Cargo Trike

Overview

The cargo trike is the working layout of urban cycle logistics and the school run in Dutch and Danish cities: a box between two steered front wheels, the rider behind it on a conventional bicycle rear end. The arrangement is called a tadpole (two wheels forward) and in the Netherlands simply a bakfiets, "box bike". Putting the load ahead of the rider and between the steered wheels keeps it visible, keeps the floor low for loading children or crates, and lets the Cargo Box grow to 100 kg capacity without the balance problems of a two-wheeled long-john. The cost is automotive-style complexity at the front: kingpins, knuckles, tie rods and a steering linkage that a bicycle simply does not have.

Chassis

The Cargo Chassis is welded chromoly steel in two functional halves. The Load Platform Frame is a ladder of box-section members sitting 35 cm above the road, bounded by two Axle Crossmember beams that carry a Kingpin Tube at each end. Behind it, the Rear Rider Frame is recognizably a bicycle: seat tube, chainstays, a Seat Assembly on top. Frame stiffness matters more here than weight; a flexible platform lets the front wheels toe in and out under load, which makes the steering vague and wears tires.

Steering

The rider's handlebar does not sit over a steered wheel. Instead the Handlebar Mast rotates in its own bearings and moves a Drag Link, which swings the central Steering Bellcrank mounted under the box floor. Two Tie Rod links run outward from the bellcrank to arms on each Steering Knuckle, with Ball Rod End ball joints at every connection to tolerate flex and assembly misalignment.

The linkage geometry is Ackermann: the tie-rod arms are angled so that in a turn the inner wheel steers through a larger angle than the outer one, since it tracks a tighter radius. Without this, one front tire scrubs sideways through every corner. Each knuckle pivots on a Kingpin inclined a few degrees from vertical; the inclination, plus a small amount of trail ground into the Stub Axle position, makes the steering self-center at speed. Toe is set by screwing the threaded tie rods in or out, typically zero to 1 mm toe-in across the front track.

Drivetrain

Drive is conventional bicycle practice stretched over a long wheelbase. The Crankset turns a 38-tooth ring; the Drive Chain runs back under the rider, kept taut by a sprung Chain Tensioner and fully enclosed in a Chainguard. The rear hub is the interesting part: the 8-Speed Hub Gear packs three stacked planetary Helical Gear Pair stages inside the Hub Shell, giving eight ratios across a 307% range with no exposed derailleur to snag cargo straps. A Shifter Cable selects which stages are locked or freewheeling, and a Pawl Set transmits drive to the shell. Internal hubs shift at a standstill, a real advantage when stopping at lights with 100 kg aboard, since the rider can drop to first gear before pulling away.

Brakes

A loaded trike at 250 kg gross needs far more braking than a bicycle, and most of it at the front, where weight transfer goes under deceleration. Each front hub contains a 70 mm Front Drum Brake; both drums are pulled by a single left-hand Brake Lever through a Brake Cable Splitter that equalizes the pull, so uneven adjustment cannot drag the trike to one side mid-stop. The rear hub carries a Rear Roller Brake, a sealed, grease-filled cam-and-roller unit chosen for fade resistance on long descents rather than outright power. A Parking Brake Lock latches the front lever applied, and a Ring Wheel Lock ring immobilizes the Rear Wheel when parked, because a trike, unlike a bicycle, will roll off on any slope.

The box

The Plywood Box Shell is 9 mm birch marine plywood, light, stiff, screw-friendly and cheap to repair, which is why plywood has outlasted every attempt to replace it in this trade. For passenger duty a Child Bench Seat folds down with two three-point Child Harness sets anchored through the shell, and a Rain Canopy on removable bows closes the box against weather.

Handling

Tadpole trikes do not lean. Cornering grip is set by track width and the height of the center of mass, and the low platform is what makes the format work: with the load at 35 cm, the trike can corner at sensible urban speeds without lifting the inside front wheel. Riders coming from bicycles need a few hundred meters to stop counter-steering; after that, the machine is steered like a small car, with the 4 m turning circle to match.