Need mental and ratio help! Please!

Discussion in 'Motorized Bicycle General Discussion' started by conradcliff, Dec 5, 2008.

  1. Dan

    Dan Staff
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    Wow Conrad. You should be uber proud. You stuck with this threw pulling your hair out at 5 am, new concepts and insane variables. Good job and I can't wait to see your work.
     
  2. conradcliff

    conradcliff New Member

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    Thanks Dan! Couldn't have done it if it weren't for people like you! (^)

    Also, kudos to 5-7, he's been helping me trod the ground of uncertainty with me from the get go..Thanks again!! :D
     
  3. Ghost0

    Ghost0 New Member

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    Good job on getting it figured out. I always try to not over complicate things. When I was designing the SBP Shift Kit, I figured the manufacture knew what they were doing. The China kits come with a 44 tooth sprocket amd has a 10 tooth output sprocket on the engine. So that is 4.4 to 1. That seemed like a good middle gear. So I just figured if I could get the final drive ratio to be the same on the middle sprocket of the rear cassette I would be in the ball park. I then had both lower and taller gears on the cassette. That way I didn't need to worry about the internal gear reduction, engine RPM, wheel size etc. So the same could apply here. If the Titan has an output sprocket of a 10 and the kit comes with a 50 then I would know that I would need to keep the overall drive at around 5 to 1. Now that I am designing the one for the 4 stroke kit I am using the same principal. And thanks to the Grubee and JL gear reductions they kindly have a 10 tooth output sprocket so the gearing will be the same.
     
  4. conradcliff

    conradcliff New Member

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    Thanks Ghost0..pretty much at this point I'm going to see how what I've got works out..
    Maybe I should have just waited till you got the 4-stroke kit ready for retail. Is it going to be a rack or frame mount?
     
  5. Ghost0

    Ghost0 New Member

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    SBP is a frame mount only company. No offense to the rackmounters out there but we just can't understand why anyone would want to put an engine where their luggage is supposed to be when there is a perfectly good place to put it.:)
     
  6. conradcliff

    conradcliff New Member

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    Rack mounted engines look horrible too! My saving grace was the cool looks of that pocket bike motor but alas I'm doomed to the ugly. I'm going to give the motor a custom paint job though so it wont be quite as bad. I wish I could do a frame mount but the full suspension frame just wont have it.
     
  7. Ghost0

    Ghost0 New Member

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    It is true that most of todays full suspension bikes do not lend themselves to frame mount engines but there are a few out there that work. Here are a few frames that it can be done on.
    Manitou FS 1993
    2006 Mountain Cannondale Scalpel 2000
    GT LTS
    GT RTS
    Marin F.R.S.
     

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    #27 Ghost0, Dec 6, 2008
    Last edited: Dec 6, 2008
  8. Dan

    Dan Staff
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    Ghost0, I have been wondering about this. The stock 44T part. I completely agree with you that it is always best to go with the original engineer's thinking and not over complicate things. But I had always wondered why a rear 44T stock sprocket when it would top out a ChinaGirl at 30 MPH rather then make it cruising speed. I think it was Andy who first said that one tooth was about 1 MPH. (Yes Andy? forgive me if I misquoted you as I can not find the post) Dax suggested a 40 tooth which seems perfect for cruising closer to 30 MPH comfortably. So what I am thinking is that the producers of kit engines went with 20 MPH to be the middle ground and adhere to federal law. This all is a question not a suggestion. Where I live the speed limit for a MB is 30, so I am aiming for a top speed of 40 MPH for just that reason.

    Not questioning you but rather my own thinking.
     
  9. Ghost0

    Ghost0 New Member

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    Like I said the 44 was just what the kit came with. And in the stock set up worked good at about 20 to 25 mph so I concluded that it would be a good ratio for a middle gear on the cassette. Then I would have 3 gears taller and 3 gear lower on a 7 speed cassette. So as it works out with my 6 speed cassette I have ratios, using the stock teminology of 10t on the engine and 44 tooth rear sprocket which is 4.4 to 1, of 5.8 to 1 in my low gear and 2.7 to 1 in my high gear and so 4.4 to 1 is in the middle. So that is like having a 58 tooth rear sprocket down to a 27 tooth rear sprocket using stock sprocket terminology.

    And BTW my bike tops out at about 40 mph in 5th, when I shift to 6th it backs down to about 37 but the engine rpm drops nicely so it is kinda like an overdrive so I can cruise at 35 and the engine isn't working at all.
     
    #29 Ghost0, Dec 6, 2008
    Last edited: Dec 6, 2008
  10. Dan

    Dan Staff
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    I was asking about stock kits and ratio. Very cool that the shift kit can do that. It just brought to mind a question I was pondering.
     
    #30 Dan, Dec 6, 2008
    Last edited: Dec 6, 2008
  11. Ghost0

    Ghost0 New Member

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    OK like why do they put a 44 in the kit instead of a 40? I think your assumption is as good as any.
     
  12. conradcliff

    conradcliff New Member

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    Those would be cool to have but I gotta go with what I got for now ^5
     

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