Most powerful eBike for long uphill journeys?

[Zlatan]

zlatan,
if you weigh 100kgs and your bike 20kgs, you ride up a hill for 9 miles, gaining 3000ft (900m) elevation, here is the required potential energy:
E = mgh = (100+20) * 9.98 * 900 / 3600 WH = 300WH
Adding to this, your bike needs some 12WH * 9 = 108WH for the roads.
Total: 408WH
It will depend on your selected assist level, if you use climb mode, you put in 25%, the bike 75%. The motor on the bike will run at around 80% efficiency, your battery consumption will be:
= 408WH * 0.75/0.8 = 382WH
Your battery is pretty much drained by the time you get to the top.
If you use a lower assist on some of the route then you saved some battery.

That's spot on Woosh..I had about 5% too get back down..Was on fire tracks in Spain...
So where does that put us with the 750 watts Dve8 speaks of... Looked to me as tho power bars were on full nearly all time..( going up)
Its a ride I could not dream of completing without e help...
Saying bike can consume ( or produce) 750 w is very misleading when its steady state max must be well below that figure. Perhaps I,ll let David Millar ride my bike next time, suspect it would need a rider of his capability to extract anything like 750 w. ( btw he lead ride on unassisted, well I sort of tagged on behind, he,s a friend of a friend who I was riding with)

 

[Deleted member 4366]

That's spot on Woosh..I had about 5% too get back down..Was on fire tracks in Spain...
So where does that put us with the 750 watts Dve8 speaks of... Looked to me as tho power bars were on full nearly all time..( going up)
Its a ride I could not dream of completing without e help...
Saying bike can consume ( or produce) 750 w is very misleading when its steady state max must be well below that figure. Perhaps I,ll let David Millar ride my bike next time, suspect it would need a rider of his capability to extract anything like 750 w. ( btw he lead ride on unassisted, well I sort of tagged on behind, he,s a friend of a friend who I was riding with)

The reason your bike can last 2 hours is that you're not using the motor's maximum consumption all the time. You only get maximum consumption (maximum torque) when your cadence is low and your pedal pressure is high. Here's a video that shows a wattmeter in real-time on a Haibike with a Yamaha motor, while the guy goes out for a hilly ride. It only reaches the very high consumption a couple of times when he's struggling on a steep hill or in too high a gear for the conditions. Even then, his cadence isn't low enough to get the maximum.

just in case you don't know, the tuning dongle doesn't affect the power in any way.It only releases the speed limit.

 

[Zlatan]

The reason your bike can last 2 hours is that you're not using the motor's maximum consumption all the time. You only get maximum consumption (maximum torque) when your cadence is low and your pedal pressure is high. Here's a video that shows a wattmeter in real-time on a Haibike with a Yamaha motor, while the guy goes out for a hilly ride. It only reaches the very high consumption a couple of times when he's struggling on a steep hill or in too high a gear for the conditions. Even then, his cadence isn't low enough to get the maximum.

just in case you don't know, the tuning dongle doesn't affect the power in any way.It only releases the speed limit.

Good link...I,d realised your point about dongle after a few outings..
In my usage I found dongle simply lowers my range...to extend range I don't change setting simply ride at / hover around 16 mph whenever poss. The dongle lifts that to perhaps 18 , consequently lowering my contribution, increasing drag and keeps motor working where normally I,d be just out of its use..
My feeling ( ok perhaps wrongly) is that to increase my range I simply pedal faster. If I change setting I slow down and probably end up drawing same overall current..I have a 28 mile mixed route and have found virtually no difference in battery usage wether on high or mid...just my time alters drastically.
Agreed ,that's probably down to my riding than characteristics of bike...
My rule when out on it now...dont use dongle,leave in highest setting but work as hard as poss all time. ( leave display on cadence and aim at keeping it between 70 and 80, which I simply could never do on standard mtb)

My only regret...not buying an emtb when they first appeared.
PS
Without dongle I rarely use top gear, even on flat...With it I,d use top but carry on drawing current...There are some tracks where bike is more fun with dongle but found battery flat on about mile 26 on my 28 mile course. Without it I generally have 10% left..( Cold weather affects battery way more than expected???)

 

[GLJoe]

I agree. The rider puts in 25%, the motor/battery 75% or less.
You need to be pretty athletic to squeeze the last pip out of a Bosch CX.

I keep seeing this mentioned by a number of people, but I'm coming to the opinion that its an erroneous conclusion. Let me explain:

The Bosch (and the same might apply to the Yamaha) system uses torque AND cadence sensing. And of course it also measures speed.
I have observed that if you want to keep a fast speed up, then yes, you do have to press those pedals with a fair bit of effort when going up an incline, and its only by doing that that you can keep the motor power meter maxed out.
BUT ... (and its a big but!), if you find yourself struggling and/or you don't want to put in as much leg effort, if you keep the cadence up, but shift down gears and let the speed drop, then the bikes seem to realise what you're doing and that you're going up a steep hill, and they seem to increase the power, so you still get the power meter maxed out, and you proceed up the hill with minimal effort. I really don't think that at this point the motor/rider ratio is following the 300% or whatever it might be, assist relationship, so I'm now doubting that all the theoretical calculation on rider wattage input are therefore valid.

Zlatan said in an earlier post
'If I'm willing to trundle up at <a slow> speed on Ebike ... my input is negligible', and this pretty much sums it up.
Get the right gear/cadence/speed, and any normal person should be able to climb 99% of commonly found hills with a modern Bosch/Yamaha driven ebike.
You certainly don't need to be 'pretty athletic' to do this. Riding at maximum allowable speed, maybe, but not just to be able to utilise the full power of the motor to climb really steep hills and if that's what's meant by 'last pip'.
Its very possible the Bosch controller is 'cheating' slightly here and is allowing a higher assist ratio, but if so, its very cleverly and subtly doing it, and it only seems to do this at the slower speeds when you really need it and would be struggling otherwise. Seems a perfectly sensible implementation to me and probably what I would do if I was designing an ebike control system! Thinking of it, isn't this type of algorithm pretty much what the new 'MTB' flow mode is? I suspect the software routines have already been in there for some time, just in another guise.

 

[Woosh]

BUT ... (and its a big but!), if you find yourself struggling and/or you don't want to put in as much leg effort, if you keep the cadence up, but shift down gears and let the speed drop, then the bikes seem to realise what you're doing and that you're going up a steep hill, and they seem to increase the power, so you still get the power meter maxed out, and you proceed up the hill with minimal effort. I

The system works as a torque multiplier.
when you shift down a gear, eg from 26T to 24T, you decrease the ratio front to rear by 8%, the motor increases your cadence by 8% as a result, reduces the required torque for you by 8% - you can feel this immediately after changing gear, and reduces also as much for the motor. If you then pedal as hard as before, your energy input increases, the motor responds by increasing its output, your cadence goes up even higher. The bike will go faster. There is no need for it to change its algorithm. It has no way of knowing which gear you are on anyway. You always get the most out of the motor when climbing in the lowest gear and while keeping the cadence as high as possible.
The thing to remember is the system works on rider's input power, that is torque times angular speed, you get twice as much out of the motor if you spin the pedals twice as fast.

I am sure there are a few members who would not hesitate to correct me if I am wrong on this.

 

[GLJoe]

It has no way of knowing which gear you are on.

Are you sure about that?

 

[Woosh]

Are you sure about that?

yes, last time I checked.

 

[GLJoe]

yes, last time I checked.

Your speed is a function of your cadence and gear ratio.
It knows your speed, it knows your cadence, why can't it simply rearrange the equation to know what gear you're in?

 

[Woosh]

In all the documentations I have read on the subject, I have never come across any mention of a function using the gear number in determining the assist ratio. It has always been a simple function (*1,*2, *2.5 *3) of the amount of energy that the user inputs.
The information on the selected gear is not needed and can vary with different models, so has no advantage over the existing algorithm.

 

[Nealh]

The 750w d8veh has quoted is the theoretical max power the bike can produce if called upon, it doesn't mean it will be a constant,Gearing will always play it's part and as you climb and select a gear for better climbing cadence. My 36v BBS01 theoretically can produce max 648w, with my watt meter I have had 630 watts output showing, for that I have had to be in top assist and top gear flat out.

 

[Deleted member 4366]

I keep seeing this mentioned by a number of people, but I'm coming to the opinion that its an erroneous conclusion. Let me explain:

The Bosch (and the same might apply to the Yamaha) system uses torque AND cadence sensing. And of course it also measures speed.
I have observed that if you want to keep a fast speed up, then yes, you do have to press those pedals with a fair bit of effort when going up an incline, and its only by doing that that you can keep the motor power meter maxed out.
BUT ... (and its a big but!), if you find yourself struggling and/or you don't want to put in as much leg effort, if you keep the cadence up, but shift down gears and let the speed drop, then the bikes seem to realise what you're doing and that you're going up a steep hill, and they seem to increase the power, so you still get the power meter maxed out, and you proceed up the hill with minimal effort. I really don't think that at this point the motor/rider ratio is following the 300% or whatever it might be, assist relationship, so I'm now doubting that all the theoretical calculation on rider wattage input are therefore valid.

Zlatan said in an earlier post
'If I'm willing to trundle up at <a slow> speed on Ebike ... my input is negligible', and this pretty much sums it up.
Get the right gear/cadence/speed, and any normal person should be able to climb 99% of commonly found hills with a modern Bosch/Yamaha driven ebike.
You certainly don't need to be 'pretty athletic' to do this. Riding at maximum allowable speed, maybe, but not just to be able to utilise the full power of the motor to climb really steep hills and if that's what's meant by 'last pip'.
Its very possible the Bosch controller is 'cheating' slightly here and is allowing a higher assist ratio, but if so, its very cleverly and subtly doing it, and it only seems to do this at the slower speeds when you really need it and would be struggling otherwise. Seems a perfectly sensible implementation to me and probably what I would do if I was designing an ebike control system! Thinking of it, isn't this type of algorithm pretty much what the new 'MTB' flow mode is? I suspect the software routines have already been in there for some time, just in another guise.

You have that more or less right, but it's not so much the intelligence of the system. Instead it's the basic motor characteristics.

All DC motors are generators. The faster they spin, the more volts they generate. The volts are the opposite way round to the battery, so they effectively reduce the power that the battery can provide. At maximum motor RPM, the voltage generated is equal to the battery voltage, so you have no power at that speed. Maximum power would come at zero rpm. That would mean that without a controller, the motor would get massive power at zero rpm, which would fry it in seconds, and no power at all at maximum RPM. The graph of power vs rpm would be a straight ramp down to zero.

The controller's function is to limit the power, so at any point on the ramp, the controller can make the current less, but nowhere can it make it more.

Let's say the controller won't allow more than 20 amps (700w) to protect the motor and battery. In the first 60% (guess) of the RPM range the controller would be able to provide its maximum, but after that, the ramp goes below 20 amps. That means that you can no longer get maximum torque no matter how hard you pedal or what the bike speed is. It's only pedal speed that counts. The faster you pedal above that 60%, the less torque you can get from the motor.

The faster you pedal, the more power you provide, so your battery will always last longer if you pedal fast. the motor has an efficiency that varies depending on RPM. Max efficiency comes at about 75% of maximum RPM, so best battery consumption would be at that cadence; however, it's not easy to keep the motor at that speed because every time you change gear, the RPM jumps. I tried some tests using a Nuvinci to keep the RPM constantly in the 75% zone, but I saw no measurable difference in range from normal riding with normal gears pedalling at a comfortable RPM.

 

[GLJoe]

In all the documentations I have read on the subject, I have never come across any mention of a function using the gear number in determining the assist ratio. It has always been a simple function (*1,*2, *2.5 *3) of the amount of energy that the user inputs.

Hmm. Well lets take the new Bosch 'MTB' mode that replaces the 'sport' mode. Isn't that supposed to dynamically alter the assist ratio? surely it cannot therefore be a simple function?

The information on the selected gear is not needed and can vary with different models, so has no advantage over the existing algorithm.

I'll have to think about that one, but my gut feeling is that an intelligent algorithm that knows what you are doing and how you are riding, could be made to have real advantages over more simple, fixed ratio based ones.

 

[GLJoe]

You have that more or less right, but it's not so much the intelligence of the system. Instead it's the basic motor characteristics.
........
The controller's function is to limit the power, so at any point on the ramp, the controller can make the current less, but nowhere can it make it more.

To clarify, I'm not saying the controller is giving more power, what I'm saying is that I believe in certain circumstances, it can provide maximum or near maximum power to the motor, but without the need for the user to also be providing maximum torque to the pedals.

When I'm next out, I'll try and experiment more. I haven't done as much as I'd like so far, as usually when I'm cycling by myself, I'm pretty much flat our most of the time! however when I'm out with the wife,I often have to cut the power right down. But I still like to spin at a 'good' cadence, and when doing so, I've noticed that often when I do this, I can be putting in what seems like virtually no pressure on the pedals (compared to what I otherwise need to do, to power up the hills fast and keep the Intuvia's LCD power meter maxed out), yet once I drop to a low enough gear and reduce to a low enough speed, the power meter will then climb back and show its maxed out. Its almost as if it knows that slowing down but keeping the cadence up, means you're going up a hill and will soon be tiring, therefore it needs to increase the assist level.
Maybe this is all in my head, but decades of noticing strange things and only later finding out there were very sound reasons behind the odd behavior of things, makes me not want to dismiss it as mere fancy

 

[GLJoe]

the Intuvia's LCD power meter

Just thinking about this - does anyone know:
Is this power meter an absolute and fixed representation of power to the motor? i.e. if the bars are maxed out all the way, it means that the maximum current is being supplied to the motor - regardless of what else is changing, such as power assist level
??

 

[topographer]

The bike I suggested has just popped up on ebay (second-hand but nearly new) for £425 incl. delivery.

http://www.ebay.co.uk/itm/electric-bike-/292155816491?hash=item4405d7fa2b:g:lUIAAOSw1~JZT9cj

 

[Zlatan]

Other thing I,ve wondered ( but by the way great posts above, all of them)
is exactly how little power is needed in bottom gear to climb at the accompanying very low speed.
In lowest gear the motor can still spin at I,d guess 2000rpm (ie I,d have thought max cadence ( 85 or so) would represent max rpm of motor.
The motor only needs to produce minimal torque to keep bike just plodding along.( say 3 mph?)
Yes the current used getting to top wiill be significant but current in respect to time will be minimum ?? ( or the bike does provide more than indicated)
I cant really see how anyone intending going cycling could not generate enough force to turn pedals on my Haibike...if they are willing to make slow progress. I cant see how this feature could be duplicated on hub drive without either a throttle or much higher current demand. The slow progress demands the low gearing associated with CD.( for rider and motor)

And , just to throw another observation in...
I,m not convinced unit takes cadence into account. If I,m cycling along at cadence if 50 and go for it, I can max out the bars..but likewise if I,m cycling along with one of 70 I can replicate the same effect..( I suspect LA could replicate this at 100, but if cadence was taken into account he couldn't)
Higher your cadence the lower your ability to exert extra force ie as a system we can also create max torque at minimum rpm. ( ie at zero, standing on pedals is maximum torque ( at crank) any of us can generate. The torque ,cadence relationship could quite easily be self governing for the motor as it is for our legs.??
Why does system need to take into account cadence when our torque is already diminishing with rising cadence.??

 

[anotherkiwi]

Other thing I,ve wondered ( but by the way great posts above, all of them)
is exactly how little power is needed in bottom gear to climb at the accompanying very low speed.

Bottom gear 32:34 and second 32:28, I provide about 150 W.

The GSM draws at a cadence of around 70-80 (must look into getting a cadence meter some day...) about 150 W in bottom gear on my test hill which is 700 metres long has a max gradient of 12% and an average of around 9%. IIRC I saw a peak of about 430 W on the 12% section because I changed up to second to see what would happen. Speed from memory around 9-10 km/h which is spot on with http://www.bikecalc.com/speed_at_cadence which is how I estimate my cadence at the moment - I know the gear I am in and GPS speed.

 

[Woosh]

You certainly don't need to be 'pretty athletic' to do this. Riding at maximum allowable speed, maybe, but not just to be able to utilise the full power of the motor to climb really steep hills and if that's what's meant by 'last pip'.

You should take a close look at EddiePJ's run from Lauterbrunnen to Wengen to see how powerful the CX motor is and how hard you have to work to squeeze the last pip out of it.

https://www.strava.com/activities/656138180

6.3 miles, 1250m elevation, 1h 14 minutes.

My estimate:

potential energy = 100 * 9.98 * 1250 / 3600 WH = 346WH
total energy required = 346 + 12*6 = 418WH
battery consumption = 418*0.75/0.80 = 392WH

Think of how long it will take you to flatten the entire 400WH battery, how many miles you travel on a full charge then compress the whole effort to just 6.3 miles and inside 74 minutes..
Eddie climbed 1250m in about the same time that Rupert1 climbed 800m
Athletic or what?

 

[soundwave]

or you could just go faster but with the bosch system it uses most power climbing under 15mph as even with my dongle the faster i go the less the motor gives me esp after 28mph but still use a lot of power and drain the batt faster as a result.

on the flat i can drain a 500w batt in 1hr 20 mins or less just depends if i can be bothered or not adding in hills will also drain the batt even faster and slow me down too ;(

 

[Woosh]

i can drain a 500w batt in 1hr 20 mins

then you are about 18% fitter than EddiePJ.
With a CD torque multiplier system, the faster you can drain the battery, the fitter you are.