What does Nm really measure and is it applied the same by ebike manufacturers.

[scout592]

I have followed EBR for some time and appreciate all the wonderful information and guidance. One area I keep hearing debates about is Nm. I am not an engineer but some of you are or have mechanical knowledge that wouldbe helpful. I understand that the bafang ultra rated at 160 Nm is the king of the more common motors available. I ran across this quote on this site saying there is sales hype trying to use Nm in different ways. I am not saying that about bafang or any others but it got me thinking, is there a standard that is commonly used and is tge dynamometer the most reliable test as stated below. Thanks for any help. Here is the quote:

" These companies may quote 100+ Nm but on the Dynamometer, at the wheels, if that numbers is replicated, then it is valid."

 

[MartsEbike]

The Newton-Meter is the standard. All manufacturers will be quoting figures "at the motor", and not "at the wheel". The torque figures "at the wheel" can change depending on your drive chain setup - Chainring/Cassette/Wheel sizes etc.

 

[Ebiker33]

Yeah it has to be at the crank spindle, to many variables in play after that.
Yet this Emotorcycle motor is only rated at 116nm, yet it will outperform the ultra a million times at every level.
105HP @ 116nm

And this has been discussed before on EBR, but logically it doesn't make sense.
Somebody is going to come in and explain to us I am sure, as they have before but I forget how and why

 

[scrambler]

The Newton-Meter is the standard. All manufacturers will be quoting figures "at the motor", and not "at the wheel". The torque figures "at the wheel" can change depending on your drive chain setup - Chainring/Cassette/Wheel sizes etc.

I wish that were true, unfortunately, I am pretty sure Some manufacturer are some times quoting at the rear wheel (when to their benefits), like for some E-motorcycle that have a small cog at the motor and a large sprocket at the rear wheel)...

 

[scrambler]

There are also different types of transmission.
A mid drive like the Bafang has internal gearing, so there is the Torque at the motor, then at the output shaft (after the internal gearing), and then at the rear wheel after the drive train ratio. Because the motor has internal gearing, the drive train ratio will often be less than one (larger sprocket in the front than at the back)
Like a 50 front and 25 rear is a 0.5 ratio. So the Torque at the rear wheel will be half the torque at the output shaft.
For these, the manufacturer benefit is to give the Output shaft Torque.

Some motors have no internal gearing (usually for e-motorcycle or motor only drive train), and in that case you usually have the inverse drive train ratio (Motor cog smaller than rear wheel sprocket)
Like a 35 sprocket at the motor, and a 70 sprocket at the rear wheel. In that case, the Torque at the rear wheel will be twice the Torque at the output shaft of the motor.
For these, the manufacturer benefit is to give the rear Wheel Torque.

 

[MartsEbike]

I wish that were true, unfortunately, I am pretty sure Some manufacturer are some times quoting at the rear wheel (when to their benefits), like for some E-motorcycle that have a small cog at the motor and a large sprocket at the rear wheel)...

I was mainly thinking of main steam brands... but yeah no doubt some are.

 

[Ebiker33]

I sell power tools and this is like the discussion I had with the Bosch Power tool rep a few years ago about their table saw rated like this
Powerful table saw – has 15-Amp saw with 4.0 max HP
Problem is it's rated at 120V, do the math 15A X 120V=1800W/746W (1 HP) =2.4HP
The peak is just seconds and then if it keeps going you blow your breaker, it's super deceptive.
And utility vacuums are even worse.
See a 120V vacuum at Home Depot rated a 6.5hp
6.5hp Vacuum

This is the type of fuzzy math Obi-wan Kenobi style......"Well from certain point view".........marketing, consumers face these days.

 

[scrambler]

Like for e-bike motors, there is the max sustained, and the peak, and these two are often blurred when convenient...

 

[PedalUma]

A pro rider can produce 400 Watts of power and bike components are designed with this in mind. That is about 80Nm. It does not matter what a motor will put out if it will destroy bike parts. Put your hands on a torque wrench and place it in a vice. Try applying 100Nm to the wrench to see the level of force. A rear sprocket may have five teeth contacting the chain. Try applying 160Nm to a bike chain, attached to a cog with 5-t in engagement to see what happens to the bike parts.

 

[biruja]

Even Bafang rates the output of the BBSHD at the same 160 NM (manual)as the Ultra. This doesn't make any sense if you look at the two motors.

 

[PedalUma]

Even Bafang rates the output of the BBSHD at the same 160 NM (manual)as the Ultra. This doesn't make any sense if you look at the two motors.

A Harbor Freight tool can have the same power usage a quality tool.

 

[Ebiker33]

One of my industrial customers has this guy on order
1" Impactor
M18 FUEL™ 1" D-Handle Extended Anvil High Torque Impact Wrench w/ ONE-KEY™ is the world’s first cordless 1” D-Handle High Torque Impact Wrench. The POWERSTATE™ Brushless Motor delivers up to 2,000 ft-lbs of nut-busting torque


That's equal to 2711.6 NM

 

[Ebiker33]

Like for e-bike motors, there is the max sustained, and the peak, and these two are often blurred when convenient...

Yes and some are intentionally degrading the posted numbers to sell into Europe, they don't care that some in North America might be put off by the lowering of the numbers.
Somebody did a test of a major well known EBike brand and when they measured the wattage input/output it was over double the posted amount, more games/deceptions to sell into those markets.
It's gotten so bad that some manufacturers refuse to reveal what their controller amps are because they know that anybody can then do the simple math.

 

[PedalUma]

A pro rider puts out 80 Nm and that is about the most a drivetrain can take, so how much to dislodge your elbow if he twisted it using his legs?
With 20V, "The EARTHQUAKE XT® Cordless Xtreme Torque Impact Wrench pounds out 1200 ft. lbs. of bolt breakaway torque to power off lug nuts and head bolts with ease. Combined with the EARTHQUAKE XT® Lithium battery system this impact wrench delivers high power, long run times and fast charging."
You are supposed to hold this thing in your hands. If true, that would shake and twist the meat off your bones.
From Harbor Freight: 1,200ft-lb= 1,626.982Nm

 

[scout592]

The Newton-Meter is the standard. All manufacturers will be quoting figures "at the motor", and not "at the wheel". The torque figures "at the wheel" can change depending on your drive chain setup - Chainring/Cassette/Wheel sizes etc.

Thanks, I can understand that explanation. I wonder if any of them ever reveal that figure.

 

[rich c]

A Nm is a unit of measure. No different than an inch is a unit of measure. One newton-metre is equal to the torque resulting from a force of one newton applied perpendicularly to the end of a moment arm that is one meter long. Since no one publishes test data on motors, it's just a marketing number like number of watts used to sell motors. It's just a random number in my opinion. My 350w Bosch feels the same as my 750w Fat Tad Trike geared hub motor.

• 1 kilogram-force metre = 9.80665 N⋅m[5][6]
• 1 newton-metre ≈ 0.73756215 pound-force-feet
• 1 pound-foot ≡ 1 pound-force-foot ≈ 1.35581795 N⋅m
• 1 ounce-inch ≡ 1 ounce-force-inch ≈ 7.06155181 mN⋅m (millinewton-metres)
• 1 dyne-centimetre = 10−7 N⋅m

 

[PedalUma]

A Nm is a unit of measure. No different than an inch is a unit of measure. One newton-metre is equal to the torque resulting from a force of one newton applied perpendicularly to the end of a moment arm that is one meter long. Since no one publishes test data on motors, it's just a marketing number like number of watts used to sell motors. It's just a random number in my opinion. My 350w Bosch feels the same as my 750w Fat Tad Trike geared hub motor.

• 1 kilogram-force metre = 9.80665 N⋅m[5][6]
• 1 newton-metre ≈ 0.73756215 pound-force-feet
• 1 pound-foot ≡ 1 pound-force-foot ≈ 1.35581795 N⋅m
• 1 ounce-inch ≡ 1 ounce-force-inch ≈ 7.06155181 mN⋅m (millinewton-metres)
• 1 dyne-centimetre = 10−7 N⋅m

A 350W nominal and optimized outruns in a group ride a 1500W nominal on climbs with longer rides because of lower weight and better handling. Heavy does not fly. Heavy is kinda dumb. Try them in a group setting.

 

[Ebiker33]

A 350W nominal and optimized outruns in a group ride a 1500W nominal on climbs with longer rides because of lower weight and better handling. Heavy does not fly. Heavy is kinda dumb. Try them in a group setting.

Say hello to my little friend, carbon fiber, 1500w with carbon fiber gets the best of both worlds.....yup that's what Watt Wagons is building, then add in rims, cranks, handle bars, and anything else.
And then put only 3" tires or 2.8 tires on it...the weight can be reduced, man I would love to see a race between a fully pimped out Hydra Watt Wagon and that 20K Specialized S-works.
of course you we need same skill and body weight, put your statement to the test. Maybe have the same rider run a coarse and time it.

 

[Mike_V]

A bike Dynomometer.
Design, model, calculate, fib and then measure the real torque of the whole electric bicycle system with:
DYNOBIKE by Eric Hicks and Team Luna

 

[Bluzrif]

A pro rider can produce 400 Watts of power and bike components are designed with this in mind. That is about 80Nm. It does not matter what a motor will put out if it will destroy bike parts. Put your hands on a torque wrench and place it in a vice. Try applying 100Nm to the wrench to see the level of force. A rear sprocket may have five teeth contacting the chain. Try applying 160Nm to a bike chain, attached to a cog with 5-t in engagement to see what happens to the bike parts.

And then just for grins... try applying 80nm of force to a riders legs from a dead stop..