energy efficiency for 2 types of travel

i live in small town and bike to work and for groceries and to town. i do some cruising but not a whole lot. i heard 20 mph or less is an efficient speed and will keep that in mind. i am wondering the most energy efficient way to travel on flat and i don't mind pedalling a little bit, especially for accelerating. and i am planning on 20 inch tires.

so i figure a small mid geared would be good for accelerating from 5 mph to 15 - 25 mph and i figure since i am in town i usually wont get far coasting at that speed with out having to stop because of stop signs or traffic or turning. but on the other hand maybe using a mid or a front dd that is designed to move 160lbs at 20mph and just manually pedal to that speed or close would be more energy efficient? any thoughts?

if accommodating for the added weight from groceries is advisable than i may, but i may also get bike trailer.

i can see both being much more useful than one another from one day to the next. if you are cruising than the dd, if not than the geared with coasting. a main reason for ebiking is to remove at least some of the pedalling. if i were to do more cruising that day i would use a dd, but if it is a mid drive dd i would have to remove the geared mid drive already in place or add a front dd which may be better for cruising than a mid dd. i would be carrying the weight of the mid geared, which would be light and wouldn't affect moderate cruising too much but would be nice to have in a quick connect setup to easily and quickly take off and put on.

they are 2 different riding styles and i may like one or both depending on my mood.

i think the front dd is best for cruising and for most of my travelling and pedalling rhythm. but a mid geared would be the most energy efficient and wacky to ride even for low duration cruising, i am guessing you would pedal to a speed of what ever like 10 mph and then use the geared mid motor to accelerate along with pedalling to 25 mph and then coast until down to 10 mph and repeat. this may entail lots of shifting which would be monotonous. you would not use a front hub dd to cruise because this would use less energy to cover the same distance. because of the higher speed being reached and coasted from, and the gear ratio for accelerating which relives my effort into accelerating which is the most efficient place for my effort to be used for, but foremost not enough cruising ground to justify. its like sprinting and gliding versus jogging, if you need to jog long enough than a front dd will be more efficient. also the power transfer of a mid drive over a hub would help in the energy efficiency.

Basically, you describe wanting to ride cruising, but sounds like your ride will be plenty of stop and go. Coasting is good, one of the advantages of geared hub motors and mid drive. But riding pulse and glide like cars do is not as beneficial for bikes. Not enough mass to coast all that far. But yes indeed, milk that coast to the next stop.

Stop and go, a dd hub motor is seldom the best choice. In order of efficiency,

1 A mid drive, if you actually shift down each stop. If you leave it in a 20 mph gear each stop, you will be about the same efficiency as hub motors.

2 Next best, a geared hub motor. Since you talked about towing a trailer, a large one, able to put out 1000w. ( motor rated 500w) And about 250rpm @ 36v.

3 A hub motor. Only if your total load, you the bike, the battery and motor, and the trailer will be well over 300 pounds would you choose a DD motor. Because of the 20" wheel, you will not need to be particular about the rpm of the motor. But don't confuse this,, for towing a trailer a mid drive is still best, because you can gear down so low 600 pounds is no problem.

Yes,, you can pedal to 15 mph, then start the motor. This pretty much makes all types of bike motor systems equally efficient, or close enough to it. However, why would you want to ride that way? If you are that strong, just pedal a regular bike. I'm just saying, that help on the starts is the real reason you want a motor. Otherwise, it might be less effort to strip 25 pounds of motor and battery off the bike and just pedal.

DO pedal hard, or at least briskly till you are going 20 mph, then if there is any cruise, back off the power till you feel the pressure on your feet. Go less than 20 mph, and you will still get 2 miles per ah of 36v.

a dd motor if my weight is over 300 pounds? why? for regen? and or too inefficient for geared motors to cruise that weight?

Because geared motors rated for 500w get overloaded and heat up when asked to haul more than 300 pounds up a long hill, or similarly, enough stops and starts. Then because of the double shell design of a geared motor, they take a long time to dissipate excess heat. There is a limit to how much weight 1000w can lift.

The answer is more power, and above 1500w, that means DD motors, that are bigger, often rated much higher than 500w.

Or, gear down, as a mid drive can.

I'd say you be better off getting a higher voltage system all the start stopping won't be push so much heat and losses through the motor and gearing is key make sure your motor is chooching in the right rev band for it to be efficient, regen vs coasting is minimal gains with the mass × acceleration we are talking about such low speeds and weight I'd say go with a freewheel.

The battery voltage makes no difference to heat or losses in the motor (unless you also change the gearing/wheel size)

Punx0r said:

The battery voltage makes no difference to heat or losses in the motor (unless you also change the gearing/wheel size)

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I would have thought a 72v system 350w 5amps vs 36v 350w 10amps both geared equally at the wheel and motors wound so 100kv for the 36v and 50kv for the 72v so both would spin identical speeds the 72v would run cooler because it has identical copper mass but runs at half the current so there's less heat losses.
I found my motor got a lot hotter going up hills at 48v 1.6kw getting 15mph at 3000rpm compared to 68v 3.8kw 35+ mph 6000rpm same motor and gearing plus the hill is over in seconds not minutes so makes half the heat at the top I don't need to stop no more too cool off but a majority of this is due to extra windage I suppose with overvolting.

Ianhill said:

I would have thought a 72v system 350w 5amps vs 36v 350w 10amps both geared equally at the wheel and motors wound so 100kv for the 36v and 50kv for the 72v so both would spin identical speeds the 72v would run cooler because it has identical copper mass but runs at half the current so there's less heat losses.

Click to expand...

You've identified that both motors have the same amount of copper in the winding, just arranged differently. This is key: equal copper fill means both motors have identical power and efficiency potential. The 100Kv motor will indeed require twice as much current to produce the same torque but the winding is also twice as fat and half as long, so its resistance is one-quarter of the 50Kv motor. Since resistive power loss is I^2R you'll find both motors dissipate identical power/heat in the winding.

This is a common point of discussion and there are a *lot* other threads on this forum explaining it very well.

Punx0r said:

Ianhill said:

I would have thought a 72v system 350w 5amps vs 36v 350w 10amps both geared equally at the wheel and motors wound so 100kv for the 36v and 50kv for the 72v so both would spin identical speeds the 72v would run cooler because it has identical copper mass but runs at half the current so there's less heat losses.

Click to expand...

You've identified that both motors have the same amount of copper in the winding, just arranged differently. This is key: equal copper fill means both motors have identical power and efficiency potential. The 100Kv motor will indeed require twice as much current to produce the same torque but the winding is also twice as fat and half as long, so its resistance is one-quarter of the 50Kv motor. Since resistive power loss is I^2R you'll find both motors dissipate identical power/heat in the winding.

This is a common point of discussion and there are a *lot* other threads on this forum explaining it very well.

Click to expand...

Thank you punx0r for being patient and explaining the identical setups for me. I would like to build a motor in the long run but I'm just too wet behind the ear yet to get my teeth into the math and formulas used. I understand the relationships between turns and Fleming left hand rule etc i would like to get more in depth with it in time if I can get a decent book etc to learn from.

From this I have learnt that the voltage increase in a system helps to keep the conductor sizes smaller meaning its easier to get say 10kw to the motor with less losses when using higher volts but from the motor case onwards its down to lamination thickness etc that makes the motors efficiency's higher.

I know it sounds basic and suck eggs type of thing but I want to start fresh and get my head around the formula and very basics of it and stitch all my knowledge together.

Bottom line always, is not overloading the motor. Many ways to do this, including the popular one, give er the juice. Even a modest by ES standards 1000w can do er for typical bike weights. Geared motors, or mid drives that have been shifted to lower gears help shorten the time period the motor is overloaded during a start.

The big mistake with a dd motor, is to underpower it,, whatever the voltage may be, then do lots of starts and stops. Particularly if it's a winding on the fast side, and the wheel is big. Then you get a very slow start, and the motor grinds away at low rpm making heat for 50 yards, instead of 20 feet.

I've seen up to 20% more power used on the same ride, 800w powered dd, vs 800w geared. But without the stops, no difference I could measure accurately enough, just because of very small differences in weather. By lot of stops, I mean downtown riding, stop sign every damn block. Much less difference if the stops are a mile apart.

A few points OP. Just sayin.

I question the logic of specifying a bike for this or that terrain. A vehicle is a vehicle, and hills are part of the job description. Even in kansas they have steep ramps (and pull bike trailers). my money is on mid drive, but tbh, 750w isnt a legal option here in oz.

similarly, obsessing about efficiency when dealing w/ the most efficient locomotion there is. Efficiency is optional pedaling . arriving sweaty isnt always a good look.

I think a line is crossed when u cant lift the bike u ride (heft a mtb on u shoulder to climb steps e.g.). striking a balance of power and weight within that limit has a good vibe about it to me.

at 160lbs/72 kg u r a good fit for a mainstream (which has many benefits) mountain bike, usually w/ a 120kg max gross load. It seems fortunate that a silly fashion for most cyclists - mountain bikes - ideally suited ebikes when doable batteries came along. Over engineered, but in a good way for faster heavier ebikes.

an alloy front suspension mtb mid drive ex battery is~23/24 kg? live with that. its a good solid start point.

over 25kph/15mph, the biggest enemy by far is wind. in ideal test conditions, maintaining 25kph is 100w. each extra 5kph needs another 100w of power. resistance is the square of velocity or some such.

i love my mid drive btw. maybe i am dumb, but there seems a gotcha with them for pedaling.

As u r using the same chain drive train for motor & pedals, u have to choose a gear that suits one (the motor) but usually not the other. The motor likes high rpm/low gears. u often cannot pedal fast enough to have effect.

With hub motors, one gears the chain drive solely for pedaling.

At times gearings agree (or contrived to) on midrives, and i am happy to pedal for the joy of it, and at times on long grades, i attack them at a speed/gear that allows me to pedal, and effectively help extend range - add ~150w of climbing power on hills.

I intuitively like not fiddling or stressing the derailleurs more than i have to, so pedaling a bit from dead stops til rolling a little sounds good.

Note that DD hubs can be seriously heavy. This plus the motors torque put serious stress on the fork wheel dropouts.

dogman dan said:

Basically, you describe wanting to ride cruising, but sounds like your ride will be plenty of stop and go. Coasting is good, one of the advantages of geared hub motors and mid drive. But riding pulse and glide like cars do is not as beneficial for bikes. Not enough mass to coast all that far. But yes indeed, milk that coast to the next stop.

Stop and go, a dd hub motor is seldom the best choice. In order of efficiency,

1 A mid drive, if you actually shift down each stop. If you leave it in a 20 mph gear each stop, you will be about the same efficiency as hub motors.

2 Next best, a geared hub motor. Since you talked about towing a trailer, a large one, able to put out 1000w. ( motor rated 500w) And about 250rpm @ 36v.

3 A hub motor. Only if your total load, you the bike, the battery and motor, and the trailer will be well over 300 pounds would you choose a DD motor. Because of the 20" wheel, you will not need to be particular about the rpm of the motor. But don't confuse this,, for towing a trailer a mid drive is still best, because you can gear down so low 600 pounds is no problem.

Yes,, you can pedal to 15 mph, then start the motor. This pretty much makes all types of bike motor systems equally efficient, or close enough to it. However, why would you want to ride that way? If you are that strong, just pedal a regular bike. I'm just saying, that help on the starts is the real reason you want a motor. Otherwise, it might be less effort to strip 25 pounds of motor and battery off the bike and just pedal.

DO pedal hard, or at least briskly till you are going 20 mph, then if there is any cruise, back off the power till you feel the pressure on your feet. Go less than 20 mph, and you will still get 2 miles per ah of 36v.

Click to expand...

Ignoring all of the above and the OP ...

But have at times thought a mid drive AND a low geared hub (same voltage, shared battery, separate controllers) would make for calm, minimal maintenance riding.

The hub (250/350wgeared hub can be under a kilo i think) maxes out at say 10mph due to low gearing, then freewheels, and then the mid drive gets used over 10mph~. Saves much stress on the mechanism and rider, and allows more gearing options for the mid-drive.

So opposite to your post, use the hub ONLY to start rolling at stops, stop start, and extra boost on hill climbs under 10mph.

It would mean also that getting rolling, the bikes gearswcould be set high enough for pedaling assistance to have some effect, which is not so in the low gear the mid drive would need to conquer stationary inertia (on my 350w mid-drive anyway).

It should also be noted the hub motor or gears getting fried, isnt always as bad as it sounds (re spoking a replacement motor into a wheel). A/ they are as cheap as chips & b/, the housing can remain in situ, only the guts need replacing - swapped in from a dismantled new/spare motor.

That sounds ok,, except the only way to "lower the gearing" of any hub motor is to make the wheel smaller. 20" wheel makes hub motors more efficient, no doubt about it. But bike type does matter. Off road, a 20" wheel will suck badly on the rock staircases.

But you are correct, the 5-1 gearing inside geared type hub motor will make starts much more efficient than a dd, and if you used a faster mid drive, it would then freewheel when the mid drive, or even your pedaling makes it go faster.

I have often thought of using a dual motor set up like you describe, but the most efficient way to use it might be to start using the mid drive, in a low gear. Then take up with the hub motor once you are moving 10 mph. Or,, as you said,, just pedal to 10mph. Either one will eliminate the most inefficient thing you can do with a hub motor, start with no pedaling.

Ohhh,, wouldn't I love it to be able to do that. That's how I rode before the West Nile Virus got me. Once I got sick, gone were the days of breaking chains, and wearing out the 11t gear on my cassette. As for carrying my bike up steps,, thank god I don't have to do that. I'd have had to live in the car for 6 years if I'd had steps into the house. I'm just so glad I got a bit better, and can at least pedal lightly when I ride the bike now.

Anyway,, one size doesn't fit all. We can't all ride the same bike, or ride the same way. Helping people find the right fit for them, for their needs is my job. A large number of the people I help have health issues. That's why they start the chat, they have questions about if an e bike kit will help enough.

In any case, not overloading the motor remains the key to efficiency. It's like a small pick up truck with a 4 cly engine. It's wonderfully efficient with one guy and a tool box for the load. Hook up a trailer, and load it with two tons of gravel, and suddenly you get the same gas mileage as a V8, and you might find using the high gear impossible on a hill.

"the only way to "lower the gearing" of any hub motor is to make the wheel smaller. 20" wheel makes hub motors more efficient, no doubt about it. "

R U sure about that dogman? I should check, but am pretty sure you can spec different gearing in geared hubs from the supplier - for just that reason - to suit various diameter wheels - 28" & 26" riders may still want same road speeds.

agree about rock hopping, but 2wd sure sounds good for snow etc., which makes me think front hub is best.

bummer about your illness. thank heavens for ebikes for bike lovers like you who cant anymore, aye?

i get angry at the lack of empathy from fitnicks who sneer at & lobby against ebikes, as they are "cheating". Screw them. I hate them more than AH motorists. they are a schism of our religion. If e.g. an ebike reduces an obese persons anxieties about shifting some errands from 4 wheels to two, and gradually increasing their pedaling comfort level and improving their lives - whats wrong with that?

not a very pc example. it could be seniors, mums - many folks.

like henry ford said - "whether u think u can or u cant, u r right". confidence is all.

I'm pretty sure you can't change the gearing ratios inside most geared hubs. It's typically 5-1 I'm not sure how that xionga hub works, it may have two ratios inside. But most are stuck with one ratio, whatever was chosen when it was made.

You can choose winding rpm, but once chosen most hubs are also stuck in one rpm. Again, some exceptions, like the old crystalyte 408-11.

One idea that intrigues me has been a high rpm wind DD motor and a low rpm wind geared motor on the same bike. Linked by the same throttle, both would turn on and pull max watts at start up. Then as the speed increases, at some point the geared motor would start to freewheel when the DD motor outruns it. So at speeds above 15 mph or whatever, only the DD motor pulls. While freewheeling, the geared motor would continue to run, but at no load, drawing very low amps. You could also have a switch to turn it off entirely, if you don't plan to stop soon.

In this way, you would get the advantages of the geared motor on the start, and double power on steep hills, but cruise on just the dd. Not sure it's worth it,, just an idea I never got around to trying. Might be better anyway, to match the rpms of the two motors.

I think matching hubs be the way to go the geared hub would create drag after its out of puff on the DD at higher speeds pushing up the amps slightly and downing the speed on the DD, I can't think of a way to have cake and eat it in regards of pulling off low amps and torque of geared while having the high speed of direct drive without having more power output than the two together.

Yeah, silly really. Hills & starts is exactly what hubs are bad at.

Also, having ridden my 24 speed mid drive in interim, i was reminded, it really does it all. There are simple ways of being really easy on chain and the easy to shift gears.

So yeah, definitely a light mid drive and be done with it.

No suspension and hard tires would help.

Definite hardtail for a high speed machine, I'd think a mid drive on a 700cc roadbike or similar would be a good way of getting good speed and wh per mile while not riding a recumbent to your death they are so low they are death traps if driven on the road.