Tandem Build

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May 9, 2020
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I finally convinced my wife that we would enjoy riding more with a tandem. Test rides on a couple different ones helped. So here we go again building a recumbent. It has been eight years since I last build a recumbent bicycle. Five of those years have been taken up on restoring a 1957 Wagemaker boat. Although the boat is not finished I'm stalled while hunting a trailer for it. So...

On to the tandem build. I am basing is loosely off of the TradeWinds and FrontRunner. Two drives, the front drive with a moving bottom bracket. (Thank you to Stormbird and others for giving me the push to try this over a linked drive system.) I've been building for a couple of days so it is time to get started on the build report.

Warning: I am having trouble posting pictures. I will have to research why that is. I hope that the links are not too much trouble.

I decided to start on the front drive system. Two days work and I got this completed.



Another day's work and I completed a couple of things. First I curved the down tube down to get me closer to the MBB and also strengthened the joint with the head tube. Then, rather than tear apart another bike simply for the BB I made a replacement BB/seat tube for the rear triangle.



 
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Hi there

Good to see you building and it is racing along !

That is what is referred to as a ' sealed cartridge BB ' that replaces the parts usually found in what is referred to as a ' three piece ' bottom bracket [ the pieces being 2 x pedal cranks and the BB ]

You need a special socket to remove it and have to be careful as some of the cups are plastic and easily broken , if that happens I just replace with the steel equivalent it just won't screw in as far.



Paul
 
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That bottom bracket cartridge should have captive threads one end and a removable cup to support the other end. They are not servicable. It's either ok or replaced and are not expensive off ebay. Is that square member to the bottom bracket removable? I can't quite make out on my phone. If not the way you've attached the front bottom bracket shell means you have no ability to remove the headset. It's more usual to triangulate to the bottom of the forks and the top of the forks just above the tyre leaving the forks fully removable.
 
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This may help

Someone gone down that path in Finland ?

MBB tandem drawings at beginning are for 2 coupled together but further on he builds a single tandem ?

 
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Thank you for the input, stormbird and popshot. I will look into a new replacement for that sealed BB but it's good enough if I cannot find a new one. There is a little drag but no grittiness. I mostly wanted to make sure the grease is good and any sand removed. I already have the necessary tool.

As for the connection on the front triangle, yes, the square section is removable and bolts in. I got the idea from the Atom Blaster with some influence from Cruzbike. The only reason I decided to attempt the to drive system is because I had the opportunity to test ride a Cruzbike and liked it. Separate drive systems will make the tandem experience better for my wife and I.
 
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Got a little more work done today. It looks like it will be a few inches over 9 feet long. The perspective of the photo makes things look a little different. The main tube is level and both wheels are 26". Once the build is complete I will change the tires to something like a 1.25" touring tire.

I did also weld up one seat frame that is not pictured. For some reason the gallery wants to turn the picture sideways when I upload the picture.

 
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hmmm

Are you happy with 9ft ?

Some will be coming from 26" wheels and it looks like you have the stoker quite laid back ?
 
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I'm okay with 9 feet. It will stick a couple of feet past the tailgate of our truck. Some of the extra length comes from the seat I have chosen. The forum gallery still turns the photo sideways. The best I can determine it will require an extra 6-8 inches to support the stoker's seat. As I write this I think that maybe I should copy the supports from Recycled Recumbents. I better take some time in my thinking chair.

 
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Borrowed the seat from my Recycle Recumbent Mach 2 for a test fitting. I like this design because it is the most comfortable recumbent seat I have found.

Short answer: I can trim eight inches from the main tube.

Long answer: Turns out that my measurements from her Burley were not so accurate. She was five inches from reaching the pedals. Using the seat back support idea from Recycled Recumbents and I can trim an additional three inches from the top tube. I will cut and bent the seat stays so that they attach at the same level as the main tube.

My only concern at the moment is that when seated she cannot reach the ground.
 
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My only concern at the moment is that when seated she cannot reach the ground.
Never ridden a tandem from either position , however I would have though that was both mandatory AND crucial ?

How many inches is she short ?

Would 24" or 20" wheels help ?
 
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She is a couple inches short of touching. We will talk after she gets off from work tonight. I might drop the back of the main tube and not shorten the length. I'll also put the frame that I have into the bed of her truck to get an idea how the overall length affects hauling it.
 
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Don't forget it will also effect turning circle ?
 
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Don't forget it will also effect turning circle ?
Thank you for the reminder. You are talking about overall length, correct? Yes, I am aware. Not sure how much better a 72" wheelbase is over an 80" wheelbase. I am also somewhat familiar with this because of the 70 wheelbase on my RR Mach 2.

We have talked about the fact that she will provide the main power for u-turns since my MBB will be far to one side making pedaling difficult. We will give it a good test run before final paint in case adjustment (major or minor) need to be made.
 
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Got a little more progress completed. Welded up the second seat frame and made some modifications to the frame completing the basic shape of the frame. Stoker's seat height was reduced by three inches, about as low as I felt the frame would support, and the frame was shortened lengthwise by five inches. Overall length is now 104 inches (8' 8"), not bad so far as I can tell.

Now I must finish the seats, plus get the seat mounts and stoker's handlebar mount fabricated so that we can take a test ride. That is when I will really find out if major changes are required.

 
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Looking good...
 
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Made some more progress, both seats are complete along with their supporting components. Put the drives in place to give it a test. The steering seems a little heavy but that could be several things... the mountain bike tires, the nature of a tandem, MBB design, or I didn't build it correctly. I'm not sure what it is. The only other concern at this point is that my knees were touching the handlebars but I may have come up with a solution. That gooseneck sticks out pretty far, I can cut a wide notch and bend a good part of the extension up and back. This will move the handlebars up and back about 2 inches.

Of course, any thoughts or suggestions would be appreciated.

 
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Looking good.

Maybe get up a little speed and then remove your feet from the pedals ? and see if the steering is still heavy ?

It appears heavy on my Python at first however it is just your legs not used to 'helping ' with the steering , once you have a few miles on it they may start co-operating and it could feel better ;)

Else is there some room to get the pilots seat further back ? then the pedals could also be further back that should reduce the pedal leverage distance from the head tube a bit ?
 
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Using lower gears and taking some time to get used to it will help. However, I believe that the long wheelbase is part of the problem. More practice is in order before making changes.
 
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