Torque Figures for comparison

[Leccy]

Does anyone know the torque figures for the most common ebikes? E.g. The Woosh Big Bear.

I've had a look on the sites that advertise the bikes and they're not immediately obvious (if listed at all).

I would have thought this was a reasonably important factor when choosing a bike.


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[Deleted member 4366]

Torque figures are absolutely meaningless. The only way you can compare is by trying them. The maximum torque the Bafang Bpm motor in the Big Bear can make at the maximum 20A from the controller is 65Nm. That happens at zero RPM, which is why it's meaningless.

 

[Leccy]

Thanks for the reply d8veh.

I see what your saying but I do see people posting saying this bike has better torque than another.

Is there no measurement that can be used to compare one bike to another in this category?

Eg with watts different bikes have different peak wattages but these are normally displayed. I'm guessing this is a more useful comparison.

I know some manufacturers display the torque but others don't and just say high torque.

It's a shame if there isn't a metric consumers can use that is somewhat useful when comparing bikes for torque.


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[Cyclezee]

Hi Leccy,

You might find this useful http://www.ebikes.ca/tools/simulator.html

 

[trex]

there is no easy way to compare torque figures between motors, especially if they are of different types, eg direct drive against internally geared against crank drive. This is because you have to take into account the RPM and efficiency of that particular measurement. As d8veh pointed out, maximum torque is at 0 RPM, not much good for any practical purpose. However, motor manufacturers try to be helpful most of the time, they do give some usable test results so you can still work out whether their motor will suit your purpose.

Example:

http://www.crystalyte.com/h35 series.htm

This is a very popular type of motors, but do you understand the torque figures of the test reports between different models? If you are not sure, I recommend you ask for the controller Amp rating instead.

 

[Izzyekerslike]

Hi Leccy,

You might find this useful http://www.ebikes.ca/tools/simulator.html

Well...who'd have thought it would be so simple.

 

[Deleted member 4366]

It's easy for hub-motors. That simulator is very good for getting a rough idea. You can see the torque at different speeds and what sort of hill it'll climb, which is the important bit.

When it comes crank and chain drives, the torque depends on the gearing, so you can't put a figure on it. A bike with a 36T bottom gear will get 20% more torque at the back wheel than one with a 30T one using the same motor.

If you take a motor like the Bafang BPM in the Big Bear and run it at 64v and 30A, it'll make enough torque to get you up any hill without pedalling pretty quickly. You can say that torque is more or less directly proportional to both voltage and current, so the Big Bear running at 20A will make 33% more torque than the same motor at 15A, or you change from 36v 20A to 48v and get another 33% more torque. That's why the KTM Panasonic has such good torque. It runs at 48v, which gives it an immediate 33% advantage over an equivalent 36v bike.

In summary, torque only has meaning if you qualify it by stating all the external conditions at the same time.

 

[paul20v]

It's easy for hub-motors. That simulator is very good for getting a rough idea. You can see the torque at different speeds and what sort of hill it'll climb, which is the important bit.

When it comes crank and chain drives, the torque depends on the gearing, so you can't put a figure on it. A bike with a 36T bottom gear will get 20% more torque at the back wheel than one with a 30T one using the same motor.

If you take a motor like the Bafang BPM in the Big Bear and run it at 64v and 30A, it'll make enough torque to get you up any hill without pedalling pretty quickly. You can say that torque is more or less directly proportional to both voltage and current, so the Big Bear running at 20A will make 33% more torque than the same motor at 15A, or you change from 36v 20A to 48v and get another 33% more torque. That's why the KTM Panasonic has such good torque. It runs at 48v, which gives it an immediate 33% advantage over an equivalent 36v bike.

In summary, torque only has meaning if you qualify it by stating all the external conditions at the same time.

I agree too a point
But you can't bring gearing into torque figures
The motor supplies a torque figure no matter what the gearing is
The gearing only makes the torque more usefull at different speeds just like a car engine
The torque figure of an engine doesn't alter because different gear is selected just the way the torque is delivered to the road wheels
In summary I think what your saying is that it doesn't matter what torque is produced by the motor as long as your in the right gear

 

[flecc]

I agree too a point
But you can't bring gearing into torque figures
The motor supplies a torque figure no matter what the gearing is
The gearing only makes the torque more usefull at different speeds just like a car engine
The torque figure of an engine doesn't alter because different gear is selected just the way the torque is delivered to the road wheels
In summary I think what your saying is that it doesn't matter what torque is produced by the motor as long as your in the right gear

And the added complication is that motors of CD units and geared hub motors have reduction gearing before their output.
.

 

[paul20v]

And the added complication is that motors of CD units and geared hub motors have reduction gearing before their output.
.

Agree totally
But it doesn't effect the initial torque reading of the motor
Only the way in which the power is delivered and feels too the end user
Back too the car and only because most people can relate too one
You can have 2 engines with exactly the same torque output but one with a lower ratio final drive than the other
so obviously one will be quicker off the mark and initially feel more powerful but they both produce exactly the same power engine wise
So all thou motor torque figures could be accurately given it doesn't mean the most powerful one will in the real world feel quicker too speed or climb better

On that note I'm going because I do go on sometimes

 

[Deleted member 4366]

To use the motor's torque would be even more useless apart from direct drive ones. Crank-drive motors have big reduction ratios, so how are you going to compare a Bosch motor's torque of say 1Nm with a friction drive of 0.5Nm, a geared hub motor of 6Nm and a big DD motor's 30Nm?

The next point is that torque is different at different RPM. Which RPM will you use?

 

[paul20v]

The next point is that torque is different at different RPM. Which RPM will you use?

To be fair as with anything you would use peak torque as a reading at whatever given rpm .

 

[Deleted member 4366]

To be fair as with anything you would use peak torque as a reading at whatever given rpm .

Peak torque comes at zero RPM! That's the point at which both your motor and controller start smoking.

 

[paul20v]

Peak torque comes at zero RPM! That's the point at which both your motor and controller start smoking.

Bikes don't go very well at 0 rpm thou lol