How does this work, Oppo?

"John_Harbinson" (jensenkid97) 12/13/2015 at 17:05 • Filed to: bikelopnik

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I saw this on BaT, and couldn’t help but wonder how in the dickens the drive system works. I would imagine that the driveshaft turns a differential, with the half shaft/bit with splines on it sliding directly into the inner hub of the rear wheel? like a car’s differential, with only one driven wheel, basically, and no hub to bolt the wheel to, because the wheel is a hub #becausemotorcycle. Now that I think of it, actually, would this be how that 2wd ROKON bike works? You’d have to have a u-joint for the front, probably, or use some kind of belt and pulley system to allow for the turning of the front wheel. Either way, this BMW bike is pretty neat, just curious as to how that drive system functions.

BmanUltima's car still hasn't been fixed yet, he'll get on it tomorrow, honest. > John_Harbinson 12/13/2015 at 17:10

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Yeah, it’s like a one sided differential.

TheAnswerIsAlwaysCitroën > John_Harbinson 12/13/2015 at 17:29

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It doesn’t really make sense to talk about a differential in this case, since its purpose is to split the torque between two outputs - and here, of course, you only have one.

I think the confusion arises because in common language, “differential” often refers to almost the whole package as shown in this figure:

while actually it only consists of the cage, small gears, and large gears.

Remove that along with the half shafts and you’re left with the propeller shaft, pinion, and crown wheel, which would be how you’d make a shaft driven motorcycle.

Shaft driven motorcycles aren’t that uncommon, by the way - BMW still makes them for instance. It’s a nice, clean way of making it, since it has no exposed chain and doesn’t need much maintenance. It is quite heavy, though, and not as efficient as a well lubricated and adjusted chain.

Have a straight-four shaft driven Nimbus for reading this far:

John_Harbinson > TheAnswerIsAlwaysCitroën 12/13/2015 at 17:53

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Ok, that makes much more sense. The basic prop shaft turning the gear was what I had in my head, I just figured that that assembly would be called a “differential” as well. Also, that wouldn’t happen to be a Nimbus 3,000 , would it?

For taking time to write that all out, I hereby grant

Now, would yourself or anyone you know happen to have the slightest idea as to how an internal gear bicycle hub works? Because I’m restoring a bike that has one, and I can’t figure out for the life of me how the thing works, but it’s awesome. It sticks a little bit and is kind of hard to shift, but I’m super scared to pull it apart, because I know I’ll never get it to go back together again.

And if you’ve taken the time to read this far, have a Quantum Syncro, covered in snow. Because I wish it would snow, and I wish I could find a rust-free one of these to drop a 20V VR5 into, with a beefy turbo, and manuel transmissiÓn.

TheAnswerIsAlwaysCitroën > John_Harbinson 12/13/2015 at 18:11

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No, it’s an older model - a Nimbus 746 Sport (yes, I had to look up the exact displacement).

That Quantum looks awesome - I guess it’s what we in EU call a Passat?

As for hub gears, I’m fairly sure they use planetary gearsets similar to those used in traditional “slushbox” auto transmissions - possibly even the more complicated Ravigneaux type shown below:

Since I barely grasp the operation of planetary gears myself, and then only right after downing a big mug of coffee, I’m just gonna say they work by magic. Yep, magic and a dose of wizardry, that’s how! And if you disassemble them without being completely sure what forces you’re about to unleash, you’re in for a world of hurt. Don’t.

(You might be able to take out the complete assembly for cleaning and lubrication. Whatever you do, do it at your own risk, because I want no part in it.)

XJDano > John_Harbinson 12/13/2015 at 18:16

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My 82 Silverwing is like this also.

Cé hé sin > TheAnswerIsAlwaysCitroën 12/13/2015 at 18:23

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Yes, they’re epicyclic gear sets. More details here although it doesn’t say exactly how they work other than the basic three speed has a single gear set with four planets.

Actually there’s more here which basically says that you get one overdrive gear from your epicyclic, you reverse the input and output to get a reduction gear and then there’s a direct drive.

They do an eight speed now which is most likely worked entirely by magic.

John_Harbinson > Cé hé sin 12/13/2015 at 18:37

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Yeah, I’m gonna just go with magic as well, I have to save my mental capacity for the rest of this ten page research paper that I started earlier this afternoon (east coast USA time) and have a rough draft of due tomorrow. Procrastination (ebay, BaT, oppo, Craigslist) is an evil, evil mistress...

John_Harbinson > TheAnswerIsAlwaysCitroën 12/13/2015 at 18:39

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Yup, I think it’s a B2 Passat to you guys across the pond. And reasoning for the VR5 20v is that my theory is it will sound even more like a V10, than an inline 5... I still have to prove that theory though. Give it time, give it time..

desertdog5051 > John_Harbinson 12/13/2015 at 19:12

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TheAmswerIs has it correct. I have worked on a few BMW motorcycles. It is a ring and pinion. The backing plate is anchored to the swing arm or in this case, with no swing arm, to something. Pretty low maintenance, but not that efficient as far as speed goes.

But hey, you are driving a cruiser. Low maintenance is your goal.