Tandem recumbent + Cruzbike front end = all-wheel drive?

[devonian]

My partner and I have an Azub Twin tandem recumbent bike, which we very luckily managed to find for sale used in the US! We've been riding it on and off for a while now, but it's always felt relatively slow and plodding - as makes sense for a big, heavy bike. The steering is slow and a bit difficult, the chain is extraordinarily long, and while it's a fun and amazingly reliable bike to ride, it's not nearly as responsive as I'd like.
So I've been thinking about how to swap the front wheel and drivetrain to a Cruzbike front triangle, with wheel, handlebars, and all. Theoretically it should be doable, if the head tube diameters and lengths match up enough. I have a QX100 currently that is in project limbo between being a road bike and a mountain bike, and so I've been thinking about someday just taking the front end off and seeing if it could be donated onto the Twin. Obviously a QX100 front end isn't nearly as nice as a Q45 or other modern front end, haha, but those are much harder to come by for relatively cheap.
Anyway, swapping out the Twin to use a Cruzbike front wheel would let the front and back wheels of the Twin be independently powered by the captain and stoker separately - thus making the bike all-wheel drive, and giving the stoker more control over their pedaling speed. The main problems I would expect, outside of the basic frame compatibility issues, would be wheel size and suspension - as you can see in the photos below, the front wheel is a 20" wheel with a suspension fork, which makes the ride much softer than it would otherwise be. With a 26" wheel, it would also push the front end of the bike up, making it potentially harder to ride - but with such a long frame anyways, that might not matter much.
If I ever do get around to building it, or if someone else does something similar, I think it might be the first true all-wheel drive, moving bottom bracket, 2-wheel tandem - which would be quite an accomplishment! I would hope it would improve power output, chain power losses, steering control, and so forth as well, at the cost of desynchronizing the captain and the stoker - which could be helpful depending on each person's riding style. What do you think, is a project like this feasible? Is it worth keeping an eye out for affordable Q45 front ends? If anyone does have a spare, however damaged, Q45 front triangle, feel free to hit me up!

Photos of the Twin as-is:

 

[Henri]

Zox makes tandems with fixed boom front drive, there are Flevo tandems and there is this long cargo MBB

MBB Lastenrad aus Holz

Heute Abend die erste Probefahrt gemacht. Es ist eine richtige Klappkiste.

www.velomobilforum.de

but I don't know of a tandem MBB. (Myself I am planning a longtail cargo MBB.)

making it potentially harder to ride - but with such a long frame anyways, that might not matter much

Or on the long bike with movable mass on the rear it might be much more important to have an easy handling front, because it's much harder and more work to always catch the mishaps of a dodgy geometry? (And it would feel less save for the stoker, if you are allways catching and correcting.)

With a 26" wheel, it would also push the front end of the bike up, making it potentially harder to ride

Did you think not only of the height, but also resulting head tube angle and trail? Also make sure, the larger wheel clears the frame! (You could of course use a smaller wheel again. The fork will still be longer and unsuspended, though.)


I would be worried to saw off the boom tube from this frame, if you don't know, how the result will ride. Might ruin a fine bike and force you to buy a new one. Please be sure about it.

 

[castlerobber]

One of the longtime members here did something like you're talking about several years ago:

Oops, I did it again... Introducing the Folding CruziTandem

Well, I got bored again... Really, it just kind of happened. O.k. That's not true. I like Cruzbikes. And I wanted a Tandem. And Cruzbike was nice enough to sell me what I needed, so, without further ado, here is the Folding CruziTandem: It is possibly the longest MBB bike in existence...

forum.cruzbike.com

 

[devonian]

One of the longtime members here did something like you're talking about several years ago:

Oops, I did it again... Introducing the Folding CruziTandem

Well, I got bored again... Really, it just kind of happened. O.k. That's not true. I like Cruzbikes. And I wanted a Tandem. And Cruzbike was nice enough to sell me what I needed, so, without further ado, here is the Folding CruziTandem: It is possibly the longest MBB bike in existence...

forum.cruzbike.com

Oh, that's amazing! Thanks for sharing the link! I guess someone has made a MBB tandem before, then - that's really cool!!

 

[Robert Holler]

Even IF this were possible - it will not make the slow and plodding feeling any better. You would have to cut off the entire front end at the head tube - rendering the bike ruined before even trying the experiment. That is also a 20" wheel fork on the stock bike, so changing that to a taller fork would radically alter the angle of the head tube and possibly adversely impact the handling.

 

[devonian]

Even IF this were possible - it will not make the slow and plodding feeling any better. You would have to cut off the entire front end at the head tube - rendering the bike ruined before even trying the experiment. That is also a 20" wheel fork on the stock bike, so changing that to a taller fork would radically alter the angle of the head tube and possibly adversely impact the handling.

Hm, that probably is true. The front boom can be removed easily enough on its own, but I had assumed a Cruzbike front end could just fit over the frame's front boom sleeve, which might not work at all - and it definitely wouldn't for shorter riders just due to the chain, regardless of whether the actual Cruzbike boom could fit. It's definitely not worth sawing the frame apart at all, but yeah - just the geometry there might make it impossible to do otherwise. Oh well! It would definitely be cool to make a MBB tandem that's actually adapted well for recumbent riding, but that might take more custom fabrication rather than building off of an existing bike.

 

[Henri]

I had assumed a Cruzbike front end could just fit over the frame's front boom sleeve

Even if the hardware fits, you can't ride it without removing the stump. It's already a nuisance to wrap your legs around the headtube of a Cruzbike in tight corners. Your legs would catch on the stump even just balancing along a straight road.

If you happen to find a recumbent tandem with front boom damage, that might be a good basis for experiments. But you'd probably need a lot of work and luck searching.

If you find a professional frame builder who does very custom stuff, sure you could order one, but it sounded like you wouldn't want to pay for that.
For doing it non professionally, one could take parts of old frams and hack something together or maybe try using wood, simple square aluminium profiles (my XYZ Cargo Fourwheeler is made with such profiles and it's great in price, weight and cargo capacity, thanks to its space frame design.) or aluminium construction profiles (probably easy to work with with their T-slots and lots of available accessories, probably strong, but probably very heavy). But it needs a few Interfaces to standard bike components, so maybe a few donor frame parts might still come into play. Parts for frame builders should be available, though. So you could get dropouts, headtubes and such to somehow put them on the self made frame.
Or visit a frame building course, get some tube and try to actually build a frame the conventional way. It might take a few tries, though.

I was just looking around the internet and also stumbled across pictures of a python with a cargo basket between seat and rear wheel. Sometimes actally great and inspiring stuff comes to surface, layers deep on Pinterest.

 

[Boreen bimbler]

I was wondering if differing cadence's on a tandem would create wobble? Maybe less likely with one being MBB?
Mad enough idea. Fair play to you if you do it.

 

[Henri]

Ah, there was one thing I wanted to mention: The coupled drive train locks gear selection and cadence together, but it also creates an intuitive way of communication. With independent drive trains you might lose something, you didn't know you had. (And two shifting mechanisms of course are more expensive than one.)
But that might be unimportant.