High power hub or medium power mid?

[Rrickyy101]

Hey all,

I'm new to the world of ebike building (of course). Ive been looking around here on ES for a while, and have not seen this particular question posed so directly anywhere else. Maybe I'm just missing something, but I have not seen an honest assessments of the capabilities of Mid-Drive systems.

Does anyone have experience with both higher powered hub motors (>= 1000 Watts) and decently powered mid-drives (>= 700 watts)? How do the two compare. Specifically, with proper gear shifting, wouldn't one be able to achieve much higher top speeds with much more efficiency? Also, is it true that mid drives have the potential to be significantly more efficient because they generally turn at a more efficient RPM, and thus lessen the frequency of higher amp spikes. I mean sure you could throw a bigger-badder hub motor on your bike to achieve higher top speeds, but wouldn't a higher volt mid-drive system do a similar job with much less strain on the battery. Say we have a mid drive and a hub motor of the same power, which would have a higher top speed, which would have more torque? It really makes sense that in both cases it would undoubtedly be the mid drive!

Thoughts? Possible links to related readings? I've been searching for over a week now and haven't seen anything from a truly unbiased source.

 

[Thud]

How do you plan to use yout bike?
Horses for courses.
Commuter, on road, off road. Weekend mountain biking?

Power consumption is relative.....& its allways worst when having the most fun.

 

[Rrickyy101]

Commuter capable of reaching 40mph burst but one which I would regularly cruise around 20-30 with moderate peddling for a 30 mile trip 3/4 times a week. There are long moderate grades both up and down hill on this ride (completely on the road). Any suggestions for such a build? My total weight (me + whatever gear I need for work) will be around 175 lb

How do you think the following would perform under such circumstances:

60V 15AH battery
1000-2500 watt mid drive (any suggestions on which particular one, excluding lightening rod's -- his is too pricey for me at the moment)
20-40 amp controller
90s era MTB with zero suspension

Im also looking into a sturdier chain and cassette combo.

Is mid-drive really the way to go here? I cant help but get over the intuition that more efficient RPM speed = more efficient and effective use of power. I would save power in heat waste while climbing hills, and the motor will have proper cadence to cruise at high speeds, no?

 

[Rrickyy101]

Excuse my double post but I forgot to mention: WHAT ABOUT CARBON DRIVE! From what I've been reading, Gates carbon drive belts are approximately 2 times stronger than a conventional belt, and quieter as well. If these claims hold true, would it be naive to assume they have a valid place in the ebike world: specifically of the mid-driven style? People complain about the noise a mid driven system produces, as well as the busy work of maintaining the drive train. This belt-centric design is a win win win win win win win (minus the initial cost of course). From what I understand, most quality hub gears boxes can be shifted even at high torques, such as climbing a hill (on an ebike). It would seem as though the combination of these 3 technologies (mid drive, carbon drive belt, internal hub transmission) is a 3-way match made in electric bike heaven.

One more small note: the hub motor simply seems like an ass-backward implementation of motorization on a bicycle. I understand it is cheaper, quicker, and more marketable (I mean hell its the reason I'm here right now); but it simply makes no sense to me. I really do like the car comparison: why dont people drive around with simplified, single gear motors (no transmission). Hell, could you imagine the savings on repair costs? But then again maybe not.... I mean, their engine components are in direct contact with a highly variable input [and output] which may or may not cause damage. Top speed? Who cares! We'll just burn more fuel and run the engine faster and faster! Now obviously not all of these intuitions carry over from the automotive industry, and maybe fewer carry over to the strictly electrical world; but there simply must be some substance to the idea of properly distributing the power output of an engine.

....again, merely an observation based view on the whole hub vs mid drive systems.

 

[Thud]

Commuter capable of reaching 40mph burst but one which I would regularly cruise around 20-30 with moderate peddling for a 30 mile trip 3/4 times a week. There are long moderate grades both up and down hill on this ride (completely on the road). Any suggestions for such a build? My total weight (me + whatever gear I need for work) will be around 175 lb

Considering this paragraph, I don't see any reason to consider any of the current "thru the gears" mid drives. Their only real advantage is the ability to get into granny gears & climb vey steep hills.

How do you think the following would perform under such circumstances:
60V 15AH battery
1000-2500 watt mid drive (any suggestions on which particular one, excluding lightening rod's -- his is too pricey for me at the moment)
20-40 amp controller
90s era MTB with zero suspension

I am not the one to ask on these...I never bought any of the current offerings. (I build my own) but the only option looks to be the GNG or the copy's. The Bafang's & Bosh units will never get to the speeds your shooting for.

Im also looking into a sturdier chain and cassette combo.allways a good idea to keep the components in spec.
Is mid-drive really the way to go here?We need another solution that get's around the over-reduced smaller motors....does it really make sence to gear a motor down to human speed just to have it multiplied in the final drive transition?

I cant help but get over the intuition that more efficient RPM speed = more efficient and effective use of power. I would save power in heat waste while climbing hills, and the motor will have proper cadence to cruise at high speeds, no? unless your climbing mountains....its pretty darn close in power consumption hubs vs mid drives...given the top speeds your looking at, you are nullifying the low speed advantage the crank drives offer. If 90% of your time in the 20-30mph range, IMHO, a mid drive is wasted in this scenario

the hub motor is efficient over a pretty wide range...once the motor is out of stall & turning a few rpms.....your efficiency is slaved to the acceleration rate.
The big problem you have to solve is: the jump from 20 to 30 mph....its not a lineal step in power required, drag on a bicycle at 30mph is a range killer. doesn't mater what your drive choice is.

Gates carbon drives...meh. It requires a bike specific, removable chain stay & rear axel tensioners to operate. (complex)
Internal geared hubs are not up to higher torque than a human can deliver...we have several fail examples on the board.

Can't really compare electric drives to ICE drive's.
The fundamental elements require a different approach & in application.
The only thing I HATE on any hub setup is the weight in the wheel....after that you can't beat the simplicity 1 moving part. That said, I prefer a lightweight motor geared to spin my rear wheel at 30 mph...& then I freewheel the crank to simplify the drive line.

I'll edit in some links in when I have more time this evening.

 

[WoodlandHills]

Nuvinci 171s are rated at 100nm continuous, is that near what a human can put out? I honestly have no idea what the capabilities are of a fit human, is there a way to extrapolate from that to an average/not young person? You have me wondering if I should bother to build it into a wheel to try.

 

[Chalo]

Nuvinci 171s are rated at 100nm continuous, is that near what a human can put out? I honestly have no idea what the capabilities are of a fit human, is there a way to extrapolate from that to an average/not young person?

It all depends more on the gearing you choose than it does on the rider. On my NuVinci bike, I decided to stay on the safe side and limit input torque to the continuous value. My full body weight (well over 300 pounds) times the crank length worked out to about 275 Nm, so I used a chain ratio of a little over 2.8:1. That way, the hub sees less than 100 Nm when I stand on the forward pedal.

That means I have more high gear range than I know what to do with, but hey-- I won't be busting my hub anytime soon. For a more normal-sized person, or the steady torque delivery of an electric motor, I don't think there is much cause for concern.

 

[WoodlandHills]

Thanks, that makes sense: if you can climb stairs you can develop your body weight in force at the pedals. Then you multiply that by the crank arm length to get the input to the chainwheel and sprocket gearing, but what is chain ratio? Is there an FAQ here that a novice could fathom on the subject?

 

[Chalo]

Excuse my double post but I forgot to mention: WHAT ABOUT CARBON DRIVE!

It's very, very expensive. Those super expensive belts don't last as long as chains. Your gearing options are sharply limited. It won't work with a normal bike frame, either-- the frame has to be able to open somewhere in the rear triangle.

It's a great example of a gimmicky solution out there looking for a problem. But, y'know, carbon is obviously better because CARBON!

A Gates belt is potentially both a remedy and punishment for someone who steadfastly refuses to oil his chain.

 

[Chalo]

Thanks, that makes sense: if you can climb stairs you can develop your body weight in force at the pedals. Then you multiply that by the crank arm length to get the input to the chainwheel and sprocket gearing, but what is chain ratio?

The chain ratio is the number of teeth on the chainring, divided by the number of teeth on the rear sprocket. In my case, it's 48/17.

Because this value is so arbitrary and can vary by so much, that's why I said your gearing matters more than your size and strength.

 

[220volf]

Hi! Powerful hub motors have one big con - big unspured mass. It is not felt on a flat road, but when you go off-road or hit bump you can break you wheel. Every vehicle manufactorers trying to minify unspured mass. But when you set up large motor in a hub, you increase it dramaticly. So every cheap motorcycle will be more comfortable than expensive e-bike with hub drive.

But if you usually have flat roads hub drive may be good variant.

 

[Rrickyy101]

Great info, thanks for the responses! I wasnt aware of the specific frame requirements, lame. What about a left side drive? Is this a good alternative for what I'm looking to achieve? I mean I imagine I could find higher quality motors that might fit alright in the triangle of a bike (with some welding) that you simply wouldnt find for a reasonably priced hub... unless Im wrong on that count as well.