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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 10-14-09, 08:45 AM   #1
Rahzel
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How NOT To Adjust Chain Tension On A Tandem

After dropping the timing chain during the STR last weekend, I decided that it was about time to adjust the timing chain tension. I checked and confirmed that there was too much play (about 1" in each direction) in the timing chain, so I set to work.

I would like to offer the following pieces of advice to anyone who, in the future, decides to adjust chain tension on their eccentric-equipped tandem:

The CORRECT WAY to adjust timing chain tension on a tandem bicycle:

1. DO NOT REMOVE THE TIMING CHAIN.
2. Adjust eccentric to give proper chain tension.
Total time: 4 minutes.

Rahzel's INCREDIBLY DUMB WAY to adjust timing chain tension on a tandem bicycle:

1. Remove timing chain and clean it.
2. Adjust eccentric, guessing at the amount of adjustment that needs to be made (since the chain is not on the bike). Be sure to rotate the eccentric more forward than you think you need, as a tight timing chain is better than a loose one!
3. Attempt to put timing chain back on bike.
4. Curse and sweat for 20 minutes because the timing chain "for some reason" won't get back on the timing rings.
5. Manage, somehow to get the timing chain mounted.
6. Notice that there is ZERO play in the chain anywhere, and that the cranks barely turn the chain is so tight.
7. Panic.
8. Remove one of the chainwheels in an effort to get the chain back off the bike.
9. Gash your hand on one of the chainwheel teeth as the chainwheel comes flying off the bike due to the huge amount of chain tension.
10. Loosen the eccentric.
11. Re-install the chainwheel.
12. Put the timing chain on the bike. (It's much easier when the eccentric is loose!!! Who knew!!!)
13. Adjust eccentric to give proper chain tension.
Total time: 134 minutes.

Who has two thumbs and is young and stupid? THIS GUY.

Oh well. The chain is adjusted, nothing is broken and all I lost was 2 hours of my time and some pride.
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Old 10-14-09, 10:14 AM   #2
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Well, at least you got the timing chain cleaned...










.

Last edited by Stray8; 10-14-09 at 01:42 PM.
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Old 10-14-09, 12:17 PM   #3
Steve Katzman
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I have to admire your humility. When I do dumb stuff (hardly ever ) I usually keep it to myself.
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Old 10-14-09, 12:48 PM   #4
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Good job! You wouldn't happen to have video or pictures of your process, would you?
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Old 10-14-09, 01:33 PM   #5
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A bit like working on a car - the second time is usually much faster.
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Old 10-14-09, 08:21 PM   #6
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I've never replaced my timing chain, or adjusted my eccentrics.

When you say there was about 1" of play each direction what exactly do you mean? I'm just not understanding...

Do people replace the timing chain at the same interval as the regular drive chain? Do you replace the timing chainrings? What advantage or disadvantage is there in going to a larger or smaller chainring on the timing side (can you effectively have a 'compact' tandem setup by using smaller timing rings and smaller cogs, and drive rings to save weight)?

Insert joke here about giant fat cyclist weighing more than most tandem teams worrying about saving 25g.

How many regular chains does it take to make a timing chain?

If everyone remembers the belt drive thread, the materials science studies that were linked showed that the tighter the chain the more efficient the driveline. Obviously, one would think there would be a point of diminishing returns. As much as I think belt drive is silly and inefficient, you have to admit it would essentially last forever and never need maintenance.
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Old 10-14-09, 08:25 PM   #7
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I will let the experts comment on some of your questions (and see Sheldon Brown's page for more info on this topic), but I have answers for a few of your questions...

Quote:
Originally Posted by mtnbke View Post
When you say there was about 1" of play each direction what exactly do you mean? I'm just not understanding...
I was able to push the chain at least 1" (sometimes more) in each direction, with the point of contact being centered between the timing rings on the top length of the chain.

Quote:
How many regular chains does it take to make a timing chain?
It seems like it requires approximately two regular chains on my bike.
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Old 10-14-09, 09:16 PM   #8
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Quote:
Originally Posted by Rahzel View Post
It seems like it requires approximately two regular chains on my bike.
For all the people with 11, 10, and 9 speed drivetrains:

Do you run 8 speed rings and chains on the timing side? Although you can't find Wipperman nickel coated 8-speed stuff anymore, there are still some decent 8-speed chains out there.

8 speed is stronger, the rings will last longer, and the chain will stretch 'less'.
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Old 10-14-09, 09:24 PM   #9
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For the benefit of our newer readers....

I've never replaced my timing chain, or adjusted my eccentrics.

Not a big deal if you don't ride it much; however, if the sync chain is visibly 'drooping' when your tandem is propped up against an object it might be prudent to adjust that excess slack out of the chain to preclude an accidental derail while you're riding.

When you say there was about 1" of play each direction what exactly do you mean? I'm just not understanding...

Slack on a sync chain is typically measured between the resting height of the chain (top or bottom run, it doesn't matter) and the upper limit that's reached when you lift the chain by hand at the mid-point. You can usually run a sync chain with zero slack to about 3/4" without having any risk of binding or a derail. Even at Zero slack, the sync chain will generate some slack along the lower run under load once the captain puts power into the front cranks. Any slack that's intentionally left in the chain to allow for manual, hand-derailing will increase under load as well.

Do people replace the timing chain at the same interval as the regular drive chain? Do you replace the timing chainrings?

Some probably do if they don't know any better; however, if you check your chains for wear using a ruler or chain-wear gauge like the CC-2 from Park Tools you'll typically find the drive chain will need to be replaced at least twice as often as the sync chain, perhaps even more often than that. A sync chain carries only the pedal loads from the captain back to the stoker + any backpedal pressure the stoker may be generating if they aren't pedaling in circles. Moreover, a sync chain is a 1:1 ratio direct drive that doesn't see nearly the wear and tear that a drive chain does given the much lower gear ratios achieved with the small alpine / granny ring and a wide-range cassette's taller sprockets and the side loads that are generated by the front and rear derailleurs.

However, you will reach a point where you may want to change your sync chain based on wear, even though a sync chain and timing rings will typically work just fine even when they're really worn out. The only problem that you might see with a badly worn sync chain and timing rings is a need to remove a chainlink once the chain and rings can't have the slack adjusted out by putting the eccentric in the forward position.

Conversely, many tandem teams simply opt to replace the chains as they reach normal wear thresholds just as a part of a robust preventative maintenance program. Now, it should be noted that if timing chains become worn the front and rear chain rings can usually be swapped on a tandem to double the life of the timing rings: it has to do with how the sync chain pulls on and wears down the drive ring teeth.

What advantage or disadvantage is there in going to a larger or smaller chainring on the timing side (can you effectively have a 'compact' tandem setup by using smaller timing rings and smaller cogs, and drive rings to save weight)?

You can use smaller diameter timing rings, but you'll get to a point where the rings can become so small that you start getting chain drag and accelerated wear. Going to something like our 34t daVinci timing rings will cause timing rings and sync chains to wear out a little more a little more quickly than they would on 42t, 46t or 48t middle chain rings. The weight savings is negligible for all but the most elite tandem teams that have already gotten their weight(s) down to their target levels.

How many regular chains does it take to make a timing chain?

About 1.5 chains, assuming you start with the average 112 - 115 link chain.

This is the simple mathematic formula that a lot of folks use to calculate chain length.
Length = 2 (C) + F/4 + R/4 + 1

(C) = chainstay length
F = front chain ring tooth count
R = largest rear sprocket tooth count

So, for a tandem with 16.5" rear stays and a 12x34t cassette and 53/42/32 chain rings you get
Length of 55.75" = (16.5 * 2 = 33) + (53 / 4 = 13.25) + (34 / 4 = 8.5) + 1
Therefore, you need a 111 - 112 link chain for this combination.

So, for a tandem with 28.5" boom tube length and a pair of 42t timing rings you get
Length of 79 = (28.5 * 2 = 57) + (42 / 4 = 10.5) + (42 / 4 = 10.5) + 1
Therefore, you need a 158 link chain for this combination.

, you have to admit it would essentially last forever and never need maintenance.

Let's not go there again... No, a belt drive does not last forever and the belt and pulleys need to be cleaned now and again. In fact, I think most folks are eagerly awaiting real world experience with belt life from the early adopters in terms of just how much longer a belt will last in terms of mileage vs. a chain drive.
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Old 10-14-09, 09:47 PM   #10
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Do you run 8 speed rings and chains on the timing side?

Until 10 speed came along I would always run the same width (8 or 9 speed) chains for drive and sync chains so that in a worst case scenario I could steal links from the drive chain to fix a damaged sync chain. With the advent of 10 speed and the realization that builders like Co-Motion are still using 8 speed sync chains on tandems with 9 or 10 speed drive systems & chains, I now carry extra 8-9-10 speed links and re-useable chain links for field repairs since the drive chain will not necessarily work as a link donor.

8 speed is stronger, the rings will last longer, and the chain will stretch 'less'

Not necessarily. It depends on the grade and weight of the chain and chain rings. There is very little difference in the overall durability of 8 vs 9 speed chains of similar grades. 10 speed is simply not cost effective, regardless of how much faster they might or might not wear compared to the various different 8 or 9 speed chains. Again a sync chain does not endure the heavy wear and tear of the drive chain as serves only one purpose: moving the power from the captain's cranks to the rear axle. Moreover, there is no side loading from gear changes to contend with and the gear ratio is 1:1.

Frankly, if you want a bomb-proof sync chain and weight is of no concern, you might as well bolt up a 1/8" Track-BMX chain and chain rings, as they're about as robust a chain and sprocket combination as you'll find. However, the weight difference is not inconsequential.
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Old 10-15-09, 10:26 AM   #11
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Quote:
Originally Posted by TandemGeek View Post
Do you run 8 speed rings and chains on the timing side?

Until 10 speed came along I would always run the same width (8 or 9 speed) chains for drive and sync chains so that in a worst case scenario I could steal links from the drive chain to fix a damaged sync chain. With the advent of 10 speed and the realization that builders like Co-Motion are still using 8 speed sync chains on tandems with 9 or 10 speed drive systems & chains, I now carry extra 8-9-10 speed links and re-useable chain links for field repairs since the drive chain will not necessarily work as a link donor.

.
Please set me straight if my thinking is wrong on this, and it probly is.
The timing chain carries the captains power to the rear so it would have no more stress on it than a single bike application.
In reality it should be less stressfull due to the fact that it is not required to shift and twist.
10 speed chains hold up well to me on my single so there should be no problem using one for a timing chain?
Currently I have 9sp timing chain and 10sp drive chain as that is how the bike came from Santana.
With 40 tooth rings it takes 1 1/3 chains to make one timing chain.
Thanks for your input TG.
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Old 10-15-09, 11:02 AM   #12
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Quote:
Originally Posted by dvs cycles View Post
Please set me straight if my thinking is wrong on this, and it probly is.
The timing chain carries the captains power to the rear so it would have no more stress on it than a single bike application. For the most part, subject to any added or reduced work you might experience based on your stoker's performance / pedaling efficiency

In reality it should be less stressfull due to the fact that it is not required to shift and twist. Correct

10 speed chains hold up well to me on my single so there should be no problem using one for a timing chain? Correct

Currently I have 9sp timing chain and 10sp drive chain as that is how the bike came from Santana. Probably so; 9 speed tends to be less expensive than 10 and builders always look for a win-win configuration: lowest cost with acceptable performance & durability

With 40 tooth rings it takes 1 1/3 chains to make one timing chain. Assuming a 27.5" boom tube, sounds about right

Last edited by TandemGeek; 10-15-09 at 11:05 AM.
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Old 10-15-09, 05:15 PM   #13
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Quote:
Originally Posted by TandemGeek View Post
The timing chain carries the captains power to the rear so it would have no more stress on it than a single bike application. For the most part, subject to any added or reduced work you might experience based on your stoker's performance / pedaling efficiency

In reality it should be less stressfull due to the fact that it is not required to shift and twist. Correct

10 speed chains hold up well to me on my single so there should be no problem using one for a timing chain? Correct

Currently I have 9sp timing chain and 10sp drive chain as that is how the bike came from Santana. Probably so; 9 speed tends to be less expensive than 10 and builders always look for a win-win configuration: lowest cost with acceptable performance & durability

With 40 tooth rings it takes 1 1/3 chains to make one timing chain. Assuming a 27.5" boom tube, sounds about right
So then there is no reason other than cost or stock you have on hand to not use the same 10sp chain all the way around providing your stoker is pedaling?
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Old 10-15-09, 05:34 PM   #14
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Originally Posted by dvs cycles View Post
So then there is no reason other than cost or stock you have on hand to not use the same 10sp chain all the way around providing your stoker is pedaling?
That's pretty much it, just as I noted in my reply to mtnbke's somewhat skewed advocacy of 8 speed sync chains, to wit:

Quote:
Originally Posted by TandemGeek
Not necessarily. It depends on the grade and weight of the chain and chain rings. There is very little difference in the overall durability of 8 vs 9 speed chains of similar grades. 10 speed is simply not cost effective, regardless of how much faster they might or might not wear compared to the various different 8 or 9 speed chains. Again a sync chain does not endure the heavy wear and tear of the drive chain as serves only one purpose: moving the power from the captain's cranks to the rear axle. Moreover, there is no side loading from gear changes to contend with and the gear ratio is 1:1.
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Old 10-23-09, 04:20 PM   #15
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Quote:
Originally Posted by mtnbke View Post
If everyone remembers the belt drive thread, the materials science studies that were linked showed that the tighter the chain the more efficient the driveline. Obviously, one would think there would be a point of diminishing returns. As much as I think belt drive is silly and inefficient, you have to admit it would essentially last forever and never need maintenance.
This might be true if the belt drive has some 'stretch.' But empirical evidence on the track using a 1/8" track chain that does not stretch has shown me that the looser you can run the chain, the easier the bike is to move. On the track, I typically adjust the chain so that it would almost fall off. (You can do this on the track because you are constantly removing and re-installing the rear wheel and readjusting the chain tension; i.e., you never have to worry about the chain stretching becaise you're constantly adjusting for it.) If you adjust it too tight, you would probably hear a "popping" noise as you pedaled around. This is from the tight chain pulling on the bottom bracket spindle and rear hub axle, compressing the bb and rear hub bearings very, very tightly against the races, and likely destroying the bearing surfaces. The same thing happens on a tandem between the two bottom brackets if you don't leave enough play in the timing chain, as this is also a "fixed" setup.

Luis
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Old 10-23-09, 10:08 PM   #16
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Quote:
Originally Posted by oldacura View Post
A bit like working on a car ........
Were there any parts left over? That always gives you something to worry about?
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