50nm mid drive vs 50nm hub drive

[Sierratim]

Okay, but it sounds like you're being a bit subjective in terms of "comparable" across the brand.

What bothers me the most, is that, when it comes to engineering, it has to be logical, objective and scientific.

The torque rating should not differ by whatever marketing plan they have.
The little tiny ebike motor can apparently create as much or MORE torque than a much bigger motorcycle electric motor.

These are scientific numbers. They should not be differing between brands to brand.

At first blush it would seem that motors providing the same rated torque should perform comparably under load. Out of curiosity I took a look at one brand of emotorcycle and compared its torque specs to my ebike. The emotorcycle I reviewed was a Zerocycles Model Zero-FX; the ebike - my Specialized Vado 5. The Zero FX specs I reviewed are published here; https://www.zeromotorcycles.com/model/zero-fx . Some Vado 5 specs are here; https://www.specialized.com/us/en/turbo-vado-5-0/p/171132 . Other data for this comparison was published a couple of years ago in a series of charts including these;

....
The Vado 5 is equipped with the Specialized 1.3 motor.

From these sources you can see that the torque specs are close enough to reasonably compare these mid-drive motors; 106Nm for the Zero FX and 90Nm for the Vado 5. So why would 'even the casual observer' overwhelmingly choose the Zero FX over the Vado 5 for hill climbing or just about any other condition other than exercise, despite the 2:1 retail price and 2:1 weight ratio (with an assumed 150lb rider)?

It comes down to this relationship;

Power = Torque x Speed; as quoted in an earlier post here. Let me elaborate -

First I looked at gearing. With these mid-dive motors the rated motor torque is available to the wheel when the gearing has a 1:1 ratio, i.e. the same speed at the motor shaft and the wheel. The Zero FX has 90t rear and 18t front gear for a 5:1 wheel speed ratio. As such it delivers 5x its motor torque to the wheel. The 11 speed cassette on the Vado 5 is 11-42t with a 48t chainring. For climbing, riders would typically select larger cogs on the cassette yielding a gear ratio of nominally 1:1 delivering 1x the motor torque to the wheel. This is compounded by the difference in drive wheel size. The Zero FX has an 18" wheel with 2.5" tires having a circumference of ~72". The Vado 5 has 700c wheels with 1.75" tires with a circumference of ~92". Based on gearing alone the Zero FX can provide up to 530Nm of torque to its wheel while the Vado 5 is at 90Nm. This ~6:1 wheel torque ratio becomes something like 6.7:1 when considering the wheel size difference. This explains a fair part of the hill climbing difference between this bikes, without even considering motor power.

Torque is part of the comparison between these 'bikes' but to know the full story we need to compare the peak developed power for each motor, and their power/speed curves. For the Zero FX, the available specs are 20KW @ 4300rpm. I didn't find a power/speed curve. The charts for the Vado 5 give us 550W @ 90rpm. Quite a difference in power with similar motor torques. I think it's safe to say that the 36:1 spread in available power will easily overcome the 2:1 difference in weight with plenty of power to spare to climb steep hills. On the other hand, even with 11 speeds available to the rider, the Vado 5s much lower power output will cause the bike to bog down on hills the Zero FX climbs with ease. The Vado 5 power/speed curve shows that the power drops off below 90rpm with the drop becoming steeper below 60rpm meaning of course that as the rider is unable to keep his cadence high, the motor power drops causing what is in effect a cascading event and the bike bogs down. With a steep enough hill this might also happen with the Zero FX, but well after the Vado has had to stop.

Conclusion, torque ratings need to be considered with along with specs for motor power and rpm. Otherwise it's like comparing apples to oranges; hence the apparent confusion.

 

[Timpo]

At first blush it would seem that motors providing the same rated torque should perform comparably under load. Out of curiosity I took a look at one brand of emotorcycle and compared its torque specs to my ebike. The emotorcycle I reviewed was a Zerocycles Model Zero-FX; the ebike - my Specialized Vado 5. The Zero FX specs I reviewed are published here; https://www.zeromotorcycles.com/model/zero-fx . Some Vado 5 specs are here; https://www.specialized.com/us/en/turbo-vado-5-0/p/171132 . Other data for this comparison was published a couple of years ago in a series of charts including these;

View attachment 56542....View attachment 56543
The Vado 5 is equipped with the Specialized 1.3 motor.

From these sources you can see that the torque specs are close enough to reasonably compare these mid-drive motors; 106Nm for the Zero FX and 90Nm for the Vado 5. So why would 'even the casual observer' overwhelmingly choose the Zero FX over the Vado 5 for hill climbing or just about any other condition other than exercise, despite the 2:1 retail price and 2:1 weight ratio (with an assumed 150lb rider)?

It comes down to this relationship;

Power = Torque x Speed; as quoted in an earlier post here. Let me elaborate -

First I looked at gearing. With these mid-dive motors the rated motor torque is available to the wheel when the gearing has a 1:1 ratio, i.e. the same speed at the motor shaft and the wheel. The Zero FX has 90t rear and 18t front gear for a 5:1 wheel speed ratio. As such it delivers 5x its motor torque to the wheel. The 11 speed cassette on the Vado 5 is 11-42t with a 48t chainring. For climbing, riders would typically select larger cogs on the cassette yielding a gear ratio of nominally 1:1 delivering 1x the motor torque to the wheel. This is compounded by the difference in drive wheel size. The Zero FX has an 18" wheel with 2.5" tires having a circumference of ~72". The Vado 5 has 700c wheels with 1.75" tires with a circumference of ~92". Based on gearing alone the Zero FX can provide up to 530Nm of torque to its wheel while the Vado 5 is at 90Nm. This ~6:1 wheel torque ratio becomes something like 6.7:1 when considering the wheel size difference. This explains a fair part of the hill climbing difference between this bikes, without even considering motor power.

Torque is part of the comparison between these 'bikes' but to know the full story we need to compare the peak developed power for each motor, and their power/speed curves. For the Zero FX, the available specs are 20KW @ 4300rpm. I didn't find a power/speed curve. The charts for the Vado 5 give us 550W @ 90rpm. Quite a difference in power with similar motor torques. I think it's safe to say that the 36:1 spread in available power will easily overcome the 2:1 difference in weight with plenty of power to spare to climb steep hills. On the other hand, even with 11 speeds available to the rider, the Vado 5s much lower power output will cause the bike to bog down on hills the Zero FX climbs with ease. The Vado 5 power/speed curve shows that the power drops off below 90rpm with the drop becoming steeper below 60rpm meaning of course that as the rider is unable to keep his cadence high, the motor power drops causing what is in effect a cascading event and the bike bogs down. With a steep enough hill this might also happen with the Zero FX, but well after the Vado has had to stop.

Conclusion, torque ratings need to be considered with along with specs for motor power and rpm. Otherwise it's like comparing apples to oranges; hence the apparent confusion.

Interesting analysis but an electric motorcycle like Harley Davidson Livewire weighs 549 lbs, has 116Nm of torque, and goes 0-60mph in 3.05 seconds.

You have provided the example of gear ratio, but ebikes have gears too.

My uneducated conclusion is power is what matters.

 

[Sierratim]

Interesting analysis but an electric motorcycle like Harley Davidson Livewire weighs 549 lbs, has 116Nm of torque, and goes 0-60mph in 3.05 seconds.

You have provided the example of gear ratio, but ebikes have gears too.

My uneducated conclusion is power is what matters.

I have no doubt that the Livewire is an impressive machine that can out perform an ebike in every category. I also have no doubt that it has equally impressive motor power requirements and battery capacity as does the emotorcycle I used as an example. None the less, from an engineering standpoint, you need to consider power, torque and motor speed (rpm) as interrelated parameters when comparing these machines. When you compare similar motors, like those in most ebikes, it seems clear that power is not necessairly the parameter that overrides the others. The curves I attached tell a more nuanced story. While peak power varies by only ~10% between the motors tested, their peak torques vary by over 40%. By relying on power as the primary guide for comparison of these motors a shopper would miss the best performing options in this gorup.

I certainly agree that ebikes have gears. I think I covered that fairly well for the hill climbing senario in my post. For other senarios, like top speed, a similar analysis would show that the ebike is again 'out gunned' by the emotorcycle, but this time by the emotorcyle's much higher speed (rpm) motor. Regardless of power requirments on a flat run, the ebike motor simply can't spin fast enough to keep up, even with its advantageous gearing.

 

[Stefan Mikes]

I totally agree with you, Tim, and your analysis is perfect. The torque has to always be discussed together with the rotational speed.

Interestingly, the Fiat 126 car (a.k.a. Fart) had torque of only 43 Nm but it was at 3000 rpm. Therefore the rated engine power was 23-25 HP.

The charts you have shown are already outdated a little bit. There is no Yamaha PW-X2 there. Yamaha have improved the torque curve for that motor making it more flat for higher cadences. When I negotiate a steep climb with my Trance E+, I ride in low gear at cadence approaching 90 rpm. I can feel how powerfully the motor is assisting my pedalling. I had an unexpected wheelie because of that only on last Sunday!

 

[CityExplorer]

Just to go back to the original post. Many of your dislikes can be cured also with a Torque sensor based Hub Drive bike, as long as it has a good controller and software. Try to test some bikes since now you know what to look for on a bike for you.

 

[Deleted member 4210]

I am currently riding an Aventon Pace 500 which I am generally pleased with. A couple annoying features though have me now looking at a mid drive bike.

The Aventon is a 500 watt, 48 volt, 50 nm, 8 speed rear hub motor ebike that is capable of ascending every hill I've tried even with my 250 pound weight. Albeit sometimes slowly.

I dislike the abrupt on-off feel of the motor due to the cadence sensor and the inability to pedal constantly in PAS 1 without going 11-12 mph.

I also dislike that the assist doesn't start helping from a stop until a pedal revolution or so.

I do like the relaxed, upright riding style as I'm 63 with some health issues.


Looking at Trek mid-drive ebikes with the 2020 Bosch Active Line Plus motor and 50 nm torque (Verve+ 3).

Or a 2020 Specialized mid-drive ebike with Brose 1.2e motor and 50 nm torque (Como 3).

Would either of these two mid drives perform as well or better on hills as the Aventon?

Do I need to go to the Electra Path Go and it's Bosch Performance line motor with 65 nm torque?

Or the Specialized Como 4 with its Brose 1.3 motor and 75 nm torque?

No. There is a significant loss of power with a mid drive from the motor to the wheel, via the chain and the internal gears in a mid drive. Their motor is also operating at only 36 volts and 250 watts. A lady who just returned a Trek Verve 3 ,after 3 days of use, and who said it was 'dog' with too much drag, and felt very little assistance and could barely reach 17 mph , purchased a Pace 500, and loved the power of it.

You will need a much stronger motor than she did with a mid drive.

You should look at the torque sensing Surface 604 line up, Colt, Rook, or Shred, or ebikes Made by Juiced, that have motors up to 750 watts. All s604s are powerful 500 or 700 watt motors and 48 volt batteries.

It's called physics, and lower voltage and lower watts just ain't gonna cut it, and unfortunately too many people are still being lured into the hype of mid drives.

 

[Sierratim]

No. There is a significant loss of power with a mid drive from the motor to the wheel, via the chain and the internal gears in a mid drive. Their motor is also operating at only 36 volts and 250 watts. A lady who just returned a Trek Verve 3 ,after 3 days of use, and who said it was 'dog' with too much drag, and felt very little assistance and could barely reach 17 mph , purchased a Pace 500, and loved the power of it.

You will need a much stronger motor than she did with a mid drive.

You should look at the torque sensing Surface 604 line up, Colt, Rook, or Shred, or ebikes Made by Juiced, that have motors up to 750 watts. All s604s are powerful 500 or 700 watt motors and 48 volt batteries.

It's called physics, and lower voltage and lower watts just ain't gonna cut it, and unfortunately too many people are still being lured into the hype of mid drives.

My personal experience differs from your example. My DIY 1,000W hub drive ebike conversion performed well on our local hills. It was retired when the battery started to fade. To my surprise '250W' mid-drive ebikes performed comparably. How could that be, I wondered? First, the 250W rating is 'nominal' for Euro motor limits. Actual peak power is well over 2x this. Still, 1,000W vs 550W? The rest of the explanation is in the relationship between power, torque and speed. I had used the motor analysis calculator at Grin Tech to evaluate the motor I selected for my DIY ebike. I was able to compare my hub motor power and torque curves to those that I posted in #21 above. To my surprise the mid-drive motors I was test riding performed as well or better in this analysis than my hub motor. Mystery solved. The new mid-drives were better engineered, more efficient and higher torque than my original hub motor.

Hub motors have advanced since my original DIY conversion, but the engineering comparison remains the same. As you point out, it is called physics and as Fox Mulder said "the truth is out there", if you're willing to dig a bit. Grin Tech still offers their motor calculator for comparisons. Sometimes manufacturers publish data, like the curves I posted.

I do agree that any ebike buyer should go into a purchase with their eyes wide open. Consider all the options. Do lots of test rides under varying conditions, then decide. You may end up with a hub drive, maybe a mid-drive. It's what's best for that rider in their conditions. I'm happy with my mid-drive in our very hilly town. Others posting in these threads are equally happy with their hub drives in their conditions. I'm only suggesting that the tools to make real world comparisons are out there. They will help cut through all the clutter and help make an 'apples to apples' comparison.

BTW - I do agree that chain drives 'suck' some power. One of my sons is lead mech engineer at WTB. He tells me that industry data shows this to be in the range of 3%, a bit lower for higher quality, well maintained parts. Is this consistent with your data?

 

[Johnny]

...The new mid-drives were better engineered, more efficient and higher torque than my original hub motor.
...

A mid drive motor is not better engineered than a hub motor. There is really not much to engineer, it is a pretty mature and simple design.

The difference is:

-Hub motors rpm completely depends on your speed(since there is no gearing in between the wheel and the motor) at low speeds the rpm drops, the motor runs in the inefficient band and its power output falls significantly below its peak.

-With a mid drive rpm is completely dependent on cadence and when climbing if the gear ratio is right one can keep the cadence hence rpm in the motor's efficient range where it can also produce close to its peak output.

Yes it is simple physics and it is all about output power vs rpm graph not the peak numbers. Ebike companies don't give you that, instead advertise those meaningless peak numbers of Torque etc.


So here is the conclusion,
On very steep hills with the right gearing you can keep the cadence of a mid drive in the efficient band hence can expect mid drive to be more efficient than a hub motor.

Otherwise, hub motor will not suffer the losses at the drivetrain and be more efficient than the mid drive.

 

[Sierratim]

A mid drive motor is not better engineered than a hub motor. There is really not much to engineer, it is a pretty mature and simple design.

The difference is:

-Hub motors rpm completely depends on your speed(since there is no gearing in between the wheel and the motor) at low speeds the rpm drops, the motor runs in the inefficient band and its power output falls significantly below its peak.

-With a mid drive rpm is completely dependent on cadence and when climbing if the gear ratio is right one can keep the cadence hence rpm in the motor's efficient range where it can also produce close to its peak output.

Yes it is simple physics and it is all about output power vs rpm graph not the peak numbers. Ebike companies don't give you that, instead advertise those meaningless peak numbers of Torque etc.


So here is the conclusion,
On very steep hills with the right gearing you can keep the cadence of a mid drive in the efficient band hence can expect mid drive to be more efficient than a hub motor.

Otherwise, hub motor will not suffer the losses at the drivetrain and be more efficient than the mid drive.

I was comparing my original 9 year old hub motor speed/torque curves to the same data for my new mid-drive. Over that 9 year period hub motor design and performance has advanced as I acknowledged, but there really is a big difference in the quality of design between by old hub motor and the new mid-drive.

 

[AHicks]

A mid drive motor is not better engineered than a hub motor. There is really not much to engineer, it is a pretty mature and simple design.

The difference is:

-Hub motors rpm completely depends on your speed(since there is no gearing in between the wheel and the motor) at low speeds the rpm drops, the motor runs in the inefficient band and its power output falls significantly below its peak.

-With a mid drive rpm is completely dependent on cadence and when climbing if the gear ratio is right one can keep the cadence hence rpm in the motor's efficient range where it can also produce close to its peak output.

Yes it is simple physics and it is all about output power vs rpm graph not the peak numbers. Ebike companies don't give you that, instead advertise those meaningless peak numbers of Torque etc.


So here is the conclusion,
On very steep hills with the right gearing you can keep the cadence of a mid drive in the efficient band hence can expect mid drive to be more efficient than a hub motor.

Otherwise, hub motor will not suffer the losses at the drivetrain and be more efficient than the mid drive.

I struggle when people write about "hub" drives discounting completely the potential for gear driven hub drives. That omission skews most of their comments into uselessness.

 

[Stefan Mikes]

@Johnny,
If we compare apples to apples (a 250 W hub motor to a 250 W mid-drive one), it is clear the hub-drive motor is a very poor climber. You have given the answer to the question "why" yourself. When riding a mid-drive motor against a steep incline, the cyclist and the motor cooperate, and their combined effort is amplified by the drive-train. It is easy to get on gearing/cadence to keep the motor efficient as well. Mid-drive motors are designed to be especially effective at the low end (it is the very idea of an e-MTB motor). Additionally, mid-drives can produce bursts of power.

A hub-drive motor works with constant power and is not amplified by the drive-train. You cannot ride uphill fast to get such a motor into the optimum rpm either. Moreover, hub-drive motors tend to overheat while climbing.

You might say "who needs a 250 W hub-drive motor?" Putting regional/legal matters aside, I would say a 750 or 1000 Watt hub-drive motor is heavy. To maintain a good range, you need a large battery. That makes the hub-drive motor e-bike very heavy. Climbing means increase of the potential energy (equals elevation gain times the total rider/bike/cargo mass times the gravity) so the heavier e-bike is, the bigger battery you need, that makes the bike even heavier, then...

For these reasons, no respected e-MTB brand will ever use a hub-drive motor anymore. A 250 W nominal Brose S Mag or Yamaha PW-X2 motor beats hub-drive motors with torque, peak power, climbing ability, light weight and reasonable sized battery.

 

[richard.rivers]

I can say that 90% of hub motor's torque value is far from real values. For example Bafang claimed to have 80 NM torque so does Rad power but Actual torque is somewhere around 35-40 Nm torque.
Only trust the torque of reputable brands like Bosch and Shimano.

High torque will be achieved by speed reduction gears. But in geared hub motors they only have single gear ratio so If a hub motor has 80 Nm torque it can't have a high top speed. Maybe top speed will be only 8mph (or they need to have a massive size hub motor). Mid-drives can achieve higher torque by reducing the speed (which increases force).

 

[Johnny]

@Stefan Mikes

I think we all agree that for emtb's mid drives are the better choice because of the reasons in my post.

But it doesn't mean that as a motor mid drives are better engineered, it is the placement of the motor that makes the difference.

 

[richard.rivers]

@Stefan Mikes

I think we all agree that for emtb's mid drives are the better choice because of the reasons in my post.

But it doesn't mean that as a motor mid drives are better engineered, it is the placement of the motor that makes the difference.

Better engineered? I think they are better engineered and more sophisticated. But it doesn't mean they are better for every situation. If you are looking for an e-bike just for cruising and don't need to do lots of hill climbing then you don't need features that comes with mid-drive motors. A hub motor will even outperform a mid-drive motor.

But mid-drive motors come with more advanced gearing, more advanced controller and more sophisticated sensors.

 

[Stefan Mikes]

A hub motor will even outperform a mid-drive motor.

Outperform in what sense?

 

[Stefan Mikes]

But it doesn't mean that as a motor mid drives are better engineered,

Are we talking Brose, Yamaha, Bosch, Shimano, Mahle or the Chinese cr*p?
P.S. As soon as I hear "Bafang", I open the fire!

 

[AHicks]

If you are serious about talking torque, I think it might be in your best interest to play with Grin's spreadsheet long enough where you can get some commonly accepted data to base future decisions on (without wading through uninformed opinions or agendas - just the facts). Find your motor, plug it in, and see what comes of it. Then compare it to whatever you want, including direct drive, geared drive, and mid!

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

www.ebikes.ca

 

[Sierratim]

If you are serious about talking torque, I think it might be in your best interest to play with Grin's spreadsheet long enough where you can get some commonly accepted data to base future decisions on (without wading through uninformed opinions or agendas - just the facts). Find your motor, plug it in, and see what comes of it. Then compare it to whatever you want, including direct drive, geared drive, and mid!

Motor Simulator - Tools

Our ebike motor simulator allows you to easily simulate the different performance characteristics of different ebike setups - with a wide selection of hub motors modeled, and the ability to add custom batteries and controllers and set a wide variety of vehicle parameters you'll be able to see...

www.ebikes.ca

I found Grin's calculator to be an invaluable tool in selecting the hub motor for my DIY ebike conversion. The ebike climbed our local steep hills just as the simulator predicted, using just about the same amount of power. I, too, would recommend this to anyone that wants to make 'apples to apples' comparisons between motors.

 

[Johnny]

Are we talking Brose, Yamaha, Bosch, Shimano, Mahle or the Chinese cr*p?
P.S. As soon as I hear "Bafang", I open the fire!

Did I say Bafang ?

Dapu, TDCM, Neodrive(and probably Grin's offerings) are all high quality hub motors. Some of them already come with a high quality torque sensor + controller. Their rated values seem to be spot on, not overrated.

Putting the torque sensor and controller in the same enclosure doesn't make mid drives more sophisticated in any way. You can start with a quality hub motor and pair it with an asi controller and a good torque sensor and you end up with a system that will be more powerful, efficient and just as smooth if not smoother than those mainstream mid drive offerings you have mentioned.


I think labeling things as "Chinese cr.p" is unfair since most of the big companies like Brose, Bosch do manufacture (at least some of their components if not the whole product) in China.
As for Bafang, they are trying to make motors as cheap as possible so it is expected that they will not match the smoothness/reliability of the mainstream.

 

[richard.rivers]

Brose manufacture in Germany, Bosch in Slovakia. TDCM is Taiwanese company. And for Dapu their quality go down so much in recent years. After their top management quit, I don't hear lot of good reviews about dapu motors. Long time Dapu users are slowly going away from Dapu. I feel so sad for it as I loved Dapu motors before.