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Old 06-14-10, 08:37 AM   #1
govindsuku
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Parallel seated tandem bike

hi guys

i am trying to design a tandem bike with two riders seated side by side.....but what i cant get quite sorted out is.....if we have two separate chain drives driving a common rear axle.......and the two riders are exerting different torques.......then will the rider exerting lesser torque contribute to the rotation of the rear axle or not?.....i know it is a silly question yet...i wud like some clarification....
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Old 06-14-10, 08:50 AM   #2
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Works fine with the two riders contributing different levels of effort. But it wouldn't be a 'tandem' since that indicates two or more units arranged in-line. A two-person bike with the riders side-by-side is called a 'sociable.' Most designs I've seen tie the two cranks together so there's only a single chain driving the rear wheel.
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Old 06-14-10, 09:05 AM   #3
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Use extended pedal spindles, and lock a double length crank onto it, with a normal pedal at the other end. This will give you ultimate low Q factors. Only have the bars for one rider conected to steering.
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Old 06-14-10, 10:50 AM   #4
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I'm assuming here that you actually meant to say a side by side quad or trike. An actual two wheel bicycle with side by side seating would only be rideable by circus folks with a hyper keen sense of balance, reflexes and excellent timing to work on the starts. And if it IS a true bicycle being done as a stunt bike then I NEED to see pictures to join in the fun

You'll need to use two freehubs or freewheels on the drive axle. This will avoid the stronger rider overcoming the weaker and allow either to go into coasting mode without any issue. Also as long as both riders are pedalling hard enough that their freewheel is locked then the torque's add up even if one is stronger than the other. So if one is producing 20 ft-lbs and the other 15 ft-lbs then the drive axle is seeing 35 ft-lbs of torque.
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Old 06-14-10, 11:04 AM   #5
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The problem of two (or more) riders of differing strengths driving the same wheel is an everyday occurance on a conventional tandem. As BCRider noted the wheel sees the sum of the two torques since the two cranksets are linked together and must rotate in unison.

And, as noted, side-by-side designs are known as Sociables and date from the late 1800's.
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Old 06-14-10, 11:40 AM   #6
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An actual two wheel bicycle with side by side seating would only be rideable by circus folks with a hyper keen sense of balance, reflexes and excellent timing to work on the starts. And if it IS a true bicycle being done as a stunt bike then I NEED to see pictures to join in the fun
Someone posted a photo here of just such a bike months ago.
I wish I had saved it.
An elderly couple was riding it.
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Old 06-14-10, 12:01 PM   #7
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I'm assuming here that you actually meant to say a side by side quad or trike. An actual two wheel bicycle with side by side seating would only be rideable by circus folks with a hyper keen sense of balance, reflexes and excellent timing to work on the starts. And if it IS a true bicycle being done as a stunt bike then I NEED to see pictures to join in the fun
Sociables are true (two-wheeled) bicycles with the riders sitting side-by-side. They don't require undue skills to balance and can even be ridden solo although they lean over quite noticeably when this is done - to a lesser extent when there is a great disparity in the weights of the two riders.

Usually the cranks are rigidly joined so there is no option for independent coasting (as is also the case on most tandems although there are exceptions).

Here's an article that also includes a few pictures:
http://en.wikipedia.org/wiki/Sociable
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Old 06-14-10, 12:07 PM   #8
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Here's an article that also includes a few pictures:
http://en.wikipedia.org/wiki/Sociable
That is one interesting crank arrangement.
I wonder how much force that outer pedal can take w/o something twisting out of place.
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Old 06-14-10, 12:24 PM   #9
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There was a company that produced these several years ago.
Google "The buddy Bike".
http://rockthebike.com/node/492
I have ridden them and they are not at all practical.
If you ride it single you have to lean the bike to keep balance.
If the riders are significantly out of proportion weight wise it makes for a wonky ride.
Turning is sketchy at best as the redistribution of weight is critical and with both riders at the outer extremes it makes balancing the redistribution difficult.
The cranks are pretty solid, I noticed no flexing. Weighs a ton.
Overall not a great ride, takes practice, and the concentration needed cancells the enjoyment of being on a bike out.

From the BF archives
http://www.bikeforums.net/archive/in...p/t-56888.html

Enjoy

Last edited by powers2b; 06-14-10 at 12:55 PM. Reason: Because I am the GOD of my posts
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Old 06-14-10, 12:49 PM   #10
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It's been said that we need to learn something new every day. Well, for me today it is the fact that there's side by side single track bicycles out there. What a chuckle! ! !

http://www.youtube.com/watch?v=kDBHO550rdw
http://www.youtube.com/watch?v=giGm7...eature=related

Then there's THIS option that would demand a lot of teamwork, agreement on where to go and some small amount of coordination...
http://www.youtube.com/watch?v=WptukDRmfJw

The cranks they are using are certainly not going to be the best for serious riding. But then this isn't the sort of thing that you'd enter in the Td'F or the local HPV races....
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Old 06-14-10, 12:57 PM   #11
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Then there's THIS option that would demand a lot of teamwork, agreement on where to go and some small amount of coordination...
http://www.youtube.com/watch?v=WptukDRmfJw
I *like* it!
No way the stoker can slack off.
Wait a minute...which one is the stoker?
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Old 06-14-10, 02:19 PM   #12
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Eggxactly ! ! !
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Old 06-14-10, 06:13 PM   #13
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Originally Posted by prathmann View Post
Sociables are true (two-wheeled) bicycles with the riders sitting side-by-side.
This is an interesting design but most of the late 1800's Sociables I've seen illustrated were indeed trikes or quads with a single or dual small front or rear wheel(s) so the riders were not required to balance it precariously.
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Old 06-14-10, 08:55 PM   #14
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Scientific American featured Albert H. Weaver's sociable design in 1895, later manufactured as the Punnett Companion and Fox Flyer. Side-by-side, single track, two wheels. Some are to be found in bicycle museums today.

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Old 06-14-10, 11:04 PM   #15
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This is an interesting design but most of the late 1800's Sociables I've seen illustrated were indeed trikes or quads with a single or dual small front or rear wheel(s) so the riders were not required to balance it precariously.
I've seen a couple sociable recumbent trikes here and there. The latest is the tandem Quest velomobile:
http://www.youtube.com/watch?v=kc6b94NdS6s

Dig the rumble seat!
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Old 06-14-10, 11:25 PM   #16
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Virtually every imaginable bike layout and drivetrain was tried, or at least patented, in the period from 1875 to 1900 or so, including some very strange ones! The Socible was only one example. Another was tandems with the lady's seat in front and the steering controlled from the rear saddle. A case of "Ladies First" carried to the logical conclusion for a tandem. Added complexity and weight added to meet the social requirements of the era, the same reason for the Sociable IMO.
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Old 06-15-10, 12:55 PM   #17
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Another was tandems with the lady's seat in front and the steering controlled from the rear saddle. A case of "Ladies First" carried to the logical conclusion for a tandem. Added complexity and weight added to meet the social requirements of the era, the same reason for the Sociable IMO.
On the tandems of old,
The gentlemen I'm told
Followed where good manners led.

For when they went for a ride,
They sat side-by-side,
Or put the lady ahead.

But they were men, too,
Right through and through,
And I doubt they cut us slack;

For why, do you suppose,
Once we got 'em in tight clothes,
We put the ladies in the back?
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Old 06-15-10, 02:16 PM   #18
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Schweet poem ! ! ! !
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Old 06-21-10, 07:05 PM   #19
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Virtually every imaginable bike layout and drivetrain was tried, or at least patented, in the period from 1875 to 1900 or so, including some very strange ones! The Socible was only one example. Another was tandems with the lady's seat in front and the steering controlled from the rear saddle. A case of "Ladies First" carried to the logical conclusion for a tandem. Added complexity and weight added to meet the social requirements of the era, the same reason for the Sociable IMO.

There was a tandem like that at the bike shop where I learned my trade. However, both sets of handlebars were connected to the steering (chains, sprockets, and adjustable links were involved). It had been built in the '30's, though- balloon tires and coaster brake were from that era.
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Old 06-26-10, 11:28 AM   #20
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Great guys....thanx 4 ur replies.....@BCrider......ya it finally boiled down to 2 freewheels on the drive axle.......with two separate chain drives.......but i still face the problem wid steering.....i didn't want to use the conventional underseat steering handles ..... i came up with a steering system with a steering wheel to be controlled with one hand.......(the steering wheel is a normal steering wheel with a handle projecting perpendicular to the plane of the wheel from a point on the circumference......the steering to be done via the handle.....just like the handwheels in a lathe machine...whew!)......ya so the steering wheel is connected to a larger sprocket mounted on the forks of front wheel via a belt/chain drive.....hope u understand frm the pic......so the handwheel rotates to rotate the front wheel.......it is supposed to work in theory....wat do u guys think?
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