Bafang G020 hub motor — conflicting specs

[Jeremy McCreary]

My 2023 Surface 604 V Rook has a rear Bafang G020 geared hub motor:

Official bike specs say this:

But some posts on this forum state unequivocally that the G020 puts out only 250W nominal. I've also seen torques of both 45 and 65 nm.

Does the G020 come in different flavors? How do I verify the specs for the one I actually own?

Thanks!

 

[JRA]

According to the label shown it is a 48v system. In order to figure out the true peak watt output you need to know what Amp your controller is set to, V x A = Watts. Usually controllers on bikes like yours are set at 15A but could be as high as 20A. The 250 nominal is just a work around EU regulations and generally flaunted by the industry.

 

[Jeremy McCreary]

According to the label shown it is a 48v system. In order to figure out the true peak watt output you need to know what Amp your controller is set to, V x A = Watts. Usually controllers on bikes like yours are set at 15A but could be as high as 20A. The 250 nominal is just a work around EU regulations and generally flaunted by the industry.

Thanks! Official specs put my controller at 25A. So 48V * 25A = 1,200W of electrical power available to the motor, though surely not on a sustained basis.

At a nominal 80% efficiency, that translates to 960W of peak mechanical power. Whether my G020 can actually deliver that to the rear wheel, I can't say. But the official Surface 604 power spec (500W nominal, 750W peak) isn't controller-limited.

 

[Jeremy McCreary]

Jeremy - you live in one of the Top Bike Area's in the US - Sunday morning - if I were you I would head South and stop for Breakfast when you get hungry !

1. Mechanically your Rook is reported to be solid

2. Please understand for every eBike - "Power" is the combined result of Battery + Controller + Motor - with or without Pedal Assist.

3. Your Rook is designed with the Bafang G020 with the Controller your Rook has (which is quite decent - with the 48V14Ah based on 18650 cells - with that battery your motor will Peak at about 650 watts - and I would expect about 50nm peak torque. With the upgraded battery 48V20Ah based on 21700 cells - your peak torque will be that 60nm mark - and hit 750 peak torque readily.

4. . Do you have a Objective in Mind - Acceleration - Top Speed - Range - on what you might look to "improve" if you can ?
Please understand - the Battery-Controller-Motor - it can be complex to get a significant change/improvement

Keep the beat !

Thanks! Yes, very fortunate to be able to ride in this setting right from my house. Lots of great eateries within a 25 minute ride — including this unexpected gem.

Asking about the motor's true specs for future reference only. If I truly have, say, 500W and 45Nm onboard, now I know what that feels like in my terrain. Good to know the next time I shop.

I have the 960Wh (20Ah) battery. I understand that battery voltage will stay up longer on any given ride. But beyond that, what does battery capacity have to do with power delivery? Do the 118650 and 21700 cells have different current limits?

 

[Tom@WashDC]

My 2023 Surface 604 V Rook has a rear Bafang G020 geared hub motor:

View attachment 161295

Official bike specs say this:
View attachment 161296

But some posts on this forum state unequivocally that the G020 puts out only 250W nominal. I've also seen torques of both 45 and 65 nm.

Does the G020 come in different flavors? How do I verify the specs for the one I actually own?

Thanks!

Jeremy, read this article on motor power ratings.

Why Ebike Motor Watt Ratings Are Meaningless

Ebike motor watt ratings are almost meaningless: the same hub motor is sold as 250W, 500W, and 1000W, with no standard way to rate motor power. Here's what really determines a motor's power, and why torque and heat matter more than the number on the label.

ebikes.ca

 

[Jeremy McCreary]

Jeremy, read this article on motor power ratings.

Why Ebike Motor Watt Ratings Are Meaningless

Ebike motor watt ratings are almost meaningless: the same hub motor is sold as 250W, 500W, and 1000W, with no standard way to rate motor power. Here's what really determines a motor's power, and why torque and heat matter more than the number on the label.

ebikes.ca

Yes, read that excellent article nearly a year ago but read it again. Quite a mess. Alas, still no G020 simulator.

Found online photos of G020s with "250" stamped where mine has "500". Also found bare G020s for sale with 250W, 350W, and 500W nominal power specs. So to answer one of my own questions — yes, the G020 appears to come in more than one power rating.

Whatever those 250W, 350W, and 500W ratings mean vis-a-vis other manufacturers' motors or even other Bafang motors, they presumably refer to the same reference case (input voltage, controller, mechanical motor load) within the G020 line. Would love to know what that reference case is but probably never will.

Very familiar with the linear torque vs. speed and (inverted) parabolic power vs. speed curves found in brushed DC motors and with the power supply and load considerations involved. Once you allow for the distortions imposed by ebike controllers, the respective curves for the brushless DC motors in our ebikes are also roughly linear and parabolic.

Interestingly, per Wilson & Schmidt, 2020, Bicycling Science, the power vs. speed (cadence) curve for an unassisted human rider is also close to a parabola — one with its peak at a cadence just a little higher than the preferred cadence riders usually report. Mathematically, a parabolic power vs. speed curve implies a linear torque vs. speed curve for any rotary motor. So the human torque vs. cadence curve could be roughly linear, too.

 

[Jeremy McCreary]

If you go a bit North on Sunday - have you hung out at Buccaneer Beach Park in Oceanside - has been a "earnest" O-Side surf break - try the Cafe:

Oe just a little North'Ier - Johnny Manana's - Mission just a hair East of the RR tracksView attachment 161312
View attachment 161311

Have ridden and driven past the Buccaneer several times. Definitely on the list to try. Will add Johnny Mananas. So far, our favorite breakfast place to the north is the Shorehouse Kitchen in Carlsbad Village — best hash browns on Earth!

On the Technical Side - the most "common" better eBike battery cells are 186500 and 21700 (the ref#'s refer to the physical size of that cell = 18mm Diameter x 65 length - and 21mm Diameter x 70 length) it's linked somewhat to the internal volume of each style cell - the 21700 size has literally colose to 50% more internal volume than the 186500 - which in turn give the 21700 a stronger power spec. Top Samsung/LG cells can have up to 5Ah discharge capacity over a 186500 cell not so much the physical size of each style cell - it's the production power spec for each different style cell. Bacially the 21700 has a higher "enery density" thast the 186500 - a top model 21700 can have a discharge capabilty of 5AH - where 186500 cells spec most commonly about 2.5Ah and best 18650 cells top out at 3Ah.
You have a top spec 20Ah battery built up from 21700 - all to the good.

Thanks for the techical info! So the larger 21700 cells have a higher discharge current limit? (That would be measured in A, not Ah.) Per the article linked by @Tom@WashDC above, voltage and current limit are the only battery properties tied to motor power output.

My strong preference is to pedal at low assist. Now that I have the gearing to do that in our hilly terrain, happy with the current electricals. The 960 Wh battery has plenty of range.

Plan A is to ride this hub-drive till it dies, then move up. When that day comes, would be handy to know what I have now.

 

[m@Robertson]

Does the G020 come in different flavors? How do I verify the specs for the one I actually own?

I missed this thread until @kevinmccune brought it back from the dead. Bafang absolutely does have different internals on *some* of their motors. In others they just stamp them with a lower rating to get past local regulations. The G060-250 was known to be identical to the G060-350 except for that stamp on the casing and I bet the G020 is the same. If you open up a 500w G060 it looks the same as the 350 except supposedly (!) there is more copper used in the stator. I would not be the least bit surprised if this is merely another switched stamp as well and Bafang just pumps out the identical motor that is capable of handling whatever the rating is. I know the 36v 350's could handle a 52v battery and an uprated 20a controller without even blinking.

My two 500w G020's are each hooked up to a 52v battery and a 25a controller. Lots of miles/years on them.

 

[Jeremy McCreary]

My two 500w G020's are each hooked up to a 52v battery and a 25a controller. Lots of miles/years on them.

Great to hear!

Last week, mine helped me up a hill with more than half a mile at well over 10% grade while I pedaled at a comfortable cadence in a 26-inch low gear. I was huffing and puffing at the top, but the casing wasn't even warm.

 

[m@Robertson]

I use my G020's as front wheel motors on my 2wd Bullitts. On a steep hill, two motors working in tandem make for a minor miracle in terms of reduced stress to the whole system. But going up those hills, I keep the power low on the front wheel (never more than 3 out of 5 on the PAS) because although I use two torque arms, I don't want to risk the front fork. I've seen too many sheared dropouts that had torque arms on them and it didn't save the fork. And since I am riding a heavy cargo bike that probably is loaded with heavy stuff...