still not to sure what to make of bosch ebike system

[Fish2]

Where do you get this powers? Bosch CX is 250W.

 

[flecc]

Where do you get this powers? Bosch CX is 250W.

That is only a nominal power rating for legal purposes, called the continuous maximum power. All e-bike motors produce very much higher maximum powers at times during use.
.

 

[Fish2]

That is only a nominal power rating for legal purposes, called the continuous maximum power. All e-bike motors produce very much higher maximum powers at times during use.
.

Oh, I see. I understand that, but do I really get 540W for 30 minutes riding at full power?
Electric motors can be overloaded for seconds, not hours.

 

[Woosh]

Oh, I see. I understand that, but do I really get 540W for 30 minutes riding at full power?
Electric motors can be overloaded for seconds, not hours.

Yes.

Electric motors can be overloaded for seconds, not hours.

don't worry about that.
When the motor stalls, the controller will reduce its current.
crank drive motors run at nearly their best at maximum torque. Only about 20% will be wasted as heat.

 

[basicasic]

Bosch do define the way they measure their motors' torque.
It's the same as with Bafang, Bewo, Tonsheng and others.



The full listing is here:

https://www.bosch-ebike.com/en/components/drive-unit/

If you want to compare the climbing ability of a Bosch motor against a rear geared hub motor, you need to convert the torque at the motor to the torque at the rear wheel.

For example, Bosch CX in turbo mode: 75NM
If you have a front ring of 18T, then it's equivalent to a chainring of 45T at the front and a 45T cog at the rear.
If your bike has a typical 11T-32T cassette, then the maximum torque at the lowest gear, 32T is:
= 75NM * 32/45 = 53.33NM
This torque is produced at around 540W * 60 / (75NM * 2 * pi) RPM = 68 RPM.
Your personal input will need to exceed =540W/3 = 180W and 25NM
If your tyres are MP 26in x 1.5in, your climbing speed is:
= 2.1M * 68 * 60 / h= 8.5kph = 5.3mph

Maximum gradient for 100 kg rider + bike: 22%.

which is roughly the kind of torque you would expect from a Bafang BPM with 20A controller except the BPM is more flexible on how it delivers its torque.

You've produced a lot of 'man-maths' to demonstrate the Bosch system will haul a 100kg person up a 22% gradient at 8.5kph and nothing at all to show the Bafang does the same or better with equivalent gearing.

How does 'flexibility of torque delivery' help in this situation? Does it mean our 100kg rider can go up this hill without pedaling?

If hub motors are so good why are respected big-named manufacturers such as Bosch, Yamaha, Panasonic and Shimano producing crank motor systems at all? Why aren't they making hub motors?

 

[Woosh]

Why aren't they making hub motors?

A crank drive motor is a geared motor placed at the chainring so that it can leverage on the gearset to extend its capabillty. Thus it can climb a bit steeper hills or ride a bit faster.

Take the CX for example, you can hold on to 28mph if derestricted.
Geared hub motors like the Bafang BPM or its smaller cousin SWX02 can't leverage on the gearset, so their useful 'bandwidth' is smaller. For example, I use the BPM and SWX02 with winding code 13, they can only hold on to 22mph-23mph derestricted. At their top speed, their torque drops fast and cannot match that of a crank drive like the CX and on the steepest hills, they waste considerably more battery compared to a crank drive.
This said, geared hub motors deliver their power regardless of your chosen gear. the motor will flatten the hills without you changing gear or cadence.
You can select a gear that suits your natural cadence, for example 16T at the rear cog, and pedal with that gear as long as you like, climb hills in the wrong gear etc.

 

[soundwave]

what you want is a big un

 

[EddiePJ]

Oh, I see. I understand that, but do I really get 540W for 30 minutes riding at full power?
Electric motors can be overloaded for seconds, not hours.

You have nothing to worry about in respect of the motor being overlaoaded or getting hot. The battery on the other hand, could be a slightly different story. The ride below shown in yellow was 10.4 miles of climbing with an elevation gain of 6,428ft. The climb required a battery change at 9.5 miles, and the battery case was worryingly hot. I certainly didn't feel comfortable about putting in my back pack, and it took hours to cool down.

I'm guessing that you are already using a cassette with either a 40/42/46/48 or even 50t low ratio, and nothing any higher than 15T or at a last resort 16T front. Many eMTB riders that I have come across in the Alps, use a 14T up front. I haven't yet felt the need for that myself. I have done similar climbs using both Performance Line and CX, and the CX offers roughly a one-two gear advantage on climbs, but I found the CX to be more fuel hungry, in respect of the battery. My ideal set up is Performance Line motor and 500wh battery running a 15T front with 11-42 rear. The next bike when it arrives, has a 16T with 11-48 cassette, so that will be quite a an interesting change for me, and one that I look forward to trying.

The aim in four weeks time is to complete the same ride again, but continue up on the red line.

One thing is for sure, I can think of a couple of 'wanna be' eMTB's that I'd not even begin to entertain trying to tackle a climb such as the one shown below on. With the road biased gearing and outdated set up for mtb use that they have, they would fail miserably within the first few feet. I have no such qualms trying to tackle this again using the Bosch system.
Note that I said "trying to tackle" I didn't make it up this climb last year, but that was not down to the Bosch system or the gearing on the bike, it was down to the fact that I was struggling to keep the front end down, whilst the rear was spinning and loosing traction.

 

[Woosh]

what you want is a big un

I am not convinced that big is beautiful.
I am rather attracted by the idea of 'small and light'.
d8veh has a thread on the Xiongda YTW-06 motor, I may make a 13-15kg bike next year with it.

 

[soundwave]

that motor is 7kw 72v 75a

 

[Jimod]

some do behave like children although they are old enough to get their state pension.

Well you know the old saying. Growing old is mandatory. Growing up is optional.

 

[Deleted member 4366]

"Maximal possible drive torque (Nm) (converted to a gear ratio of 1:1 crankset to chainring)"

What size wheel is that? That makes a difference too. At least we're getting closer!

Edit: Sorry, the torque is the same in any wheel, but the force to climb up the hill is less with a bigger wheel.

 

[chris_n]

You have nothing to worry about in respect of the motor being overlaoaded or getting hot. The battery on the other hand, could be a slightly different story. The ride below shown in yellow was 10.4 miles of climbing with an elevation gain of 6,428ft. The climb required a battery change at 9.5 miles, and the battery case was worryingly hot. I certainly didn't feel comfortable about putting in my back pack, and it took hours to cool down.

I'm guessing that you are already using a cassette with either a 40/42/46/48 or even 50t low ratio, and nothing any higher than 15T or at a last resort 16T front. Many eMTB riders that I have come across in the Alps, use a 14T up front. I haven't yet felt the need for that myself. I have done similar climbs using both Performance Line and CX, and the CX offers roughly a one-two gear advantage on climbs, but I found the CX to be more fuel hungry, in respect of the battery. My ideal set up is Performance Line motor and 500wh battery running a 15T front with 11-42 rear. The next bike when it arrives, has a 16T with 11-48 cassette, so that will be quite a an interesting change for me, and one that I look forward to trying.

The aim in four weeks time is to complete the same ride again, but continue up on the red line.

One thing is for sure, I can think of a couple of 'wanna be' eMTB's that I'd not even begin to entertain trying to tackle a climb such as the one shown below on. With the road biased gearing and outdated set up for mtb use that they have, they would fail miserably within the first few feet. I have no such qualms trying to tackle this again using the Bosch system.
Note that I said "trying to tackle" I didn't make it up this climb last year, but that was not down to the Bosch system or the gearing on the bike, it was down to the fact that I was struggling to keep the front end down, whilst the rear was spinning and loosing traction.

That does look a bit steep, the constant battle to keep the front wheel down while stopping the back spinning is a major challenge on that!
I suspect either of us would kill a BPM in short order!
There are no hub motor e bikes going up the mountains off road around here. You do occasionally see them but never off road.
I've never had the Yamaha motor hot but yes the battery can certainly get a little warm.

 

[Deleted member 4366]

Oh, I see. I understand that, but do I really get 540W for 30 minutes riding at full power?
Electric motors can be overloaded for seconds, not hours.

My calculation says that 540w is a bit optimistic. As far as I can figure out, the Bosch runs about 19 amps max - could be 18, but I'm not sure of the difference between the different versions. 19 x 36 = 648w from the battery. You have to take the motor's efficiency into consideration. i'd say a practical max of 80%, then you'd lose another 5% in the drive train (at least), so 648 x 0.8 x0.95 = 519w

 

[soundwave]

 

[Woosh]

Edit: Sorry, the torque is the same in any wheel, but the force to climb up the hill is less with a bigger wheel.

I did the calculation assuming MP 26" x 1.5" tyres, bike + rider = 100kgs.

 

[EddiePJ]

@chris_n I very much doubt that I'll make it this time either. I'm actually100% certain that I won't for two reasons. The first reason being that I have now put a shorter stem on the bike 70mm from 110mm, and the second reason is that I want to get through the trip in one piece! Last nights fall backwards was bad enough. I'll still give one good shot though.

 

[Deleted member 4366]

That went to 18.4 amps, so about 500w at the back wheel.

 

[chris_n]

I am not convinced that big is beautiful.
I am rather attracted by the idea of 'small and light'.
d8veh has a thread on the Xiongda YTW-06 motor, I may make a 13-15kg bike next year with it.

That sounds like a good plan, my MTB is 11kg unpowered, with something that small and a reasonable battery 15kg should be easilly achievable. A good hybrid with solid forks and road orientated tyres would be considerably lighter. Biggest problem I have with the Haibike is the weight of it, I'm sure it could (should) be at least 5kg lighter.

@EddiePJ good luck!

 

[Emo Rider]

That sounds like a good plan, my MTB is 11kg unpowered, with something that small and a reasonable battery 15kg should be easilly achievable. A good hybrid with solid forks and road orientated tyres would be considerably lighter. Biggest problem I have with the Haibike is the weight of it, I'm sure it could (should) be at least 5kg lighter.

@EddiePJ good luck!

The bike weighs 22.3kg as far as I can find out. The motor and battery weighs 6.4kg. If it were a non electric bike it would weigh 15.9kg. My Marin Muirwoods commuter weighed 19kg. The Hardseven could be lighter but would cost much more because of the components required. One can dream