Never too much torque

[Sierratim]

This thread was linked as a reference in a recent post at https://electricbikereview.com/forums/threads/50nm-mid-drive-vs-50nm-hub-drive.34726/ . I wanted to bring this up as the interrelationship between motor power, rotational speed and torque is discussed in more detail in the new thread that some here may be interested in. See page 2 for this discussion.

 

[Sierratim]

Okay so to make it clear.. do some ebikes produce more torque than cars?

If you're asking me, my answer is simply "I don't know". I do know that power, speed and torque are all interrelated and need to all be considered in any discussion of motor performance. To discuss one without the others can easily lead to misunderstanding a motor's capabilities. Simple as that.

 

[Ebiker33]

Why is it then that 48V Ebike with 75nm of torque can't climb a hill but a different Ebike with a 48V with a 120nm of torque can climb that same hill ?

Battery Watt output is a variable of coarse, however I would like to see what a unlocked 75nm Bosch motor could do with a 52V battery and 30 amp controller it might surprise people.
It could be manufactures are intentionally throttling their numbers to get into larger more restrictive markets. Somebody did a test on one of these low nm/watt motors and it was like triple it's rating, so stupid.
These countries need to scrap their low restriction on watts, just govern speed and that's it. So what if I want cilmb 35% grade at 10mph it's not an issue.

 

[Ken M]

E-bike torque is measured at the rear wheel. I say that because having the advantage of the bike's gear set is the ONLY way they're going to see some of the torque values advertised with the mid drives.....

I think mid drive manufacturers are reporting stall torque at the crank. When you are in a lower gear that torque may actually be increased slightly due to gear ratio but at higher speeds the torque a lot of the torque is lost due to mechanical inefficiency (if that is the right word). When on a 44T front and 11T rear only 25 of the torque from motor is reaching the rear wheel.

Most motorcycles report the torque at the motor axle as well but gearing is almost always from a smaller front chain ring to a larger rear so that torque is amplified...significantly in some cases and in lower motor gears.

Would be interesting to see ebike motors put to full dyno testing for comparison as the static max torque may not always be that great of indication of real world performance (for the most part though it's good enough).

 

[Ebiker33]

Why is it then a 60 lb ebike with 75nm of torque can't climb a hill but a 400 lb motorcycle with 40nm can climb a hill at 100mph?

Power output in terms of wattage and HP if 750W of power go to a motor that is 1HP

One the very strongest motors with the controller to allow it will be the Archon X1 by Watt Wagons it peaks at 3000 watts that is still only 4hp pushing that 160nm

A motorcycle can have 50 -100hp pushing it's much smaller nm rating.

But again their is another variable, the amp controller some have changed theirs from 15 to 35 and said it makes a world of difference, and it would with a 48V battery you would be jumping from 720 watts to 1680 watts that's like a 1.25hp gain, of coarse that would also pull your distance run time way down and companies want to market a long run time, so they do it for 2 reasons the laws and advertised distance run time.
And you will most likely shorten the life span of the motor, especially pushing that in hot weather, now if you were running that on a fat bike in the winter in sub zero temperatures you have built in cooling going on.
Even then the components might not have been designed to take that level of stress.

 

[Sierratim]

Why is it then a 60 lb ebike with 75nm of torque can't climb a hill but a 400 lb motorcycle with 40nm can climb a hill at 100mph?

It doesn't seem like you really read my detailed post here, https://electricbikereview.com/foru...ve-vs-50nm-hub-drive.34726/page-2#post-294466 . It's the interrelationship between speed (rpm), power, and torque that defines a motor's performance. In the detailed example I went through I did show how an emotorcyle with nearly equivelent torque to an ebike will out perform the ebike despite a weight disadvatage.

 

[Sierratim]

I think mid drive manufacturers are reporting stall torque at the crank. When you are in a lower gear that torque may actually be increased slightly due to gear ratio but at higher speeds the torque a lot of the torque is lost due to mechanical inefficiency (if that is the right word). When on a 44T front and 11T rear only 25 of the torque from motor is reaching the rear wheel.

Most motorcycles report the torque at the motor axle as well but gearing is almost always from a smaller front chain ring to a larger rear so that torque is amplified...significantly in some cases and in lower motor gears.

Would be interesting to see ebike motors put to full dyno testing for comparison as the static max torque may not always be that great of indication of real world performance (for the most part though it's good enough).

Specialized actually published test data on several mid-dive motors a few years ago. Some of the resulting performance graphics have been posted on several threads in this forum including here, https://electricbikereview.com/foru...ve-vs-50nm-hub-drive.34726/page-2#post-294466 . They reported motor data, and like emotorcycle data, you need to account for gearing to get wheel torque. I covered this in some detail in my post in the thread I've linked above. In my example, the ebike only delivered max torque when in its lowest gear pair. The emotorcycle delivered 5 times its motor torque due to gearing. It had an added advantage with a smaller rear wheel than the ebike. The result being 90Nm max wheel torque for the ebike and nearly 600Nm wheel for the emotorcycle, without even discussing the difference in peak motor power (0.55KW vs 20kW).

Some of the motor test fata published ~2 years ago.

 

[Sierratim]

Power output in terms of wattage and HP if 750W of power go to a motor that is 1HP

One the very strongest motors with the controller to allow it will be the Archon X1 by Watt Wagons it peaks at 3000 watts that is still only 4hp pushing that 160nm

A motorcycle can have 50 -100hp pushing it's much smaller nm rating.

But again their is another variable, the amp controller some have changed theirs from 15 to 35 and said it makes a world of difference, and it would with a 48V battery you would be jumping from 720 watts to 1680 watts that's like a 1.25hp gain, of coarse that would also pull your distance run time way down and companies want to market a long run time, so they do it for 2 reasons the laws and advertised distance run time.
And you will most likely shorten the life span of the motor, especially pushing that in hot weather, now if you were running that on a fat bike in the winter in sub zero temperatures you have built in cooling going on.
Even then the components might not have been designed to take that level of stress.

Absolutely, you have to include power, speed (rpm), and torque to define a motor's performance. Torque alone isn't enough data...

 

[AleksR]

When I was in my 20s, before there were cellphones, computers and electric bike, the mantra for my generation was “ You can never have enough horsepower.” Fast forward 54 years and the mantra for the ebike generation is” You can never have enough torque.” When I was in my 20s my cars had far more horsepower than I ever could use safely and used more gas than I could afford. What I want to buy a new electric bike I tried hard got to get a bike with more torque than I actually needed and that wouldn’t run my battery down before I completed my ride. I know there are exceptions to my thinking. Back in my day a lot of horsepower was very important to a drag racer and today a lot of torque is very important to a mountain bike or down hill rider. But what about the rest of us? My best guesstimate is that 30 Newton meters of torque for people who do most of their riding on flat terrain and 50 Newton meters of torque for the rest of ebike riders. What do you think? Ed

When I was younger, I played soccer and I worried about soccer balls. It was tough in Eastern Europe 30 years ago........

 

[TomW]

Torque is a static measurement, with no time involved, and is used in the definition of power. Power takes into consideration the duration or amount of time involved to perform the operation.

So torque by itself can have no meaning, but when inserted into the formula for power, then it becomes useful.

You can have gargantuan amounts of torque, but if there is no power you will be disappointed.

Exactly high torque without many revolutions/cadence per minute gives low power output.
You need to convert Newton Meter's into Pound Feet. 1 nm = 0.74 ft lbs
Then it is a simple equation
HP = torque x rpm divided by 5252

for example with rough numbers.
A motor bike engine may only have 60nm of torque but it spins at 10000 revs.
60 nm = 44.2537 ft lbs
44.2537 x 10000 = 442537
442537 divided by 5252 = 84.26066260472201
round that to the closest whole number and that = 84 hp

My Ebike motor has 160nm of torque and I pedal at max 100 rpm.
160 nm = 118.00994383999999 ft lbs
118.00994383999999 x 100 = 11800.99438399etc
11800.99438399etc divided by 5252 = 2.2 rounded down.
So that is 2.2hp.

If I convert that into wattage that that equates to 1640.54 watts but the peak torque on the motor is at about 90rpm so this would fit nicely with the what power my motor claims to provide at peak.

Edit
Both of these conversions show the power from the crank on the ebike or spindle on the motorbike engine, so also you need to account for the lower gearing the motorbike has going to the rear wheel which would lower its revs but increase its torque,
So the Motorbike is producing a lot more than 60 nm at the wheel.
The gearing on a Ebike does the opposite it converts torque into revs except in the lower gears depending on your ratios.
Hope I have not confused things more lol.

 

[Ebiker33]

So basically there is a massive step down to what is supplied to the potential NM, supplied via wattage/HP/RPM and it seems rpms is a very big variable.

 

[TomW]

yes rpm is the biggest variable,

edit,
when comparing a ebike to a motorbike.

 

[Sierratim]

Torque, speed(rpm), and power are interrelated variables;

Power = Torque x Speed

 

[Ebiker33]

yes rpm is the biggest variable,

Those belts must be just flying at 1000 rpm on a motorbike

 

[TomW]

Those belts must be just flying at 1000 rpm on motorbike

Maybe,
I'm all maths out and i'm not doing more because my head will start hurting but I am pretty sure the torque and rpm on a motorbike is recorded before going through the gear box. so at the belts drive pulley it will already be at a lower rev's and higher torque. Not sure what average ratios are in a motorbike gear box but it will be geared down with a final drive ratio, (and it introduces 6+ more variables) the selectable gears.
Then the ratio is reduced further from pulley to pulley then there is the size of the wheel which will actually increase the ratio a little, there are so many variables.

 

[Sierratim]

Maybe,
I'm all maths out and i'm not doing more because my head will start hurting but I am pretty sure the torque and rpm on a motorbike is recorded before going through the gear box. so at the belts drive pulley it will already be at a lower rev's and higher torque. Not sure what average ratios are in a motorbike gear box but it will be geared down with a final drive ratio, (and it introduces 6+ more variables) the selectable gears.
Then the ratio is reduced further from pulley to pulley then there is the size of the wheel which will actually increase the ratio a little, there are so many variables.

Could calc wheel rpm from the tire outer diameter and the cycle's top rated speed...I think I'll go for a bike ride instead...

 

[TomW]

Yes you could but I think going for a bike ride is a better idea
I concidered working it out but the estimates I did in my head will do,