50nm mid drive vs 50nm hub drive

[mikecoin56]

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?

 

[Katysax]

I have the Specialized Como 4.0 and regularly use it to climb local mountain passes. It has power to spare. Recently my partner test rode the Como 3.0 and 4.0 and concluded that the difference in the motor was meaningful and worth the cost for the upgrade.

 

[TMH]

We can down to the conclusion that torque number is marketing hype.

I haven't read the referenced thread, but based on personal experience I don't agree with your conclusion. And that experience is based on a pretty apples-to-apples comparison - all mid-drives, similar wheel/tire sizes, similar bike weights, different motors from the same manufacturer, etc.

 

[TMH]

And... there is no way that your motorcycles are as light as your e-bike. Nor are the drive components on your motorcycle (wheels, tires, chain) nearly as light as those on your e-bike, so the torque of your motorcycle ICE is comparatively masked as compared to an e-bike. Plus electric motors make a lot more torque for their size as compared to ICE. Plus your motorcycle is not as dependent on having a high torque due to its huge (comparatively speaking) fuel tank as compared to an e-bike battery. yada yada

But what I actually said is that I don't agree with your conclusion that the torque numbers are only marketing hype. I can easily feel the difference between an e-bike which is marketed as having 60nm of torque, and one which is marketed as having 75nm of torque, both from the same manufacturer and in similar platforms. So whether or not the motors actually put out the specified torques is unknown to me, and is potentially marketing hype. But differences in motors marketed as having higher or lower torque, in my personal experience, are quite discernible and are more than just marketing hype. Maybe I just disagreed with the inaccurate blanket statement?

 

[TMH]

I'm afraid that your analogy of a motorcycle to an e-bike is too much of an oversimplification to be accurate or to make your argument. Torque (a measure of rotational force) is only a single factor in determining a vehicle's functionality. Higher torque allows higher work (a measure of force over a distance). Power is a measure of how quickly work can be performed.

To differentiate between e-bikes and ICE motorcycles:

Torque may be similar, but
A motorcycle can work longer (apply the motor's torque for a longer period of time) since its energy supply (fuel in its tank) is much larger than the energy available in an e-bike battery (for example 1 gallon of gasoline has 124,000 Btu of energy content while a 1Kwh battery has 3,413 Btu of energy content); and
Power of a ICE motorcycle engine is so significantly higher than that of an e-bike (a 500 watt e-bike generates less than 1 HP, but your motorcycle generates 50, 80, 150HP?)

So arguing that an e-bike can't have anywhere near the same torque as your motorcycle (and therefore it is all just marketing hype) is inaccurate as you have only addressed a single measured factor in the entire system, and not the system as a whole.

 

[Scott Adams]

this is a bit of a thorny issue and manufacturers don't help when they release non-standardized numbers which don't include the torque value along the relevant range of RPMs from zero to no-load (top speed) at a given voltage

no doubt that marketing plays a role in what torque value is assigned to a motor as well

I'm not even sure if the torques are all measured at the shaft of the motor and without having been through any gears, or at what RPM

a motor with half as much torque, but produced at four times the RPM will be twice as powerful and so on

power = torque x RPM

work (or energy) = torque x degrees of rotation

gears function to trade torque for RPM, every time one goes up, the other goes down proportionally, so you can play with torque to no end using gears

in a better world, an independent tester (perhaps EBR if it weren't so expensive to do) would generate test numbers on a dynamometer, one from BionX was for sale after the recent bankruptcy...

what can be measured and recorded more readily, but with a bit of work and equipment, is the watt draw of the motor during operation of your bike

working backwards from the watts to the torque can then be done if you make some fairly safe assumptions about the efficiency curve of the motor and what gear your bike was in if it is a mid-drive, and also what gears are in the motor

as you guys pointed out, the hub motor can only hit it's efficiency sweet spot at a narrow range of RPM, while the mid-drive is decoupled from the wheel by the gears and can run closer to it's desired RPMs at a wide range of wheel speeds

if enough users ask for the information we need, one day we might get it!

 

[EMGX]

Personally I would stick with 70nm or greater, assuming that torque value ratings are equivalent across different brands, but I live in a very hilly area. I'm happy with my Yamaha PW-SE mid drive powered gravel bike which is rated at 70nm and thankful that it doesn't have less power when climbing steep roads. I don't use the "high" setting very much but I wouldn't want to be without the power that it provides for some situations. Even with that degree of torque I once stalled the motor pedaling hard when I turned on to a very steep short hill in too high of a gear. This with a very light (for an ebike) 40# bike, more torque might be a good thing with most bikes I see weighing 60# and up. Power delivery seems very natural and smooth to me.

 

[TMH]

ICE=internal combustion engine

Torque is a very meaningful measure of as it can show a comparative difference between 2 motors in how much work (for example, climbing assistance) one might be able to provide as compared to the other. But it is not the only important factor in an overall system. This addresses my point to your original claim to a new Forum member that " torque number is marketing hype ". This is an incorrect statement to make to someone who is attempting to learn more details about different e-bikes. So your statement above "(or torque doesn't mean everything)" is highly accurate.

My claim, and I stick with it, is that my experience has shown me that in 2 different e-bikes, of similar weight, drive type, tire size, etc. (note I am not comparing to motorcycles since I am comparing motors in similar systems) with differing motor torque specifications, I can tell the motor with the higher torque based on hill climbing performance. Higher torque is an important variable to consider. It is not just marketing hype.

 

[EMGX]

Some of the hills I've done on this bike which I would not want to ride (or could not ride) with a regular pedal bike.

 

[EMGX]

What does 70nm mean though?

That's as much torque as Harley Davison electric motorcycle.

It has what? Nearly 600 lbs and still pull harder and goes a lot faster on steep hill.

I know ebikes with 70nm torque are barely moving (if throttle only) on steep hill.. or moving very slowly

What it means to me (based on experience with this bike) is that it is enough, but I wouldn't want less. I'm not concerned about comparing it to a motorcycle or car but if the numbers are equivalent across brands of ebike motors it seems to me to be a useful measure for comparison of similar bicycles.

 

[EMGX]

Ok so what you're saying is that Bosch 75Nm "might" be just as powerful or torquey as Bafang 160Nm motor?

Not at all. If the torque ratings are comparable across brands I would expect that a 160nm motor would deliver approximately twice the assistance than one with 75nm would at the same rpm.

 

[AHicks]

Timpo, let's keep it simple. Let's assume electric motorcycles, and motorcycles in general, are rated differently than an e-bike. If you would like to figure out/discuss what that difference is, maybe start a new string on that topic?

I would agree that the advertised torque (nm) rating on bikes, all else being equal, is a big help when comparing one bike to another - especially when it comes to newbies trying to figure out what's going on.

 

[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.

 

[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!

 

[Explorer-1]

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.