How Much Motor Torque Do You Need for Hilly Commutes?
Sections in this piece:
Two e-bikes, same shop. One says 50 Nm on the spec card, the other says 85 Nm. Most people assume the 85 climbs better. Sometimes it does. Sometimes the 50 walks away from it up the same hill, because those two numbers are measured in different places and one of them gets multiplied by gearing before it reaches the ground.
Torque specs are useful. They're just not comparable across motor types, and they tell you almost nothing about the thing that actually decides whether a bike gets you up a long grade without slowing to a crawl.
Let's do the arithmetic, because a hill is one of the few things in cycling you can calculate exactly.
The number on the sticker isn't the number doing the work
Three problems with reading torque off a product page.
Peak versus sustained. The published figure is almost always peak — what the motor can deliver briefly before the controller starts pulling back to protect it from heat. A climb that lasts eight minutes doesn't care about peak. It cares about what the motor can hold indefinitely, and that number is rarely published.
Where it's measured. A mid-drive's torque is quoted at the bottom bracket, before the drivetrain. A hub motor's is quoted at the axle, which is the wheel. One of those gets amplified by whatever gear you're in. The other doesn't.
It's not a power spec. Torque is turning force. Power is torque times how fast it's turning. A motor can have plenty of torque and still crawl up a hill if it doesn't have the watts to spin that torque at a useful speed. Both matter, and the marketing usually gives you one.
How much force a hill actually asks for
Gravity doesn't negotiate. On a slope, the force pulling you back down the road is your total mass times gravity times the grade — and for the grades you'll actually ride, that simple version is accurate enough.
Take a realistic system: 80 kg rider, 25 kg bike, 5 kg of bag and lock. That's 110 kg, or about 240 lb all in. Here's what each grade demands, with wheel torque worked out for a typical 27.5-inch wheel with a fat-ish tire (about 0.35 m rolling radius), and power calculated at 8 km/h — a normal e-bike climbing speed, not a racing one.
| Grade | Force pulling you back | Torque needed at the wheel | Power at 8 km/h (5 mph) |
|---|---|---|---|
| 3% (a long gentle drag) | 32 N | 11 Nm | ~95 W |
| 5% | 54 N | 19 Nm | ~145 W |
| 8% (a hill you notice) | 86 N | 30 Nm | ~215 W |
| 10% | 108 N | 38 Nm | ~265 W |
| 15% (steep residential street) | 162 N | 57 Nm | ~385 W |
| 20% (brutal, short blocks only) | 216 N | 76 Nm | ~505 W |
Rolling resistance and air drag are folded into the power column as a rough 25 W, which is about right at that speed. Scale the whole table by your own weight — at 130 kg total, multiply everything by 1.18.
Now the part that reframes the shopping. You are not a passenger. A moderately fit rider holds 100 to 150 W for the length of a climb without much drama, and even a casual rider contributes 70 or 80. On a 10% grade needing about 265 W total, your legs cover roughly half. The motor is being asked for 130 to 150 W and something like 20 Nm at the wheel.
That's a much smaller ask than the spec-sheet arms race implies.
Why 50 Nm can out-climb 85 Nm
Here's where the gearing multiplier earns its keep.
A geared hub motor rated at 50 Nm delivers that at the axle. Divide by the 0.35 m radius and you get about 143 N of thrust at the tire, motor alone. Set against a 110 kg system, that's enough to hold roughly a 13% grade with your legs doing nothing at all. Add your own pedaling and it climbs more. The number on the box is the number at the road.
A mid-drive rated at 85 Nm delivers that at the crank spindle, and then your drivetrain multiplies it. Run a 34-tooth chainring into a 46-tooth cog and the ratio is 46÷34, or about 1.35, so 85 Nm becomes roughly 115 Nm at the wheel — over 320 N of thrust. That's a 30% grade's worth of force. It's why mid-drives feel unstoppable on steep pitches.
But shift into a high gear and the multiplier inverts. Same motor, 34-tooth chainring into an 11-tooth cog, and the ratio drops to about 0.32 — that 85 Nm arrives at the wheel as roughly 27 Nm. Less than the hub motor. On the same hill.
The effective torque of a mid-drive swings by a factor of three or four depending on which gear you're in. The published number is one point on that curve, and nobody tells you which one.
Two practical conclusions follow. First, cross-comparing Nm between a hub motor and a mid-drive is a category error — treat them as separate scales. Second, a mid-drive bike with a narrow cassette wastes its own advantage. If you're buying a mid-drive for hills, the gear range matters as much as the motor. A bike with a wide-range cassette and a small chainring will out-climb the same motor bolted into a bike geared for flat commuting.
Direct-drive versus geared hubs
If you're shopping hub motors, this distinction matters more than the torque figure. A geared hub has internal reduction gearing, so it produces more torque per amp and stays reasonably efficient at low wheel speeds. A direct-drive hub has no reduction — it's quiet, nearly maintenance-free, lasts forever, and is genuinely poor at slow climbing, because it's being asked to make torque at an RPM it hates. It gets hot doing it.
For a hilly commute, geared hub or mid-drive. Direct-drive is for flat, fast, and quiet.
Heat is the real limit on a long climb
Every motor makes torque. What separates them on a real hill is how long they can do it before thermal protection intervenes and your assist quietly fades to half.
The failure looks like this: you start a climb feeling strong, and four or five minutes in the bike starts pulling less than it did at the bottom. That's not the battery. That's the controller reading a motor temperature it doesn't like, or the motor's copper resistance rising as it heats and losing efficiency on its own. A short steep block never triggers it. A two-mile grade does.
Three things make heat worse:
- Low RPM at high load. An electric motor is least efficient when it's barely turning and pushing hard. Grinding up a hill at 5 km/h in a high gear is the worst thing you can do to a hub motor.
- Ambient temperature. The same climb in August is a different job than in February.
- Enclosure. Hub motors dump heat through a sealed shell in a moving airstream, which is mediocre. Mid-drives sit in the open near the cranks, which is better, and the good ones have real thermal management.
Which is why the answer to "my bike struggles on my hill" is usually not a bigger torque number. On a mid-drive it's downshifting sooner and spinning a higher cadence. On a hub motor it's picking a geared hub over direct-drive, and accepting a slower climb rather than a hotter one.
What to shop for, by how bad your hill is
| Your worst regular climb | Reasonable setup | What to check |
|---|---|---|
| Rolling, under 5%, short | Any decent hub motor, 40–50 Nm class | Nothing special. Don't overspend here. |
| 6–8%, a few minutes at a time | Geared hub around 50–60 Nm, or an entry mid-drive | That it holds speed the whole way, not just the first minute |
| 8–12%, sustained for a mile or more | Mid-drive with a wide-range cassette | Smallest chainring and largest cog; assist fade after 5 minutes |
| 12–15% pitches | Mid-drive, 70 Nm and up, low gearing | Chain wear rate — motor torque goes through it |
| 15%+, or heavy cargo on hills | High-torque mid-drive built for cargo, plus strong brakes | Thermal behavior on repeated climbs, and rear hub strength |
A test ride that tells you something
A lap around a shop parking lot tells you nothing about hills. If a dealer won't let you take the bike to a real grade, that's information about the dealer.
Do this instead. Find the worst hill on your actual route. Load the bike the way you'd load it — laptop, groceries, whatever you carry — and ride the climb at your normal effort, not hero effort. Then note four things.
- Speed at the bottom versus the top. A bike that starts at 18 km/h and finishes at 10 is fading. One that holds 13 the whole way is fine.
- Whether you ran out of gears. On a mid-drive, if you were in the lowest gear halfway up, the gearing is wrong for your terrain regardless of the motor.
- Motor noise and smell. Rising pitch under constant speed means the controller is working harder. Hot electronics have a smell, and you'll know it.
- Do it again at half battery. Output sags as pack voltage drops. A bike that climbs beautifully at 100% and struggles at 40% is a bike that will annoy you on the way home every single day.
The decision rule, if you want one sentence: figure out your steepest sustained grade, look up the wheel torque it needs in the table above, subtract what your own legs will contribute, and buy the cheapest bike that clears the remainder with the gearing it actually ships with. Extra torque past that point buys you a heavier bike and a bigger bill, not a better commute.