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Old 12-19-2010, 11:05 AM   #1
Padmei OP
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Airhead chain conversion

Anyone ever seen a driveshaft to chain conversion on an airhead?
I'd like to see some pics if anyone has any.
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Old 12-19-2010, 11:58 AM   #2
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Second photo in the first post...

http://www.advrider.com/forums/showthread.php?t=567268

More below that too
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Old 12-19-2010, 05:09 PM   #3
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Michel BMW from Germany:



More great stuff on this page : http://www.michel-bmw.com/index.html
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Old 12-19-2010, 05:59 PM   #4
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Did they machine a complete new rear cover for the transmission? Or just mount a bevel drive to the rear?
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Old 12-19-2010, 07:32 PM   #5
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I'd guess that it it is a machined rear cover and that they extended the gearboxes output shaft to replace the RDU's pinion shaft, perhaps welding them together. Very trick, and no doubt expensive to replicate.

I like the fact that the front sprocket is concentric to the swing arm pivot.
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Old 12-19-2010, 07:52 PM   #6
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Quote:
Originally Posted by bmwrench View Post
I'd guess that it it is a machined rear cover and that they extended the gearboxes output shaft to replace the RDU's pinion shaft, perhaps welding them together. Very trick, and no doubt expensive to replicate.

I like the fact that the front sprocket is concentric to the swing arm pivot.


Nicely engineered, and it looks as though a lot of thought went into the design.

Simple in concept, not-so-simple in execution.
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Old 12-19-2010, 08:52 PM   #7
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That's real "interesting" and all that, but why?
If I recall basic engineering, the more stuff ya gotta turn and move, the less HP gets to the rear wheel.
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Old 12-19-2010, 09:00 PM   #8
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Its like moving the rear diff as far forward as you can get it, and putting a sprocket on it in place of the wheel.

fascinating location for the rear brake, as well.

I think the point here would be to minimize the unpsrung weight. There's virtually no thing back there at the rear wheel.

Plus for a race bike, you can now change gearing at will.
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Old 12-19-2010, 09:08 PM   #9
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Originally Posted by wirewrkr View Post
That's real "interesting" and all that, but why?
If I recall basic engineering, the more stuff ya gotta turn and move, the less HP gets to the rear wheel.
I was thinking of something a lot smaller than a big final drive- a smaller rightangle unit running like the pictured one ( & the new G450x type) with the pivot.

After looking at this
http://www.advrider.com/forums/showp...9&postcount=17 I started pondering...

What I was thinking was how you could make up a twin sided swingarm or adapt another brands swingarm to suit. That way you could maybe have a longer wheelbase, disc brakes, higher ground clearance, cheaper wheels if they get trashed.

Just wondering if anyone else had gone down that path.
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Old 12-19-2010, 09:11 PM   #10
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Originally Posted by wirewrkr View Post
That's real "interesting" and all that, but why?
If I recall basic engineering, the more stuff ya gotta turn and move, the less HP gets to the rear wheel.

The final drive,disk,and brake caliper are not unsprung weight with that setup. Also no jacking effect. Easy gearing changes. Lighter swingarm.
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Old 12-19-2010, 10:51 PM   #11
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Originally Posted by robtg View Post
The final drive,disk,and brake caliper are not unsprung weight with that setup. Also no jacking effect. Easy gearing changes. Lighter swingarm.
And no mo' driveshaft issues.
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Old 12-22-2010, 12:49 PM   #12
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Quote:
Originally Posted by wirewrkr View Post
That's real "interesting" and all that, but why?
If I recall basic engineering, the more stuff ya gotta turn and move, the less HP gets to the rear wheel.

Shoulda gone this route:

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Old 12-22-2010, 01:03 PM   #13
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Quote:
Originally Posted by bmwrench View Post
I'd guess that it it is a machined rear cover and that they extended the gearboxes output shaft to replace the RDU's pinion shaft, perhaps welding them together. Very trick, and no doubt expensive to replicate.

I like the fact that the front sprocket is concentric to the swing arm pivot.

My guess would be that they punched out a K100 universal joint to fit the pinion shaft and assembled it inside an airhead transmission yoke.
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Old 12-22-2010, 02:11 PM   #14
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Shoulda gone this route:

Egg-Zackly
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Old 12-22-2010, 04:58 PM   #15
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Originally Posted by wirewrkr View Post
That's real "interesting" and all that, but why?
If I recall basic engineering, the more stuff ya gotta turn and move, the less HP gets to the rear wheel.
Perhaps it would be interesting to weigh the reciprocating componentry as well, just to do a really fair comparison.

Its not just the number of things you have to turn, friction, weight, etc. all play in to the amount of HP to the rear wheel.

If eliminating the length of drive shaft, and the ring/pinion set, and replacing it with a more compact, perhaps lighter set of gears for the 90 degree drive, which looks way smaller than a factory bmw rear end, then you add the weight of the chain, and sprockets and accessories. Then you factor in the drag of the chain vs the drag of the driveshaft's u joint, and such, and then you sum it up, then you could really understand what the overall change in the efficiency is.

I suppose you could also just dyno it. I just cannot ignore the fact that there is atleast a slight chance that if a race team did this, that they paid a lot of attention to the actual numbers in the rotating mass machine. Afterall its the rate of change that will change acceleration. Not the number of bits. Of course there is a simplicity arguement as well. But in the racing world so long as the failure takes >1 race... You're ok.
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