SPB Shift Kit and Chain Bounce on terrible roads

Discussion in 'General Questions' started by HseLoMein, Jan 24, 2014.

  1. HseLoMein

    HseLoMein Member

    I am really surprised that one other guy and I only have this problem.

    Let me explain the issue. I have the SBP Shaft Kit installed on my Giant Stiletto Chopper. When I ride the roads of Boston, I frequently lose my chain. The problem isn't with the kit but its the derailleur chain bounces wildly causing to remove its self from the front sprocket. This causes all sorts of issues, chain breaking, derailleur suck, general bike breakage.

    When I take the bike out of town like a more rural area, Lebanon, PA for example. I never have this issue. But those roads are pristine.

    Well will researching using internally geared hubs to resolve this issue. I came across a post in another forum. This guy came up with a solution he made a triangle shaped bracket the will "hold" the chain within a defined area. This allows, is the chain can move just enough to not affect shifting but it keeps the chain from bouncing all over the place while under power.

    This guy has a much better explanation and fix. I will be implementing this shortly and testing it out as soon as it warms up a bit.


    If anyone else has experiences this issue please chime in.

  2. jaguar

    jaguar Well-Known Member

    Also you can take some links out of the chain or use a stronger derailer spring.
    But I like the idea of a chain guide. That would work independant of chain tension.
  3. Fabian

    Fabian Well-Known Member

    That will not solve the problem because the return side of the chain has a long unsupported length in the faster (smaller rear sprocket) gears.
    Last edited: Jan 25, 2014
  4. Fabian

    Fabian Well-Known Member

    The triangular chain stabilisation device isn't enough. You need to run double idler wheel system and chain loop enclosing the idler wheels, to prevent chain bounce making it's way back to the front sprocket.
    The biggest problem on rough roads is the combination of excessive vertical and lateral oscillation of the chain. The vertical element is what causes chain suck as the downward movement (from it's peak upper movement) has the disengaging chain links (coming of the front sprocket) with no tension on the sprocket teeth; a prime recipe for chain suck.
    The second element is excessive lateral chain movement which allows the chain to hit the side of the rear tyre; causing the chain to be picked up the side knobs of a mountain bike tyre. When the chain catches on a side knob, it is dragged downwards until the chain falls of the tyre knob. When this happens the chain snaps back, which then allows the a momentary level of complete slackness in the chain; manifesting itself as chain slack at the bottom of the front sprocket; which causes chain suck.

    It took me a long time and a heck of a lot of damage to the drive train to work out what was going on; requiring a video camera to analyse what was happening to the chain drive system.

    Having a triangular chain stabilisation device isn't enough to solve the problem, because you need to stop vertical chain bounce from reaching the front sprocket. This requires the use of a double idler wheel system.

    You will never see chain suck issues when travelling on smooth roads, but when the bike starts bouncing around like crazy on bad roads, and especially when throttling on and off (at speed, whilst desperately trying to avoid the worst pot holes), the chain suck problem will become a huge problem without a complete chain stabilisation solution.
    professor likes this.
  5. Fabian

    Fabian Well-Known Member

    The triangular chain stabilisation device main purpose is to control lateral chain movement, which prevents ghost shifts to an adjacent larger sprocket. On bad roads and with a chain that's wildly whipping about (and you would be gobsmacked to see how much the chain whips about), the lateral chain inertia is so great that it overcomes the derailleur pantograph spring tension, allowing the chain to jump up a gear, then back down to the pre-selected gear, which can tear off a sprocket tooth or split a chain roller in half, because the system is under full power when it happens.

    A 9 speed chain and 9 speed cassette system is far more susceptible to this condition than an 8 speed system, but the best solution to help prevent ghost shifts is to use 9 speed chain on an 8 speed cassette.

    The other side benefit of the triangular chain stabilisation device is to divide the length of unsupported chain by half; drastically reducing the maximum amount of chain bounce that can potentially feed back to the double idler wheel system.
  6. HseLoMein

    HseLoMein Member

    Excellent points Fabian. With the double idler system where would you place it, on the top or bottom?
  7. Fabian

    Fabian Well-Known Member

    As per the photos.
    Chain disengages the front sprocket teeth on it's return journey to the rear derailleur, then runs over the first idler roller and travels under the second idler roller and makes its way through the triangular chain stabilisation device.