Conundrum : tandem

[Doug Burton]

Ok folks,

I have an R82 Vision tandem. I paid $3300 to get it shipped here from California in 2005. The objective was to get my son interested in riding with the family. It didn't work.

I have discussed potential Cruzbike tandems with John T many times. The issue with tandems is they very rarely return adequate money to the business. They're just not that popular.

I want a tandem for me and my wife to ride mainly to cement our 31 years of marriage and to have something to do together. Cruzbike technology makes me much more effective as a part of a tandem team, and the R82 doesn't have it.

So I have a decision to make. Do I cut up the Vision R82 to convert it to Cruzbike technology (i'd have to cut the boom off the front and modify the head tube to accept a 26.5mm fork), or should I sell it and develop a tandem frame from scratch? Typical resale value for an R82 these days is about $1500-1700.

Interested to hear what you folks think.

Best,

Doug

 

[Andrew 1973]

Build it From Scratch - Maybe?

Doug,

You have the skills and the resources to modify and build some amazing bikes. I have no doubt that you could modify the Vision into a "Cruz-tandem" and that could potentially be the easiest (with the exception of the headtube modification) route. Once it's done, it's done and there is no going back.

You could always sell the Vision and put the funds into building your own design from the ground up. I don't know, I'm torn. I thought I was decided on a new build, but I see both sides. The one thing going for modifying the Vision is breathing new life into an old bike. There's something satisfying about doing that.

 

[Charles.Plager]

Another option:
Find a

Another option:
Find a folding tandem and use two kits to convert it.
(I've even got the two kits ready to go).

 

[Kim Tolhurst]

one sided view

Accept challenge of tandem build from selling the Vision. (would like to make money out of visions myself) Ok, collect many bike frames for free from round-about. Cut and weld, Cruzbike front end, rear wheel driven by crank forward frame style. These two parts joined by quick release mechanism for easy bike rack carrying or stowage.

done, I mean there you go.

best, Kim.

 

[John Tolhurst]

Maybe there will be a

Maybe there will be a cruzbike frame produced one day that happens to have really solid connection points, so that you could link them together? Perhaps we could build a couple of prototypes of these frames?

 

[super slim]

Doug,the best option is to

Doug,
the best option is to bolt two Softriders together, back to back with the rear suspensions replaced with a lattice frame.

The stoker drive wheel would need to be a 8 speed hub gear with no idler, as with the wheel being turned around, and going backwards, the rear deraileur would have to be above the wheel and next to the fork instead of below it. (see the attached pdf)

The stoker headset bearings would need to be replaced with steel serrated bushes so it did turn.

The stoker would have to be happy seeings things as they went by, AND could peddle backwards!
Communication between the caption and stoker would be good as their heads would only be inches away from each other.

The wheel base would only be 1.900 m compared to 2.48m for the addition of the Vision R82 rear section bolted onto the rear suspension of a Softrider, using a U shaped gussets so a quick release and two serrated spacers at a 100 mm gap at the rear wheel dropout, and a 20 mm tube welded into the 75??? mm dia ?main tube of theVision R82 , and a bolt going down to the Kick stand plate, also with gusseted bolt plate to loctae the main tube sideways and stop it rotating.

The max. length of the back to back option with one half removed would be 1.86 m, compared to 1.7m for the Vision R82 if the split was done at the existing joint just in front of the stoker crank.

Both options would be AWD, with each rider choosing their own cadence, and the caption have control of both brakes.

Two brake eyelets would be required at a reasonable spacing on the rear suspension, so a brake cable joiner can be used on the inner cables only and there is 3" of travel available. This allows the Sofrider to be quickly changed back to a single rider, OR for when splitting the bikes to go on a car rack.

I would strongly recommend that 180 or 203 mm disk brakes are added to the Sofrider Caption drive wheel as the load has just doubled.
The stoker drive wheel in the back to back arrangement would need to be a rim brake as the wheel needs to be reversed so the freewheel is rotating the correct way. This means that the disk bracket is now on the wrong fork side. A conversion kit could be used with a suspension fork as it would NOW be on the right side to be used.

I think the back to back arrangement would be better aerodynamically??
But I don't know!

Regards

Super Slim

 

[Doug Burton]

Hey Slim, Thanks for the drawing...

I had considered this route using two Silvio v1 frames and a purpose-built connecting subframe, that would grab the Silvio frames in the same places as the rear fork and the carboyoke, with some select strengthening here and there.

Problem 1: My wife will not ride backwards. Rejected it out of hand.

Problem 2: Massive sheer loading on all the attachment points, particularly at the lower carboyoke mounts. I don't think these can take double static loading in addition to impact loads, and any twisting at all would amplify the fatigue over time. I'd have to use Sofrider forks (or fabricated steel replacements) to even get close to safe fork loading.

Attractive idea, though, because the resulting bike would be fast, light for a tandem, and short for easy rack carrying.

Ahh, well - tempted to break out my old drawing board and drafting machine.

A Barcroft Columbia with the front boom sawed off would be perfect, as would a Zox 20/20 tandem similarly de-boomed.

Thanks,

Doug

 

[1happyreader]

happy stokers

Doug,

does your vision tandem separate into two pieces as mentioned in this manual ?

I wish you could make a new front piece and keep the old front piece in reserve.
I guess i just hate seeing a nice bike frame cut up while in working condition.

I remember your interest in a shorter wheelbase for your tandem.

My own musings /design put the captain at a low enough recline to allow the stoker forward vision.

good luck ,,,, and please send LOTS of pictures .

 

[John Tolhurst]

The two bikes joined together

The two bikes joined together sounds obvious but is devilish when you try to think it through.

 

[super slim]

Doug,
     Here are two other

Doug,
Here are two other options, based on the Silvio V2.0 hydroformed 76*38 frame, but using 26" wheels (36 spokes) and rigid suspension as the larger tyres (40 mm to 60mm) are the suspension.

Both layouts allow leg length adjustments with the same chain length, with the handlebar directly connected to the BB, and uses the existing Silvio V2.0 +100 mm extension on the rear of the long wheel base tandem.

The short wheel base has a 120 kg rear wheel load (needs a 40 spoke stoker tandem wheel with a 250 mm disc rotor, and 60 mm tyre) with a 60 kg stoker, so this would be the max stoker weight, but uses 1.1 chain length as per V2.0 with a 100 mm extension.

The long wheel base has a 82 kg rear wheel load, so the front and rear wheels and tyres are the same 40 mm tyre with 36 spokes.
The rear chain length is 2.6 times the standard, so 3.7 X std total, compared to 5? to 6? X for a RWD Tandem.

The stoker can pedal at his/her cadence and power, AND AWD!

There a LOT of space for 6 off rear ortlieb panniers under the main frame, but tyre size and wheel spoke count would need to increase!

Folded lengths are very similar at 2.06 m, without the seats clashing with each other.

 

[John Tolhurst]

I did look into this a long

I did look into this a long while back. Really there is no alternative to getting two nice HF tubes on the welding table and doing the deed.

 

[super slim]

Silvio 2 tandem drawings.
I

Silvio 2 tandem drawings.
I attached the softrider in the previous reply

 

[Shakey]

In-Line Tandem Tricycle

Hi Doug, I have been pondering a Cruzbike Tandem for a while.
I wish I had some Sketchup skills, but I will have to just try & describe my idea.

It is an In-Line Tricycle, similar to a childs trail-a-bike
The Pilot drives the front wheel, typical Cruzbike drive train.
The Stroker drives the middle wheel, typical Cruzbike drive train.
The third wheel trails along like a typical Cruzbike rear wheel.

There is a universal joint between the Stroker's seat & handle bars to allow cornering & vertical undulation.
The Stroker's handle bars are fixed to the Pilot's part of the frame.
Should be able to make it break down into two parts for transport.

There are a few issues that I can foresee.
-> Making the Stroker's bottom bracket adjustable like a typical Cruzbike, I have a few ideas but none that I am really happy about.
-> Stroker's peddle clearance with the Pilot's seat, probably have to extend the wheelbase on the front part of the bike.
-> Suspension on the middle wheel, might just have to make the first prototype without suspension, (proof of concept)

Clear as mud?
Should be a fun build, show me some pics when you get 'er done

cheers
Richard

 

[super slim]

How fast would Maria and Jim

How fast would Maria and Jim be on a Cruzbike Tandem OR how easy to tour with 6 panniers, and NO BOB trailer like DF tandems do!!!!!!

Look at the much reduced frontal area of the Cruzbike tandem compared to the DF Tandem, especially with panniers (on the http://cruzbike.com/forum/data/sites/default/).

The Banana S bags give a much better front profile than the Ortliebs on the Cruzbike.

The rear wheel of a DF tandem with bob trailer is 116 kg, compared to 105 kg on the Cruzbike, but I have seen lots of DF tandem photos with 120 L of rear panniers and bag, AND 40 L front panniers, so the rear wheel loads would be 150kg++++, no wonder so many DF Tandem rear wheels fail, even with 48 spokes.


The folded length is 1.8 m, so it could fit across the back of a car or in the tray of a Pick up.

 

[hamishbarker]

i prefer the layout of the

i prefer the layout of the back to back tandem by tom traylor (except have the stoker pedal backwards into a flipped over wheel rather than use his many idler layout which is used to allow the stoker to have a normal forward pedal stroke).

http://www.recumbents.com/wisil/racing2004/sanjose/TomSimaTraylor.jpg

detail of stoker's direction reversal idlers

http://mysite.verizon.net/ts72/graphics/b-2-b_rear_detail.jpg

downside is I guess two drive trains, but at least the chains are short and drive trains are triangulated.

 

[John Tolhurst]

What you can do, what Tom

What you can do, what Tom didn't try, is to make the chain a direct figure eight, no idlers.

 

[hamishbarker]

hmm, that might also result

hmm, that might also result in a different sort of chain wear since the rollers would be reversing direction each time they go around the chainwheel and cluster. might be good, or bad or more likely, no difference.

I have never ridden a back to back tandem, but the possibility for luggage space (or fairing) in the middle looks better to me than for inline tandems.

For a really wild tandem layout, check out team cieo in switzerland! the stoker luxuriates on their back under a shower of sweat from the captain. ugh!

http://www.cieo.ch/wp-content/uploads/2012/11/Kopie-von-2013_Rendering_Rollout.jpg

 

[John Tolhurst]

I've seen the figure eight

I've seen the figure eight chain implemented, just not for this purpose. I didn't see any wear issues - keeping a good axle crank distance is important, and a (very) slight bend in the RD cage might be worth looking at.

 

[super slim]

Hamish,
Here are some

Hamish,
Here are some examples of rear drive fig 8 chain path

 

[richa]

MBB Back-to-back tandem

Here's a MBB back-to-back tandem. I have no information on it, but would certainly be interested in knowing how well it works.