Nm Numan Meters --- Perspective Please ?

[CSH]

As I drill down in my understanding of ebikes and their components, I wonder if one Spec is simple, or more complex.

Nm Numan Meters 40/50/60/90/120

Is it as simple as More is Better ?
ie: for Urban Hill Climbing (in my case)

As I narrow bike choices down, Do I look for the one with more Nm ?
or is there more to it than that ?

I'm eager to understand, better.

Any advice is appreciated,

Craig

 

[6zfshdb]

A Newman meter is a device for measuring tension.

The symbol Nm refers to Newton meters. In this case, the higher the number the better but the number can be deceiving.

A post by Ravi Kempaiah a few years back might be of help:

https://electricbikereview.com/forums/threads/torque-rating-on-e-bikes-marketing-gimmick.2467/

 

[CSH]

A Newman meter is a device for measuring tension.

The symbol Nm refers to Newton meters. In this case, the higher the number the better but the number can be deceiving.

A post by Ravi Kempaiah a few years back might be of help:

https://electricbikereview.com/forums/threads/torque-rating-on-e-bikes-marketing-gimmick.2467/

WOW !
THAT was an education........

Thank You
P.S. I didn't use Torque as a Search criteria , so I never found that Thread.

Craig

 

[TimJohn]

Lets get picky here. Nm is Newton meters which is a measure of torque. The larger the number the more torque. The higher number is not necessarily a better number...this is not a value judgement or good or bad or happy or sad but a measurement of the twisting power of the motor.

 

[CSH]

Lets get picky here. Nm is Newton meters which is a measure of torque. The larger the number the more torque. The higher number is not necessarily a better number...this is not a value judgement or good or bad or happy or sad but a measurement of the twisting power of the motor.

So, in a Moderate Up Hill scenario, with a (not super fit) individual riding, which number would you wish to have ?

 

[Ravi Kempaiah]

A Newman meter is a device for measuring tension.

The symbol Nm refers to Newton meters. In this case, the higher the number the better but the number can be deceiving.

A post by Ravi Kempaiah a few years back might be of help:

https://electricbikereview.com/forums/threads/torque-rating-on-e-bikes-marketing-gimmick.2467/

Thanks for linking that @6zfshdb (BTW, I am curious to know what your username means!)

@CSH

Torque numbers and watt numbers on a E-bike are good as DJTrump's tax returns.

Unless you see Dynamometer testing, the specs/data sheet doesn't tell you much.

If a motor is running at 48V or 52V and with a 20 or 25A controller, you should be able to climb hills.

You should always base your opinion on real world testing and ebike market is not like electronics where if someone says 128GB, you will have so many GB of data.

Watts and Nm numbers can vary widely and is very deceiving. Here is an example. In the Motorcycle world, Suzuki Hayabusa is a coveted bike. It produces 155Nm at 7200rpm using a 1350cc engine.
https://www.suzukimotorcycles.com.au/range/road/supersport/hayabusa/features

Whereas, some motor manufacturers claim 160Nm (Bafang Ultra) and I do not believe that. Does it have sufficient power, Yes..... but is it 160Nm, no!
The armature of 350W or 500W mid-motors are the size of your palm and using tiny copper winding, it can't produce 100Nm of torque at the wheels and if they did, there is no Dyno results available.

Also, 100Nm+ torque would really damage the cassette like Shimano Deore or Acera. These are made for human power not motor power.

Anyway,

You should look at the battery voltage and controller ampere reading and if the battery is providing 52V and controller runs at 25A, you should have a very capable system.

 

[6zfshdb]

Thanks for linking that @6zfshdb (BTW, I am curious to know what your username means!)

It's my old user ID when I worked for the Bell System years ago. I used it so much, I never forgot it. It was computer generated based on my name and SS#.

 

[Ken M]

OMG. There is a lot misleading information being stated in this thread.

The motorcycle torque stated was most likely a dynamic torque at a specific motor RPM which is entirely different than the stall torque usually reported by most ebike motor companies. Essentially ignore that information because it also says nothing about the gear ratio of the drive train of a motorcycle vs an ebike.

Torque is very relevant but every motor has a torque curve that falls off faster at higher speeds if the Kv is lower. Higher Kv is the result of fewer copper windings which tend to be motors better suited for higher speed commuting ebikes but their stall torque will typically be lower.

Mid-drives take advantage of bike gearing to be a great slow speed climbing solution because the torque at the crank can be multiplied via the chain rings at slow speeds but at high speeds they suffer from high speed mechanical inefficiently via gearing intended to keep the cadence reasonable for human contribution. A hub drive delivers torque directly at to the wheel so at higher speeds they can outperform mid-drives and even be more efficient.

I'm just touching the surface of the complexity of performance so don't get caught up with marketing claims. Best thing you can do is become educated and know what level of performance you want and a single performance number is not going to give you the total solution answer an ebike buyer needs to know.

 

[Ravi Kempaiah]

The motorcycle torque stated was most likely a dynamic torque at a specific motor RPM

That is more meaningful and correct way of reporting torque. Rev the engine to certain RPM and then measure the torque produced at the wheels on Dyno at that rpm.

stall torque usually reported by most ebike motor companies.

None of the ebike companies mention that it is stall torque!! And stall torque has very little meaning for ebikes because you want torque when you are pedaling at different cadences not just start and stop.
If I am in a very high gear, again stall torque would be very low.
They tend to show it is average dynamic torque at human cadence but none of the ebike companies provide Dyno measurements and it is disappointing!

One of the forum readers here to did reverse engineer the torque values based on charts provides by these eBike companies.
https://electricbikereview.com/foru...yamaha-shimano-brose.14085/page-3#post-141848

Here is a graph from Yamaha, which again shows dynamic torque and this drops down after certain rpm.

 

[The duke]

I'm confused

 

[AHicks]

Well, I can share that a 1500w direct drive hub, with in excess of 20 amps available (35 amp controller), WILL struggle on a longer hill (not a mountain!) found in a rolling coastal area - sometimes leaving you (me!) panting at the top. It's NOT just about watts and amps.

I would also agree with the thought that comparing an advertised torque value available with a mid drive, to one available with a gear drive rear hub, to one available with a direct drive, is comparing apples to oranges. From a practical standpoint, the different gear ratios between them make all the difference in the world. That said, if you live and plan on using the bike in a mostly flat area, the gear reduction (or Nm rating) may make very little difference in how much you enjoy riding the bike.

 

[CSH]

I'm confused View attachment 35169

 

[Ken M]

That is more meaningful and correct way of reporting torque. Rev the engine to certain RPM and then measure the torque produced at the wheels on Dyno at that rpm.




None of the ebike companies mention that it is stall torque!! And stall torque has very little meaning for ebikes because you want torque when you are pedaling at different cadences not just start and stop.
If I am in a very high gear, again stall torque would be very low.
They tend to show it is average dynamic torque at human cadence but none of the ebike companies provide Dyno measurements and it is disappointing!

One of the forum readers here to did reverse engineer the torque values based on charts provides by these eBike companies.
https://electricbikereview.com/foru...yamaha-shimano-brose.14085/page-3#post-141848



View attachment 35167

Here is a graph from Yamaha, which again shows dynamic torque and this drops down after certain rpm.

View attachment 35168

This is "marketing" information which is always going to deceptive. My guess is the first chart is from Bosch so I would expect them to show better torque values across the entire possible cadence range but actual motor torque values fall off as speed increases for the BLDC (or more accurately Brushless DC Permanent Magnet Synchronous motors) utilized in ebikes. Back emf is always going to reduce torque as motor speed increases.

Unless the motor manufacturers want to provide full performance specs we can be sure what their claimed torque value represents but I believe they tend to report the highest torque value which will be start-up / stall torque (it's not a meaningless parameter as the torque at slower speeds is where most riders perceive the ebikes performance is most important (the feeling of acceleration matters to perceived performance but may not be such a big deal to those of us that ride for more than a few minutes).

What everyone needs to understand is that because of bike gearing a mid-drive has advantages at slower speeds and a hub drive will tend to have better performance at higher speeds (probably one of the reasons why companies like Bosch lobby to have lower regulated assist speeds). A hub drive bike like a Stromer may be easier to sustain a higher speed of say 40kph than a mid-drive ebike that reports a higher torque value. The main reason for this is the torque of hub motor is delivered directly at the axle and a mid-drive has gearing ratio issues at higher speeds because it shares the chain rings with the rider.

 

[DavidBer]

By no means am I knowledgable about this subject. From what I am reading though, this reminds of the horsepower ratings of motorcycles. The manufacturers would always say that the bike had X horsepower. That was the horsepower at the crank, not at the rear wheel. The horsepower at the rear wheel was always less than at the crank because of the gearing issue. So here it seems to be the same. You have it at the wheel and at the crank

 

[Ken M]

By no means am I knowledgable about this subject. From what I am reading though, this reminds of the horsepower ratings of motorcycles. The manufacturers would always say that the bike had X horsepower. That was the horsepower at the crank, not at the rear wheel. The horsepower at the rear wheel was always less than at the crank because of the gearing issue. So here it seems to be the same. You have it at the wheel and at the crank

Horsepower is not a parameter measured at the crank like torque is. Torque can always be increased or decreased via gearing. Everyone just needs to understand how ebike performance is not parity and each motor configuration (mid vs hub) has some advantages and disadvantages.

 

[AHicks]

Horsepower is not a parameter measured at the crank like torque is. Torque can always be increased or decreased via gearing. Everyone just needs to understand how ebike performance is not parity and each motor configuration (mid vs hub) has some advantages and disadvantages.

YES, BINGO!

And not just mid vs hub, it's mid vs. gear driven hub vs. direct drive hub! Each is WAY different from the other, in nearly all aspects. The only commonality between the types is that they are all electric, and all are used to power an e-bike.

 

[CSH]

YES, BINGO!

And not just mid vs hub, it's mid vs. gear driven hub vs. direct drive hub! Each is WAY different from the other, in nearly all aspects. The only commonality between the types is that they are all electric, and all are used to power an e-bike.

Dare I ask if someone could spell out those "Differences" in a Real world application (riding experience) way ?

mid vs.
gear driven hub vs.
direct drive hub

I read all the Tech Talk (which is like eating the whole elephant) and I do appreciate it, BUT I need help in understanding how these differences effect things like

Starting from Stand Still:

How much Human Effort needed while pedaling:

Exercise vs Let the Bike carry you:

Throttle or Not:

Please,

Craig

 

[Ken M]

Keep in mind that power rating does play a role in the performance capability of an ebike but each motor type (mid, DD hub, geared hub) has some innate differences.

Mid-drive: Very good climbing and low speed performance because they benefit from the chain ring gear ratios slower speeds. They suffer significantly when say cruising a high speed on say a 44T front & 11T rear which results in a 75% reduction of torque transmission to the rear wheel simple due to gearing (mid-drive companies will never tell you this fact and it's absolutely why they want the assist limits set at lower speeds (< 25kph Europe and 32kph US and Canada but there are high speed classes to 45kph). These bikes will accelerate faster at lower power ratings. Since there are always internal gears or belts in these motors they are more complex than DD hub drives so they inherently will be less reliable long term. Do not allow for regenerative braking which biggest benefit is not actually recapturing energy to the battery but the reduced wear on brake pads if good progressive braking is done with a DD hub.

Geared hub motors: Have some of the same advantages of mid-drives because of gearing inside the motors that mulitplies the torque of a smaller motor. They do not increase wear and tear on chains/belts/chainrings/etc. because the torque is applied directly to the wheel axle. This has a negative impact on their potential at slower speeds but helps at higher speeds vs. mid drives (people rarely understand that gears on a bike are designed to optimize human power and cadence and not what motors are capable of).

Direct Drive Hub motors: At lower power ratings these motors will not match up well vs geared or mid drives because they do not having internal gears but that makes them very reliable long term. At higher power ratings (say 750 - 1500W) they can perform as well as a mid-drive and geared hub drive but will have much better overall performance at higher speeds (ie less effort needed to sustain a high speed). Offer regenerative braking, very quite, and more reliable.

 

[CSH]

Keep in mind that power rating does play a role in the performance capability of an ebike but each motor type (mid, DD hub, geared hub) has some innate differences.

Mid-drive: Very good climbing and low speed performance because they benefit from the chain ring gear ratios slower speeds. They suffer significantly when say cruising a high speed on say a 44T front & 11T rear which results in a 75% reduction of torque transmission to the rear wheel simple due to gearing (mid-drive companies will never tell you this fact and it's absolutely why they want the assist limits set at lower speeds (< 25kph Europe and 32kph US and Canada but there are high speed classes to 45kph). These bikes will accelerate faster at lower power ratings. Since there are always internal gears or belts in these motors they are more complex than DD hub drives so they inherently will be less reliable long term. Do not allow for regenerative braking which biggest benefit is not actually recapturing energy to the battery but the reduced wear on brake pads if good progressive braking is done with a DD hub.

Geared hub motors: Have some of the same advantages of mid-drives because of gearing inside the motors that mulitplies the torque of a smaller motor. They do not increase wear and tear on chains/belts/chainrings/etc. because the torque is applied directly to the wheel axle. This has a negative impact on their potential at slower speeds but helps at higher speeds vs. mid drives (people rarely understand that gears on a bike are designed to optimize human power and cadence and not what motors are capable of).

Direct Drive Hub motors: At lower power ratings these motors will not match up well vs geared or mid drives because they do not having internal gears but that makes them very reliable long term. At higher power ratings (say 750 - 1500W) they can perform as well as a mid-drive and geared hub drive but will have much better overall performance at higher speeds (ie less effort needed to sustain a high speed). Offer regenerative braking, very quite, and more reliable.

Great Information Ken.

"Speed" isn't as big a deal to me and my Wife, but Adequate Power (to get up a hill, or move us along easily) is.
Which motor addresses that best.

 

[Ken M]

Great Information Ken.

"Speed" isn't as big a deal to me and my Wife, but Adequate Power (to get up a hill, or move us along easily) is.
Which motor addresses that best.

If you are going to spend 90% or more of your riding time below 20mph any Class 1 mid drive ebike will be a good choice. I do sometimes worry that there is going to be limited availability of parts &/or replacement mid-drive motors because I think only Bosch has committed to having auto industry like assurances of support for up to 10 years after a drive system is no longer produced. There are no mounting standards so it seems every mid-drive has a custom mounting bracket so future motor issues could be the end of life for the ebike.

Strangely I think only Bafang is allowing buyers to service their mid-drives and do plan to sell replacement parts for owners to do self-service or to have shop access to parts for them to do so.

A good geared hub motor would also be a good choice for you and if the motor ever fails you can always replace the rear wheel and motor assembly with a replacement because there are some industry standards on rear drop outs.

Maybe mid-drives will last say 25,000 miles or more but there are some concerns about future servicing or replacement of the motors. It's something to consider given the pace of change in this industry.

On the bright side, all ebikes, regardless of the motor technology, make riding fun. Avoid the super low cost ebikes because I do think there are some really ???? quality compromises being made by some companies to achieve bottom feeding prices.