-07-18, 05:12 PM
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Originally Posted by tyrion View Post
I don't think using some chainrings more than others indicates something is wrong.
Maybe 'wrong' is too strong a word here.
Let's say 'unsuited' for your riding habits.

pick a different gearset that has your most used gears in the middle; that's where the shifting works best.
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Old 01-07-18, 05:16 PM
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Originally Posted by xenologer View Post
Maybe 'wrong' is too strong a word here.
Let's say 'unsuited' for your riding habits.

pick a different gearset that has your most used gears in the middle; that's where the shifting works best.
Most people ride in the middle or low ring more than the others. That's normal.
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Old 01-07-18, 05:32 PM
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Originally Posted by xenologer View Post
Maybe 'wrong' is too strong a word here.
Let's say 'unsuited' for your riding habits.

pick a different gearset that has your most used gears in the middle; that's where the shifting works best.
That's the way it is now: most used gears are in the middle (of both cassette and chainrings). We're still stuck with the fact that the granny gear is used much less than the other chainrings.
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Old 01-07-18, 06:42 PM
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Originally Posted by tyrion View Post
That's the way it is now: most used gears are in the middle (of both cassette and chainrings). We're still stuck with the fact that the granny gear is used much less than the other chainrings.
My gears are pretty non standard (to some) but they do the job I need.
I've got bad knees, ankle, back, sciatica on both sides, emphysema and will be 70 in a couple weeks.
I basically ride my 3X9 as a 1X9, since I don't have hills to deal with.
The granny has still come in handy a few times when a strong head wind came up. I had an new "low range" with closely spaced gears. Someday I hope to have a strong tail wind and see what the large ring is like.
My large ring is only 6T more than my middle and get used once in awhile when out of the city (stop lights/signs) and can actually just ride and a bit of a tail wind.
Use what works for you and don't worry about justifying it to anyone else. They probably won't understand anyway.
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Old 01-08-18, 01:55 AM
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Originally Posted by tyrion View Post
I have a 3x10 with 48, 36, 22 chainrings. Let's assume I use the 48t 30% of the time, 36t 50%, and 22t 20%.

Would it make sense to remove one of the BB spacers on the drive side (or relocate the spacer to the other side), moving the chainrings inward a hair? The assumption is this will reduce cross chaining on average given that the small chainring is used infrequently.

(of course if this causes clearance issues that negates the idea, but it doesn't look like it will cause any clearance issues.)
IMO it would make perfect sense. Better option, but manufacturers seem to not make (many) of those, would be getting a cassette that starts with 14 teeth smallest sprocket. You'd get a slightly lower top gear ratio, but less cross chaining when on the big ring.
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Old 01-08-18, 09:27 AM
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Never hurts to experiment. Sometimes you have to keep quiet about it though less you be denounced and ridiculed by the "Cycling Inquisition", similar to Galileo Galilei and the Roman Inquisition.
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Old 01-08-18, 10:53 AM
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Originally Posted by tyrion View Post
Let's assume I use the 48t 30% of the time, 36t 50%, and 22t 20%.
That sounds like pretty well distributed usage to me.

If you are really that worried about optimum chain alignment, you could achieve far greater impact simply with gear combo selection.

I would not bother moving the crank over. I would rather keep the q-factor of the pedals the same on each side.
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Old 01-08-18, 01:05 PM
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Derailleur chain, triple crank and a multi speed cassette? you are overthinking this .. let it rest.
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Old 01-08-18, 01:20 PM
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Originally Posted by fietsbob View Post
Derailleur chain, triple crank and a multi speed cassette? you are overthinking this .. let it rest.
As I said, after I soaked my chain I can hear the cross chaining. I CAN'T LET IT REST! MUST MINIMIZE CROSS CHAINING!!! (until I get a new chain, then my cross chain audio feedback feature will be gone)
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Old 01-08-18, 01:29 PM
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The fact that there are bottom bracket spacers on this bike *now*, indicates to me that the chainline (and/or bottom bracket length) has already been fudged with. Just removing them doesn't strike me as a mortal sin.
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Old 01-08-18, 01:43 PM
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do the ratio math , cross chain gears are redundant , being in overlapping ranges , with the similar ratio in a better alignment..
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Old 01-08-18, 02:20 PM
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Originally Posted by tyrion View Post
I have a 3x10 with 48, 36, 22 chainrings. Let's assume I use the 48t 30% of the time, 36t 50%, and 22t 20%.

Would it make sense to remove one of the BB spacers on the drive side (or relocate the spacer to the other side), moving the chainrings inward a hair? The assumption is this will reduce cross chaining on average given that the small chainring is used infrequently.
No harm in trying it to see whether you like it.

Another option is to look at chainring bolt spacers. I have used them on a couple one-by setups to dial-in the chainline.
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Old 01-08-18, 04:54 PM
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I've been in the same boat a few times, where I went for the limits of a shorter bb while having to respect both chainring clearance with the chainstay and the ability of the front derailer to still shift to the smallest chainring with authority.

I have a preference for using the biggest chainring as much as practically possible.
The bigger ring has the chain moving faster and under less tension, so shifting is faster and can be completed under a higher level of sustained power without slippage.
As well, the big ring keeps the chain better under control when off-roading, or when crossing railroad tracks at speed for instance, so there will be less slapping of the chain onto the chainstay.

And then there is the consideration of drivetrain reactivity lost to elasticity of the entire complex load path from chain to chainstay. Did you know that a 10% reduction in chainring tooth count actually causes a 22% increase in drive elasticity between the pedal and the road? I'm betting that you heard it here first!

Lastly, many of us, as mentioned, end up using bikes for riding where the smallest ring just doesn't get much use, and a chainline modification can be the cheapest fix as long as there is still chainring clearance and the front derailer can still pull inward far enough to shift to the smallest ring.

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Old 01-08-18, 06:07 PM
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Originally Posted by Bill Kapaun View Post
I tend to use the smaller cogs more, so I just use a slightly longer BB. (I use sq. taper)
Same idea as yours. I assume you are locked in to a specific BB because of your crank?
As I understand it, it's a 68mm bracket and fits a road crank without spacers, but with a mountain crank (which mine is) it needs spacers. Currently there are (IIRC) 3 spacers, 2 left, 1 right.
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Old 01-09-18, 11:11 AM
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count teeth, do the math (Yet?)

a 16t gap like 40 to 24 offers maybe 4 ratios lower than the 40:34..

so rather than shift to that 5th gear on the 24t, double shift to a similar gear ratio on the 40t.. middle.

>You may have different tooth count numbers < but the idea is transferable.





.....
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