3 speed rack mount shifter

Discussion in 'General Questions' started by TWalker, Jan 21, 2009.

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  1. TWalker

    TWalker Guest

    Shifter for rack mounts with full freewheeling capabilities for engine and pedaling using one existing freewheel cluster.

    We know a simple bike/BMX chain will hold up to engine torque as seen with SBP shifter kits.

    Why not run a rack mount with bike chain to the tallest 3 gears on your existing freewheel and leave the bottom 3-4 gears for pedaling?

    Ive already did a test run a while back by sliding my Titan drive gear to the right side and running a bike chain to the tall 32t gear, it works but I had no real tensioner or deraileur to change gears and it slipped off, I ran out of time for the project and took it off.

    1. You need the front freewheel system ala SBP (which I used) because the engine will spin your pedals with this setup.

    2. Im looking at the Titan and possibly the Staton Inside drive as potentials. The Staton would need a longer shaft. See the pic below. But the Titan will work as is with a 20t middle sprocket and a deraileur. 18:1 reduction (titan PTO, 20t middle gear and 32 tooth freewheel gear)

    3. A common shimano mega-range freewheel is best I believe going from 9t to 32t range.

    With this set up you have 3 gears for engine and 3-4 for pedaling or 6-8 gears if you utilize both sprockets on an SBP front chainring.

    This is a great set up and I was keeping it quiet until I got perfected but I figured I would throw it out for some of you genuises to see if we could get er done.

    Attached Files:

    Last edited by a moderator: Jan 21, 2009

  2. Happy Valley

    Happy Valley Active Member

    I'm liking the concept but explain to me again how you shift gears to get 3 speeds off the engine?:dunce:
  3. TWalker

    TWalker Guest

    You would use a seperate rear deraileur just like you change gears for the pedals. On the non tensioned/drive side. front side of chain.

    I guess thats the biggest challenge and why I havn't had time to complete it. I did hold up up a deraileur it seems as if it would bolt directly onto the Titan rack and work, but we know what happens when we assume.
  4. cooltoy

    cooltoy Member

    Not too long ago I remember seeing a rear 7 speed wheel that had it's inner gear , closest to the spokes , on a freewheel set up. I think it was built for purposes like yours.
    I know you solved this with the SBP freewheel crank but I just thought I'd throw it out there.
    Nice looking bike, by the way!
  5. skyl4rk

    skyl4rk Guest

    You may be able to switch out the jackshaft input sprocket for a larger sprocket, which would change your reduction ratio. The stock Dax jackshaft input sprockets are 10t. If you change the sprocket to a 12t, you will get a good ratio on a wheel sprocket set of 24t, 29t, 34t.

    My spreadsheet says:

    	Dax Titan - 5:1 Reducer			7 speed hub, 11t - 34t							
    	Motor RPM	3600	rpm	
    	Motor Sprocket	10	teeth								
    	Jackshaft Input Sprocket	12	teeth								
    	Jackshaft Output Sprocket	10	teeth								
    	Wheel Sprocket	34	teeth								
    	Wheel Diameter	26	inches								
    	Primary Reduction	6	ratio								
    	Secondary Reduction	3.4	ratio								
    	Overall Reduction	20.4	ratio								
    	Wheel rpm	176	rpm	
    	Wheel Speed	14	mph	
    		Motor rpm	1000	2000	3000	4000	5000	6000	7000	8000
    	Sprocket Overall									
    	teeth	reduction	mph	mph	mph	mph	mph	mph	mph	mph
    	11	7		11.71	23.42	35.12	46.83	58.54	70.25	81.96	93.66
    	13	8		9.91	19.81	29.72	39.63	49.53	59.44	69.35	79.25
    	16	10		8.05	16.1	24.15	32.2	40.25	48.3	56.34	64.39
    	19	11		6.78	13.56	20.33	27.11	33.89	40.67	47.45	54.23
    	24	14		5.37	10.73	16.1	21.46	26.83	32.2	37.56	42.93
    	29	17		4.44	8.88	13.32	17.76	22.2	26.65	31.09	35.53
    	34	20		3.79	7.58	11.36	15.15	18.94	22.73	26.52	30.3
    The jackshaft input sprocket is the bottom sprocket in the attached image.

    Attached Files:

    Last edited by a moderator: Jan 22, 2009
  6. TWalker

    TWalker Guest

    yea thats the plan, i ran the numbers a while back and it would require a different jackshaft input. I cant remember what my numbers were but it was defintely doable.