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I'm used to single rider bikes, but new to tandems. We have a specific creak that I (as captain) can also feel through the pedals. It's on every strong stroke of the captain's pedals, left or right, but if I take my feet off and let my stoker pedal, it doesn't happen. She also can't feel it reliably through the pedals when I cause it. But she is only about 1/3 my weight (also 1/5 my age, and inexperienced).

The bike has an eccentric front BB, and the creaking started a few tens of km after I had to change the front crankset (the previous owner is not to be trusted with screw threads). I've already made sure the cranks and pedals are on tight. I plan to check the chainring bolts, but could the BB cause this? Is there something else tandem-specific I should look at while I'm at it?

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  • Is the frame intact? The one time I had a persistent creaking sound when pedalling that I couldn't track down to any problem with the cranks or BB, it turned out that there was a crack growing across the down tube.
    – DavidW
    Dec 22, 2022 at 20:34
  • @DavidW I can't see any sign of damage, and it hasn't had any hard use in the few months I've had it
    – Chris H
    Dec 22, 2022 at 21:05

2 Answers 2

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It did turn out to be (almost) tandem-specific: the eccentric bottom bracket was moving slightly even though the bolts securing it seemed tight (when tested with a multi-tool).

This model uses two M8 bolts into the underside of the BB housing on the frame (not a Thorn but a similar design). Other designs use a wedge. The left bolt was holding but the right allowed a fraction of a millimetre of play. I adjusted the chain tension slightly at the same time so the bolts are now clamping onto a different bit of the BB shell. I didn't remove the cranks so haven't inspected the BB itself.

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Try attaching something damping to the keel tube and see if that changes things. The keel runs between both bottom brackets and can function as a resonance amplifier because it has vibrations at both ends.

As a test, temporarily wrap on some scrap cloth rags with some tape to stop them sliding back. If that helps, there are more elegant solutions like that stick-on foam used in cars for noise damping - a strip of that down the underside might be all it needs.

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  • I'm wary of damping things until I've ruled out a real cause, so I was keeping this in reserve. But I got the chance to look at it in good light, and I'm pretty certain I've caught it
    – Chris H
    Dec 24, 2022 at 20:31

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