The first number to settle is not the motor rating but the weight the motor has to move. A steel or aluminum adult trike with a rear axle, two rear wheels, a basket and a battery frequently lands somewhere between seventy and a hundred pounds before anything is loaded into it, and a full grocery run can add another thirty. Add the rider. The total mass climbing the hill is often close to double what a comparable rider on an upright bicycle is asking a similar motor to lift, and every specification below has to be read against that.
Hub drive and mid drive, judged on a heavy machine
A hub motor sits inside a wheel and pushes that wheel directly, at whatever speed the wheel happens to be turning. A mid drive sits at the crank and sends its power through the chain and the gears, which means the drivetrain multiplies its torque exactly as it multiplies the rider's. That distinction matters far more on a loaded trike than on a light bicycle. Hub motors on trikes typically advertise torque in the middle range of newton-meters; mid drives commonly advertise substantially more, and then gear it down further in the lowest cog, which is the combination that gets weight up a grade slowly without overheating.
The trade is maintenance and geometry. Many trikes drive a single rear wheel or use a differential, and a hub motor drops into that layout with no change to the chainline, no extra chain wear, and no need for the rider to shift correctly under load. A mid drive asks the rider to downshift before the hill rather than during it, and it wears chains and sprockets faster because it is putting motor torque through them. Both work. The question is which failure mode you would rather manage.
Why the fallback of walking it up does not exist
On a bicycle that runs out of power, a rider steps off, stands beside it, and pushes. A trike will not cooperate. It is too wide to walk beside on a sidewalk, the handlebars are too far away to steer comfortably from the side, and the whole assembly wants to roll backward on a grade with no way to hold it and steer at once. That single fact should shift your motor sizing upward. You are not buying assistance that makes a hill pleasant; you are buying the only mechanism that gets the machine and the shopping to the top at all, which is why underspecifying is expensive in a way that overspecifying is not.
Throttle, pedal assist, and what each is good for
Pedal assist reads your pedaling and adds power in proportion, which is efficient and smooth but gives nothing when you are stopped. A throttle gives power on demand at zero cadence. On a trike that difference is practical rather than philosophical: starting from a stop on an uphill cross street, backing out of a driveway, or easing a loaded machine through a gate is far easier with a thumb throttle, and many riders who rarely use one still want it there. Check whether the throttle works up to full assisted speed or cuts out early, because the cheaper controllers often do the latter.
Battery capacity translated into an actual errand
Capacity is volts multiplied by amp-hours, expressed in watt-hours: a 48-volt pack rated at 15 amp-hours holds 720 watt-hours. Flat riding with modest assist on a heavy trike tends to draw well under twenty watt-hours per mile; a hilly route with a full basket and high assist can draw two or three times that. Work your own route in those terms, then halve the result to leave margin for cold weather, headwind, and a pack that is several years old. The Department of Energy oversees battery research and standards work in this field, and the practical lesson from it is simple: rated capacity is a ceiling, not a promise.
What to check before the money moves
Ask for torque in newton-meters rather than watts, because watts describe input and torque describes what reaches the hill. Ask the gear range if it is a mid drive, since a strong motor geared badly still stalls. Ask whether the controller limits current on long climbs and whether the motor has a thermal cutoff, then ask what the replacement battery costs and whether that model will still be sold in four years. A dealer who answers all six plainly is telling you something useful about the rest of the ownership.
Sizing a trike motor is mostly an exercise in honesty about the route and the load, done once, in advance, with a calculator. Riders who do that arithmetic before buying almost never wish they had bought less motor, and they spend the following years simply riding the hill instead of thinking about it.
