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Improper timing chain tension is probably the most common cause of derailment problems. Please read our Timing Chain Adjustment article for a suggested procedure.

Consider the thoughts below should derailment problems persist after attaining proper chain tension.

1. Make sure you do not have a bent chainring or any bent teeth.

2. Use a chain designed for shifting.

YES, as strange as this sounds, it will work much better in this non-shifting application than a non-shifting BMX chain.

Chains designed for shifting have side plates chamfered internally which allow the chain to grab and slide onto the tooth of a cog or chainring as opposed to a chain not having this feature which will ride up on top of the tooth and thus derail. We WANT the chain to grab the tooth when the chain runs at an angle. The chamfered side plates permit the chain to slide onto the tooth with the chain running at a much greater angle than a chain not having this feature.

Some say that a BMX chain is less flexible than a shifting chain and thus purport its use in this application. This is simply not true and the use of a BMX chain will cause derailment problems to increase by its very design. Test chain flexibility by lining up a variety of BMX and typical shifting chains. Flex all of them to their maximum and note how some chains bow less without regard to whether it is a BMX or shifting chain. The manufacturer is the most important element in flexibility.

It is my opinion that chain flexibility has little or no influence with timing chain derailment since the chain goes slack under extreme load causing it to basically swing back and forth when hitting bumps or during irregular pedaling associated with a high cadence or muscle fatigue. When the chain swings, it is resultant of lateral play involving many links and does so without approaching the lateral limits of chain motion making chain flexibility in this situation a non issue.



The extreme frame damage pictured was resultant of final drive chain derailment despite the use of a Chain Watcher. There is no practical way to repair an aluminum frame that has sustained damage of this extent.

Timing chain derailment can also cause frame damage, hopefully not this severe!


3. Reduce the winching action and frame flex which causes the chain to go lax when the captain pedals hard. Sometimes this is referred to as the "bow and arrow" effect. The frame will actually bow when the captain pedals forcefully.

This effect can be minimized by positioning the chainrings inboard as far as possible thus reducing the lever action against the frame.

Sometimes one can mount the chainrings on the inside of the spider and still maintain frame clearance. Shorter bottom brackets also help if yours are excessive in length. One can generally install a shorter captain's bottom bracket without any problem regarding chainline since the angle is so minimal resultant of the great distance from one crank to the other. Also any chain angle resultant of mismatched bottom brackets pales by comparison to angles seen with the final drive.

I personally run 44 and 46T chainrings for less winching action, reduced chain tension and lower rolling resistance. The immediate benefits include longer chainring, bottom bracket and chain life. The captain and forward most stokers of triplets and quads will also experience a more solid feel at the pedals. The only downside that comes to mind is a bit of added weight from a couple of extra chain links and larger chainrings. Decreased ground clearance is not an issue with road tandems but certainly a consideration for off road use.

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