Bicycle Cargo Trailer Product

Overview

A bicycle cargo trailer carries load on its own wheels instead of on the bicycle. That single fact drives everything about the design: a bike's handling degrades quickly with 20 kg on a rear rack, but the same bike tows 40 kg in a trailer with almost no change in balance, because the cargo mass never enters the bike's lean dynamics. The trailer connects through an articulating hitch at the rear axle, rolls on two small wheels straddling a low cargo box, and adds only rolling resistance and inertia to the rider's task. EN 15918 governs the product class in Europe; typical commercial trailers carry 30–45 kg in 70–130 litres and weigh 7–12 kg empty.

Frame and box

The Frame & Cargo Box separates structure from enclosure. A welded Main Frame of ~25 mm aluminum or steel tube takes all road and towing loads, so the Side Walls and End Walls can be lightweight mesh, coated fabric, or thin plastic — they only retain cargo, they do not carry it. The Floor Panel is the working surface, usually marine ply or HDPE sheet. Load placement matters: the axle line sits slightly behind the volumetric center so a centred load puts a small download on the hitch, the same tongue-weight rule as automotive trailers. A load placed behind the axle lifts the hitch and produces the characteristic low-speed fishtail; Tie-Down Rails exist because a shifting load does the same thing dynamically. Corner Bumpers acknowledge that trailers spend half their life being wheeled through doorways.

Wheels

The Wheel & Axle Set use two 16–20 inch spoked Wheel Assembly units on Stub Axles — 12 mm steel stubs with push-button ball detents that release the wheel without tools, dropping the trailer flat for car transport. The stubs lock into Axle Receivers welded to the frame, which fix track and camber; hubs run on cartridge Ball Bearing pairs. Small wheels lower the cargo floor and the centre of gravity, at the cost of higher rolling resistance and harsher response to potholes. Mudguards keep spray off both the cargo and the rider drafting half a metre behind the trailer's wheels.

Single-wheel trailers (the touring style) put one inline wheel behind the box and lean with the bicycle; they track a narrow line for singletrack and rough roads but give up payload and standing stability. The two-wheel layout described here dominates utility use.

The hitch

The Hitch Arm & Coupling is the defining mechanism. A cranked Tow Arm runs from the trailer's left chassis rail, around the rear wheel, to the bicycle's left dropout — cranked so panniers still fit. It terminates in the Articulating Coupling, which must permit three rotations at once: yaw for cornering, pitch for kerbs, and roll of ±45° or more so the bicycle can lean while the trailer stays flat. Most designs use a torsionally soft elastomer cylinder, which provides all three freedoms in one moulded part and damps the jerk of pedal-stroke accelerations; others use a true universal joint with a roll pivot.

The bike-side Axle Hitch Fitting stays on the bicycle permanently, clamped under the axle nut or threaded onto the quick-release skewer, and the trailer attaches with a Hitch Pin in seconds. Hitching at the axle, on the bike's roll axis and low to the ground, is what keeps trailer loads from steering the bike; seatpost hitches exist but feed yaw moments into the frame at a long lever arm. A Safety Strap around the chainstay is the mandated backup — like a car trailer's chains, it converts a forgotten pin from a runaway trailer into a noisy nuisance. An Arm Fold Joint folds the arm flat against the box for storage.

Steady-state towing loads are modest — about 50 N pulls 40 kg up an 8 % grade — but braking and pothole jerk loads reach an order of magnitude higher, which is what the coupling and arm are actually sized for.

Weather and visibility

The Cargo Cover tensions a seam-taped Cover Fabric over Cover Bows so rain sheds rather than pools; hard-box variants use lockable Lid Hinges instead. The Visibility Kit addresses the trailer's real hazard: it is knee-high in a traffic environment scanned at car height. The fluorescent Safety Flag on its flexing Flag Pole puts colour at driver eye level, the Reflector Set meets regulations such as the German StVZO, and the Light Mount carries a separate rear lamp because the trailer body shadows the bicycle's own. A sprung Parking Stand holds the unhitched trailer level for loading.

Operation and limits

Loaded trailers change braking, not balance: total system mass can double while braking force still comes only from the bicycle's two contact patches, so stopping distances grow accordingly and manufacturers cap recommended towing speed around 25 km/h. Width is the other adjustment — a 750 mm track does not follow the bike's line through gaps. Within those limits the cargo trailer remains the cheapest way to add serious carrying capacity to any existing bicycle, which is why it persists alongside purpose-built cargo bikes: the bike is unchanged, the trailer detaches in five seconds, and the same hitch tows shopping on Monday and a canoe on Saturday.