Which Bafang motor to choose for your use
Choosing a Bafang mid-drive kit comes down to five questions, and none of them starts with watts. Taken in order, they rule out impossible models before comparing desirable ones — which keeps you from falling for a motor your frame will refuse. Set aside fifteen minutes and a caliper: the first two questions are answered on the bike, not on a forum.
1. What does your bottom bracket measure?
This is the measurement that governs all the others. Record the shell width, from one outer face to the other, and check that it is indeed a threaded shell.
| Width measured | What's possible |
|---|---|
| 68 to 73 mm, threaded | BBS01B, BBS02B, BBSHD |
| 100 mm | BBSHD, or long-axle versions of the BBS01B and BBS02B |
| 120 mm (fat bike) | Dedicated versions of all three kits |
| Press-fit shell | No standard install: check frame by frame |
A width outside these values can't be fixed with a spacer or a makeshift adapter: the motor's axle runs through the shell, and its length is a fixed dimension of the product.
2. How much clearance is there around the shell?
This is the measurement almost nobody takes, and the one that causes most installs advertised as compatible to fail. The motor housing doesn't sit inside the bottom bracket: it presses against it, on the right side, occupying the space in front of the shell.
Three obstacles keep coming up: a right chainstay that passes too close, a derailleur housing running along the shell, and the pivot of a rear suspension. On a BBSHD, whose housing is the bulkiest of the three, this point is by far the most limiting — a bike that accepts a BBS02B doesn't necessarily accept a BBSHD. The full method is in the Bafang kit installation guide.
3. Does your bike need to stay a bicycle?
If the bike rides on public roads and uses cycling infrastructure, the answer decides the choice: only the 250 W version of the BBS01B, with assistance that cuts off at 25 km/h, stays within the pedelec category. Every other model in the catalog falls outside it, with the consequences described in 250 W or 750 W, what the regulation says.
This question can't be fixed later
No display setting brings a 750 W motor back within the legal framework. If this point matters to you, settle it before ordering, not after.
4. What are you carrying, and on what terrain?
| BBS01B | BBS02B | BBSHD | |
|---|---|---|---|
| Flat commute, light panniers | ✓ | ✓ | ✓ |
| Moderate terrain, a few climbs | — | ✓ | ✓ |
| Mountain, regular passes | — | ✓ | ✓ |
| Child trailer, heavy load | — | — | ✓ |
| Two-wheel cargo bike | — | — | ✓ |
| Controller (maximum current) | 15 A | 25 A | 30 A |
A simple rule for reading this table: torque serves load and grade, amperage serves the pull off the line. A flat, light use will never make the most of 30 A; a loaded cargo bike will use it every day. And the weight you carry matters more than your own: it's the total mass being moved that decides how much torque is needed, trailer and groceries included.
5. Which battery, and for what total budget?
The motor sets the battery's specification, never the other way around. The BBS01B accepts 36 V as well as 48 V and is content with 15 A; the BBS02B requires 48 V and 25 A; the BBSHD calls for 48 or 52 V and 30 A continuous. An undersized pack will cut out on a climb and give the impression the motor is out of breath, when it's really the power supply giving up.
Add to that the gear-shift sensor, motor-cutoff brake levers and, on the higher-torque models, a reinforced chain. The total always exceeds the kit's price: Bafang motor prices breaks down every line item and gives the ranges actually seen in practice.
The three most common profiles
The daily commute, in town, on bike paths
BBS01B at 250 W, with assistance cut off at 25 km/h. It's the only setup that keeps the bike within its original status, and its 80 Nm are enough on gently rolling terrain.
Loaded touring and hilly terrain
BBS02B. 120 Nm, 25 A, the same install as the model below: the default choice of the range, detailed in our BBS02B review.
Cargo, mountain, fat bike
BBSHD, provided you check frame clearance and plan for a reinforced drivetrain. The full arbitration is in BBS02B versus BBSHD.
If no answer stands out
Two cases come up regularly. The first: your frame accepts none of the three kits. There is then no clean solution on the mid-drive side, and the question becomes one of a different bike. The second: you're torn between two neighboring models because your use is mixed. In that case, take the less bulky of the two — a housing that fits everywhere can be resold, removed and refitted on another bike, while an oversized motor remains a permanent constraint.
Once the model is identified, the full comparison of the Bafang kits lets you check your choice line by line, and our ranking of the three motors gives the verdict by profile.
FAQ
Where do I start if I know nothing about this?
With two measurements on your bike: the bottom bracket width and the clear space around the shell. On their own, they rule out half of the possible choices, and no motor spec can work around them.
Should I choose the motor or the battery first?
The motor, because it sets the voltage and current the battery will have to supply. A BBSHD needs a pack able to deliver 30 A continuously; choosing the battery first often means having to replace it later.
Is a more powerful motor faster?
Not in the way most people imagine. It mainly helps maintain speed on a climb or with a load. On flat ground, the gap between a BBS02B and a BBSHD comes down more to the cut-off speed setting than to available power.
