Torque rating on E-bikes - marketing gimmick?

[Ravi Kempaiah]

Torque on a mid-drive e-bike is measured at the crank

Thanks for your sharing thoughts.
Since the posting of this thread, more analysis has been done and as @Trail Cruiser reported above, the main difference is: E-bike companies mention electrical torque output but not the mechanical torque.

The only way to report the correct torque is to use a dynamometer. If the torque is indeed measured at the crank.. it leads to several deeper questions:
if the crank is smaller, it leads to smaller torque and if the crank is larger, it leads to more torque, which is not the case for E-bikes. Moreover, these are pedal-assist bikes and they only output power when there is a differential force on the spindle in the bottom bracket (or the motor axle).

As mentioned in the Wikipedia link.
Yamaha motorcyle produces tremendous power and related torque.
There is simply no way an E-bike motor can produce that kind of mechanical torque.

 

[Johnny]

...
As mentioned in the Wikipedia link.
Yamaha motorcyle produces tremendous power and related torque.
There is simply no way an E-bike motor can produce that kind of mechanical torque.
...

Even a tiny motor can produce as high torque as we want (in theory) as long as we use the appropriate gearing (in your picture, it is similar to increasing the distance under the same force and getting as high torque as you like).

For the motorcycle motors which are way more powerful but advertise the same torque, the important number is Torque x RPM not just torque. You see motorcycles are outputting 100nm at 8000 rpm while a 250W ebike motor can output 100nm at most at 25 rpm which is not even comparable. Since there is mechanical conversion (between the motor and the wheels) that power is converted to the desired rpm/torque value at the tire. (Also most mid drive ebike motors seem to have gearing inside to increase the torque output).

And you are right, since peak torque number without cadence information is almost meaningless, torque numbers are just marketing gimmick. The high torque can only be had for the very low rpms.


This is why in these forums I have asked for the real power/cadence (power or torque /cadence give exact the same information, power in watts= torque in nm x rpm) of motors and never had a proper answer(I remember asking this question about bosch/brose / yamaha etc as well as bafang motors and didnt really get an answer).

 

[J.R.]

Seeing more and more new people coming to the forum using torque numbers advertised by the brands to compare one bike against another, as if there were a standard in the industry to measure this. The numbers advertised are meaningless when comparing one brand against another, or one drive system against another. The only way to compare one ebike drive against another for torque is if the bike were mounted on a dynamometer and the torque were measured at the rear wheel. The only way this could be fairly achieved is if there was a calibrated mechanical device to activate the PAS rpm evenly across different drive systems. Torque at the rear wheel is the only measurement that matters. 'Where the rubber meets the road'.

With all the bloviating by sellers, and with so many sellers now, it's getting more and more important to test ride.

100 pound feet of torque = 135 newton meters of torque. An ebike claiming 80 to 120 Nm of torque

There are standard practices for measuring torque of vehicles. There are standards for measuring the power of bike riders. Hopefully the ebike industry will come up with a standard we can count on.

 

[Sierratim]

Motor torque, power, and speed (rpm) are inter-related by the relationship Power = Torque x Speed (with appropriate scaling factors for units). @TomW has a nice sample calc of ebike vs motorcycle torques HERE. Other threads discuss this as well, including THIS ONE where I compared an emotorcycle to an ebike, taking into account torque, power, rpm, gearing, and wheel sizes.

The conclusion of these other posts is that torque and power are useful for comparing motors between ebikes when you can rely on the data. What do I mean by that? I mean some manufacturers have published bench tests comparing motor performance. Other motor brands have not. In these cases test rides are all you can really rely on, but then I always recommend test rides regardless. Bike performance, fit, quality, etc are too personal to judge by specs alone.

 

[J.R.]

Motor torque, power, and speed (rpm) are inter-related by the relationship Power = Torque x Speed (with appropriate scaling factors for units). @TomW has a nice sample calc of ebike vs motorcycle torques HERE. Other threads discuss this as well, including THIS ONE where I compared an emotorcycle to an ebike, taking into account torque, power, rpm, gearing, and wheel sizes.

The conclusion of these other posts is that torque and power are useful for comparing motors between ebikes when you can rely on the data. What do I mean by that? I mean some manufacturers have published bench tests comparing motor performance. Other motor brands have not. In these cases test rides are all you can really rely on, but then I always recommend test rides regardless. Bike performance, fit, quality, etc are too personal to judge by specs alone.

I don't compare ebikes to motorcycles. Torque is a known metric, not widely understood, but known as it relates to vehicles. What the ebike industry is doing is using a known metric for a sales tool, yet not following the known metric's standard for measurement.

I see some making the statement 'this hub motor has 70 Nm and that mid drive has 50 Nm'. It confuses many that come here. There needs to be standards and procedures to measure the torque of an ebike. For the sake of the consumer.

Hopefully models within a brand spec the torque the same across the entire line. But you can't compare one brand's specs against another, and certainly not hub versus mid drive. The ebike industry needs a SAE. The torque specs, as used across the industry, are meaningless.

 

[bluecat]

The ebike industry needs a SAE. The torque specs, as used across the industry, are meaningless.

A) This will not come, unfortunately!
B) This is without doubt true, but mostly unknown.

The e Bike market is rapidly growing. Huge torque numbers are arguments to gain new customers. As the power is limited by law, the sales forces brought "peak power" into marketing speech.

But there is also a technical hurdle: A hub drive has its torque right on the axle, no more loss. A mid drive motor has always the drive train to overcome. But in which gear should you measure? With other words: mid drive motor torque values are more like SAE gross HP (=big, but non realistic values).

The make torque values of mid drives comparable with those form hud drives, you need three parameters:

1. torque measured in NM
2. rpm of the motor at measuring point
3. speed of the eBike at measuring point

At this point, the excessive EU bureaucracy could help. If the implement this into their already shoreless eBike rules...

 

[Sierratim]

I see some making the statement 'this hub motor has 70 Nm and that mid drive has 50 Nm'. It confuses many that come here. There needs to be standards and procedures to measure the torque of an ebike. For the sake of the consumer.

This really is the crux of the issue in this thread, isn't it? How does a buyer compare one set of claims to another? An industry wide testing protocol would do it, but I don't see that happening anytime soon. So what can be done to actually reduce confusion now?

We can make reference to the data that does exist, often in the form of manufacturer publications. Here are some examples that have been posted and discussed in other threads.

data by Brose



data by Specialized


data compiled by riders from public sources

We can openly acknowledge that buyers are going to need to do some research to actually understand and then compare the available specs. Discussing motor output vs wheel torque and power has cleared up confusion in other threads. There are also online tools that amount to virtual ebike dynamomotors that provide ebike performance data under conditions selected by the user. I often refer people to Grin Technologies' MOTOR SIMULATOR when they ask questions about motor specs and real world riding conditions. I wouldn't doubt that other simulators exist, but I've found Grin's to be be flexible and accurate.

Bottom line, as Fox Mulder said, "The truth is out there", and, like Fox, ebike buyers have to search for it. We can take the role of guides in this search, if we choose.

Oh, and one more suggestion, we can acknowledge the interrelationship of torque, power, and rpm and refrain from throwing more dust in the air by comparing ebikes to motorcycles as this and other threads have done. Published torques may be similar, but the motorcycles' power and rpm so overwhelm the ebkies' that any comparison is more likely to obfuscate people than help.

 

[bluecat]

I often refer people to Grin Technologies' MOTOR SIMULATOR when they ask questions about motor specs and real world riding conditions

You should not do this if it is about Stromer.

Since many years, Stromer uses a dedicated motor mapping. This is far away from just giving full current / amperage to the motor.

 

[Sierratim]

You should not do this if it is about Stromer.

Since many years, Stromer uses a dedicated motor mapping. This is far away from just giving full current / amperage to the motor.

Correct, the Grin Tech motor simultor does not model every available motor. There is a "Custom Motor" setting that in theory allows modeling of any motor, but the user does need to provide electrical characteristics that will be difficult to get, unless you have access to engineering specs or a lot of test equipment.

Can you provide a link to the Stromer motor mapping site?

 

[Johnny]

100 pound feet of torque = 135 newton meters of torque. An ebike claiming 80 to 120 Nm of torque

Because torque by itself does not give any information about power without rpm. Even a human being can produce as large torque as we want with the right setup that can go as small rpm as necessary(Lever for example works with this principle). What creates motion is enegry and the amount of energy you produce at a unit time is power.


Ladies and Gentlemen, torque or power are not notions that are specific to a vehicle. Torque can not be used to compare anything without rpm information.


An ebike can claim 120nm and a peak power of 500w. Regardless of gearing or where you measure it, if you are traveling at 15mph your rear wheel, depending on the size, will do around 180rpm and at that point at the wheel you will see a mere 26.5nm of torque (if you can transfer all what 500W power to the wheels without any losses). A motorcycle with 25hp can put 100nm to the wheels even at 1800rpm!


Use power output at the speed you like to travel as your measure, everything will become clear and it is foolproof.

 

[Sierratim]

Because torque by itself does not give any information about power without rpm. Even a human being can produce as large torque as we want with the right setup that can go as small rpm as necessary(Lever for example works with this principle). What creates motion is enegry and the amount of energy you produce at a unit time is power.


Ladies and Gentlemen, torque or power are not notions that are specific to a vehicle. Torque can not be used to compare anything without rpm information.


An ebike can claim 120nm and a peak power of 500w. Regardless of gearing or where you measure it, if you are traveling at 15mph your rear wheel, depending on the size, will do around 180rpm and at that point at the wheel you will see a mere 26.5nm of torque (if you can transfer all what 500W power to the wheels without any losses). A motorcycle with 25hp can put 100nm to the wheels even at 1800rpm!


Use power output at the speed you like to travel as your measure, everything will become clear and it is foolproof.

A 180lb rider with 175mm cranks can produce over 140Nm of torque at the cranks just by standing on them in the horiz position. This in no way means that the rider can climb hills like a motorcycle. You do need all 3 pieces of the puzzle; torque, power, and speed (rpm). The picture is incomplete without all 3.

 

[Iridebikez]

A 180lb rider with 175mm cranks can produce over 140Nm of torque at the cranks just by standing on them in the horiz position. This in no way means that the rider can climb hills like a motorcycle. You do need all 3 pieces of the puzzle; torque, power, and speed (rpm). The picture is incomplete without all 3.

Right, but you all seem to be acknowledging that the rider is also part of this equation. On the one hand, a rider is never going to pedal at 1800rpm like a motorcycle (Also, to give you some idea of the difference, if we convert 25hp to watts, where 1hp is 750w, that's 18,750 watts. Way above any ebike that might conceivably be pedaled.).

On the other hand, a rider does input power and torque into the system. Cycling power meters even measure rider power in watts, so we can estimate that an average rider is putting around 100-400w into the system themselves. Manufacturers may bench test these motors, but they aren't closed systems. So a mid-drive motor with 500w peak power is actually going to put closer to 750w into the crank arms when we add in the rider's power. Right? Am I missing something here?

In addition to that, rider power varies wildly based on fitness, terrain, pedaling efficiency, the type of bike, the type of motor, etc. So the same rider going up the same hill on might struggle to hold 60 rpm on a road bike but do it easily on a mountain bike, due to the different gearing ratios.

From the graphs posted earlier, it's clear that manufacturers are tuning these motors for what they think are average rider cadences. It would be helpful if they published the peak power and torque numbers at a given rpm to at least give the rider an idea of the sweet spot of the motor. Going a step further, it would be even better if manufacturers developed ebike-specific gearing to account for this and allow riders to more easily hold the "best" rpm ranges in most riding conditions.

 

[Sierratim]

Right, but you all seem to be acknowledging that the rider is also part of this equation. On the one hand, a rider is never going to pedal at 1800rpm like a motorcycle (Also, to give you some idea of the difference, if we convert 25hp to watts, where 1hp is 750w, that's 18,750 watts. Way above any ebike that might conceivably be pedaled.).

On the other hand, a rider does input power and torque into the system. Cycling power meters even measure rider power in watts, so we can estimate that an average rider is putting around 100-400w into the system themselves. Manufacturers may bench test these motors, but they aren't closed systems. So a mid-drive motor with 500w peak power is actually going to put closer to 750w into the crank arms when we add in the rider's power. Right? Am I missing something here?

In addition to that, rider power varies wildly based on fitness, terrain, pedaling efficiency, the type of bike, the type of motor, etc. So the same rider going up the same hill on might struggle to hold 60 rpm on a road bike but do it easily on a mountain bike, due to the different gearing ratios.

From the graphs posted earlier, it's clear that manufacturers are tuning these motors for what they think are average rider cadences. It would be helpful if they published the peak power and torque numbers at a given rpm to at least give the rider an idea of the sweet spot of the motor. Going a step further, it would be even better if manufacturers developed ebike-specific gearing to account for this and allow riders to more easily hold the "best" rpm ranges in most riding conditions.

I agree. For a real world simulation of an ebike's performance the rider's contribution should be taken into account. The Grin Tech MOTOR SIMULATOR does account for rider power with a user defined input, among other real world variables (weight, wheel diameter, gearing, and drive train efficiency, among others) that this virtual dynamometer takes into account. Set the rider power to 0 for throttle/motor only, higher to match varying fitness levels. I've found this to be a very handy tool to go the next step beyond motor only data.

 

[Iridebikez]

I agree. For a real world simulation of an ebike's performance the rider's contribution should be taken into account. The Grin Tech MOTOR SIMULATOR does account for rider power with a user defined input, among other real world variables (weight, wheel diameter, gearing, and drive train efficiency, among others) that this virtual dynamometer takes into account. Set the rider power to 0 for throttle/motor only, higher to match varying fitness levels. I've found this to be a very handy tool to go the next step beyond motor only data.

I've checked that out, and I definitely appreciate Grin providing the information for reference. But it doesn't seem like a great resource for the average ebike buyer. None of the major manufacturer mid-drives in the charts posted above are available options and the options appear to be a little outdated. The instructions for entering a motor not on the list are: "Custom Motor: The ability to enter custom motors is a new feature for advanced users only (emphasis mine). Details are explained in the pop-up fields." I have no idea what most of the values in the pop-up fields are for my ebike motor (Yamaha PW-SE), nor where I would find that information.

It would be like if regulations limited all automotive manufacturers to "150hp nominal," so all manufacturers just advertised that number along with a max torque number (800 lb/ft!) and no other information. And, the only way to find out how your car might actually perform was to go online and enter several variables into a virtual dyno meant for custom engine builders. Most buyers wouldn't even know where to start other than to recognize that, for example, a full-size truck engine is probably going to be very different from a supercar engine.

Except in the current ebike market, most manufacturers want us to think they've got the ebike equivalent of a supercar engine.

 

[Sierratim]

Motor simulators, like Grin's, are definitely the next level for those wanting to gather as much info as possible. Not all motors are modeled by Grin, or any other simulator I've found, but with a bit of tweaking I've been able to model other motors as well. These aren't for everyone, but they do work for those wanting to do the homework.

I personally haven't found that most major ebike manufacturers are over promoting their bike capabilities beyond the usual 'we're the best' hype that every marketing campaign has. I've actually found it annoyingly difficult to get performance specs, to the extent that one major brand won't even publish weights! Most major brands seem to prefer test rides to tech specs perhaps to 1) avoid buyer spec confusion (high battery capacity = high speed?), and 2) avoid promising performance the bike can't deliver (i.e. "it'll climb anything!"). YRMV.

 

[Iridebikez]

Correct, the Grin Tech motor simultor does not model every available motor. There is a "Custom Motor" setting that in theory allows modeling of any motor, but the user does need to provide electrical characteristics that will be difficult to get, unless you have access to engineering specs or a lot of test equipment.

Not all motors are modeled by Grin, or any other simulator I've found, but with a bit of tweaking I've been able to model other motors as well. These aren't for everyone, but they do work for those wanting to do the homework.

I'm just confused. Where would I even start to do the homework to know what the values would be for this simulator to be useful to me? I'm an enthusiast coming to this as a lifelong cyclist. I'm not an engineer and I don't have access to "engineering specs or a lot of test equipment." And if I'm finding it confusing, it will be useless to people who come on this forum asking, "I'm looking at X and Y brand bikes, I live around lots of hills, which is better for me?" Sometimes those people should do more research, but the information should also be orders of magnitude more accessible to the average consumer.

I've actually found it annoyingly difficult to get performance specs, to the extent that one major brand won't even publish weights! Most major brands seem to prefer test rides to tech specs perhaps to 1) avoid buyer spec confusion (high battery capacity = high speed?), and 2) avoid promising performance the bike can't deliver (i.e. "it'll climb anything!"). YRMV.

Here I think we're on the same page. The information is so vague that any manufacturer can claim their motor performs like a supercar or a Tesla or some other useless comparison because they aren't providing an objective way to compare performance characteristics between competitors. So for example, earlier today someone posted they're expecting the Spinciti to be shipped this week, an indiegogo bike. Putting the other issues with crowdfunding aside, how is that bike marketed? Both "supercharged" and "scary fast high performance." How do they achieve such supercharged performance? A "500W Spinciti E-Motor." The 500W version is supposedly for "super hilly" riding. That's particularly cringe-worthy, but they aren't the only company to advertise like that.

I think part of the problem with the way things are now is that it opens the door to people relying solely on their subjective experiences to understand differences between options. That part is important, but it shouldn't be the only good way to understand your options. It's also a problem when almost all the options at lower price points are online-order-only, and therefore impossible to test ride.

 

[bluecat]

It's also a problem when almost all the options at lower price points are online-order-only, and therefore impossible to test ride.

You get what you deserve!

• Buy from your local dealer after excessive testrides - and you get the bike which fits.
• Buy from the internet a cheap extra super high performance and quality bike - and you will get...

 

[Iridebikez]

You get what you deserve!

• Buy from your local dealer after excessive testrides - and you get the bike which fits.
• Buy from the internet a cheap extra super high performance and quality bike - and you will get...

I don't agree with this sentiment. If ebikes are going to stay in the realm of hobbyists with thousands of dollars in disposable income, fine. However, I think they can (should) become a legitimate means of alternative transportation, particularly for individuals who otherwise may not be able to afford a reliable car. But before that can happen, consumers need to have better information available to inform themselves about their options (at all price points).

 

[bluecat]

The lineup form Stromer goes from ST1 to ST2 over ST3 up to ST5. The variety of these models is much more than only motor output. Each has its own geometry - and for the most of them are different options for the seating position available. This is something you have to test before you buy.

 

[Johnny]

The lineup form Stromer goes from ST1 to ST2 over ST3 up to ST5. The variety of these models is much more than only motor output. Each has its own geometry - and for the most of them are different options for the seating position available. This is something you have to test before you buy.

Adjust-ability is important and can be achieved without much effort. You can not have your top of the line model less adjustable than a lesser model, that is a design flaw. These models you mention are all non suspension bikes designed for smooth paths it is not like one is a mtb and the other is a drop bar roadbike.