Mid motor vs Hub motor.

[Nealh]

In other threads the merits of both have been talked about many times but they end up derailing the course of a thread, so it would be far better for the them to be discussed under a specific thread. The virtues of both types have been extolled many times especially on here.

The latest incursion in the subject has moved on to progress of both motor types, though as always reliability and terrain usage is always thrown in as a Red rag to a Bull.

The mid motor in size. weight and development seems somewhat to have stalled over the last few years, not a bad thing as progress/R & D is exhaustive and time consuming. We have seen motor size stagnate in both OEM motors and kit motors, though there are at least a couple of lightweight kit mid motors that are available at under the 2.5kg mark.
Quoted torque power figures are banded around 50,60,75, 80, 100 & 120 N.m supposedly all from weedy generic 250w rating which is the legal status almost worldwide for ebikes/pedelecs to be used in the same breath as a Pushbike. Not being an engineer this is beyond me as I can't see how a motor can produced more quoted N.m without the wattage being increased, current can be upped to get more temporary watts/power and gearing to an extent can be changed but to go from 50 or 60 to double those figures I feel that somewhere the output figures are being massaged like the cases we have seen in the Car industry.

Hub motors have been a favourite for many years using geared hubs and heavier D/D (Direct drive) hubs but for our purposes and 250w the geared hub is king.
Here we are seeing size /weight movement in their design with more coming online for a lighter bike build, sub 2.5 kg hubs and less then 100mm dia.
The latest from Keyde even incorporates the controller within the motor, and now mini hubs resemble a hub the size of an Alfine/Nexus or Rolhoff hub geared unit.
Again the torque figures are similar to the mid drive 25 N.m values have increased and now we see 40,45 & 50 N.m banded around as torque figures.

Lots more to add to this thread for sure and I know a few on here are biased to a particular drive so lots of discussion I think to be had with the hopes that most of the info can be put in a main thread without others threads being derailed into another mid motor vs hub deabte.

 

[Ocsid]

The power [Watts] and torque [Nm] thing ought to be easily understood.

Power brings in the time element, how fast or how slow doing something is achieved.

Doing the task at all is where torque is involved.

Agricultural tractors up till the latest fast ones had small powered engines, but could drag a plough needing lots of torque, that being available because that power was deployed at a very low speed.

So returning to our bikes with the 250 nominal Watts, they can have whatever torque a designer chooses, but with that 250 Watts there comes a limited speed for that torque.

Power is torque multiplied by speed, as simple a relationship as that.


A significant argument for CDs in the pedelec case, is the assist is applied at the same point as the pedaller, so the bike's variable gear options are available to both the motor and the human. This ought to be an obvious advantage where a wide range of torques would be encountered, hills and some off road use, just as with a conventional bike we prefer to have a geared bike for hills. The torque at the wheel contribution from a hub motor, unless it features variable gearing, will always be limited to one maximum value.

In my case a CD enables the use of hub gearing and of a belt drive, way my preferred option for my particular needs. Fundamentally, I need a geared system, ideally a low maintenance one, and importantly as the bike goes in the car and house as clean a bike as possible. A front hub would IMO make a very poor functional alternative, a rear hub, clearly a non starter for my needs.

 

[Woosh]

If you look at the functionality, there is no difference whether the torque is generated at the crank then transferred to the rear wheel via the chain or generated directly at the rear wheel.
The difference in feel is not a matter for physics but for the riders. It comes mainly through two things:

1. control electronics (pedal sensor and controller's power)
2. inertia of the bike

control: If you have a crank drive with cadence sensor, you lose the 'man and machine as one' feel.
If you have a crank drive bike with a torque sensor, you have to put in a lot more effort to climb a steep hill.

Inertia: you will feel the effect of inertia when turning or tilting the bike.
Crank drives are invariably better positioned compared to hub.

My conclusion? if you have arthritic joints, you will be better off with a cadence sensor and a hub motor but if you can afford about £200 difference and are fit and well, crank drives are better.

 

[darren66]

In other threads the merits of both have been talked about many times but they end up derailing the course of a thread, so it would be far better for the them to be discussed under a specific thread. The virtues of both types have been extolled many times especially on here.

The latest incursion in the subject has moved on to progress of both motor types, though as always reliability and terrain usage is always thrown in as a Red rag to a Bull.

The mid motor in size. weight and development seems somewhat to have stalled over the last few years, not a bad thing as progress/R & D is exhaustive and time consuming. We have seen motor size stagnate in both OEM motors and kit motors, though there are at least a couple of lightweight kit mid motors that are available at under the 2.5kg mark.
Quoted torque power figures are banded around 50,60,75, 80, 100 & 120 N.m supposedly all from weedy generic 250w rating which is the legal status almost worldwide for ebikes/pedelecs to be used in the same breath as a Pushbike. Not being an engineer this is beyond me as I can't see how a motor can produced more quoted N.m without the wattage being increased, current can be upped to get more temporary watts/power and gearing to an extent can be changed but to go from 50 or 60 to double those figures I feel that somewhere the output figures are being massaged like the cases we have seen in the Car industry.

Hub motors have been a favourite for many years using geared hubs and heavier D/D (Direct drive) hubs but for our purposes and 250w the geared hub is king.
Here we are seeing size /weight movement in their design with more coming online for a lighter bike build, sub 2.5 kg hubs and less then 100mm dia.
The latest from Keyde even incorporates the controller within the motor, and now mini hubs resemble a hub the size of an Alfine/Nexus or Rolhoff hub geared unit.
Again the torque figures are similar to the mid drive 25 N.m values have increased and now we see 40,45 & 50 N.m banded around as torque figures.

Lots more to add to this thread for sure and I know a few on here are biased to a particular drive so lots of discussion I think to be had with the hopes that most of the info can be put in a main thread without others threads being derailed into another mid motor vs hub deabte.

A Dewalt 18v 2.0ah cordless drill has a max torque rating of 65Nm...

 

[mike killay]

A Dewalt 18v 2.0ah cordless drill has a max torque rating of 65Nm...

From what I understand, torque rating is meaningless unless it is coupled with "How fast?"
It is easy to gear things down to produce massive torque, after all consider a car jack.

 

[Nealh]

The hub motor torque is dependant on the rpm speed of the hub motor a 201rpm will have much better climbing ability then a faster wound 328rpm one, then the bikes actual gearing needs to be low enough to prevent motor stall.

 

[Nealh]

Reliability wise I have had none with my hubs all having 20 - 25a controllers being used, during the recent heavy rains and flooding I have ridden thru water at crank level and have had no water ingress in my Bafang CST ( circa 7000 miles ), this confirmed when I carried out a major service on my Norco 700c yesterday which included opening the hub for inspection which took all of 5 -10 mins.
We do here and see pics of rusty hubs but mainly due to wrong fitting of the motor upside down.

The OEM mid motors I have had have all failed, two GSM's with internal controller both failed. One managed 250miles and the second about 60/70miles, the BBS01 also suffering two controllers failures with about 3500 miles and for now consigned to the spare parts bin.

Bosch mid motor we here a lot about and have some issues with bearing failures and water ingress to said bearings, routine grease packing and after market seal is spoken of but for your average Joe/Jo not something they would get involved with.

 

[Deleted member 25121]

The hub motor torque is dependant on the rpm speed of the hub motor a 201rpm will have much better climbing ability then a faster wound 328rpm one, then the bikes actual gearing needs to be low enough to prevent motor stall.

Power is proportional to torque times rpm.

For a given power (eg 250W), if rpm goes up the torque will go down.

The 328 rpm motor will have lower torque but will be capable of a higher speed if the size of the wheel is constant.

 

[Woosh]

two GSM's with internal controller both failed.

the early internal controller in the GSM made by a company I shall not name was a disaster.
I later replaced it by a Lishui controller but the latter was still subject to heat related failure, forcing me to sell only GSM without internal controller.
Mind you, the early Bafang controller wasn't very good either compared to the later B version.

 

[Woosh]

there are two attractions to the crank drives:
1. the ability to have a lightweight high speed bike - you can cruise at 30mph with a derestricted 100NM CD motor.
2. like a car with manual gearbox, you can ride more efficiently if you so wish - but you have to think hard, be always in the right gear and capable of modulating your pedal pressure with your cadence. In other words, you have to be an excellent cyclist.

Basically, if you can push 175mm cranks on average at 60kgf pressure at 100 RPM, you produce 110W (the formula is 2*pi * 0.175m * 100/60s * 60kpf) .
That is way beyond the level of fitness most of my customers are capable of and before the ability to shift gears under load.
If you climb a hill in the wrong gear, your cadence may drop. Pushing the same 60kpf at half the optimal cadence, 50 RPM for example, your output will be halved, 55W, and the motor output drops also to a half of its best. You would wish you have bought a hub motor instead.

 

[Ocsid]

Removed; original miss read.

 

[sjpt]

Crank drive with hub gear is a good combination. Big advantage is you can easily change when stationary (especially in some situations just before starting up a hill). Though the Nexus 7 seems to require no load (not just light load) for a significant fraction of a second to change; this can be an issue if you realize you are in too high a gear once on a hill.

With the hub drive on the tandem we still have to think carefully about gears, and to think about best assist setting as well. (Admittedly that is partly because we have an XF07 which is extremely helpful, but underpowered and overgeared for what we ideally want. We were aware of that when we bought, and Woosh made it very clear. It still does what we need; to give lots of help especially on hills. Not much else available at the time; also we wanted a fairly low cost entry to see if we like ebikes (we do). May upgrade some time but doing us fine. Main upgrade would be the tandem, to low step at the front. )

 

[Woosh]

You are therefore saying here that all CD unit torque sensing is used linearly, there is no profiling of the motor output to the pedal input torque?
I would have thought the products would be more sophisticated than that.

no, I am not saying that. Bosch give clearly maximum torque figures for their motors.

For example, for the basic Bosch Active Line*:

TURBO: 40NM
SPORT: 38NM
TOUR: 35NM
ECO: 30 NM

You get 40NM at most at 100 RPM if you are an excellent cyclist, if you are someone with poor health, you would manage 50RPM on hills, that motor does not give you 80NM @ 50RPM to compensate, you'll get 40NM @ 50 RPM, half of the motor output at its best.
Then you lose some of that torque through the gearing. There is no wonder in observing that those who rubbish hub motors own Bosch CX and not Bosch Active Line.
You see why I add a throttle to my crank drive bikes?

Source: https://www.bosch-ebike.com/en/products/active-line/

 

[Ocsid]

I am not seeing why adding a throttle to a CD can increase the motor's maximum torque, power yes, but that would be available only if the motor could rev faster.

To rev faster would require some extra gearing to be available. However, somebody struggling up a hill, already would be in the lowest gear available, to ease struggling.

Clearly to my mind adding a throttle is desirable, CD or HD, if you don't actually want a pedal assist e-bike, just a motorised bike.

 

[Andy-Mat]

In other threads the merits of both have been talked about many times but they end up derailing the course of a thread, so it would be far better for the them to be discussed under a specific thread. The virtues of both types have been extolled many times especially on here.

The latest incursion in the subject has moved on to progress of both motor types, though as always reliability and terrain usage is always thrown in as a Red rag to a Bull.

The mid motor in size. weight and development seems somewhat to have stalled over the last few years, not a bad thing as progress/R & D is exhaustive and time consuming. We have seen motor size stagnate in both OEM motors and kit motors, though there are at least a couple of lightweight kit mid motors that are available at under the 2.5kg mark.
Quoted torque power figures are banded around 50,60,75, 80, 100 & 120 N.m supposedly all from weedy generic 250w rating which is the legal status almost worldwide for ebikes/pedelecs to be used in the same breath as a Pushbike. Not being an engineer this is beyond me as I can't see how a motor can produced more quoted N.m without the wattage being increased, current can be upped to get more temporary watts/power and gearing to an extent can be changed but to go from 50 or 60 to double those figures I feel that somewhere the output figures are being massaged like the cases we have seen in the Car industry.

Hub motors have been a favourite for many years using geared hubs and heavier D/D (Direct drive) hubs but for our purposes and 250w the geared hub is king.
Here we are seeing size /weight movement in their design with more coming online for a lighter bike build, sub 2.5 kg hubs and less then 100mm dia.
The latest from Keyde even incorporates the controller within the motor, and now mini hubs resemble a hub the size of an Alfine/Nexus or Rolhoff hub geared unit.
Again the torque figures are similar to the mid drive 25 N.m values have increased and now we see 40,45 & 50 N.m banded around as torque figures.

Lots more to add to this thread for sure and I know a few on here are biased to a particular drive so lots of discussion I think to be had with the hopes that most of the info can be put in a main thread without others threads being derailed into another mid motor vs hub deabte.

Firstly, I would like to thank you for the topic, really interesting.
But, as a confirmed rear hub user on two bikes that I have owned, and several others I have borrowed and tested, I have read nothing here that would convince me to buy a mid motor bike, in fact, the complete opposite.
I have ridden both of my bikes in huge downpours and through streams (Not yet any rivers!), the worst that happened was the LCD display got water inside, as did my throttle. I sealed up the display, except for a small opening underneath, to allow air expansion and contraction, since then, no more problems. The throttle took several days to dry out, in fact I was of the opinion that the controller was damaged for a time, as it took 4 or 5 days to dry out. I even looked inside the controller for water, but it was completely dry, wasted effort!
I am and was very happy with the balance of both my bikes, (and I have been riding on 2 wheels for over 60 years), as the battery on my latest is in the crossbar, and the motor is at the rear of course. What some mid motor fans say about hubs, rear ones at least, are complete and utter fairy tale rubbish - probably sad that they wasted their money on a mid motor.
My current bike was really cheap, and including transport and import fees, for well under €1,000 (around £910), I got a full set up, two batteries, and all the other extras. The only bad point was that the upper headset bearing was wrongly installed in China, and it took a long time for the supplier to send a new one.
Once installed, the bike has had no further problems, just charge the batteries and pump up the tyres and ride ride ride.....Oh yes, and occasionally a cleaning and rub down with WD-40, avoiding the brakes of course!
Furthermore, even if there are any future problems, I have saved more than enough (and had already several years riding) in comparison, so that I could replace many expensive parts and still not be out of pocket, as I do all the work myself.
Friends and acquaintances with trouble free mid motors, are usually the "Sunday rider", only in the summer, who stays at home when it rains!
Many of the others have had expensive arguments with Bosch one way or another...
I know no one with any other make of mid motor, sadly.
Andy

 

[Woosh]

Clearly to my mind adding a throttle is desirable, CD or HD, if you don't actually want a pedal assist e-bike, just a motorised bike.

Why do you think having a throttle means you stop pedalling?

If you have asthma for example, you'd be grateful for a throttle just in case.

 

[Nealh]

I have asthma and very rarely use the throttle I am able to exhale up to about 440 l/min, someone worse might struggle to exhale even 300 l/min so a throttle might well be indispensable. An unaffected rider will easily exhale 600 l/min or more.

 

[Nealh]

The 201rpm BPM front hub I have is quite immense in power esp up hill in PAS 5, bike gearing though is still critical to prevent motor stall/heating. The penalty though for the hub is 4.4kg of mass at the front end, it will be interesting to see how the 1.7kg G370 front hub performs when it arrives. The 210rpm BPM on level ground at 20a is also quite potent and the use of PAS above level two is simply not needed as the torque is strong and easily moves me along at a max 19mph.

I may have to self quarantine the G370 for 14 days when it arrives , seriously though I will disinfect the product with a neat wipe of bleach just in case.

 

[Woosh]

then leave it in the midday sun for a couple of hours.

 

[GLJoe]

... mid motor vs hub deabte.

One thing I think is particularly important in this conversation, is to clearly distinguish between the motor types, and the control technology implemented, and not to lump them in together.

All too often I see people saying that crank drive bikes are more 'natural' feeling to ride , however where when you dig into it, its because most of them use torque sensing and sophisticated algorithms, and many hub drives only use a crude cadence sensing implementation.
A high end hub drive bike with a quality torque sensor like the TMM4 can give a very, very natural feel.