Hub vs middrive efficiency?
Posted by catboy519@reddit | ebikes | View on Reddit | 35 comments
I own a bike with front wheel hub motor 250w geared brushless .
I've seen it about 100 times on this sub, "hub motors are terribly inefficient"
But I can't understand why a mid drive would be more efficient. It has nothing to do with RPM because when I operate my hub motor ebike, the motor spends 99% of its time close to optimal RPM. I maintain a constant speed most of the time. Although depending on battery and wind, my hub motor usually operates between 68% and 85% of its max RPM.
Any RPM outside of that range is either accelerating (which is only a tiny part of the whole ride) or exceptional conditions (storm, offroad)
So if we compared a hub motor vs mid drive at the same power/speed/rpm/torque, why would the mid-drive be more efficient?
THALLfpv@reddit
for the same reason manual cars get marginally better gas mileage if the driver knows how to use it properly. The driver can select the gears that provide maximum torque and speed from a dead stop. The hub motor just has to waste energy until it gets to its optimal state. The mid-drive is in the optimal state from a dead stop, all the way up to max speed.
The efficiencies of the mid drive increase even further when you start adding inclines. The hub motor will be at a lower RPM than is optimal, creating excess heat which is just wasted energy, where the mid drive can simply gear down and be in its optimal state while climbing the hill.
The mid drive also has better weight distribution and riding characteristics. There is no way to offset the weight of the hub motor, it will always be unsprung dead weight. The extra weight of the mid-drive gets absorbed by even the most basic front suspension setups which makes for a nicer ride.
hub motors are good for stuff like food deliveries because you can use the hub motor even if the chain is broken. They have their purposes and aren't "terribly inefficient", but they are absolutely less efficient than someone who knows how to properly use a mid drive with a decent gear range. Some people own mid-drives and don't use their gears properly and their bikes may be less efficient than your hub drive because of it. The assumption is that you know how to use the gears if you have a mid drive
catboy519@reddit (OP)
You're making a comparison to cars, but.. electric cars (and motorcycles) don't have gears.
THALLfpv@reddit
ok sounds like you're an expert. good luck
catboy519@reddit (OP)
No, just pointing out the comparison isn't fair.
Agitated-Country-969@reddit
If you can't understand why he used a car analogy that's on you.
What's unfair is comparing to EVs and electric motorcycles when they have advanced cooling systems and regenerative braking, none of which an e-bike has. So an e-bike motor is likely to overheat if you push it too hard.
THALLfpv@reddit
You asked about hub vs mid drive efficiency and you got a post about why mid drives are generally more efficient. to make it easier to understand I used a car analogy. Anybody should be able to understand this, if you can't that's on you. Good luck in your search for answers.
Arcanum3000@reddit
An electric motor is most efficient at about 85% of its max RPM and 15% of its max load. For a direct drive hub motor, you're only hitting that at close to top speed on a flat route. If you're climbing hills or doing stop-and-go riding, or fighting against a strong headwind, you're not hitting those optimal conditions. If you're pulling or carrying a heavy load, getting up to that speed will take longer, also reducing overall efficiency.
A mid drive, between its internal reduction gearing and the gearing of the bicycle itself, can spend more time closer to those optimal conditions when climbing hills, pulling loads, or doing stop-and-go riding. Or fighting against a headwind. Or plowing through snow.
Agitated-Country-969@reddit
Yup. If you look at OP's post history he mentions headwinds a lot. So compared to a mid-drive, in a strong headwind a hub motor is suboptimal since the motor won't be hitting 85% of max RPM. Like if you go to the Grin e-bike simulator, the max efficiency for the default motor selected is at 40.9 km/h, but you are not hitting that in a strong headwind.
https://old.reddit.com/r/ebikes/comments/1ad5ekr/why_is_it_legal_to_use_downhillmuscletailwind_to/kk4dka3/
https://old.reddit.com/r/ebikes/comments/1ewasp8/are_batteries_not_manufactured_with_headwind_in/lixfrmd/
catboy519@reddit (OP)
In very strong winds maybe. But in normal headwind I can still get up to 80% rpm easily
Agitated-Country-969@reddit
Well, you've talked about 50 and 70 km/h headwinds before, so clearly it's something that matters.
With a hub motor you're literally just crap out of luck but my mid-drive works 365 days out of the entire year. In strong headwinds like those you might as well not even have a motor at that point due to low RPM and low efficiency. It also works if I ever want to go riding in the mountains or anything and has gravel tires. My e-bike is far more versatile than yours is.
catboy519@reddit (OP)
I mean that yes, a mid drive is more efficient under rough conditions like.steep hills and stormy winds but under normal circumstamces on rhe flat, is it still mote efficient?
Agitated-Country-969@reddit
On the flat under baseline conditions they're equivalent.
catboy519@reddit (OP)
Hence 99% of the time a hub should have as much efficiency as there is.
Agitated-Country-969@reddit
I also wanted to mention that if in 70 km/h winds you can just pedal and deal with it, then range doesn't matter for bad conditions since you can just pedal with your legs and deal with it, right?
catboy519@reddit (OP)
If there is 70kph headwind then firstly it just sucks. Some days of the year are just more difficult to get through.
But I'd have 3 options still:
70kph headwind sucks no matter what you do, but it happens probably just once in a year.
As soon as the battery is empty it would be necessary to step off and walk.
Agitated-Country-969@reddit
If the efficiency doesn't matter for bad conditions, then the range doesn't matter for bad conditions.
If the range matters for bad conditions, then the efficiency matters for bad conditions.
It's that simple, because the efficiency affects the range.
catboy519@reddit (OP)
There is a difference betwen "bad" and one in a year conditions.
If mid drives are much more efficient in normal levels of wind then I would want a mid drive.
If they are only significantly better one day per year then you might aswell get a hub drive.
You could say mid drives are more reliable, but "much more efficient" seems like a big statement that is not always right.
Agitated-Country-969@reddit
My only point is if you're saying strong headwinds is only 1% of times so the low efficiency doesn't matter because it happens so rarely, then okay, you definitely don't need range for strong headwinds. You can't have it both ways.
catboy519@reddit (OP)
An ebike should have enough range for strong headwinds.
If its a once per year storm thats an exception.
Agitated-Country-969@reddit
It's funny to me that you talk about logic yet the logic does not support this conclusion. Clearly you don't really care about logic.
You said this:
And range is intrinsically tied to efficiency because if you have 20% efficiency you will not get much range.
Thus...
QED.
Note here that Premise #2 is the Contrapositive of Range matters -> Efficiency matters. I have a feeling you've never formally studied logic, such as in Philosophy or Discrete Mathematics (the prerequisite to Algorithms).
catboy519@reddit (OP)
The efficiency is not one fixed number. If a hub motor can run at high efficiency 99% of the time then its an efficiet motor. The other 1% is just rare and extreme weather where most people stay home anyway.
There is a difference between bad conditions and extreme conditions.
Agitated-Country-969@reddit
I knew you were going to go for your usual "if this, then that", so let me clarify the argument.
QED.
catboy519@reddit (OP)
I don't see why youre trying so hard to prove that during extreme headwind the lack of range doesnt matter , because thats exactly my point too.
70 kph headwind isnt just "bad", its an extreme that rarely happens hence you should not expect it to happen. But if it happens youll have to accept the downsides of it.
If you refer to my "minimum range to rely on", what I actually mean there is normal bad circumstances and not the therotetically qorst case scenario possible.
If 364 days of the year my range >= 30km, and 1 day I get 20km range, I will consider 30km to be my minimum range because the 20km was an extremely rare case.
An ebike should have range and efficiency under normal bad circumstances. Not extreme and rare bad circumstances.
Agitated-Country-969@reddit
Okay, so you don't need good range in 70 km/h headwinds then and there's no need for e-bike manufacturers to take 70 km/h headwinds when determining the size of batteries to purchase.
You said this:
So you can just accept one day out of the year you will have really crappy range and will have to pedal home.
catboy519@reddit (OP)
Manufacturers should, but for some reason dont, build batteries with normal headwind in mind. 30kph headwind happens quite often so if your commute is 25km and you wanna do it in 1 hour, it takes exactly as much energy as 55kph with no wind.
Is the headwind more extreme, you can still get the range bu going slower. I have never tested it yet but I assume that pas 13kph would get me 30km range in even the strongest headwind.
A sufficiently sized battery should allow for either of the 2 situations: 1. Normal headwind, max power, max speed 2. Extreme headwind, reduced power and speed The range should then be as much as the customer desires. I guess most people do close to 20 km rides one way regularly so you would need 20km range at max power in a normal heafwind.
Agitated-Country-969@reddit
This is where you ignored what other people were saying about economics in your other thread. Just because that happens in the Netherlands, doesn't mean it happens often in other countries, and the Netherlands is small compared to France. And big batteries cost more money, and people don't like paying more money.
.
But what I was saying is that efficiency is inherently linked to range, so a mid-drive is important if you care about range.
What I can tell you though is with your hub motor you have to do all sorts of tiring calculations on the fly but I just don't worry about it with my mid-drive, because I have maximum efficiency at any speed, so I pick the right gear for the occassion and that's literally it. It's no different from a road cyclist on a pedal bike. I can't imagine it's better to have to do all those tiring calculations all the time, but you do you, I suppose.
catboy519@reddit (OP)
I dont strictly have to do calculations, I could use the lowest PAS and know my battery wont be empty.
If I use the lowest PAS which is 13kph then my range is limited by time. Not energy.
Agitated-Country-969@reddit
If you use the lowest PAS, your hub motor is not running at high efficiency in a headwind.
catboy519@reddit (OP)
300km is a bad example because thats extremely far and can only be done if there is very little wind.
But say 50km and moderate headwind. That would require me to go slower, so using pas 2 or 3 (16 or 19 kph)
The rpm would be lower but the motor would also be running at very low power. Therefore, the low RPM has less effect on efficiency (there is less ampere)
Which my earlier experiment also represents. I went uphill repeatedly at low and high speeds. The total energy used to get ontop of the elevation was the same every time. So I guess the lower power compensates for the lower RPM.
Agitated-Country-969@reddit
You've definitely mentioned 260 km before, so that's literally an example you brought up. It is true the less power you use, the less power gets converted to heat, but it doesn't change the fact you will never have the same range as a mid-drive. So if you ever go bike touring or want to travel to a farther place away, your e-bike will be ill-suited for that. Meanwhile, my e-bike works for all scenarios.
You were specifically questioned here about 260km:
https://old.reddit.com/r/bicycletouring/comments/1fjbz1z/what_to_do_if_very_strong_headwinds_comes_up/lnn4gkv/?context=3
Since you've brought it up, it must be something you've thought about and been concerned about.
Agitated-Country-969@reddit
I knew you were going to go for this, so let me clarify the argument.
Arcanum3000@reddit
No. Your personal experience (which I frankly question anyway) is not everyone's experience.
catboy519@reddit (OP)
In the EU, ebikes are legally limited to 25 km/h.
The motors of those bikes (if hub) are usually built with a topspeed close to 35 kph (and the controller software limits it to 25)
So anyone who uses an ebike to go from one city to another will be cruising at 25 (which is 71% rpm) the whole time.
What part of my personal experience do you question and why?
Arcanum3000@reddit
You just literally described a circumstance where a mid-drive could be more efficient than a direct-drive hub. 71% of max RPM is not 85% of max RPM. A mid-drive could operate in gears running at 85 max RPM while still cruising at 25km/h.
I question your description of your personal experience because you've literally made posts complaining about headwinds.
Agitated-Country-969@reddit
Yup. Here are some more. It's just so interesting to me OP defends his hub drive despite complaining about headwinds all the time, when efficiency is inherently linked to range.
https://old.reddit.com/r/ebikes/comments/1h3fhp3/why_do_so_many_ebikes_come_with_underpowered/lzqhcfc/?context=3
https://old.reddit.com/r/ebikes/comments/1gnm9xk/question_about_peak_power/lwg7ttj/?context=3 https://old.reddit.com/r/bikecommuting/comments/1fsvsqz/what_do_you_wear_to_make_biking_in_the_wind_less/lpphdnc/?context=3
https://old.reddit.com/r/bikecommuting/comments/1fsvsqz/what_do_you_wear_to_make_biking_in_the_wind_less/lpphdnc/?context=3
https://old.reddit.com/r/bikecommuting/comments/1fljpf9/long_distance_by_bike_instead_of_ebike_why/lo3jf3q/?context=3 https://old.reddit.com/r/bicycletouring/comments/1fjbz1z/what_to_do_if_very_strong_headwinds_comes_up/lnn4gkv/?context=3
https://old.reddit.com/r/ebikes/comments/1h3fhp3/why_do_so_many_ebikes_come_with_underpowered/lzslj5k/?context=3