I have no experience with mid-drives, but do have some familiarity with hub motors. My original upgrade plan from my first DD hub motor was to go with a mid-drive, since these drives seemed to me at that time to answer better to my needs. Because of cost and simplicity, however, I ended up going with a geared hub motor for my upgrade. My new system is functioning quite well so far, incidentally.
This should give an indication of my own opinion about these two drive systems: namely, that both have their advantages and disadvantages as compared to the other, and that there is not going to be a universal answer as to which is going to be better in every possible scenario. Each individual will have to decide, rather, based on his own circumstances and needs, which will be the better option.
To speak to my own circumstances, since my main application for electric assist was to get some extra propulsion when going up hills, a mid-drive seemed like it would work best. It could perform well the job of helping get me up those hills without pushing myself to total exhaustion, but it could also be brought to bear, in rare circumstances when I might need it (think unexpected approaching thunderstorm), to increase my top speed as well. So it would meet the main need as well as having some flexibility to meet other, less pressing needs.
But, like I said, I ended up, for the sake of simplicity and economy, going with a geared hub motor. It does a great job of meeting my main need (assistance on hills) and I'm quite happy with it for that reason. I have yet to experience a need for it to increase my top speed, but since its maximum speed is only about 12 mph, it does have a bit less flexibility than would a mid-drive.
I still may, on one of my other bikes, end up installing a mid-drive, though, so I'm keeping track of developments. And as I continue to consider that option, I've wondered whether I might find some resource on the web that offers a relatively unbiased comparison of the relative advantages/disadvantages of hub motors as compared to mid-drives. By unbiased, what I mean is a comparison premised on the fact that either might be better or worse for any given real-world scenario, and a comparison that does not try to argue that one or the other is going to be the better option for all scenarios.
A lot of what I've found in my searching is marketing-oriented and represents the viewpoint of someone whose final aim is to sell the reader one or other of the systems. So, of course mid-drive sellers are going to be touting all the advantages of their systems over hub motors, and vice versa. Take, for example, the discussion initiated by Rakesh (of Falco Motors) that I found at http://www.linkedin.com/groups/Mid-Driv ... 5503069184. Though there are some good points being made in the discussion, it starts off from a faulty premise; namely that mid-drives are being overhyped and are actually inferior to hub motors--the latter of which, <begin sarcasm> believe it or not, are produced and sold by Falco Motors</end sarcasm>. A reasonable discussion would, instead of starting from a flawed premise like that, proceed from the frank recognition that either might be better or worse for a given application. So, though that discussion contains some pertinent points for a fairer comparison, the points would have to be identified and excised from that sort of partisan context.
As that may be, I thought this forum might be a good place to try and generate something more like an unbiased comparison of the relative strengths and weaknesses of the two drive systems--one that could be of help to someone like myself, who is interested in finding out which might be the better choice for their own application. The closest thing I found so far to an unbiased comparison, is a page that lists the pros and cons of a recent (2012, it seems) GNG mid-drive kit. Some of the cons from this write-up are, or could readily be translated into, pros on the hub motor side. It therefore seemed like it might offer a good starting point for putting together a real unbiased comparison, so I'll re-post it here (original located at http://topsecretev.blogspot.com/2012/10 ... -hype.html )
From what I'm reading, a con for the mid-drive as compared to hub motors that might be added to this list is the inability, using the standard rear derailleur, to shift while the mid-drive motor is under power. That could be a big downside for me, since I would be bringing the motor into play primarily when climbing grades and might thus want to shift down a gear or two.PROS:
- * Great hill climber
* Lower center of gravity
* Very good traction in soft sand (perfect for the 2 biggest e-bike markets in the US (S. Florida and S. California.)
* Allows you to cycle the motor's power through all the bicycle gears
* More efficient (from my personal testing a mid-drive kit is nearly 40% more efficient than a hub motor in some cases.) So it is safe to say a 750 watt hub motor is nearly equivalent to a 450 watt mid-drive in terms of current draw per Nm torque output.
* Motor is less prone to current saturation over hub motors. It just climbs hills and goes through soft sand never bogging down.
* The motor draws less current per Nm torque output so the system runs cooler
* You can change rear flat tires easily as with any normal bike.
* You can use any cassette and or disc brake caliper without clearance issues
* Saves your frame's drop outs and omits the use of a torque arm.
* Can use a smaller/ lighter amp hour battery to achieve a similar range and speed.
* Easier to use off the shelf DC motors to lower tooling and replacement costs.
* Gives new meaning to the term "Freeriding" hitting a trail at 25~30 mph on a DH mid-drive is absolutely amazing and will open up the sport to an older crowd.
- * Chain drive is extremely noisy (would like to see all belt drive)
* A chain rear derailleur and or front derailleur is for the most part out of the question with anything over 350 watts. You almost need to cut power to the motor like a clutch to shift or else you hear a large grinding and thumping noise.
* Derailleur must be dialed in perfectly and needs adjustment more often
* Chain is prone to stretching and or premature wear/ breakage.
* The entire pedal drive train is put under extra stress and it's lifespan will be greatly diminished.
* Riders have belts or gears to worry about slipping, and or wearing out.
* The entire crank system spins the chain-ring much faster so if a pant leg gets caught, the effect can be devastating.
* The bottom bracket, and chain stays are put under tremendous stresses causing excessive flex (even my downhill mountain bike above has 4 bearings and 1 bushing in the "main pivot" and the flex is really noticeable under load.)
* All the added freewheels mean no-regen, and the bike is difficult to push in reverse.
* The initial start-up torque is harder to dial in than a hub motor in the controller programmer settings (it just takes off like a rocket.)
In addition to the above list, I also found this page--http://www.avdweb.nl/solar-bike/hub-mot ... ation.html--which offers some simulations of both hub motors and mid-drive systems. So some technical specifications for the sort of comparison I'm hoping to create could be extracted from a page like that.
Can anyone else add additional pros/cons for either and help to fill out the list so we can come up with a more comprehensive comparison? If there already exists some resource like this that I've overlooked, I beg pardon here and will ask that this posting be removed.