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I have just acquired a like-new (ridden 3 times) 20" folding generic full suspension bike- front fork enclosed springs and rear coil spring/piston with tension adjustments by locking plate screw on the shaft. Bike has off road type trail tires. Bike frame is regular steel and its folding hinging is robust and secure.

The problem is that every time I try to ride just on the street- the chain comes off while pedaling forward or with casual reverse.

The local bike shop has serviced/tuned the derailleur and say it is not the source of the problem, but that this is caused by the geometry of the bike frame changing/flexing with road bumps and is enough to cause the chain to de-rail? They tightened the chain by removing one link- but I still have occasional problems. The chain comes off the rear axle first- mainly mid gear sprockets, and then off the front. I cannot tell where the chain tension changes/slackens, but the links/gears are oiled and not stiff/sticking. This bike is spec-ed to 6'2/230 pounds, I am well within this at 6'/200. Is there any solution to this issue? Thanks

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  • Can you tell us where the chain comes off? Does it come off the rear cassette or the front chainrings? Does it come off in any gear or is it worse in specific ones? Does the tension of the chain change as the rear suspension flexes? Does the rear suspension have any form of lockout to make the frame more rigid ? Please use EDIT link to add this info to your question, which will help people answer. A photo of the chain area, from the right side of the bike might help too.
    – Criggie
    Mar 5, 2016 at 2:47
  • It come off every time you ride but it is not derailleur issue because the shop told you it was not? You did not post picture as suggested.
    – paparazzo
    Mar 5, 2016 at 23:21
  • Two possible solutions - stop coasting through bumps, or stop going over/through bumps. Could be you're suffering from chain slap where the low chain tension of coasting allows the chain to wave wildly and fall off. Try locking out your suspension either with the proper switch, or a bogan way with a suitably-sized hunk of timber. Could be your bike is just a BSO and only intended to go a couple hundred KM in its life due to poor design. Photos would help.
    – Criggie
    Mar 6, 2016 at 2:36

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