Torque claims.

[JohnCade]

How do the manufactures measure claimed torque? Is it at the crank or at the wheel? If it's at the wheel then it would be dependent on gearing so how would that work? Bosch claims 60 Nm I think while the Impulse 11 claims 70 Nm which is nearly double the 40 Nm for the first Impulse. I don't know if that 40 NM was prior to the Impulse 1 2013 Sport software update which upped climbing ability, and so I assume torque substantially? Or in fact if any of these figures mean a thing.

70 Nm is about 50 ft/lb so more than an original 850 Mini which stated 44 ft/Ib at about half of max revs. How can that be?

Are we in something like the old horsepower wars? Then Jaguar for instance following industry practice claimed 265 bhp for the E type at the crank, by running a bare motor on the bench without ancillaries and manually adjusting the ignition and carburetion all the way through the rev range. The truth was that it would have been pushed to get 160 bhp at the wheels.

So how do they measure torque on e bikes and how true are the claims?

 

[trex]

torque figures given by manufacturers are difficult to use, especially for crank motors because as you said, the resulting torque at the wheel is modified by the gear ratio. Torque x rotational speed = power output.
Manufacturers don't always publish the maximum power output of their motors which is a shame because that would make comparison a lot easier.
For crank drives, torque is measured at the cranks. 40NM, 60NM,80NM etc are meaningless without their angular rotational speed - some quote their torque figure at 60 RPM, some at 70 RPM, some at 75 RPM. woosh quote 35NM @ 75 rpm, 70NM max for their CD motor, 45NM @75 rpm, 85NM max for the Krieger.

 

[JohnCade]

Thanks trex. So Bosch and Kalkhoff have more torque at the crank than a 1959 Mini? You could get four people up a steep hill in one of those in first gear. I wonder if I got three circus acrobats to balance on my bike if I could get us all up the same hill? The Mini had a lot of metal in it to shift too.

Of course you would be using a lot more power in the Mini and using maybe a few more revs than the max torque revs

 

[trex]

the Mini's figure is given at about 4,000 RPM - the Bosch figure is given at much lower RPM, about 35 RPM. The Mini outputs 70 times more power than the Bosch.

 

[flecc]

Some use the best possible figure, truthful but not helpful for comparison. For example Tonaro making crank drives have claimed 120 Nm, but that's at the rear wheel measured using the lowest gear available.

Hub motor makers don't have that much flexibility. Their torque starts by being at the maximum at zero revs and then declining as revs rise. Thats the opposite of the power which rises from zero as revs rise. The torque only becomes useful at the optimum climb speed point where the decline in torque coincides with sufficient rising power, which is usually around half the maximum assist speed. The steepest climbable hill is at that speed point. Trying to climb steeper at a lower speed to use the higher torque then will fail due to the lack of power at that lower speed.

If quoting only one unqualified figure, ideally the hub motor maker should claim only the torque at the optimum climb point, they usually do.

i.c. engines and electric motors cannot be directly compared, their torque and power behaviours are somewhat different.
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[JohnCade]

the Mini's figure is given at about 4,000 RPM - the Bosch figure is given at much lower RPM, about 35 RPM. The Mini outputs 70 times more power than the Bosch.

Yes I amended my post to take account of that before you replied. The Mini is about 3000 revs for max torque, and that's about the revs you'd be using on a steep hill in first gear. So torque would be coming into play as much as maximum power which would be at almost twice those revs.

 

[JohnCade]

Some use the best possible figure, truthful but not helpful for comparison. For example Tonaro making crank drives have claimed 120 Nm, but that's at the rear wheel measured using the lowest gear available.

Hub motor makers don't have that much flexibility. Their torque starts by being at the maximum at zero revs and then declining as revs rise. Thats the opposite of the power which rises from zero as revs rise. The torque only becomes useful at the optimum climb speed point where the decline in torque coincides with sufficient rising power, which is usually around half the maximum assist speed. The steepest climbable hill is at that speed point. Trying to climb steeper at a lower speed to use the higher torque then will fail due to the lack of power at that lower speed.

If quoting only one unqualified figure, ideally the hub motor maker should claim only the torque at the optimum climb point, they usually do.

i.c. engines and electric motors cannot be directly compared, their torque and power behaviours are somewhat different.
.

Yes. I've heard this idea of maximum torque being at zero revs before. But in practise it's really as meaningless as Schrodinger's cat. So what sort of torque and power is a Bosch or Kalkhoff outputting at the crossover point where torque has diminished and power risen?

 

[flecc]

Judging from real world ability, I think those makers quote the optimum crossover figure at the unit's output shaft, i.e. the crank, so an honest figure. From that we can derive the actual torque at the rear wheel in each gear available. As Trex says though, not publishing a maximum power figure means we are still short of useful data.

However, if we know or measure the maximum amperage delivered and assume around 75% efficiency, that gives a good enough idea of the maximum useful power in Watts, certainly good enough for comparison.
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[JohnCade]

torque figures given by manufacturers are difficult to use, especially for crank motors because as you said, the resulting torque at the wheel is modified by the gear ratio. Torque x rotational speed = power output.
Manufacturers don't always publish the maximum power output of their motors which is a shame because that would make comparison a lot easier.
For crank drives, torque is measured at the cranks. 40NM, 60NM,80NM etc are meaningless without their angular rotational speed - some quote their torque figure at 60 RPM, some at 70 RPM, some at 75 RPM. woosh quote 35NM @ 75 rpm, 70NM max for their CD motor, 45NM @75 rpm, 85NM max for the Krieger.

I just noticed that you had edited your post with some useful info. The max that Woosh quote would be the theoretical max at zero revs I assume? So if that is correct then the others are probably doing the same. Therefore the scepticism in my OP was justified and these figures really don't mean anything.

So if I guessed that an Impulse claiming 70 Nm was really giving 35 Nm at 70 revs would I be far wrong?

 

[flecc]

So if I guessed that an Impulse claiming 70 Nm was really giving 35 Nm at 70 revs would I be far wrong?

The way i read it Trex said the Woosh maximum was 70Nm but 45Nm at 70rpm for the CD motor. We could probably assume something similar for the Impulse, I think 35Nm would be much too low for those units, judging by ability.
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[JohnCade]

The way i read it Trex said the Woosh maximum was 70Nm but 45Nm at 70rpm for the CD motor. We could probably assume something similar for the Impulse, I think 35Nm would be much too low for those units, judging by ability.
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I was thinking of the standard CD which I think he said was 35Nm at 75 revs. The higher figure was for the new Krieger which is a higher powered CD motor I think, and that's 85Nm max 45Nm at 75 revs.

Judging from my experience of the Woosh CD Sport I think the Kalkhoff Impulse 1 has more torque with the same gearing but not vastly more. So I reckon it probably has about 40 Nm at around 70 revs; and coincidentally 40 Nm is what they claimed for its torque when it was current. But now they claim 70 Nm for the Impulse 11. A big step up.

So being an old cynic I wonder if it really is almost twice as torquey as the old one? Or if they just changed the way they were stating it to outdo the Bosch, and at 70 rpm it's still putting out around 40/45 Nm and so is the Bosch.

 

[flecc]

Could well be John, once they stray from the factual it's all guesswork. Although it might seem likely that they have similar actual torque, now the Impulse has it's transmission protection measure it could well be that they've stepped up it's torque and power to gain a market advantage.

Bosch have already had to reduce those on some models due to transmission problems on the first models, perhaps giving this opening to the Impulse designers.
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[JohnCade]

Could well be John, once they stray from the factual it's all guesswork. Although it might seem likely that they have similar actual torque, now the Impulse has it's transmission protection measure it could well be that they've stepped up it's torque and power to gain a market advantage.

Bosch have already had to reduce those on some models due to transmission problems on the first models, perhaps giving this opening to the Impulse designers.
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That could well be true too and I expect it does have more of both. How much more is the question.

I've got to go to 50 Cycles in Bristol this week to exchange my battery and I hope to ride one of the Impulse 11s then. So I'll see if it really does have nearly twice the grunt.

 

[JohnCade]

I tried the Pro Connect 9 Impulse 11 at Bristol the other day when I had to go there to pick up an exchange battery. I have an early 2013 built Impulse 1 with the mid 2013 Sport profile software upgrade, and that gives it more power than the first Impulse. But this was significantly more powerful again, and it got me up some steepish hills faster than my bike on similar hills around here. It doesn't have twice as much grunt as mine though. So that 70 Nm is a bit theoretical I think.

I wanted to go up St Michael's Hill, which is close to where I was and is about as steep as many of the hills where I live, but it was semi blocked with building work and nose to tail traffic. So I didn't get to go up a really steep hill.

The new motor interrupt function seems to work well and I changed up and down the Deore mech without having to think about easing off. The Shimano disks were good, and better than the Magura hydraulic rim brakes I have, and the only thing that let the bike down apart from the colour were the fairly low end Suntour forks. So I don't think I'll be buying one. But the Pro Connect 10 has a better spec and one of those might tempt me if they knock a bit off in the sales....