Tandem Cycling - newbie with chain tension question

Hi,

I recently bought a used inexpensive-brand tandem with a missing idler pulley. The pulley sits on a mount halfway between the two front cranksets. I now have a pulley, but now the question is: How much tension should there be in the chain? I assume you check the tension with the chain length running on the top of the chain loop from the Captains crankset(not sure if terminology is correct) to the stoker crankset. There is currently @1/2" available movement in the chain when I pull it up.

Thanks.

Rod Wylie

The sync chain that connects the front (captain) and rear (stoker) timing ring / cranks should have about .5" to .75" of slack on a tandem that uses an adjustable eccentric bottom bracket for the captain's crankset. Chain tension needs to be checked throughout the entire rotation of the cranks to ensure that any non-concentric timing ring orientation that could create highly unequal chain tension is discovered and minimized by loosening and recentering the timing rings on the crank spiders.

For a tandem that uses fixed, non-adjustable bottom brackets and a fixed idler wheel, not more than .5" of chain tension is more appropriate to ensure the chain can't jump off the idler wheel when the tandem travels over rough pavement or terrain. The idler wheel's position should also be periodically checked to ensure it that remains in line with the front & rear timing rings. If the idler arm gets bumped and knocked out of plumb from the timing rings chain drops become more likely.

And how do you measure slack?

When there is no pressure on the pedals, both top and bottom chain runs sag; I suppose I could measure top and bottom slack (and then add together?).

If I press on the pedal with my hand, that takes up the slack on the top run, but the bottom run still has some slack. So, I could measure slack this way -- with the slack taken out of the top run of chain.

(Bike is a new to use Burley Rumba with eccentric BB and no idler.)

Thanks!
David



The sync chain that connects the front (captain) and rear (stoker) timing ring / cranks should have about .5" to .75" of slack on a tandem that uses an adjustable eccentric bottom bracket for the captain's crankset. Chain tension needs to be checked throughout the entire rotation of the cranks to ensure that any non-concentric timing ring orientation that could create highly unequal chain tension is discovered and minimized by loosening and recentering the timing rings on the crank spiders.

For a tandem that uses fixed, non-adjustable bottom brackets and a fixed idler wheel, not more than .5" of chain tension is more appropriate to ensure the chain can't jump off the idler wheel when the tandem travels over rough pavement or terrain. The idler wheel's position should also be periodically checked to ensure it that remains in line with the front & rear timing rings. If the idler arm gets bumped and knocked out of plumb from the timing rings chain drops become more likely.

I always strive for equal slack on the top and bottom runs with no pressure on the pedals. I think I remember one time putting the timing chain back on and getting the top run tighter than the bottom. The solution was to take the chain back off and restart putting it back on one link sooner.

And how do you measure slack?

It's a relative measurement, same as on a fixed gear bike or motorcycle's drive chain. Pull up on the top or lower run of the sync chain; the difference between the position at rest and upper position is the 'slack'.

For complete accuracy the first time you check it you can use a rule standing on it's end to measure the difference between the two positions.

However, once you see it and get a sence of what the chain tension feels like when it's in the ballpark you can usually eye-ball hence forth.

I always strive for equal slack on the top and bottom runs with no pressure on the pedals. I think I remember one time putting the timing chain back on and getting the top run tighter than the bottom. The solution was to take the chain back off and restart putting it back on one link sooner.
After I stopped laughing, I realized there was no smiley here, and it wasn't April 1st any more. You do realize this is silly, right?