Geared Hub vs Mid-Drive?

[PeteCress]

For an upcoming tadpole trike build (215# rider who is happy in the low-to-mid teens speed-wise and climbs a 1.25 mile 9% grade at the end of most rides) I had been thinking that a 750-1,000 watt mid-drive limited to 500 watts going in to a Roholoff hub was the no-brainer - at least for somebody who doesn't want his survivors to have too much fun.

But now I'm not so sure.

Geared Hub Pros:

• Fault Tolerance: It seems like there is nothing that one can break on a geared hub that will prevent pedaling home.
• Less Noise: Fewer gears being spun slower, plus the thing is behind/below me rather than in my face.
  

Geared Hub Cons:

• Ease of Installation: One has to lace up a wheel and route more wires (for the external controller).
• Less Absolute Hill-Climbing Ability: Since it's power is not routed through the trike's gearing system.

Am I even close?

 

[PeteCress]

For an upcoming tadpole trike build (215# rider who is happy in the low-to-mid teens speed-wise and climbs a 1.25 mile 9% grade at the end of most rides) I had been thinking that a 750-1,000 watt mid-drive limited to 500 watts going in to a Roholoff hub was the no-brainer - at least for somebody who doesn't want his survivors to have too much fun.

But now I'm not so sure.

Geared Hub Pros:

• Gearing: You get to keep the three forward chain rings instead of having them replaced by the mid-drive's single ring. This, of course, is moot if you combine a Rohloff or Nuvinci rear hub with the mid-drive.
• Stealth: The right hub can hide behind the cassette.
• Free-Wheeling/Drag: Zero drag when not used.
• Fault Tolerance: It seems like there is nothing, short of spokes, that one can break on a geared hub which will prevent pedaling home.
• Less Noise: Fewer gears being spun slower, plus the thing is behind and below me rather than in my face.
• Zero Chance of Blowing Out The Trike's Drive Train: Obviously no Rofloff, and the low-ness of the gear I am pushing does not amplify the torque applied to the cog, chain wheel, or chain
  
  

Geared Hub Cons:

• Aesthetics: The mid-drive installs I have seen are significantly cleaner-looking: fewer wires, no external controller, and so-forth.
• Ease of Installation: One has to lace up a wheel and route more wires (external controller)
• Less Absolute Hill-Climbing Ability: Since it's power is not routed through the trike's gearing system.
• Harder to Fix a Flat in the Field: Not a lot harder, but harder...

Am I even close?

 

[sleepy_tired]

The problem with geared hub is overheating. Since it's a motor spinning on the inside of the hub it's essentially running inside of a sealed metal box. That means there is no direct path between the motor and the outside and thus cooling is a problem.

Electric motors are capable of generating a massive amount of torque for their size, but you need to run high amperage to get that. Amperage is a measurement of electrical current and that current directly relates to the power of the electromagnets inside of that motor. More amps means more heat. So without a way to easily shed that heat then the motors are prone to overheating if you run them slow at high throttle levels.

That doesn't mean that they are inefficient when ran slow. They can be very efficient at slow speeds, just not at full throttle. They are inefficient, and thus produce a lot of heat, when you are running high load at slow speed.

If you have a trike with a 20 inch wheel they will climb much better because smaller wheels run faster. It's the same thing as running a mid-drive through a gear reduction for a 26 or 29 inch wheel.

With a mid-drive through a multi-gear transmission they trade speed for mechanically amplified torque. So you can climb steep hills without overheating, but slowly.

What you want really depends on how much effort you want to put out personally.

If you want to put out zero effort on hills and climb slowly to the top on motor only then mid-drive is the way to go. But if you can climb a hill with pedal-only then certainly a geared hub motor, or DD hub motor, can help to get you up the hill faster.

If you have temperature sensor and a controller, or whatever, that can protect the motor from overheating you never have to worry about damaging your motor from overheating.

 

[Triketech]

I'm just approaching 6 years and 5000+ miles on an HPV Scorpion FS26 assisted with a MAC 10T Geared Hub, Phaserunner Driver, CA3 Computer, and Thun Torque Sensing BB. No issues other than burning out a battery. I have a couple of these and recently had it apart; gears/clutch in fine shape.

I run 35A battery/90A Phase on a 52 V battery. The majority of my riding is in the foothills of the desert. It gets a workout.

I posted this article on my website about 5 years ago. I did some major updating with an integrated underboom battery mount and a console for the CA3 on the DER Post.

http://www.triketech.com/Drivetrain/PowerAssist/HPV-MAC-V2.html

Bafang is a good drive and will work with a Rohloff within limits.

Rohloff shear pins are designed for 200 NM torque, the BBS02 puts out 120 NM at peak. Lets say you've the 46T Lekkie Ring up front driving an 18T on the Rohloff : 18/45 = 0.4, and 0.4 * 120 NM = 19.2 NM force. You're good.

Nice thing with that combo is one hand can work the shifter while the other hand can tweak the throttle. That's probably the way I'll go on my next trike. I did test one in the early days with an SRAM Dual Drive. No matter how I programmed it it just felt better to use with the throttle for me.

Here is an article with the BBS02:
http://www.triketech.com/Drivetrain/PowerAssist/MidDrive.html

 

[dogman dan]

I know nothing of mid drives and the R hub combination. I would be inclined though, to even more severely limit the mid drive with that hub. Like a 350w bafang kit on 36v.

But to combine that rear gear hub with a geared motor, you'd have to put the motor on the front wheel. Not a deal breaker, but many prefer the motor on the rear wheel.

At your weight, a 500w rated geared motor, running on up to 1200w, is not going to overheat on that grade. But for 9%, I'd say you will prefer a 48v--22 amps controller kit, for 1000w, 1200w max.

A mile of 9% is not a motor killer, but it is a serious hill, I bet its close to 1000 foot of vertical.

 

[MikeSSS]

9% is a significant grade, but it's at the end of the ride so you'll be warmed up.

Road speed during the climb is a big deal, slower uses less total watts. Motor watts = total watts minus human watts. The lower the climb speed, the lower the motors share of total power output. There is a tendency to climb faster when using assist though. A CA V3 shows you motor watts, just keep them at your desired level by adjusting road speed and your pedal effort.

If you buy a MAC, purchase it already built into a wheel of your correct size. The GMAC has a built in torque arm, that's a really nice feature. I use a plain MAC and really like the free wheeling clutch feature, GMAC doesn't have a clutch for coasting.

A big advantage of a MAC is that you can use a Cycle Analyst Version 3, it has cruise control, I set mine to turn on after 3 seconds of stable power output. On a climb the cruise control engages and I pedal and shift to keep about 80 rpm at the pedals and use as much pedal power as I'm comfortable with. Motor watts is adjusted via road speed and pedal effort. The cruise control does not hold exact road speed on varying road grade, neither does it hold constant motor power, but it does work very well and comes close enough.

I don't use pedal assist, just throttle and pedaling. Torque sensing pedal assist works very well for me, if it is combined well with throttle. Pedal rpm assist is counter intuitive for me, especially if it is not well integrated with throttle. Throttle is far superior to pedal assist only. Throttle works the same way as your motorcycle, scooter, car, truck, boat, plane, etc.

The Bafang BBS mid drives I've used did not integrate throttle and pedal sensing well, not even close. I did ride a Bafang Ultra mid drive, it used torque sensing and throttle and they worked well together, but the frame has to be made specifically for this mid drive.

That said, a mid drive running through an internally geared hub or through a derailleur and cogset system should work well too. Motor watts = total watts - human watts still applies but shifting to a low gear at the wheel causes the mid drive to run at higher rpm and less torque, a good thing for the motor and gears in the mid drive.

In any case, low motor rpm and high motor power output gives higher motor heating, compared to higher motor rpm and lower motor power output.

 

[MikeSSS]

Pete, keep us posted on what you do and how it works.

 

[PeteCress]

Pete, keep us posted on what you do and how it works.

Will do.

Got a 1-week rental from Outrider arriving next week for proof-of-concept 'bent-wise.

It will not be the bike I buy, but a week on it should tell me if I can find sufficient pleasure in 'bent riding.

Given that it's still a "Go" after that, I will be forced to put my money where my mouth is.

But what I have heard from dealers about the supply chain in general is not encouraging in terms of getting something this year.

I come away from reading http://www.triketech.com/Drivetrain/PowerAssist/HPV-MAC-V2.html thinking that a MAC 10 is the best fit for my use... It looks messier by far than a mid-drive, but quieter, more reliable, more fault-tolerant, and speed/power-appropriate.

I have been going on the assumption that full suspension is a must.

But now I am obsessing over curb-climbing ability. My use case involves negotiating curbs on a regular basis - no problem riding a bike, just shift weight back and pull up on the bars.... not so much on a 'bent...

One solution is those monster 4.0" low pressure tires like on ICE's "Full Fat" and if that turns out tb the only means, I will re-think the full suspension requirement in light of the suspension effect of a 4.0 or 4.8" tire at 12 PSI.

 

[dogman dan]

Curb hopping a bent will be a problem.

 

[MadRhino]

Far tires are expansive and thin as baby skin. They are a specialty, that people are using everywhere for fashion, and end up paying the cost of poor choice.

Rough riding is best done on 2.5-3.0 mtb tires. 4.0-5.0 are for loose surfaces, sand or snow. Good tires of this size that can ride rough, are motorcycles tires.

 

[Alex W]

A big mid-drive con for me is that it gives you less flexibility in designing the system (controller, motor, bottom bracket, cranks are all a fixed system).

Many mid-drive systems (like the popular Bafang BBS series) don't have torque sensing bottom brackets. I find torque sensing pretty essential for my riding (which may not be typical[1]) and I also know from experience that I get better battery life when I'm using that feature.

Mid-drives typically have very wide cranks, with a Q-factor (width) that is about 35% wider than standard road cranks (200mm vs 150mm).

Mid-drives typically have a maximum cadence of around 100-120rpm. 120rpm is reasonable, but I often pedal at over 100rpm.

Grin Tech hub drives give you a lot of flexibility by breaking out the motor driver, control logic (CAv3) and input devices (torque sensing, throttle, cadence). I haven't seen a BB with quite the same level of optionality.

[1] My goal with e-bikes is to still get sweaty on most rides, but to get a higher speed or ability to carry more gear. I build light systems (5-8lbs) to avoid changing how the bike rides. I typically ride with the system matching motor power to my human power and consume about 6wh/mi (so 25-30 mile range on a 200wh battery). Most people ride with larger motors and want more motor power.

 

[markz]

Each has their pro's and con's with geared you'd be limited on power before destruction happens, not sure what that limit is for a MAC geared hub but you couldnt mountain goat climb from a standstill on a steep hill a geared hub, as you can easily with a mid drive, 375lbs on a 22% grade cyclone 4kw, zero pedaling, already in the a 22 crank gear, 36 rear gear...... climbed like a champ.

Never hill tested a BBSHD with my weight, people love that mid drive.

 

[dogman dan]

Buy a good kit, and you wont have to lace your wheel. But its easy, for anybody with decades of real bike riding. So much easier than trying truing a bent wheel. Installing a mid drive wont be much less wiring to run.

A 500w rated geared motor such as a mac running on 750-1000w as measured entering the controller will easily climb that grade, with some brisk pedaling to keep its rpm close to 15 mph. A little harder if you had a stop sign on the way up that hill, but not a deal breaker. If you weighed more, the mac could smoke, since even with brisk pedaling it would slow to 5 mph. IF, just you weighed nearly 300 pounds or more.

But a mid drive, even 350w, could pull a 300 pound rider up that hill. It wouldn't care if you ran it in a 3 mph gear, and if you weigh around 200, it would pull you up that hill much faster than that. So with any mid drive, pulling a trailer could be done.

Your decision could come down to how well a mid drive kit fits, meaning mounting it on the bent you are choosing. It may fit nice, or be very awkward to mount depending on the type of bent you choose. A semi recumbent, the frame is pretty similar to a regular bike, but others have the pedals out on a pole.

I've rode some very nice recumbent trikes, with a 500w rated, 1000w powered rear geared motors in them. Its a VERY GOOD choice, for a rider of my weight, 190 pounds. But I very much like how hub motors ride. You pick a speed, then pick the gear for that speed. Then you just pedal away, adjusting the throttle to keep your speed and cadence steady. I find it much easier to just adjust the throttle, and keep the cadence steady. Since I'm old, that steady easy cadence is what i'm after. I want a hub and a throttle. simple, easy, and best for my ageing legs.

I never owned a mid drive, but I did demo the top of the line mid drives at Interbike about 4 years ago. I was VERY impressed with them, especially the bikes with the bosch mid drives. But personally, I did not like the lack of a throttle on some of those bikes.

 

[PeteCress]

Buy a good kit, and you wont have to lace your wheel.

The lacing is a wash because with a mid drive, I would still lace a wheel to use one of the Rogloffs from my upright bikes.

I am coming around to the idea of a mid-drive partially because Rohliff shifting is such a convenience and I already have a couple of the things.

The biggest attraction of a geared hub is lack of noise: the MAC-10 with a sine-wave controller seems tb about noise-free as one can get short of DD.

OTOH, the Outrider trike I am renting for proof-of-concept is really heinous noise-wise and, although I would never knowingly buy something that noisy, it's nothing I could not live with if I had to.

 

[PeteCress]

Buy a good kit, and you wont have to lace your wheel.

The lacing is a wash because with a mid drive, I would still lace a wheel to use one of the Rogloffs from my upright bikes.

I am coming around to the idea of a mid-drive partially because Rohliff shifting is such a convenience and I already have a couple of the things.

The biggest attraction of a geared hub is low noise and the MAC 10 with a sine-wave controller seems tb about as close to noise-free as one can get short of DD.

OTOH, the Outrider trike I am renting for proof-of-concept is really heinous noise-wise and, although I would never knowingly buy something that noisy, it's nothing I could not live with if I had to.

For me, the emerging deal-breaker is torque sensing and that brings it down to MAC 10 vs Bafang Ultra vs TSDZ2.

 

[spinningmagnets]

I shouldn't care about having a mid-drive because I really don't have any significant hills. I do have a lot of rolling hills that are fairly short, and not long enough to overheat any common hubmotor.

I have a BBSHD @ 52V putting out 1500W. I have swapped-in a smaller chainring because I don't really need 35-mph, and I'm at roughly 28-mph as a top speed.

The smaller chainring loses top-speed, and improves wheel torque, so acceleration is improved. There are a few steep places to test hill-climbing, so this combo climbs well without the motor/controller getting hot. Acceleration is excellent.

It's not as powerful at accelerating as a 1500W DD hubmotor at 2500W, but it's also lighter, and it doesn't seem to draw much attention.

A builder here (Dogati) put together a 2WD bike with dual geared hubs. He bought the fastest windings he could source, but not so he would have a faster top-speed, he chose the high kV because they have less internal resistance.

By having two of them to share the load, it was equal to one huge geared motor, instead of two medium ones. He said the acceleration was exceptional.

 

[dogman dan]

Again, my only possible reason not to do the mid drive, would be some type of problem actually mounting it to the type bike you are choosing. I just haven't seen bafang kits mounted on recumbents, have no idea what the mounting requires.

But if one won't work, you are still going to be happy with the hill performance of any decent powered geared hub motor. Only if you weighed 300 pounds would you have any trouble getting up a mile of 9 %.

 

[PeteCress]

...any decent powered geared hub motor. Only if you weighed 300 pounds would you have any trouble getting up a mile of 9 %.

On the beast that I am renting from Outback, CycleAnalyst said it was pulling up to 900 watts as I climbed that hill yesterday.

I was trying to keep it around 250-350, but it kept spiking - throttle only, no pedelec mode.

The trike itself weighs about 120# in addition to my 215. Part of it has to be my pitiful condion as I was housebound for most of 2020 plus I have never ridden a trike until now.

Gonna try it again today and every day until it goes back to Outback on the ninth.

Even keeping it under 500 watts would make me feel better...

 

[AHicks]

Pete, just do what you can to minimize the watts and stay at it. It is what it is. If you had the bike long term, my bet is that your battery mileage will increase and your wattage will drop in many situations. Most of us, when we first started riding e-bikes, sucked completely when it came to wattage and battery mileage, not realizing that doing well with both is much tougher than it looks! You don't even know what's possible for sure! Coordinating your speed, proper gear, and PAS level, to various conditions (wind, surface, load, etc.) encountered on every ride takes experience you just don't have early on! If you stay at it, you DO get better.

I've been riding for 5 years now, and maximizing my battery mileage is a mental game I play still. I judge myself on mileage achieved for every charge! Every shift or change in PAS level is based on achieving battery mileage..... -Al

 

[PeteCress]

Pete, just do what you can to minimize the watts ...

Today was pretty good - in line with your prediction of improvement.

First stage of the hill was 6 minutes at 6-7 mph and never exceeding 300 watts.

Second stage was 8 minutes at 3-4 mph and 300-350 watts.

Total climb 14 minutes. 77 watt-hours/1.5 ah including the trip down.

Those numbers are conservative bc the rented beast I am riding weighs about 120# and I cannot imagine that the ICE Adventure that i will build on could top out at more than sixty.

So I feel like I am in the green with whatever motor I choose - although it seems like the MAC10T is a done deal bco noise level.

I am totally with you on the improvement angle.

 

[Triketech]

A 500w rated geared motor such as a mac running on 750-1000w as measured entering the controller will easily climb that grade, with some brisk pedaling to keep its rpm close to 15 mph. A little harder if you had a stop sign on the way up that hill, but not a deal breaker.

Indeed it will, and steeper. Short video of MAC 10T climbing 17% grade....
http://www.triketech.com/Drivetrain/PowerAssist/MAC/MacHillClimbWeb.mp4

From what I've found as long as the wheel is turning over 40-50 RPM the MAC 10T will take 25 amps continuous in near triple digit heat until the battery dies.

 

[PeteCress]

Short video of MAC 10T climbing 17% grade....
http://www.triketech.com/Drivetrain/PowerAssist/MAC/MacHillClimbWeb.mp4.

That sounded fairly noisy. Or was the apparent noise an artifact of the video method?

Have you ever put your MAC10T up against a Bafang 310 noise-wise?

The Babang would save me a hundred bucks by letting me use one of me on-hand MTB cassetts but noise is paramount to me.

 

[Triketech]

Short video of MAC 10T climbing 17% grade....
http://www.triketech.com/Drivetrain/PowerAssist/MAC/MacHillClimbWeb.mp4.

That sounded fairly noisy. Or was the apparent noise an artifact of the video method?

Have you ever put your MAC10T up against a Bafang 310 noise-wise?

The Babang would save me a hundred bucks by letting me use one of me on-hand MTB cassetts but noise is paramount to me.

The hillclimb video was shot when I had a Trapezoidal Wave motor driver; thats most of the noise. Updated to a Sine Wave motor driver which has almost eliminated the electrically induced noise. Up to about 200 watts the sound level is less than running knobs on the pavement. It doesn't get a lot louder.

Helped someone install the same components as mine except for the 20" wheel Bafang 31x Std wind, 36V battery. Gears were virtually silent although we only had 18A Peak. Pulled strong to about 18 MPH and peaked at 20MPH for what its worth in regards to useful speeds & voltage.

Problem with the Bafang 310 is this its an easy motor to burn up. I would want to have the internal thermistor linked to the CA3 to monitor temps; just something with some discipline that comes naturally.

 

[DrV]

OK, so I've installed both a hub motor and mid-drive on two different bikes (BBSHD and a 500w Bafang Rear Hub) both of which seem to do fine on the hills I need to climb. I recently bought a trike (catrike 559) with the idea that I would swap one of those two motors over to the trike, as I have already bought them, and I live in a hilly area and have one to climb to get home from my usual ride. I decided to go with the 500W bafang rear hub on the trike instead of a mid-drive so I could keep the front chain rings, reduce wear on the chain and drive train, etc. Although it's fine in the flats, I find myself wanting some more power (speed) going up steep hills.

Now although my Bafang is reasonably powerful (48v/500w), it is certainly not in the MAC range of power, although it is probably as if not more powerful than the g310. If you get the Mac from grin, they have controllers that can really maximize that motor. I only have a 20a controller, though, so I have considered upping that a little bit to see if that helps, but haven't done that yet, as I've only had the trike out a few times and want to see how it does on the hills next time I take it out. If I didn't have the hills I probably wouldn't even have electrified it.

BTW, you might know that Utah Trikes has been doing BBSxx conversions on some of their trikes for a while now and that seems to work well. I've ridden one that someone that rides here has (it was a bbs02) and it was quite powerful. Anyway, my very limited experience is that it is difficult to generate the same speed going uphill on a trike as you can on a bike, so in terms of motors, bigger is better. I would definitely pick the mac over the g310 if you are going with a geared hub!! Also, I don't know if your ICE is suspended, but if not, get wide tires!!

 

[PeteCress]

Also, I don't know if your ICE is suspended, but if not, get wide tires!!

It has a sort of half-ass suspension: elastomers.

But I hear you on the rires.