Torque v cadence - which has more efficient battery usage (my wife's battery ran out, mine did not...)?

[Lumo]

We went on a trip on our ebikes last weekend. My wife has what I believe is a cadence sensor (Fischer ebike) and I have a torque sensor (Bosh ALP). Her battery is 422wh whereas mine is 500wh. She was in power assist mode 1 the whole time and I used eco (level 1) for most of it, with periods of tour (level 2) and sport (level 3) every now and then. The route was mostly flat with some inclines here and there. About 60km into the round trip, her battery was flat, leaving her to pedal the 15km home whereas my battery still had three bars left when hers ran out, and still had three bars left when we got home (my bike is far too big for her, so there was not the option of swapping bikes for some of this pedal-only time).

I know my battery has a larger capacity, but that alone doesn't seem to be enough to explain why her range was so much less than mine. So I am wondering if it's the cadence v torque sensor - the whole time she was pedaling the motor was running, whereas with mine if I was pedaling lightly, presumably the motor was running less than when I was pedaling more heavily (even in eco mode). Given that the route had some quite flat stretches in it, for a good few km I was cruising along without too much force on the pedals.

Are there any other differences which would explain the shorter range? Her bike is lighter than mine and she is lighter than me. I did not try to take my battery down to empty, so I don't know how long those last three bars would really have lasted.

 

[Woosh]

torque sensor beats cadence sensor on battery economy in most cases.
You are forced to pedal harder with torque sensor.

 

[vfr400]

The type of sensor doesn't make one iota of difference to the efficiency of the motor. The control system regulates how much power it feeds to the motor. The more power it feeds to the motor, the less hard you need to pedal. There is approximately 30% efficiency loss in converting the battery energy into motive power. From tests I've done, that efficiency is very similar across different types of motor.

Physics is simple. You need a certain amount of power to maintain a certain speed under certain conditions. The conditions are mass, incline, wind resistance and rolling resistance. On an electric bike, that power comes as a combination of power from the rider and the motor, and the effect of gravity on your mass when going downhill.

Torque sensor wins because you pedal harder. The harder you pedal, the further you can go. It's very simple. There's no magic.

 

[Lumo]

Well I never implied there was magic and I also never mentioned motor efficiency. I wasn't thinking that narrow.

I was meaning on a long route where both systems are in the lowest assist mode and neither person is pedaling with all that much force, the cadence sensor based system seems markedly less efficient (meaning km per wh, not transfer of electrical energy to kinetic) as it has a minimum amount it drives the motor and does not go lower. Yes, presumably this makes the rider pedal with even less force to maintain the same speed, but when both riders considering their pedaling to be 'light' and really would not notice a small increae or decrece in the force with which they had to pedal, the torque sensor based syetem will get them further for the same amount of battery power.

 

[vfr400]

the cadence sensor based system seems markedly less efficient (meaning km per wh)

the torque sensor based syetem will get them further for the same amount of battery power.

Only if they pedal harder.

Of course if your wife had switched her power off at the start, her battery wouldn't have gone flat at all and you would have been saying that the cadence sensor bike is more efficient and would have a longer range.

 

[wheeliepete]

It could be that your wife's bike uses speed control in which case it would run at full power more of the time even when being ridden in low PAS level. It would depend on the speed she was travelling at.

 

[Lumo]

Only if they pedal harder..

Yes well of course...BUT the perceived pedaling was light and there was no way of making it lighter without shutting the motor off competently, not having more control of the power at this end of the scale seemed to result in the motor ending up working more than it needed (and yes the user thereofre pedaling slightly less) and therefore draining more battery than it needed to.

It could be that your wife's bike uses speed control in which case it would run at full power more of the time even when being ridden in low PAS level. It would depend on the speed she was travelling at.

That's something I had not thought of, I don't think it does, but will certainly check and see.

 

[sjpt]

I agree.

Speed control would probably be even less efficient; unless set to a speed lower than she was riding at in which case she would have had to do all the work. eg it would suffer the lack of control at the low end even more than the cadence current control.

 

[Edward Elizabeth]

Torque sensor is more economical in most scenarios - it provides power in proportion(ish) with the effort the rider themselves inputs, instead of simply providing power because the chainset is turning. The maths are quite simple.

 

[Stanebike]

If you look at Wisper bikes they have the same bikes with a choice of either cadence or toque drive and suggest that toque gives up to 30% more distance.

Wisper 705 26” Step-Through eBike | Wisper Bikes

The Wisper 705 Step-Through Electric Bike is the perfect eBike for touring. Comfortable, reliable and packed with great features! Shop Now

wisperbikes.com

Of course as has been suggested the extra distance with toque drive is down to that system requiring the rider to put in more effort, even if it feels like you were both taking it easy.

I have a torque drive bike (not a Wisper), my sister a cadence bike. Riding my bike compared to her bike I find myself working harder for the same speed on the same terrain but the exercise and extra range are worth it.

 

[it is i footpump]

i have ktm macina bosch moter 50nm active line 400w battery at 71 i use sport mode a lot , tour on the flat and otten do around 25-30 miles with some hills normally nice sunny days not much wind . and 2 bars left on display.

i also have a kudos ebike 10ah battery, with low/medium/high settings. speed/cadence sensor, max range in medium 25-30 miles.

on local hills the kudos is much easier on my legs, i can peddle slow or faster and get full power in a particular mode.

the ts bosch gives much better range but you have to input a faoir amount of effort.

my m8 has orbea ebike shimano moter etc but uses eco all the time so gets more range than myself both have 400w batteries.

it also might be that the bosch 500w batter y has better cells than the fischer bike battery as the 500w bosch is over £700

 

[Nealh]

One can't really just compare TS drive to cadence drive and say A will have better range then B, because if B uses current control the range will be as much as 50% + or more then a cadence sensor bike that uses a speed controller.

 

[Lumo]

Interesting comments, thanks.

She now wants a second battery.

We are going to try a trip with quite a few hills soon, I wonder how our ranges will compare there, and whether I will end up with a tougher ride than she has.

 

[Amoto65]

We are going to try a trip with quite a few hills soon, I wonder how our ranges will compare there, and whether I will end up with a tougher ride than she has.

The ALP engine will be much better up the hills and use less battery, I have used both the ALP and a Wisper 905 around the Peak District and while the Wisper is excellent the ALP is better up steep hills power and battery wise.

 

[Nosweat]

I have a torque sensor front hub set up. I know in theory that should be less efficient than a torque sensor crank motor. However, on flat level ground I tend to cruise at around 18mph so just over the cut off (with good aerodynamics as I have drop bars). That means my motor is in use accelerating me from standstill or taking me up the occasional hill but cuts out just as I reach cruising speed after which I'm on my own. So I find I get very good range on my commute (which is mostly canal towpath) and that's at a comfortable cruising speed which I don't get hot and sweaty as I'm going fast enough to have a nice breeze.

Slow down and my range worsens!

 

[Woosh]

Slow down and my range worsens!

you found your own sweet spot where man and machine work in harmony.
I am surprised that TS kits don't sell as well as cadence kits but that's how it is.

 

[Lumo]

Well we did the route with hills, 20km roundtrip, 7km or so up, so 7 down and the rest mostly flat. Not sure how to quantify the hills, on the map they are 8-18% with shorter parts of 20+%. Another way of describing them is that I would not have managed them on my non-ebike without it being long and very hard. I found the best gears to be slightly different to what I would have done with pedal alone (seemed to work better 1-2 lower than I would have normally used), but I managed the hills, yes, it was a bit of a workout compared to the flat, but I got up fine. My wife did also. The most noticable thing was when I stopped pedaling to check the directions, the bike just stopped dead on the hill - it really felt as if someone had slammed both breaks on, because of the relative ease of pedalling I had expected there to be some momentum to carry me on a little as it would on a flat terrain, and this really showed me how much the motor was helping.

With regards to finding the sweet spot - I fear my wife and I have different ones and there will always be one of us working outside of this range. I tend to go faster in a higher gear with little adjustment to speed once I am comfortable. Her comfortable speed is quite a bit slower and varies a lot depending on the surroundings.

 

[vfr400]

Well we did the route with hills, 20km roundtrip, 7km or so up, so 7 down and the rest mostly flat. Not sure how to quantify the hills, on the map they are 8-18% with shorter parts of 20+%. Another way of describing them is that I would not have managed them on my non-ebike without it being long and very hard. I found the best gears to be slightly different to what I would have done with pedal alone (seemed to work better 1-2 lower than I would have normally used), but I managed the hills, yes, it was a bit of a workout compared to the flat, but I got up fine. My wife did also. The most noticable thing was when I stopped pedaling to check the directions, the bike just stopped dead on the hill - it really felt as if someone had slammed both breaks on, because of the relative ease of pedalling I had expected there to be some momentum to carry me on a little as it would on a flat terrain, and this really showed me how much the motor was helping.

With regards to finding the sweet spot - I fear my wife and I have different ones and there will always be one of us working outside of this range. I tend to go faster in a higher gear with little adjustment to speed once I am comfortable. Her comfortable speed is quite a bit slower and varies a lot depending on the surroundings.

So, on the hilly ride, your bike emptied the battery quicker than hers?

 

[Lumo]

So, on the hilly ride, your bike emptied the battery quicker than hers?

No, hers still went down quicker. Here it was harder to do a fair comparison as we both played around with the power levels a lot and I generally also went faster and waited at rest points etc, but her battery was lower than mine by the time we got home.

 

[Nosweat]

you found your own sweet spot where man and machine work in harmony.
I am surprised that TS kits don't sell as well as cadence kits but that's how it is.

And continuing that theme, on the strength of my conversion my wife is now looking at getting herself an ebike. I can't tell from the Woosh website which models have torque sensors and which have cadence sensors - or whether you can swap them round to whatever the customer wants. Can you advise?