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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 09-07-12, 07:31 PM   #1
Mr Yum Yums
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Dual drive system

Hey fellas,

I've been searching the web for a system like this. Basically, I am looking to complete a bike with two chain rings at the crank and having dual freewheels on the back hub. Is this even possible? Please give any input you want, stupid idea, good idea, etc. Any info will help. I will post a drawing of what I am thinking of for all of you visual learners.

Thanks
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Old 09-07-12, 07:34 PM   #2
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Don't.
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Old 09-07-12, 07:38 PM   #3
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Theoretically I assume it would be possible if you used two of the same drive crank arms, and a symmetrical BB, and the same gearing on each side.

Sounds kinda neat actually. Serves no purpose, but eh.
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Old 09-07-12, 07:42 PM   #4
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It's possible. It's been done. It's pure novelty, no practical use; just extra weight.
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Old 09-07-12, 07:45 PM   #5
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SSFG engineering at its finest. You should have put the word "thread" in the title so Carleton could **** his pants.
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Old 09-07-12, 07:50 PM   #6
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Old 09-07-12, 08:03 PM   #7
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I understand how it could work fixed but with freewheels wouldn't the freewheel on the left side just spin not doing anything?
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Old 09-07-12, 08:17 PM   #8
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I'm pretty sure it would prevent you from coasting.
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Old 09-07-12, 08:20 PM   #9
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I'm pretty sure it would prevent you from coasting.
You know...just like a fixed cog but more stupid.
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Old 09-07-12, 08:23 PM   #10
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Both chains upside down FTW.
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Old 09-07-12, 08:40 PM   #11
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I understand how it could work fixed but with freewheels wouldn't the freewheel on the left side just spin not doing anything?
ACS makes a left side drive freewheel, called the south paw.
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Old 09-07-12, 08:40 PM   #12
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Both chains upside down FTW.
What kills me is a well respected shop built this monstrocity.... the same guys that make the broakland bikes...
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Old 09-07-12, 09:02 PM   #13
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They do make left side drive freewheels: http://www.amazon.com/ACS-SouthPaw-L...uckduckgo-d-20

It's been done, in practice they would never both be engaged at the same time.

Examples: http://www.ridemonkey.com/forums/f85...a-unit-130683/

Last edited by wesmamyke; 09-07-12 at 09:10 PM.
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Old 09-07-12, 09:06 PM   #14
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I think it's the dumbest thing since the slapchop.
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Old 09-07-12, 09:19 PM   #15
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If you looped one of the chains into a figure-eight, you could have a retro-direct. But that would disqualify you from the Single-speed forum...
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Old 09-08-12, 05:24 PM   #16
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Haha wow I did not expect to have this many replies. Thanks for all the heads up, I was just looking at doing something different and a new project to play around with. I appreciate it fellas and I look to be talking with you guys more on here. Take it easy.
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Old 09-09-12, 01:54 AM   #17
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Quote:
Originally Posted by Leukybear View Post
What I see here are two track cogs on the rear wheel. If that's the case, then this setup can't possibly work well, because either one of the track cogs will be stripped, or at the very least be loosened from the hub, immediately. IOW, one of the drivetrains is just tagging along while the other one does all the.... driving.

A stupid way to add 1 Kg of unnecessary components to your bike, plus it will actually make the power transmission less efficient. And it becomes horribly inefficient if you don't maintain (clean, lube) the "inactive" chain.

EDIT: not sure what would happen if one used two freewheels, though. Maybe then it could work? Didn't think through that scenario.

EDIT2: I came to the conclusion, after some thinking, that this setup could work (correctly, i. e. with drive on both drivetrains) if one had cogs that aren't threaded onto the hub, but bolted or splined - and provided that the two cogs are exactly identical. And that the chainrings are symmetrical.

Last edited by wroomwroomoops; 09-09-12 at 07:12 AM.
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Old 09-09-12, 02:01 AM   #18
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SSFG engineering at its finest. You should have put the word "thread" in the title so Carleton could **** his pants.
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Old 09-09-12, 02:42 AM   #19
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Did you just say Kilo TT?!
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Old 09-09-12, 03:17 AM   #20
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What I see here are two track cogs on the rear wheel. If that's the case, then this setup can't possibly work well, because either one of the track cogs will be stripped, or at the very least be loosened from the hub, immediately.
If properly installed, it will work just fine. You shouldn't strip or loosen a cog. My thought is that since the cogs are threaded on, the will most likely be within a couple degrees of each other, so unless they and the hub are machined perfectly, one cog will be doing more propelling and one will be doing more braking.
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Old 09-09-12, 03:29 AM   #21
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so unless they and the hub are machined perfectly, one cog will be doing more propelling and one will be doing more braking.
IOW, the setup will never work well: you have to spin both chainrings and pull both chains all the time, so the efficiency is reduced while only one drivetrain is actually doing the driving.

I'm glad we agree on the main points.
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Old 09-09-12, 03:43 AM   #22
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Wouldn't your left pedal keep coming unscrewed? Or is there some kind of tandem crankarm you'd have to use on the left side?
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Old 09-09-12, 05:21 AM   #23
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You can prevent precession by using a conical washer.
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Old 09-09-12, 06:08 AM   #24
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Originally Posted by Mr Yum Yums View Post
Hey fellas,

I've been searching the web for a system like this. Basically, I am looking to complete a bike with two chain rings at the crank and having dual freewheels on the back hub. Is this even possible? Please give any input you want, stupid idea, good idea, etc. Any info will help. I will post a drawing of what I am thinking of for all of you visual learners.

Thanks
op specified freewheels & did not say anything about requiring the rings & fws to be on opposite sides of the bike...

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Old 09-09-12, 06:30 AM   #25
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^^Good point!
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