Stalling halfway up a hill isn’t just embarrassing—it’s a sign your e‑bike lacks the torque to keep you moving. On a 10% grade, a 100 kg rider+bike has to overcome roughly 100 newtons of uphill force. That translates to about 35–45 N·m at the wheel just to hold steady, more if you want to accelerate or start from a stop. This matters whether you’re commuting through a hilly neighborhood, hauling a kid and groceries, or planning mountain routes with 12–18% ramps. The right torque keeps your cadence smooth, your motor cool, and your climb safe. You’ll learn how much torque you actually need for steep grades, how rider weight, wheel size, and gearing change the numbers, and how mid-drive and hub motors deliver torque differently. Expect clear examples and simple calculations you can do on your phone, plus realistic recommendations drawn from real-world climbs—without guesswork or marketing fluff.
Quick Answer
For sustained steep hills (10–15% grade) with a 90–110 kg rider+bike, aim for about 50–60 N·m at the wheel, which typically means a 70–85 N·m mid‑drive using a low gear (e.g., 32T chainring with a 42–50T rear). For heavier loads, long climbs, or 15–20% ramps, plan for 80–100 N·m at the wheel: an 85–95 N·m mid‑drive in a very low gear, or a high‑torque hub (60–80 N·m) in a smaller 20–26" wheel.
Why This Matters
Torque is what keeps an e‑bike from bogging down on a steep grade. When the motor can’t supply enough, you feel it immediately: cadence collapses, speed drops, and current spikes. That’s when controllers thermal‑limit and hub motors cook windings. On a 12% hill, a 100 kg rider+bike needs roughly 43 N·m at the wheel just to hold speed with a 700c wheel. Try to start from a dead stop in that situation and you’ll want closer to 60–70 N·m so the bike doesn’t stall or wheel‑slip.
Real lives aren’t flat. A 95 kg commuter with a laptop and panniers might hit a 300 m climb on the way home every day. A parent pulling a 25 kg trailer turns a mild hill into a true test. Cargo riders, heavier cyclists, and folks with knee pain rely on the motor to do the grunt work; under‑torque means walking the bike, overheating mid‑climb, or avoiding routes entirely. Getting torque right improves safety too: steadier low‑speed control, fewer wobbles when traffic pressures you on a climb, and less stress on your drivetrain. The payoff is simple—predictable, confident hill starts and smooth, sustainable ascents.
Step-by-Step Guide
Step 1: Gather your numbers (weight, grade, wheel size)
Start with total system mass: rider + bike + cargo. Then note your steepest grade. If your steepest street sign says 12%, use that. Wheel radius matters because torque is force times radius; a 700c with 2" tires is roughly 0.35 m radius, a 26" about 0.33 m, and a 20" BMX/cargo wheel about 0.26 m. You might find how much torque do i need for an ebike on steep hills kit helpful.
- Rule of thumb: Required wheel force ≈ mass (kg) × 9.81 × grade (decimal). Rolling resistance adds roughly 0.5–1% of weight.
- Wheel torque ≈ wheel force × wheel radius.
Example: 100 kg total on a 12% hill. Force ≈ 100 × 9.81 × 0.12 ≈ 118 N (plus ~6 N rolling). Wheel torque ≈ 124 N × 0.35 m ≈ 43 N·m just to hold speed. Add 30–50% for starts and headroom: ~55–65 N·m at the wheel.
Step 2: Convert wheel torque to motor torque (hub vs mid‑drive)
Hub motor: the motor drives the wheel directly, so the torque rating is effectively wheel torque (minus ~10% losses). If you need 60 N·m at the wheel, a 60–70 N·m geared hub is appropriate.
Mid‑drive: torque is quoted at the crank. Wheel torque ≈ motor torque × (rear cogs teeth ÷ chainring teeth) × drivetrain efficiency (~0.9). You might find how much torque do i need for an ebike on steep hills tool helpful.
- Example: 85 N·m mid‑drive, 32T chainring, 42T rear cog. Wheel torque ≈ 85 × (42/32) × 0.9 ≈ 100 N·m. Plenty for 15–18% ramps, even with a heavier rider.
- Shifting to a bigger rear cog boosts wheel torque immediately. Moving from 36T to 46T increases wheel torque by ~28%.
Step 3: Check power and speed so you don’t cook the motor
Torque gets you moving; power keeps you moving at a given speed. Power ≈ force × speed. On that same 12% hill (≈124 N):
- At 10 km/h (2.78 m/s): ~345 W mechanical. Accounting for efficiency, the motor may draw ~450–550 W electrical.
- At 15 km/h (4.17 m/s): ~517 W mechanical; electrical draw can exceed 700–900 W.
Climbing slower dramatically reduces heat. If your motor is rated 250–500 W continuous, aim for 6–12 km/h on long grades and contribute 100–200 W with your legs when possible to keep temperatures in check.
Step 4: Match motor and gearing to your hills
- 10–12% grades, 90–110 kg: target 50–60 N·m at the wheel. A 70–85 N·m mid‑drive with a low gear (30–34T chainring, 42–50T rear) works well. A 55–70 N·m geared hub in a 26" wheel is also viable.
- 15–18% grades, heavier riders or cargo: aim for 80–100 N·m at the wheel. Look for 85–95 N·m mid‑drives with very low gearing, or high‑torque hubs (60–80 N·m) in smaller wheels (20–26").
- Short 20% ramps: you can clear them with the above setups if you start in a low gear, keep cadence 70–90 rpm, and accept slower speeds.
Step 5: Battery and controller settings influence torque
Motors make torque mostly in proportion to current. Controllers limit current, and batteries limit how much current they can safely provide without excessive voltage sag. You might find how much torque do i need for an ebike on steep hills equipment helpful.
- Voltage sets speed potential; current sets torque. A 48 V, 25 A controller can deliver up to ~1,200 W peak; many street‑legal systems cap continuous power much lower.
- Ensure your battery’s continuous discharge rating (in amps) meets or exceeds your controller’s continuous current. Undersized packs sag, throttle back power, and heat up.
- For mid‑drives, firmware often caps torque in higher gears. Use the lowest gear that keeps cadence in the 70–90 rpm sweet spot to avoid lugging.
Expert Insights
Professionals think in wheel torque, not just the motor’s spec sheet. A common mistake is assuming an 85 N·m mid‑drive guarantees hill prowess. It doesn’t—until you put the bike in a low gear. That same motor in a 38T chainring and 36T rear may feel average on a wall; swap to a 30–32T chainring and a 46–50T cassette and the bike transforms. Another misconception: chasing maximum speed up hills. That’s how riders overheat hub motors and trip controller limits. Climb at a speed where the motor sounds relaxed and cadence stays steady.
Two quiet performance boosters: smaller wheels and smart cadence. A 20" cargo wheel needs ~25% less torque than a 700c for the same grade and load because of the shorter radius. And mid‑drives are happiest around 70–90 rpm; if you’re grinding at 50 rpm, you’re wasting current and making heat. When in doubt, downshift early, especially before a stop on a steep block.
Finally, plan for starts. Starting on a 15% grade demands much more torque than maintaining 8 km/h. If you regularly stop on hills, size for the start, not the cruise. Give yourself 30–50% torque headroom, keep your controller’s thermal protections enabled, and don’t be afraid to add 100–200 W of human input when things get really steep.
Quick Checklist
- Measure your steepest regular hill (grade in % or rise/run).
- Add up rider, bike, and cargo weight to get total mass.
- Note wheel size; smaller wheels reduce required wheel torque.
- Set a low gear target (e.g., 30–34T chainring with 42–50T rear).
- Aim for 50–60 N·m at the wheel for 10–12% grades; 80–100 N·m for 15–20%.
- Confirm controller current and battery discharge ratings match your torque goals.
- Plan to climb at 6–12 km/h on long grades to manage heat.
- Practice hill starts in your lowest gear and keep cadence near 80 rpm.
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E Bike for Adults
Unleash Your Next Adventure — Go Electric→ Read full review →Frequently Asked Questions
What’s more important for steep hills: torque or power?
Torque determines if you can start and keep turning the wheel at low speed without stalling; power determines how fast you can climb once moving. For steep grades, you need enough wheel torque first (e.g., 50–60 N·m for 10–12%), then match power to your desired speed. Climbing slower reduces power demand while the torque requirement stays roughly the same.
How does my weight change the torque I need?
Required uphill force scales with total mass. A 20 kg increase in rider+cargo adds roughly 20 × 9.81 × grade newtons. On a 12% grade with a 700c wheel, that’s about 1.2 × 9.81 × 0.12 × 0.35 ≈ 8.2 N·m extra wheel torque. Heavier riders or cargo bikes benefit from lower gears and, if using hubs, smaller wheels.
Mid‑drive or hub motor for steep hills?
Mid‑drives excel on steep climbs because they use the bike’s gears to multiply torque, letting the motor spin efficiently at 70–90 rpm. A mid‑drive rated 85 N·m in a very low gear can exceed 100 N·m at the wheel. Geared hubs can work on hills if they’re high‑torque models and paired with smaller wheels, but they can overheat on long, slow climbs if pushed near their limits.
Does wheel size really make a difference?
Yes. Wheel torque is force times radius, so a smaller radius reduces the torque required for the same climb and load. Swapping from a 700c (~0.35 m radius) to a 20" wheel (~0.26 m) lowers the torque need by roughly 25%. This is why cargo e‑bikes and high‑torque hub builds often use 20–26" wheels for hilly routes.
Can a 250 W legal e‑bike handle 15–20% grades?
It can, but slowly and with the right gearing and rider input. At 6–8 km/h, a fit rider contributing 120–180 W plus a 250 W motor can crest short ramps of 15–20% if the gearing is low enough. Long climbs at those grades risk thermal limits; plan to climb slower, use very low gears, and watch for power roll‑back.
How do I estimate my hill’s grade accurately?
Use a short, known distance and measure elevation gain. For example, if a 100 m segment rises 12 m, that’s a 12% grade. Many smartphones show elevation change along a recorded track; you can also count contour lines on a map segment. If in doubt, assume the steeper value you find and size torque with extra headroom.
Will changing my chainring size help on hills?
Absolutely. Dropping from a 38T to a 32T chainring increases wheel torque by about 19% at the same rear cog because torque multiplication equals rear teeth divided by chainring teeth. Pair a small chainring with a wide‑range cassette (up to 46–50T) to make the most of a mid‑drive’s torque on steep grades.
Conclusion
Steep hills demand enough wheel torque to avoid stalling, plus sensible gearing and speed to manage heat. For most riders on 10–12% grades, 50–60 N·m at the wheel is a solid target; tougher 15–20% ramps call for 80–100 N·m. Choose a mid‑drive with low gearing or a high‑torque hub in a smaller wheel, match controller current to your battery, and climb at a cadence that keeps the motor happy. Measure your hills, set your gears, and give yourself 30–50% headroom. You’ll ride farther, cooler, and with a lot more confidence.
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