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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 05-26-10, 03:31 PM   #1
Rapport
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Home-brewed Belt-drive system [research stages]

I've recently been looking into the Gates belt-drive system. (Mostly out of intellectual curiosity since i probably won't be able to afford it.) The first thing I noticed is that it looks strikingly similar to a to a timing belt system on a car, or any number of industrial applications.


After finding the specs (tooth count/pitch for belts and pulleys) on the Gates/carbondrivesystems website,
http://carbondrivesystems.com/cd_specs.php?lang=us, I decided to check my favorite online "hardware" store http://mcmaster.com. It turns out they have belts and pulley in similar sizes (tooth counts and dimensions) to many of the ones produced by Gates. They even have carbon reinforced belts of the same tooth count and pitch (8mm) which is used widely in the automotive world. This got me thinking... how hard would it be to adapt a 50tooth cam gear onto a crank. I would wager that the two below could be adapted to a crank rather easily with minor machine work (milling, drillling/tapping), by the looks of the you could even choose your own offset for correct chain-line (belt-line?)





The rear gear/pulley may not be as easy to source, ( at least one that will fit with minimal modifications) However, it shouldn't be hard to find one with the correct tooth count and pitch since 8mm pitch is pretty standard. I'm thinking a water pump pulley may be the ideal candidate. Here is a Honda timing belt picture, notice 4 different potential rear pulleys, and this is just one car.



Anyways, just wanted to share my recent brainstorming. I intend to go to the junkyard pretty soon and do some poking around and teeth counting. If i can do this for cheap enough I may just try it.
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Old 05-26-10, 04:02 PM   #2
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My only suggestion is to start from a disc hub and use the 6 bolt pattern to connect the rear pulley to the hub rather than going for the thread-on system, assuming you're talking fixed rather than freewheel.
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Old 05-26-10, 04:25 PM   #3
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Seems to me that the car parts would be way overbuilt for a bike, and a car belt possibly too stiff since it's designed to deal with the stress and heat of much higher RPM and tension and runtime

also you have to cut your seatstay.
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Old 05-26-10, 04:36 PM   #4
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As for the crank, it might be easier to run a keyed pulley with a one piece crank.
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Old 05-26-10, 04:41 PM   #5
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how are you getting the bent on?
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Old 05-26-10, 04:46 PM   #6
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I have had passing thoughts of a belt driven bike, too. What are the advantages? Is it just quieter? I will definitely keep tabs on this thread, especially if you figure it out with a "minimal" cost!
Also, I think automotive belts would be ok as they are not hard to bend even when cold. However, the pulleys themselves may be overbuilt as far as weight is concerned. Please keep us posted!
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Old 05-26-10, 04:50 PM   #7
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seems pretty cool. it would be nice if you knew someone with access to a mill.
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Old 05-26-10, 04:51 PM   #8
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Thanks for the input guys, I don't believe that the gear being over-engineered would be a problem. So long as the gears are fitted to the bike properly the only drawback would be they are slightly heavier than the Al ones that carbondrivesystems offers. The carbon reinforced belts at mcmaster.com are not automotive belts. If it is a problem, the gates belt could be used with the modified automotive pulleys with no problems since the tooth pitch and shape is the same.

The necessity of frame modification is a huge drawback for me, which may derail (no pun intended) the whole idea. I have been talking about making a bamboo bike with a friend of mine. Maybe it will be our test mule.


For $32 + the cost of welding this could be an option worth looking into (as far as cutting the seat stay)


Last edited by Rapport; 05-26-10 at 08:02 PM.
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Old 05-26-10, 05:47 PM   #9
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it will be cheaper to buy one, you'll see.
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Old 05-26-10, 05:56 PM   #10
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Cool project. Good luck with it!

Now, for my real question,

can someone explain to me how a belt drive is different from a regular drivetrain besides the cog, belt or chain and chainring? Or is that it? Is the eccentric hub on that bike just for... belt tension? Or is there something I'm missing?

i'm also very confused why that bike has a cha... i mean, belt guard. aren't they squeaky clean?
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Old 05-26-10, 06:12 PM   #11
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i'm also very confused why that bike has a cha... i mean, belt guard. aren't they squeaky clean?
well, still dont want pants to get caught and im sure road grim still works its way around the drive train
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Old 05-26-10, 07:05 PM   #12
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So, what's the downside to th belt drive? is it heavier? less efficient energy transfer?

What about those shaft driven bikes?

Chain is better than shaft driven bikes, but is belt driven superior in all ways? Are you, like shaft driven, unable to have anything but SS or internal shifting?
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Old 05-26-10, 07:42 PM   #13
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it will be cheaper to buy one, you'll see.
Well i am confident I can adapt a 50t cam gear into a front "chainring" for cheaper than ~$150 As long as I can find a rear gear to make work with minimal machining then I will be in business, and much cheaper than the ~$400 it will cost to buy the parts (not counting frame modification). Point is, if I can't do it for cheap i'm not going to do it, but you may be right.

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So, what's the downside to th belt drive? is it heavier? less efficient energy transfer?

What about those shaft driven bikes?

Chain is better than shaft driven bikes, but is belt driven superior in all ways? Are you, like shaft driven, unable to have anything but SS or internal shifting?
A chain is really hard to beat, and the advantages of belt drive are few. It's slightly lighter, more durable, cleaner, quieter, and of comparable efficiency if it's a SS. BUT it can only be a SS or internally geared.
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Old 05-26-10, 08:54 PM   #14
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Well i am confident I can adapt a 50t cam gear into a front "chainring" for cheaper than ~$150 As long as I can find a rear gear to make work with minimal machining then I will be in business, and much cheaper than the ~$400 it will cost to buy the parts (not counting frame modification). Point is, if I can't do it for cheap i'm not going to do it, but you may be right.



A chain is really hard to beat, and the advantages of belt drive are few. It's slightly lighter, more durable, cleaner, quieter, and of comparable efficiency if it's a SS. BUT it can only be a SS or internally geared.
How would it be lighter? I mean, Sure the belt itself is lighter, but the larger cog/chainring would balance that out at least somewhat, so for an SS it might be ok, but if you add an Internal Shifting system, those tend to be much heavier than traditional derailleurs.

Last edited by cg1985; 05-26-10 at 09:18 PM. Reason: sleepy.
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Old 05-26-10, 09:35 PM   #15
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I have had passing thoughts of a belt driven bike, too. What are the advantages? Is it just quieter?
I think the biggest advantage is that you never have to lubricate them. Having a clean, maintenance free transmission would be an advantage for people who do multimodal commutes on folding bikes* in fancy office clothes. Same for rental fleets near salt water.

For most bike applications, though, they aren't better than a chain. Or at least the disadvantages (SS or IGH only, proprietary parts, etc) probably outweigh the benefits.


*some folding bike designs also wouldn't require a gap in the frame, if the rear isn't triangulated.
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Old 05-26-10, 09:42 PM   #16
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Well i am confident I can adapt a 50t cam gear into a front "chainring" for cheaper than ~$150 As long as I can find a rear gear to make work with minimal machining then I will be in business, and much cheaper than the ~$400 it will cost to buy the parts (not counting frame modification). Point is, if I can't do it for cheap i'm not going to do it, but you may be right.



A chain is really hard to beat, and the advantages of belt drive are few. It's slightly lighter, more durable, cleaner, quieter, and of comparable efficiency if it's a SS. BUT it can only be a SS or internally geared.

Please do count the frame and the modification. ;0)
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Old 05-26-10, 09:48 PM   #17
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find a frame with elevated chainstays
weld or braze one some horizontal dropouts to it.
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Old 05-26-10, 09:53 PM   #18
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Interesting idea ... more project photos please ...
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Old 05-26-10, 09:58 PM   #19
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find a frame with elevated chainstays
weld or braze one some horizontal dropouts to it.
Cool it'll be a starfµckers xenon then!
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Old 05-26-10, 10:02 PM   #20
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I think most manufacturers have that silly cutout because they're just retrofitting their existing frames with inferior cutouts for belts, instead of a proper frame that avoids the cutout all together.
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