Watt's Occurring?

[RickBradford]

This is a bit of a long story about motor types, and effectiveness. I evaluate my e-bikes for effectiveness by their combination of speed, range, and rider power input which are optimal.

For 2 years I rode a 500W 36V front-hub motor from a Chinese company called Jueshuai, which features 3 modes - Eco, Trail and Boost - which put out approximately 125W, 250W and 500W respectively. The cadence sensor is on-off and the electronics is square wave - turn the pedals at any cadence and you get the full power of whatever mode you are in.

This makes calculating power output very easy. In Trail mode, my preferred mode, the motor is constantly pushing out 250W, and with the 360Wh battery I have installed, that gives me about 80 minutes of continual riding. The distance I travel depends on the speed I go at, which in turn is directly related to how much extra power I apply.

I have recently switched to a 500W 36V mid-drive Tongsheng motor with torque sensing which has 4 modes - Eco, Tour, Sport and Turbo, although I still cannot get an accurate view of how much assist each mode gives - 50% or 100%, that sort of thing. I can guess at the amount of power being consumed by looking at the battery voltage before and after and using a crude discharge vs voltage graph. Or if I run out of power completely ....

I have compared the two motors (on the same frame) and my conclusion is that the front hub motor is considerably more efficient.

My standard commute is a 30km round trip on good asphalt, not flat, but not exceptionally hilly. Using the Jueshuai front hub motor in constant 250-watt Trail mode, I can maintain a speed of 28kph with moderate effort so that the round trip take about 65 minutes, well within my 80-minute limit. Using the Tongsheng, I decided to match the 28kph speed, and found myself working the pedals a lot harder and calculated that the motor was putting out an average of 305 Watts. More rider effort, more motor power, same speed. I've done other experiments, which show that to keep average motor output to 250 watts, I have to dial back the average speed to around 25.5kph on the Tongsheng motor.

Anecdotally, the Jueshuai front hub just eats medium inclines, and even on the steepest inclines outpaces the Tongsheng comfortably. It's an anti-gravity device. The Tongsheng, on the other hand, sends immediate signals when it hits even the slightest incline.

I've done enough riding on the Tongsheng to generally confirm this diagnosis - the Jueshuai front hub delivers more speed for more range for less rider input. But this goes against everything I read about mid-drive torque sensor motors, which one enthusiast described as "incredibly effective".

Anyway, that's my experience, apologies for the long post and I would welcome any insights from more experienced members.

 

[Viking1]

Wow, nice synopsis. One question, with the front hub motor gear shifting is optional as whatever selected gear has no effect on the motor performance. That said are you using your mid drive in the same manner as a “single speed” or actually using the gears to match the terrain ridden?

 

[RickBradford]

That's another factor which favors the hub drive.

With the front-hub motor, I stay in top gear unless there's a serious hill coming up. With the mid-drive, I'm constantly working the gears along with the assist level to try to get the optimal amount of power.

 

[AHicks]

Which agrees with what I've been saying for a while now. Hub drives are MUCH easier to ride, especially when compared to a mid drive. You need big hills to justify a mid drive.....

 

[harryS]

Nick, I ride slower than you, so I get a lower number on my hub motors. At 12 mph, I;m usually at 8-10 WH/mile, The Bafang BBS02B mid drive was my second conversion back in 2016, That uses about the same burn rate, at the same speeds. I measure the WH with an external RC wattmeter on the battery. Done it many times, while riding or when recharging,
.
Another way to estimate power, if the bike has a watts on its display is simple math, On my bikes, it's 100-120 watts to go 12 mph. One hour is 100-120 watt-hour. Divide by 12 miles, and it's 8-12 wh/mile, Compares to the wattmeter, as long as it's continuous. My wife pedals then coasts, then pedals again,. She uses about 30-40% less power than me, but then I have 80 pounds more weight,
,
Enter the dreaded TSDZ2. I installed one last Fall. Using an external wattmeter, in Eco mode at 12 mph, I get 5-6 WH/mile. It means I have to put in 50 extra watts myself, It's not really that much, because I've put it on my lightest bike with the skinniest tires. The advantage is that I can power it with a 48V7AH battery, which has about 300 real watt-hours, and predicts a 50 mile range. In real life low 40's.







.

 

[mschwett]

This is a bit of a long story about motor types, and effectiveness. I evaluate my e-bikes for effectiveness by their combination of speed, range, and rider power input which are optimal.

For 2 years I rode a 500W 36V front-hub motor from a Chinese company called Jueshuai, which features 3 modes - Eco, Trail and Boost - which put out approximately 125W, 250W and 500W respectively. The cadence sensor is on-off and the electronics is square wave - turn the pedals at any cadence and you get the full power of whatever mode you are in.

This makes calculating power output very easy. In Trail mode, my preferred mode, the motor is constantly pushing out 250W, and with the 360Wh battery I have installed, that gives me about 80 minutes of continual riding. The distance I travel depends on the speed I go at, which in turn is directly related to how much extra power I apply.

I have recently switched to a 500W 36V mid-drive Tongsheng motor with torque sensing which has 4 modes - Eco, Tour, Sport and Turbo, although I still cannot get an accurate view of how much assist each mode gives - 50% or 100%, that sort of thing. I can guess at the amount of power being consumed by looking at the battery voltage before and after and using a crude discharge vs voltage graph. Or if I run out of power completely ....

I have compared the two motors (on the same frame) and my conclusion is that the front hub motor is considerably more efficient.

My standard commute is a 30km round trip on good asphalt, not flat, but not exceptionally hilly. Using the Jueshuai front hub motor in constant 250-watt Trail mode, I can maintain a speed of 28kph with moderate effort so that the round trip take about 65 minutes, well within my 80-minute limit. Using the Tongsheng, I decided to match the 28kph speed, and found myself working the pedals a lot harder and calculated that the motor was putting out an average of 305 Watts. More rider effort, more motor power, same speed. I've done other experiments, which show that to keep average motor output to 250 watts, I have to dial back the average speed to around 25.5kph on the Tongsheng motor.

Anecdotally, the Jueshuai front hub just eats medium inclines, and even on the steepest inclines outpaces the Tongsheng comfortably. It's an anti-gravity device. The Tongsheng, on the other hand, sends immediate signals when it hits even the slightest incline.

I've done enough riding on the Tongsheng to generally confirm this diagnosis - the Jueshuai front hub delivers more speed for more range for less rider input. But this goes against everything I read about mid-drive torque sensor motors, which one enthusiast described as "incredibly effective".

Anyway, that's my experience, apologies for the long post and I would welcome any insights from more experienced members.

interesting post! same frame, same tires, same gearing? are you using a heart rate monitor or other method to determine that the human input is consistent?

in your post, you refer to determining the the mid was putting out an average of 305w; do you mean it was consuming 305w? without knowing your input to the total power you don’t really know how much power the motor is outputting, but the method you describe could roughly determine how much power the motor is consuming.

if i had to hazard a guess… the cadence you’re riding at and the power output you’re looking for from the motor sit at a very inefficient spot on that particular motor’s power curve. what’s the cadence and gearing at your 25-28kph target range? do you have an efficiency curve for the motor? the motor power ratings on these things are quite, well, arbitrary, and it could be that you’re operating the tongsheng (TSDZ2?) at a speed/power level in which it’s very inefficient.

there’s also the possibility of drivetrain losses being more significant than they should, but even a truly horribly maintained drivetrain shouldn’t be more than a few percent.

 

[Gionnirocket]

Though very interesting your methods are not very scientific and open to quite a bit of interpretation and error.
You should be using the method HarryS. uses to measure Wh used for both as your scale of power used.
Additionally... Did you use the same battery and start off with the same SOC? Is now the battery used for the mid drive 2 years older than when used with the hub? You should be comparing them at the same time.
The Tongsheng is tunable.. Did you adjust for your riding needs and efficiency? I know my BBSO2B is far more efficient after tuning and I'm averaging 8wh/mi in a relatively hilly 20mile ride... but ymmv

 

[tomjasz]

But this goes against everything I read about mid-drive torque sensor motors, which one enthusiast described as "incredibly effective".

I have ridden a front DD for 7 years and have had every BBSxx series mid-drive and a TSDZ2. In my experience, those that prattle on about how bad a hub motor is on grades are just repeating what they've read and have NO actual experience with hub drives. Direct Drive motors can be "fixed" and stay much cooler with statorade and/or cooling fins.

Using the Grin simulator link we can see the real-world temperatures of various grades.

 

[tomjasz]

Link to a worthwhile read.​

​

Where do BBSxx and similar mid-drives shine?​

There are a certain areas where bottom bracket middrive motors are hands down better suited than hub motors. Offroad mountain biking is one great example. The motor weight is low and on the unsprung frame so it has minimal effect on handling even in full suspension bikes. In these situations you are often going slowly uphill through trails with short steep sections and a small motor working through the drivechain in the granny gears of the bike can do this with excellent efficiency. Another example would be say fat bikes riding in sandy beaches or through fresh snow. These are areas where the bike is moving at lowish speeds through high resistance terrain, and the mid-motor in an easy gearing will do this with better efficiency than most hubs drives, while still performing just as well on the faster roads.

For us though, a majority of our customers are using their ebikes for daily use commuting, riding on roads where maintaining a steady speed regardless of the hill grade is important. For that requirement a mid-drive offers almost no advantage and we continue to believe that hub motor kits shine the strongest for reliable and low maintenance commuter ebike conversions, and that's the bulk of who we serve.

Hub Motor Advantages​

Here are a few benefits to a hub motor system to keep in mind and help inform your decision. Please don't see this as us taking sides and saying that hub motors are universally better than mid-drive motors, all we want to do is balance out the discussion a little by highlighting the many benefits of a hub motor drive which are frequently missing from popular discourse at the moment.

 

[Gionnirocket]

Link to a worthwhile read.​

​

Where do BBSxx and similar mid-drives shine?​

There are a certain areas where bottom bracket middrive motors are hands down better suited than hub motors. Offroad mountain biking is one great example. The motor weight is low and on the unsprung frame so it has minimal effect on handling even in full suspension bikes. In these situations you are often going slowly uphill through trails with short steep sections and a small motor working through the drivechain in the granny gears of the bike can do this with excellent efficiency. Another example would be say fat bikes riding in sandy beaches or through fresh snow. These are areas where the bike is moving at lowish speeds through high resistance terrain, and the mid-motor in an easy gearing will do this with better efficiency than most hubs drives, while still performing just as well on the faster roads.

For us though, a majority of our customers are using their ebikes for daily use commuting, riding on roads where maintaining a steady speed regardless of the hill grade is important. For that requirement a mid-drive offers almost no advantage and we continue to believe that hub motor kits shine the strongest for reliable and low maintenance commuter ebike conversions, and that's the bulk of who we serve.

Hub Motor Advantages​

Here are a few benefits to a hub motor system to keep in mind and help inform your decision. Please don't see this as us taking sides and saying that hub motors are universally better than mid-drive motors, all we want to do is balance out the discussion a little by highlighting the many benefits of a hub motor drive which are frequently missing from popular discourse at the moment.

I'd also add and to me more important at this point... Mid drives are more fun if you enjoy riding engaged.
To me a hub is like an economy car with an automatic transmission where a mid drive is a rear wheel drive/ manual transmission. I don't ride solely for efficiency, I ride for exercise and fun
ymmv

 

[RickBradford]

Nick, I ride slower than you, so I get a lower number on my hub motors. At 12 mph, I;m usually at 8-10 WH/mile, The Bafang BBS02B mid drive was my second conversion back in 2016, That uses about the same burn rate, at the same speeds. I measure the WH with an external RC wattmeter on the battery. Done it many times, while riding or when recharging,
.
Another way to estimate power, if the bike has a watts on its display is simple math, On my bikes, it's 100-120 watts to go 12 mph. One hour is 100-120 watt-hour. Divide by 12 miles, and it's 8-12 wh/mile, Compares to the wattmeter, as long as it's continuous. My wife pedals then coasts, then pedals again,. She uses about 30-40% less power than me, but then I have 80 pounds more weight,
,
Enter the dreaded TSDZ2. I installed one last Fall. Using an external wattmeter, in Eco mode at 12 mph, I get 5-6 WH/mile. It means I have to put in 50 extra watts myself, It's not really that much, because I've put it on my lightest bike with the skinniest tires. The advantage is that I can power it with a 48V7AH battery, which has about 300 real watt-hours, and predicts a 50 mile range. In real life low 40's.

.

This is a great all-round measure of efficiency. With my hub motor in Trail mode, averaging about 18mph, I use up 14.4 Wh/mile. In ECO mode at 14mph, I only use 9.4Wh/mile. Very similar to your figures.

I did a tour with the TSDZ2 yesterday, mixing modes strategically, averaged about 15mph and was burning 11.8Wh/mile, and I was working quite hard throughout the 1-hour ride.

It may be that I still haven't learned how to ride the TSDZ2 properly - I read somewhere that the motor works best at a cadence of 60rpm and falls away rapidly either side of that. I have no idea whether that is true or not - it seems rather low. My preferred cadence is well above that, I know.

I'm coming round to the idea that I will have to attempt the daunting task of tuning the firmware - I know there is plenty of good advice on how to do that.

 

[tomjasz]

I'd also add and to me more important at this point... Mid drives are more fun if you enjoy riding engaged.
To me a hub is like an economy car with an automatic transmission where a mid drive is a rear wheel drive/ manual transmission. I don't ride solely for efficiency, I ride for exercise and fun
ymmv

Very good analogy. For me, and many here, an eBike is a BSO, bicycle shaped object, and really more of an alternative form of transportation.

 

[rtp]

The short difference in your 'estimated' measurements (e.g. 250W vs ~305W), could be down to motor or controller efficiency, as well as drivetrain losses. In the automotive world, there's a reason most tuners call out 'wheel HP and torque' values, versus manufacturers typically calling out 'crank HP/torque' because having it at the motor doesn't mean you have the same #s at the wheels, with typical drivetrain losses ranging but around 15% or more, so a 300HP vehicle may dyno at 250HP measured at the wheels, or less. mid-drives have drivetrain losses from the chain/derailleur, etc. and hub drives do not, at least for the most part. I'm saying for the most part because we could get into shades of grey, e.g. is the power needed to trigger the motor to assist for a hub motor a 'drivetrain loss'? I'd say no, because once the power (from the motor) is produced, it's not impacting that power output, although it can be argued it's impacting the overall net power transfer. Of course, the spokes/hubs/rims/tires are a 'loss' from motor output, but those are basically the same given the same bike but with hub vs mid-drive.

It would be interesting to have more granular data like torque values from the motor, but short of someone spending time and $ on a science project, it may not be some easy to get, so I guess Wh/mile along with perhaps added instrumentation for pedal cadence or input force is probably the best we can get.

Regardless of the data it'd be nice to have, there are some places, for some people and some uses, hub drives are just fine, assuming decent-enough motor quality.

 

[AHicks]

The short difference in your 'estimated' measurements (e.g. 250W vs ~305W), could be down to motor or controller efficiency, as well as drivetrain losses. In the automotive world, there's a reason most tuners call out 'wheel HP and torque' values, versus manufacturers typically calling out 'crank HP/torque' because having it at the motor doesn't mean you have the same #s at the wheels, with typical drivetrain losses ranging but around 15% or more, so a 300HP vehicle may dyno at 250HP measured at the wheels, or less. mid-drives have drivetrain losses from the chain/derailleur, etc. and hub drives do not, at least for the most part. I'm saying for the most part because we could get into shades of grey, e.g. is the power needed to trigger the motor to assist for a hub motor a 'drivetrain loss'? I'd say no, because once the power (from the motor) is produced, it's not impacting that power output, although it can be argued it's impacting the overall net power transfer. Of course, the spokes/hubs/rims/tires are a 'loss' from motor output, but those are basically the same given the same bike but with hub vs mid-drive.

It would be interesting to have more granular data like torque values from the motor, but short of someone spending time and $ on a science project, it may not be some easy to get, so I guess Wh/mile along with perhaps added instrumentation for pedal cadence or input force is probably the best we can get.

Regardless of the data it'd be nice to have, there are some places, for some people and some uses, hub drives are just fine, assuming decent-enough motor quality.

That's it, right there in the bold, if looking for the long story summed up in a nutshell!!

A quality built 1000w geared hub is qoing to perform nicely when riding with/next to a similarly powered mid drive on the level, and even in hills to a certain extent (while using very similar levels of power BTW). That's been my experience anyway. Same story when running 500w geared hubs with 500w mid drives. I have the bikes in these classes and have a lot of miles on each. They both have their upsides and down sides in my experience.

My take away on the mid drives is similar to GR's above, they're awesome for those that like riding "connected". To that I would add that the big ones (1000w+) can be absolute torque monsters that are easier to ride due to less picky gearing demands, and no matter what size they are, when push comes to shove, they can get the job done in the hills.

Where the geared hubs have it, with the fact most will have a throttle, is in their brain dead simplicity to ride. Point it and go. Pedal for exercise, and use the throttle when/if you need it. My thoughts anyway, FWIW. -Al

 

[tomjasz]

“Brain dead”, post TIA a perfect match.