still not to sure what to make of bosch ebike system

[Woosh]

I still cannot understand why the lower gears are not used.

allow me to put the situation into numbers for you.
On this particular hill, his maximum speed is 11mph. His bike has 18T front ring, he's selected 26T at the rear.

11mph = 11 *1609 M = 17.7kph

Assuming he has 26in * 1.5in MP tyres, the circumference of his tyres is 2.1M
The rotational speed of his rear wheel is = 17,700 / (2.1 * 60) = 140.5 rpm
His front ring has a divider of 2.5,
the rotational speed of his cranks = 140.5RPM * 26T / (18T * 2.5) = 81.2 RPM

That's as much as he can manage. He clearly will spend much more energy moving his legs if he tries to spin faster and can't hold higher than 81 RPM.
If he shifted to 28T or 32T or greater, his speed will drop.

26T is the gear that suits him best on that hill.

PS:

If his legs were stronger, he could use 18T rear cog, his speed would have been 15.5mph. It's still within the ability of his Active Line motor.

 

[Deleted member 4366]

active 48nm
performance 63nm
cx 75nm

tbh i doubt you could tell the difference if you never knew what motor was on which bike as its just 15% more or less.

That's all bollcox anyway because the torque depends on your gearing more than the motor. What gearing are they assuming? An active with low gearing will have higher torque than CX with high gearing.

 

[Danidl]

I think the answer is much more simple, I ride mine like I would drive a car using the gears in exactly the same way, after all you are riding a motorized vehicle are you not? You would never attempt to set of on or drive up a hill in a high gear in a car or motorcycle so why would you do that on an electric bike?
The bigger the hill the lower the gear!
Works for me!

Shame,Shame on you gubbins, this thread had all the makings of one to rival the Brexit one and there you go , using facts and common sense.
Look at all the topics you have nipped in the bud, we were only getting started on orthopedics and biomechanics, we had only a few entries on muscle fibre interactions and we had not even got down to ATP molecular activity.
Are you not ashamed of yourself? Snipping this thread, just as the Brexit one is running out of steam..

 

[Gubbins]

Shame,Shame on you gubbins, this thread had all the makings of one to rival the Brexit one and there you go , using facts and common sense.
Look at all the topics you have nipped in the bud, we were only getting started on orthopedics and biomechanics, we had only a few entries on muscle fibre interactions and we had not even got down to ATP molecular activity.
Are you not ashamed of yourself? Snipping this thread, just as the Brexit one is running out of steam..

Common sense and brexit mentioned in the same post?

 

[Danidl]

Common sense and brexit mentioned in the same post?

... I take that as no apology then?.. otherwise fair comment.

 

[Trevormonty]

That's all bollcox anyway because the torque depends on your gearing more than the motor. What gearing are they assuming? An active with low gearing will have higher torque than CX with high gearing.

My CX is considerable more powerful than wife's Shimano Steps (Active equivalent).

 

[chris_n]

allow me to put the situation into numbers for you.
On this particular hill, his maximum speed is 11mph. His bike has 18T front ring, he's selected 26T at the rear.

11mph = 11 *1609 M = 17.7kph

Assuming he has 26in * 1.5in MP tyres, the circumference of his tyres is 2.1M
The rotational speed of his rear wheel is = 17,700 / (2.1 * 60) = 140.5 rpm
His front ring has a divider of 2.5,
the rotational speed of his cranks = 140.5RPM * 26T / (18T * 2.5) = 81.2 RPM

That's as much as he can manage. He clearly will spend much more energy moving his legs if he tries to spin faster and can't hold higher than 81 RPM.
If he shifted to 28T or 32T or greater, his speed will drop.

26T is the gear that suits him best on that hill.

PS:

If his legs were stronger, he could use 18T rear cog, his speed would have been 15.5mph. It's still within the ability of his Active Line motor.

That is all well and good and is fully understood but the 11mph is irrelevant if that is all the power that is available then that is terminal velocity. It is for me more about the second part of the OP where he says he didn't get up a steeper hill.
No where do we have any indication of the actual steepness of the hill or the length of the hill. As I have said many times before there are plenty of hills that regardless of the OP's strength he will not get up at 11mph. If you look at http://www.kreuzotter.de/english/espeed.htm then even with the default settings for weight etc 550W will not achieve 11mph on a 15% slope.

 

[Woosh]

550W will not achieve 11mph on a 15% slope.

he stalls on some very steep hills(s), his speed is zero mph, he only wants to ride instead of push, so he knows that already.
Let's assume for a moment that on the previous (moderate) hill, if his legs were stronger, he could have used 18T instead of 26T and held on to 15.5mph instead of 11mph. What does it tell us? that his legs produce less or equal to 500W * 18T/(26T * 3) = 115W.
His lack of fitness limits how steep a hill he can climb on pedaling.
Assuming that the minimum speed he feels safe when climbing a hill is 6mph, his weight is 95kgs, bike 20kgs..
The maximum gradient he can climb is 15%. I can post the calculations if you want.

 

[chris_n]

I don't dispute any of that. As I said he stalled because he was in too high a gear when he still had two lower gears available.

Off out now to ride my bike on some real hills with 32f x 40r gearing (not on max power though)

 

[Woosh]

even with your gearset, he will still stall where he stalled before unless he can climb at lower speed than he does now. That's the problem with not being fit enough.

enjoy your morning.

 

[cosybike]

Right children! I'm turning off the internet! Away you all go and ride your bikes! Don't come back till it's dark.

Sent from my Lenovo YT3-850F using Tapatalk

 

[Deleted member 4366]

Right children! I'm turning off the internet! Away you all go and ride your bikes! Don't come back till it's dark.

Interesting comment from someone reading and posting on a forum.

Surely, the whole point of the forum is to bring knowledge and opinions and challenge and discuss them to broaden the understanding and knowledge base. If we were all out riding our bikes instead of writing about them, there would be no forum to read or post on, and when people had problems, there would be no help.

 

[Woosh]

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

 

[Woosh]

Surely, the whole point of the forum is to bring knowledge and opinions and challenge and discuss them to broaden the understanding and knowledge base.

if only.
I use the forum to promote my bikes but it is not the only reason to post.
What matters more to me is the critiques.
They challenge me to produce products better suited to the needs of the many and still to a budget.

 

[nemesis]

 

[Croxden]

I've got one of those but it doesn't quite go like that.

 

[Fish2]

My Bosch CX has enough torque and power to easily get me up the steepest hills. Sometimes really just about to fall of the back. But I do use 1st gear and SPORT mode on those occasions.

I found no info to suggest the new eMTB mode will give more power at lower cadence?

In my understanding, it will seamlessly provide low to high power depending on user input. This should solve the current problem with riding in SPORT. The moment you stop pressing hard on the pedals, the motor cuts out. And then again gives too much power when you start. So I really change modes all the time when in the mountains.

 

[Fish2]

I've got one of those but it doesn't quite go like that.

How did you get it? New bike? It supposed to be available from July.

 

[Croxden]

How did you get it? New bike? It supposed to be available from July.

I might have exaggerated a little.

 

[Woosh]

active 48nm
performance 63nm
cx 75nm

tbh i doubt you could tell the difference if you never knew what motor was on which bike as its just 15% more or less.

That's all bollcox anyway because the torque depends on your gearing more than the motor. What gearing are they assuming? An active with low gearing will have higher torque than CX with high gearing.

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

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

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.