still not to sure what to make of bosch ebike system

[KTM Bike Industries UK]

The graph you posted earlier is misleading you and some others because it shows output power, not torque.

Your opening statement that the motor isn't giving maximum assistance is sort of wrong, but it depends what you mean by assistance. If you mean power, you're correct, but to get the motor to give it's maximum power, you have to give a greater proportion of the total power yourself than you would at a lower speed, so proportionally, it's giving less assistance.

From the graph:

At 70 rpm the power is 540w
At 85 rpm the power is 570w (maximum)

Rotation x torque = power

we therefore have:
70 x T1 = 540, so T1 = 7.71, where T1 is the torque the motor produces at 70 rpm
85 x T2 = 570, so T2 = 6.71, where T2 is the torque the motor produces at 85 rpm

You can see that the torque is significantly less at a cadence of 85, so the only way to get the motor from 70 rpm to 85 rpm is to put in significantly more torque yourself. That assumes that you're already in bottom gear. You'd have to cover the 13% missing torque from the motor plus 15/70, which is another 21% ,to get to 85 rpm. That means that when hill-climbing in bottom gear, to go from 70 rpm to 85 rpm, you'd have to pedal 34% harder.

If you look at a graph of the power a person gives when walking, trotting, running and sprinting, i.e. speed vs power, it'll show that they produce more power at high speed, but that doesn't mean it's easier to sprint everywhere.

I'm afraid you lost me at about the 2nd line. I'm a cyclist, we sell bikes to people who ride bikes for fun or as a form of transport. This sort of detail puts 95% off them off, because they think they have to worry about it. They don't.

Its a bike, ride it an enjoy. There are just some things to understand when you ride different types. With Bosch, its simple to say if you spin more, the bike will give you more assistance. The details are not important as to why or how to 99% of the people who buy eBikes.

 

[Woosh]

I'm afraid you lost me at about the 2nd line.

I can calculate the user input for 85rpm if you want to read. The point is, Bosch bikes are perfect for normally fit cyclists (ie your legs can output up to 200W continuously and you can spin up to 85 rpm at the same time). If your fitness is less, a more flexible system is better.

 

[basicasic]

if he's at 70rpm the motor isn't giving maximum assistance.... yes.

if he's at 11mph, and in third gear, the motor speed isn't limiting, and he can change gear.

So if he changes into an easier gear, he can spin his legs and won't be personally putting in any more power, if he spins a bit faster with the same power, the motor will give him more assistance, and he'll go faster, with no extra input from himself.

You need to try a Bosh bike if you don't understand this. It won't take any extra effort.

This. Exactly.

A good way to ride easily up a hill I find is to approach it with no assistance (or you could use eco or tour) and change down the gears as you start up the hill until you find one that you can pedal with a small amount of effort - then hit the plus button to go up an assistance level; it feels like your legs have become supercharged. Hit the plus button again and you're flying.

In my experience slogging in too high a gear won't get the best out of the Bosch motor.

 

[Artstu]

If your fitness is less, a more flexible system is better.

I think you mean one dimensional and fixed, unresponsive, dreary, boring, frustrating, lacking engagement, I could go on but you get the idea.

 

[Deleted member 4366]

This sort of detail puts 95% off them off, because they think they have to worry about it. They don't.

They don't need to know the detail, but what I posted above are the facts.

With Bosch, its simple to say if you spin more, the bike will give you more assistance. The details are not important as to why or how to 99% of the people who buy eBikes.

That's misleading. When you're in bottom gear climbing a hill, you can't make it any easier by pedalling faster. The only way to pedal faster is to put in disproportionately more effort.

 

[Woosh]

I think you mean one dimensional and fixed, unresponsive, dreary, boring, frustrating, lacking engagement, I could go on but you get the idea.

if you mean by engagement panting your lungs out then I won't go there but I'll give you a good enough bike to compete with Bosch bikes in a couple of years and still under 2k.

 

[Danidl]

The graph you posted earlier is misleading you and some others because it shows output power, not torque.

Your opening statement that the motor isn't giving maximum assistance is sort of wrong, but it depends what you mean by assistance. If you mean power, you're correct, but to get the motor to give it's maximum power, you have to give a greater proportion of the total power yourself than you would at a lower speed, so proportionally, it's giving less assistance.

From the graph:

At 70 rpm the power is 540w
At 85 rpm the power is 570w (maximum)

Rotation x torque = power

we therefore have:
70 x T1 = 540, so T1 = 7.71, where T1 is the torque the motor produces at 70 rpm
85 x T2 = 570, so T2 = 6.71, where T2 is the torque the motor produces at 85 rpm

You can see that the torque is significantly less at a cadence of 85, so the only way to get the motor from 70 rpm to 85 rpm is to put in significantly more torque yourself. That assumes that you're already in bottom gear. You'd have to cover the 13% missing torque from the motor plus 15/70, which is another 21% ,to get to 85 rpm. That means that when hill-climbing in bottom gear, to go from 70 rpm to 85 rpm, you'd have to pedal 34% harder.

If you look at a graph of the power a person gives when walking, trotting, running and sprinting, i.e. speed vs power, it'll show that they produce more power at high speed, but that doesn't mean it's easier to sprint everywhere.

... And you suggested I was making it complicated?.

 

[Danidl]

They don't need to know the detail, but what I posted above are the facts.



That's misleading. When you're in bottom gear climbing a hill, you can't make it any easier by pedalling faster. The only way to pedal faster is to put in disproportionately more effort.

.... Of course , has anyone suggested otherwise. I think the other enthusiastic Bosch and other central drive users were saying keep your speed cadence at what is comfortable rate and keep dropping gear ratios , the speed will drop so then keep upping the assistance level, up to turbo .

 

[Danidl]

if you mean by engagement panting your lungs out then I won't go there but I'll give you a good enough bike to compete with Bosch bikes in a couple of years and still under 2k.

.. l hope you do and wish you well. But note that even today Raleigh have two models with Bosch motors under this magic 2k price point.

 

[Woosh]

.. l hope you do and wish you well. But note that even today Raleigh have two models with Bosch motors under this magic 2k price point.

thanks for the encouragement, I am making £1,200-£1,300 bikes this year, it will take time to build up the expertise.
at £2k price point, most Bosch bikes have cheap fork, brakes, headset, handlebars, pedals, rack, grips, lights and a 500WH battery at most.
About the same sort of stuff that I put on my £1,100 bikes.

 

[Deleted member 4366]

... And you suggested I was making it complicated?.

It's as simple as, the harder you pedal, the faster you go up the hill. You can't mysteriously pedal faster and somehow the motor makes it easier for you. People keep trying to say or imply otherwise, so I have to give the detail that shows why they're incorrect. That's assuming that the graph on page 1 is correct, and it looks reasonable to me.

 

[Emo Rider]

I think the OP wonders how he can get more speed out of the bike on hills. That's no difficulty with a rotational system but with a torque sensing system, you need to be able to hit 90 rpm to get the best out of the bike. His cadence is about 70 rpm, he is stuck more or less at 11mph on third gear (26T) on moderate hills. Shifting down, he can't push up the cadence, shifting up, he has not got enough strength.

I certainly can go up a steep hill without pedalling at 90rpm. In the right gear and power setting it is almost effortless. I am over 60. Have you ever ridden a Bosch or Yamaha system up a hill? All I and others are saying is that we find the higher rpm easier on us and the bike. Pedaling faster does not need to translate into more effort.

 

[chris_n]

thanks for the encouragement, I am making £1,200-£1,300 bikes this year, it will take time to build up the expertise.
at £2k price point, most Bosch bikes have cheap fork, brakes, headset, handlebars, pedals, rack, grips, lights and a 500WH battery at most.
About the same sort of stuff that I put on my £1,100 bikes.

You want to give me a Rio to test in the Alps against a Yamaha Haibike and see which I can kill first ;-) . Bearing in mind I can sustain 200W but still find myself in 32 front x 40 rear gearing going up inclines at 7kmh ( not using highest power levels to keep range sensible).
Of course Yamaha / Bosch drives are not for everyone but I can't understand why someone would allow themselves to stall out with two lower gears to go. I suspect (am open to other ideas) given similar terrain a legal hub motor would have fried long before I stall the Haibike unless it was one of the two speed motors d8veh raves about.

 

[Crockers]

It's a bit like walking. If you walk on the flat at say 40 paces a minute you maintain a speed a x. Then you come to a hill. You have choices.
Walk at the same rate...same speed but put in more effort until knackered.
Or walk at the same rate but shorten the step. You slow down but effort should be similar.

Or just talk ****** and try to convince everyone you know what you're talking about.

 

[Deleted member 4366]

It's a bit like walking. If you walk on the flat at say 40 paces a minute you maintain a speed a x. Then you come to a hill. You have choices.
Walk at the same rate...same speed but put in more effort until knackered.
Or walk at the same rate but shorten the step. You slow down but effort should be similar.

Or just talk ****** and try to convince everyone you know what you're talking about.

You have everything right there. Shortening your step is equivalent to changing down a gear on a bike. Both make climbing easier, but climbing a hill on a bike in first gear, you cannot change down to shorten your step.

 

[chris_n]

You have everything right there. Shortening your step is equivalent to changing down a gear on a bike. Both make climbing easier, but climbing a hill on a bike in first gear, you cannot change down to shorten your step.

But if it is a hill that causes you problems regularly then you should get your gearing changed so that you do have a low enough first gear.
Having said that I'm still not sure the Bosch is the correct power unit for the OP.

 

[Deleted member 4366]

But if it is a hill that causes you problems regularly then you should get your gearing changed so that you do have a low enough first gear.
Having said that I'm still not sure the Bosch is the correct power unit for the OP.

That's what we said in the beginning until people kept saying thay all you need to do is pedal faster. I think everybody has the right idea, which is basically that you use gearing to increase your own and the motor's torque, but some people are not thinking through how that would be achieved.

 

[spinellino]

It's a bit like walking. If you walk on the flat at say 40 paces a minute you maintain a speed a x. Then you come to a hill. You have choices.
Walk at the same rate...same speed but put in more effort until knackered.
Or walk at the same rate but shorten the step. You slow down but effort should be similar.

I think that this is as clear as it gets.
I bought a Bosh CX bike only a few weeks ago, and find it difficult to imagine stalling the motor, but I also noticed that when climbing you have to chose between speed and lack of effort. You can't have both.
It's also true that pedaling at least at 60rpm the motor assists you better. So the OP should at least try that first. But if he's expecting to climb at the same speed and effort then when he's on a flat road, than I'm afraid he got the wrong bike.

 

[basicasic]

If I understand correctly the OP had 2 lower gears available which he wasn't using. Changing down 1 or 2 gears would probably solve his problem, though he would be ascending at a slower speed.

It sounds to me like he wants to fly effortlessly up hills in a high gear with little or no effort and that isn't going to happen with a Bosch bike (or maybe any legal bike).

But there is a good chance that if he continues with the Bosch bike his fitness will improve and in a month or two he will be able to fly up the hills in a higher gear.

 

[Will Tinker]

If I understand correctly the OP had 2 lower gears available which he wasn't using. Changing down 1 or 2 gears would probably solve his problem, though he would be ascending at a slower speed.

It sounds to me like he wants to fly effortlessly up hills in a high gear with little or no effort and that isn't going to happen with a Bosch bike (or maybe any legal bike).

But there is a good chance that if he continues with the Bosch bike his fitness will improve and in a month or two he will be able to fly up the hills in a higher gear.

Yep, agreed on this and the post above it. An easier ascent will be slower (lower gear). A faster ascent will be harder (higher gear, harder pedalling).