Cargo Bicycle

Overview

A cargo bicycle carries loads that a standard bicycle cannot: groceries, tools, trade equipment, or two or three children. The long-john layout shown here, also called a box-bike, places a low cargo area between the rider and the front wheel. Keeping the load low and ahead of the rider gives a stable feel even when the box is full, because most of the weight sits close to the ground and inside the wheelbase rather than hanging off a rear rack. The trade-off is length: the frame stretches to about 2.5m, so the front wheel sits far from the rider and cannot be steered by a normal fork and stem. A remote steering linkage solves that. The bike in this entry is electric-assist, with a mid-drive motor and a downtube battery that make a 100kg load manageable on hills and from a standing start.

Frame and cargo box

The Main Frame is TIG-welded from 4130 cromoly tube. Steel is common on cargo bikes because it tolerates the bending loads of a long frame and is easy to repair. The main tube runs forward and low from the head tube, then sweeps up to the bottom bracket and the rider. The battery sits inside the downtube section. A bolt-on rear rack adds about 25kg of rear capacity for panniers or a child seat.

The Cargo Box mounts on a bolted aluminium subframe above the front wheel. The floor is 12mm marine plywood with an anti-slip coating, and the walls are 6mm aluminium-composite panels that stay light while resisting knocks. A folding bench seat turns the box into child seating for two, each held by a three-point seatbelt. A removable rain cover stretches over flexible glass-fibre hoops with clear PVC windows so children stay dry and visible. Loose cargo is held by lashing straps.

Steering linkage

Because the rider cannot reach the front wheel, steering is remote. The Handlebar and Stem turn a steering column that pivots in the head tube near the rider. A steering arm clamped to that column converts the rotation into back-and-forth travel of a rigid push-pull linkage rod that runs forward alongside the box. At the front, a second steering arm on the fork steerer turns that travel back into rotation of the front fork. Spherical rod ends at each joint let the rod follow the arms through their arc without binding. The geometry is tuned so a given turn of the bar gives a sensible turn at the wheel, neither twitchy nor vague. The headset uses sealed cartridge bearings so the column turns smoothly under load.

Electric assist drive

The bike uses a mid-drive motor at the bottom bracket rather than a hub motor. A mid-drive feeds its power through the same chain and gears the rider uses, so the cassette can be selected to keep the motor in an efficient range on steep climbs with a full box. The motor is a brushless unit built around a stator and rotor, with three hall sensors for rotor position and a single-stage reduction gear that steps the high motor speed down to chainring speed at up to 80Nm. A one-way clutch lets the rider coast and pedal without back-driving the motor.

Power comes from a 36V 14Ah battery, built from 40 18650 cells in a 10S4P array, locked into the downtube with a key. A battery management board balances the ten series groups and cuts off on over-current or over-temperature. The motor controller reads a bottom-bracket torque sensor and scales assist to how hard the rider pedals, then drives the motor through six power MOSFETs. A bar-mounted display shows speed, assist level, and charge. Assist cuts out at 25km/h to meet pedelec rules, and brake cutoff switches drop motor power the instant a lever is pulled.

Braking and wheels

Stopping a 200kg loaded bike needs more than rim brakes. The brake system uses hydraulic disc calipers front and rear on 180mm rotors, with sintered pads for fade resistance on long descents. Each lever is a master cylinder that pushes mineral oil through a hose to the twin pistons.

The two wheels differ in size. The front wheel is 20in to keep the box low, and the rear wheel is 26in to roll well and carry the cassette. Both are laced with 36 spokes to double-wall rims for strength under load, and both run puncture-resistant tires.

Materials and use

The structure mixes cromoly steel in the frame and fork with aluminium in the box subframe, rims, and crank arms, and plywood and composite in the box. A double-leg center kickstand lifts the rear wheel and holds the bike upright for loading children or cargo. The accessory kit adds battery-powered front and rear lights, full-length fenders, a bell, and reflectors.

Common variants change the front load area. A box version like this one suits families and is the most stable for children. A flatbed version drops the walls for pallets and bulky freight. A trike variant adds a second front wheel for parking stability and heavier payloads at the cost of weight and width. Non-assisted models drop the motor and battery entirely and rely on a very wide gear range, which works on flat ground but is hard going uphill with a full box.