The following is mostly a project post from about a year ago. I started ordering some parts but still haven’t settled on a final prototype design yet, even after I got some very good advice on a lot of aspects on the AtomicZombie forum. I don’t know if I will ever actually build it.

The idea: a recumbent Python delta trike, but make it foldable.

Design requirements:

• Comfortably haul a 10kg 40L backpack, to go on hiking trips I otherwise can’t do without a car
• Be able to take it (plus backpack) on a Dutch train, which means it has to fold down to a small size
• Max 75cm total width, to fit through shed door and comply with Dutch traffic regulations more easily
• Fun project to build together with my dad, who is an experienced aluminium welder and has worked on bikes before

Nice-to-haves:

• Functions as seat when folded
• Still rolls when folded
• Can carry heavy/large items, e.g. using a 60x40cm Eurocrate
• No dimension over 85 cm when folded – this would make it easier to carry on international trains too
• Lightweight
• 26” wheels – probably won’t work with the other design requirements though

What I’ve learned about Python trikes so far:

• Inspiration: the only other folding Python trikes seem to be Howard Stevens’ Porta Velo’s, but folded up they’re still a little too big/wide for what I want, and the Russian Denedi trikes which more closely resemble what I want to do
• Pivot point & seat should be as much forward as possible, to put more weight on front wheel. This is extra important because of the added weight of the backpack
• Wheelbase should be as long as possible, also to put more weight on front wheel
• Seat should be as low as possible for cornering stability, but not so low that there is no ground clearance

Current design idea:

• Python type recumbent, with two rear wheels. Open space between the rear wheels for mounting a backpack, maybe with straps under the seat
• Folding: the rear wheels are on double pivoted swing arms that allow the wheels to fold all the way against the front wheel. The seat folds forward over the three folded up wheels. When folded, the backpack can stay attached to the seat and the whole thing acts as a luggage trolley running on the rear wheels
• Wheel size: 20”, because 24″ or 26″ would make the whole thing just so much bigger :(
• Suspension: none. Perhaps a balloon tire in the front (Big Ben?) for a smoother ride, or even 3x balloon tires
• Wheelbase: 90 cm
• Track: 67 cm (total width 75 cm)
• Pivot angle: 60°
• Pivot type: Rod end bearings M12
• Seat angle: 50°
• Seat height from ground: 20.0 cm
• Trail: -18.4 cm
• Ground clearance: 11.9 cm – 15.0 cm
• BB-EOS: max 76 cm (my inseam is 89 cm)
• BB: Press fit in 40x3mm tube, adjustable with clamping bolts
• Front hub: 8 speed gear hub with roller brake?
• Rear hubs: Sturmey Archer 70mm drum brake, single mounted (12mm axle)?

Alternate designs that might fit requirements

• Instead of folding, detachable rear wheel arms?
• Upright two-wheeled folding bike design with rack for backpack?