Is mid-drive vs hub drive efficiency differential affect by pedaling cadence?

[hankj]

I've read that as a general rule mid motors will use battery more efficiently than hub because hub takes advantage of planetary gears to keep load/torque in a more optimal band for the spinning motor. So same amount of battery goes farther with a mid-drive.

Correct me please if this is not generally correct.

But I'm wonder if, and if so to what extent, a rider's pedalling cadence/style reduces (or increases) this difference?

The practical issue is that I'm a 100 mile a week minimum analog cyclist, 52 weeks a year for decades. As such my native cadence is high, around 85 relaxing, 90-95+ if I'm whipping up a bit of effort. It seems like this way of pedaling would significantly reduce the times when an e-bike would need to grunt out higher torque. And maybe be of greater benefit to a hub motor than mid? The mid afterall has its own gearing to keep high strain situations to a minimum. But with the hub motor does constantly spinning lower gears with your legs have the same effect?

I'm wondering because I want long battery life at lowest assist levels and light weight so batteries as small as possible. Wheel seems more simple/clean to retrofit onto an existing bike, but don't want to lose a lot of overall range for the convenience and weight savings.

So what's your take? Thanks!

 

[fooferdoggie]

The thing is, the mid-drive motor speed is set by how fast you pedal. The optimum speed is around 80 to 90 rpms cadence. . A hub drive needs to be at its highest speed to be efficient. that's maybe 28mph or whatever the gear is set at.. so if you climb hills or not going flat out it is never at its best. Plus most of the hubs your stuck with 7 or 8-speed cassettes so you won't be able to peddle well at all speeds. if you want your bike to feel like a bike but with help go mid drive with a torque sensor.

 

[Jeremy McCreary]

But I'm wonder if, and if so to what extent, a rider's pedalling cadence/style reduces (or increases) this difference?

Agree with @fooferdoggie : To maximize ebike motor efficiency, you have to keep motor shaft speed in its sweet spot.

On a mid-drive, you do that by keeping your cadence in the range recommended by the manufacturer. For my Vado SL mid-drive, Specialized strongly recommends pedaling above 70 rpm and ideally in the 80-90 rpm range.

Experience bears this out. On a hill with a steady 200W output on my part, I can definitely feel a fall-off in motor power as cadence slows below 80 rpm and especially below 70 rpm.

Most if not all the gears on a typical mid-drive put the motor at a mechanical disadvantage over the drive wheel. Their real role in a mid-drive is to help you stay in the motor's cadence sweet spot as external resistances vary.

On a hub-drive, motor shaft speed is tied, not to cadence, but to drive wheel speed — and therefore to ground speed. Since efficiency peaks at high wheel speed and typically drops off dramatically under 10 mph or so, your job is to keep ground speed as high as possible on climbs.

Once a hub motor starts bogging down on a hill, downshifting tends to make matters worse for the motor, but it does help your legs finish off the climb. In general, your best bet is to hit the bottom of a big hill with as much speed as high assist and conditions allow. The role of gearing will then be to keep your own optimal cadence so as to lose as little speed as possible.

 

[Chargeride]

Hilly.. mid drive regardless of cadence.
Flat..hub drive wins.

But..midrive is better on the flat than hub is on hills.
I'm talking legal bikes here.

 

[Stefan Mikes]

Hilly.. mid drive regardless of cadence.

Incorrect. Cadence is extremely important here. Have you mastered the derailleur yet?

The mid-drive motor is deadly inefficient at low cadence.

 

[Chargeride]

Not as inneficent as a hub, unless youre in a stupid high gear.

 

[Stefan Mikes]

Not as inneficent as a hub, unless youre in a stupid high gear.

Any electric motor likes spinning fast. Try this: Whenever you are on a steep ascent, downshift a way more than you think would be appropriate and then start spinning the crank. The mid-motor e-bike will climb as easily as if dragged by an invisible lift

I had to do several very short but very steep climbs up the Vistula embankments yesterday. It was my 240 W peak power Vado SL in 42-51T gearing.

At such high cadence...

with such maximum leg power compared to the average. Trust me, I was maxing the motor out!

 

[Chargeride]

Thats what confuses me with the Yam motor, it likes to change up for hills, it runs out of cadence, I used to just slow down, but you can go up a gear and it pulls better.
Lots of 'mid range' torque

 

[Stefan Mikes]

Lots of 'mid range' torque

These motor are factory tuned with mountain biking in mind Yamaha motors support "zero cadence", that is, the motor becomes engaged as soon as you have exerted torque on the pedal with your foot.

The motors used by Specialized get either "Street" or "Trail" tuning. The Street tuning prefers speed and high cadence. The "Trail" gives you tons of motor torque at low speed and "mid range" is preferred. However, Specialized gives its e-MTBs additional parameters. For instance, the user can set how quickly the motor would engage when the pedal is pushed (with Zero Cadence possible) and whether high cadence is preferred or not.

 

[Mr. Coffee]

Incorrect. Cadence is extremely important here. Have you mastered the derailleur yet?

The mid-drive motor is deadly inefficient at low cadence.

True, but if you are riding a bike like a normal person you aren't likely to often find yourself pedaling at those low cadences.

In practice, a normal cyclist riding a normal e-bike over typical terrain is likely to get more Wh/km in a mid-drive than in a hub drive. Sometimes far more depending, again, on how they are riding and the terrain.

Bluntly, I know of no e-bike designed for efficiency over long distances.

 

[fooferdoggie]

Hilly.. mid drive regardless of cadence.
Flat..hub drive wins.

well on the hub only if you're going full speed.

 

[hankj]

Great chat gents, quite informative.

My instinct that spinning a hub powered e-bike at a fast cadence in a low gear would make the battery last longer was wrong. Hub efficiency is pinned to how quickly the is rotating and that's it.

But if one gears down a mid-motor and whips the crank around quickly, like on a long hill, then you are helping efficiency and saving battery over going the same speed but at a lower cadence.

Stephans Mike, 118 is quite the high cadence! Even though I average around 90, and can spin 120 for a very short time, I'm still a bit of a diesel rider. I will grind power at a lower cadence, or gear up but still spin 90, if I want to go fast for a while. My lungs tend to give up before my legs give up

It's interesting that mid-motor efficiency favors experienced/sport cyclists, who have a tendency to spin higher cadences than casual or beginning cyclists. Home base cadence for a lot of competitive road racers is 95 or a little above. While when you look at cycle path casual Sunday riders a lot of them are pedaling well under 70. I assume this bias towards more efficiency at higher cadence is just the reality of small electric motors, not the bike industry purposely designing motors that favor experienced cyclists comfortable with high cadence ....

 

[Stefan Mikes]

True, but if you are riding a bike like a normal person you aren't likely to often find yourself pedaling at those low cadences.

Tell me more I close my eyes and in my mind see a typical e-bike user riding in the highest gear, achieving cadence of 50 rpm or even less, and helping himself with a throttle

In practice, a normal cyclist riding a normal e-bike over typical terrain is likely to get more Wh/km in a mid-drive than in a hub drive.

And I didn't mean efficiency in the terms of several Wh/km. At a low cadence, a mid-motor output drastically drops. Also, a slow pedaller usually does not grind the cranks, so the leg power input remains very low, which results in a low motor assistance.

It's interesting that mid-motor efficiency favors experienced/sport cyclists, who have a tendency to spin higher cadences than casual or beginning cyclists. Home base cadence for a lot of competitive road racers is 95 or a little above. While when you look at cycle path casual Sunday riders a lot of them are pedaling well under 70.

Specialized has recognized that and the Mastermind Turbo E-Bikes have a color slider on their display. The indicator becomes green only when the rider pedals faster than 70 rpm! (My usual cadence pre e-bikes was 78, now it is 80-90 rpm).

118 is quite the high cadence! Even though I average around 90, and can spin 120 for a very short time, I'm still a bit of a diesel rider.

I usually stay a little above 80 rpm, and my mid-motor e-bikes appreciate that The 118 was a burst as I needed to climb a river embankment for several times. Such embankments are very steep but you only need to climb several metres up. Low gearing and high cadence made that possible, especially with the leg power burst and maxing a low power mid-drive motor out. It would be very difficult to do such a climb by grinding.

 

[harryS]

I believe high cadence works for both geared hub motors. and mid drives, Also it's better for mu heart too. Battery range always depends on rider contribution.

You'll find, if you ride them, that cadence sensor bikes are overboosted, If you have enough gears, you might find a gear where your pedaling contributes to your liking at a given. but not always, A torque sensing arrangement is more natural for the long term biker.

If you're thinking of retrofitting a favorite bikes, well, it's often the case that a purchased ebike is a better choice, both on cost and usually on features. That hasn't stopped me from converting ebikes, and I have two projects this winter, One will be a torque sense mid drive on a older steel 10 speed.

 

[hankj]

Harry I agree, torque sensing just seems to be the better way all around. At least if you want a motor to feel like a completely integrated part of your legs

 

[Stefan Mikes]

Harry I agree, torque sensing just seems to be the better way all around. At least if you want a motor to feel like a completely integrated part of your legs

The ultimate system found in good mid-drive motors combines up to five parameters (the most important being torque * cadence = Leg input power) to determine the natural assistance.

No hub drive assistance system can even match that.