Ebike Trailers and Towing: What the Load Actually Costs

Bicycle trailers were built for people willing to grind a 100 lb load up a hill on leg power alone, which kept the category small. Add a motor and a 750W bike pulls a loaded cargo trailer up a 6 percent grade without drama, which turns the trailer from an endurance event into a genuine car replacement for the school run and the weekly shop.

The catch is that the motor only solves the going part. Nothing about an ebike improves the stopping part, and on a mid-drive the towing load rides through the same chain the motor already overloads. Both problems are manageable, but only if you know they exist before you buy the trailer.

Three shapes of trailer, and what each is actually for

Two wheel cargo trailers

A box or a flat platform on two wheels, riding on a low axle, connected to the bike by an arm that reaches forward on the left side. Rated capacity is typically 100 lb. The wheels are usually 16 inch, the track is around 28 to 32 inches, and the whole thing weighs 15 to 25 lb empty.

This is the workhorse. It stands up on its own when you unhitch it, which is the single biggest practical advantage over a single wheel design, because you can load it at the kerb without a third hand. It is stable at low speed and tolerates awkward loads. The weaknesses are width and drag: at 30 inches it will not pass through the bollard gaps and chicanes bike paths are full of.

Single wheel trailers

One wheel directly behind the bike, with the load carried in panniers or a drybag over the wheel, and the arms attaching either side of the rear axle. Capacity is usually around 70 lb. The BOB pattern is the long running example.

These track exactly where the bike tracks, which means anywhere the bike fits, the trailer fits. That makes them the only sensible choice for narrow paths, gravel, and anything resembling touring. They lean with the bike rather than fighting it, so at speed they feel far more like part of the bicycle.

The trade is that they fall over when unhitched, they load higher so the centre of mass is worse, and the mounting is fussier. Most require a proprietary skewer or a trailer specific thru axle, and a bike with a nutted rear hub motor axle may need an adapter or may not fit at all.

Child trailers

Two wheels, a roll cage style frame, a fabric cabin, a five point harness per seat, and typically a total capacity around 100 lb covering one or two children plus their kit. The good ones convert to a stroller or a jogger with a wheel kit, which is what justifies the price for most families. They are taller than cargo trailers, they catch crosswinds, and they are the only type where getting the setup wrong involves a person.

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Before buying any of them, be honest about whether a trailer is the right answer at all. A trailer costs $350 to $1,400 and lives in the garage taking up the space of a small motorcycle. If you tow every day, an electric cargo bike carries the same load with none of the width, none of the hitch fuss, and better handling. A trailer wins when the towing is occasional, when the load is bulky rather than heavy, or when you want to keep riding the bike you already have.

Where the trailer attaches, and why it matters more on an ebike

There are two ways to connect a trailer to a bicycle and they are not close to equivalent.

An axle mounted hitch replaces the rear quick release skewer or clamps around the axle, sitting on the non drive side. The pulling force enters the bike at the dropout, three or four inches from the ground, and the dropout is one of the most heavily engineered parts of any frame because it already carries the entire rear of the bike plus braking torque. The pivot is low, close to the tire contact patch, so the trailer pulls the bike forward rather than trying to rotate it.

A seatpost hitch clamps around the seatpost, typically 15 to 25 inches above that axle. Every pound of drag now acts on a long lever. Three consequences follow, and they get worse with motor assist.

• The clamp is the wrong component. A seatpost binder resists a post sliding downward under static weight. It is not designed for a repeated horizontal tug plus torsion, and on a carbon seatpost a clamp like this is simply not allowed.
• The high pivot amplifies sway. Lateral movement in the trailer is transmitted into the bike as a yaw moment through that long lever, felt as the back of the bike being steered by the trailer.
• Motor torque is abrupt. A cadence sensor system delivers power as a step rather than a ramp, so the trailer gets yanked rather than accelerated. A low axle hitch turns that into forward push; a high seatpost hitch turns part of it into a pitching moment that lightens the front wheel as you pull away from a junction.

One setup detail decides whether the trailer behaves: load the mass low and very slightly ahead of the trailer axle, giving a few pounds of downward force at the hitch. Load it behind the axle and the hitch is pulled upward, and the trailer will weave at speed. Same principle as caravan loading, same failure mode.

What a load does to braking, in physical terms

Consumer bike trailers have no brakes. A handful of heavy duty cargo trailers offer an overrun brake that engages when the trailer pushes into the hitch, but a Burley, a Thule, or a BOB does not. That means the bike's brakes stop the whole system.

The arithmetic is unforgiving. Take a 180 lb rider on a 60 lb ebike, so 240 lb. Add a 20 lb trailer with 80 lb of load and the system is 340 lb, roughly 42 percent heavier. Where the limit on braking is the force the brakes can generate, stopping distance rises in direct proportion to mass, so the same 42 percent increase applies to your stopping distance. From 20 mph, a stop that took 30 feet now takes closer to 43 feet, and that is before any allowance for reaction time.

Two behaviours change on the road and neither is intuitive. On a descent the trailer pushes the bike from behind, so releasing the brakes lets speed build much faster than you expect, and hard braking with a pushing trailer can start it swinging. On a corner the trailer cuts inside your line, so you have to take a wider entry than feels natural, particularly past kerbs and parked cars. Give yourself two to three times your normal following distance and brake in a long steady application rather than a late hard one. If your bike has anything less than 180 mm hydraulic rotors, read how ebike brakes actually cope with weight before you commit to towing regularly.

Motor type, chain wear, and range

This is the section where the answer runs opposite to the usual advice, so it is worth being precise about the mechanism.

On a mid-drive, motor torque is applied at the chainring and travels through the chain and cassette on its way to the wheel. Your legs use the same path. Motor torque alone roughly doubles the peak chain tension a drivetrain sees, which is why mid-drive chains typically need replacing at 1,000 to 1,500 miles rather than the 2,000 to 3,000 an unassisted bike manages. Hitch a loaded trailer and you add a sustained resisting load on top, exactly in the low gears where chain tension is already highest. Regular towing on a mid-drive can pull chain life down towards 700 to 1,000 miles.

On a hub motor, the motor is bolted into the wheel and drives it directly. The trailer load never touches your chain. Your legs still work harder, but leg torque was never the thing wearing the drivetrain out. Towing on a hub motor bike costs the drivetrain essentially nothing extra, which is a rare and genuine advantage for a motor layout that loses most other comparisons. The full argument is in mid-drive versus hub motor.

The hub motor's compensating weakness is heat. It cannot gear down, so on a long climb with a trailer it turns slowly, sits far below its efficient rpm, draws heavy current, and warms up. Thermal cutback partway up a hill with 100 lb behind you is the specific scenario where a mid-drive earns its chain bills back.

Whichever motor you have, check chain elongation with a wear gauge more often than the manual suggests and replace at 0.5 percent, because a worn chain destroys a cassette and a cassette costs three to five times what a chain does. The routine is covered in ebike maintenance and repair.

Range. A loaded trailer typically costs 20 to 40 percent of your range, and the low end only applies on flat ground. A bike that manages 22 watt hours per mile solo will often land at 30 to 35 with a trailer. Plan on being loaded going home and empty going out.

Towing children

The legal position in the United States is mostly an absence. Federal law says nothing, and most states have no statute that either permits or prohibits towing a child trailer behind a bicycle. What does bind you, in practical order:

• Manufacturer instructions. Trailer makers generally specify a minimum age of 12 months, and require that the child can sit upright unassisted and hold their head up while wearing a helmet. This is the constraint that actually matters, and it is the one a court would look at.
• Passenger helmet law. Most states with a helmet requirement apply it to passengers as well as riders, usually under 16 or under 18, and a trailer occupant counts as a passenger. Read that as a floor rather than advice.
• Class and speed rules. A few state vehicle codes restrict what a motorised bicycle may tow, and the higher your bike's class the more likely it is to be caught by a rule written for mopeds. If you are on a Class 3 ebike the sensible reading is to check the code rather than assume.

Speed is the part people get wrong. Child trailers are engineered around bicycle speeds, and manufacturers commonly advise staying under about 15 mph. A Class 3 bike will hold 28 mph without effort, and a trailer at that speed is outside its design envelope, has more crosswind sensitivity than you expect, and gives you far less time to react to a pothole that a rear wheel would have shrugged off. If you tow children, ride the bike as though it were Class 1.

Trailers worth buying

Four trailers covering the useful range. Capacities are the manufacturers' published figures; your bike's brakes and frame are a separate limit and usually the binding one.

The default for a general purpose cargo trailer. The enclosed body keeps a week of shopping dry, the axle hitch is the correct design, and Burley have supported the same hitch pattern long enough that spares are easy.

Priced like a piece of furniture and built like one. It is worth the money because families use the stroller and jogger modes far more than the towing mode, which turns a seasonal purchase into a daily one.

The sensible entry point. You give up suspension and the stroller conversion and keep the safety structure, the harnesses, and the correct hitch design.

For touring and mixed surface riding rather than the school run. It goes anywhere the bike goes and is irritating to load at the kerb because it needs propping. Check hub motor axle compatibility carefully; this design is the most likely to conflict with a wide nutted motor axle.

Choosing, and riding with one attached

Work through it in this order. Decide what you are carrying: bulky and light points to a two wheel cargo box, narrow and far points to a single wheel, children point to a purpose built child trailer and nothing else. Then check your rear axle and confirm the hitch physically fits. Then look honestly at your brakes, because that is the constraint most likely to stop you towing safely and the one that costs the most to fix afterwards.

Once it is on the bike, three habits do most of the work. Ride wider through corners than feels right, because the trailer cuts inside. Brake earlier and longer, not later and harder. And check the hitch pin and safety strap every single time before you set off, because the strap is the only thing between a failed hitch and a trailer going its own way, and on a child trailer that is not a theoretical concern.

If the towing you have in mind is really about getting bikes to a trailhead rather than moving cargo, the answer is a different piece of equipment: our guide to ebike racks and car carriers covers the weight ratings that rule out most of what bike shops sell.

Frequently asked questions

Sources and further reading

• Range AssistantBosch eBike Systems
• Electric bikes and the three-class systemPeopleForBikes
• 15 U.S.C. 2085: Low-speed electric bicyclesLegal Information Institute, Cornell Law School