Single speed mid drive: a good idea?

Joined
May 22, 2016
Messages
3
Hi!

I've been reading these forums for a while, first time poster. I've never owned an e-bike, and my only experience riding an e-bike was when I rented one for a city trip in Tokyo while on vacation. It was lots of fun, and I've been thinking of getting one ever since.

However, I find the selection in stores either boring, expensive or both. Most e-bikes are either $2500+ mountain bikes or heavy and bulky city bikes with hub motors (also expensive). So I've been thinking about building my own, mostly for commuting to work every day (12 km one-way, industrial areas, not too hilly).

I currently own a 1970's steel frame derailleur gear road bike, and it's great, but I'd like to make something simpler as an e-bike. Are single speed road-type bikes a good idea for conversions? Where I live (Sweden), laws limit me to 250W pedal assist and no throttle, so I won't be trying to go fast with this build. I just want a bike that will allow me to get to work without too much of a workout.

I've been looking at the Bafang bbs01 250W mid drive kit with a 10Ah frame/bottle battery, and with no gears a gear sensor will be unnecessary. Is a single speed e-bike even a good idea? Will it be underpowered? A motor supplier i contacted suggested that a hub motor would be better for a single speed conversion, is this true?

I can probably assemble a single speed bike myself, out of high quality vintage steel frames which are quite easy and cheap to find here, with some modern parts, for less than $400. With that in mind, I'd like the whole e-bike to cost around $1000 or less, if at all possible. Shipping and customs costs not included.

Hope I've provided enough info, appreciate any suggestions. Thanks!
 
Single speed rear hubs are not a very common thing these days.
I was looking at this concept a few months ago.
I finally concluded most likely options were:

1) single speed with coaster brake (may be 120mm)
2) standard derailleur hub with spacers and a single cog
3) 3 speed IGH (various widths between 124mm and 135mm)

A bafang mid drive can be used with the the coaster brake rear hub but the coaster brake will not function
Number two is a valid option and it will likely fit a 135mm road frame
Number three is also a valid option and gives you something to work with if the battery dies (or other calamity).

The other type I considered was a single speed flip-flop track hub but ti seemed to defeating the purpose (KISS = Keep It Simple).
 
If you haven't looked already, you might want to check out this forum section:
https://endless-sphere.com/forums/viewforum.php?f=28
there is at least one thread about a fixie and middrive; still ongoing I think. (sorry I don't remember which one)
 
Sort of easiest, and most likely cheapest, to go with a very small hub motor, and 7 speed freewheel.

Pry the steel frame open to 135mm, that's easy. Then put your chain on the gear that lines up best with your front crank. That will eliminate the need to use a derailleur to align and tension the chain. It also will most likely put you in a middle gear, perfect for riding at moderate speeds, like you do with only 250w of power.

Using the 7 gear rear freewheel will eliminate to fuss around all day figuring out the ideal spacer to use to line up your chain for a single speed.
 
Thanks for all you replies. Perhaps I need to clarify: I don't intend to build a fixie bike with a coaster brake, the goal was to build a bike using a freewheeling flip-flop hub, but without any gearing at all. These bikes are fully rideable and popular in city environments and for commuting, which is my purpose here. The end result would look very much like this, albeit with thicker tires:

http://www.mytenspeeds.com/My_TenSpeeds_1/Bicycles_Table/Canadian_Bicycles/Sekine/Sekine_56_Cream_SS/Sekine_56_Cream_SS_Full_Side_1.jpg

Simple and light. Just add a small 250W motor and 10Ah frame-mounted battery to it. I will be using a simple front caliber brake, hopefully combining it with an e-brake for the motor. Don't the use of gears (hub or derailleur) make the motor redundant anyway?

So are these bikes a waste of time to electrify using a mid-drive? Are the only advantages of mid-drives that they allow manual gearing on the bike? I was under the impression that assisting the crank mechanism would be more efficient than say, assisting the front wheel, no matter the gearing. Why are hub motors better in this case?

I also should point out that the maximum pedal assist speed legally allowed here is 25 km/h, a limit I do not in any way intend to surpass. And I would be mostly riding on bike tracks where it is illegal to surpass this limit even through pedaling. And again, throttle is out of the question. I see many projects both here and around the Internet that focus on getting the maximum speed and power out of an e-bike build, this is not what I'm after here. I want to build a pedelec.
 
The bbso1 250w would be fine and would work fine :wink: if that is your preference then go for it.

The thing is every electric motor has an efficiency peak. The motor should be used between 50% and 100% speed to be efficient mid drive have the man advantage to always be at the good speed since you can change gears. The mid drive has to lower the speed a lot to get to 100rpm speed of the crank (the motor goes much faster) that is why they tend to be less reliable.

In my opinion The hub option would be better since it would be lighter, more reliable and when put in the rear wheel it would look like a igh hub.
The hub would also be less expensive and you can lace it to any rim you like.

That's my 2 cents
Leo
 
Should be fine. Just select the appropriate gearing for 15 mph and the motor will facilitate attaining and maintaining that speed. I rode a Haibike, 350w system for three weeks and basically left it in one gear all the time when running errands around town.
 
I e-mailed em3ev to ask whether a single speed ebike was a good idea, and this was their reply:
The great advantage of a middle motor is the ability to use the bicycle gears to keep the motor at an efficient RPM. Using a single speed negates that advantage. You would probably be better off with a hub motor if you were to use a middle motor on a single speed. A bicycle with gears would be recommended with a BBS01. 250W is very underpowered for a hub motor but with gearing it can be more than adequate.

There's also the issue of the motor burning out if the rpm is too low, according to the manual. Which may occur when biking up steep hills with a high gear ratio. Right?

What I'm really looking for is a clean, reversible and above all light build. A gear system kind of goes against this, especially one with a derailleur. And I keep seeing posts where people say they've just set their gear to the one they use the most, and leave it there after the e-bike conversion. Doesn't that make gearing redundant?

And wouldn't a 250 W hub motor be underpowered on a single speed bike? Surely there must be an optimal solution. Why have an e-bike at all if you're just going to use the gears anyway?
 
Automobiles and Lorries all have much larger and more powerful engines than ebikes. Are their transmissions redundant ?

Any solution must be matched to the problem and its environment. An single speed e-bike with appropriate gearing might be the perfect solution for a for a person riding exclusively well paved roads over flat terrain but would be a poor match for the dirt biker that likes to explore mountains ranges. The optimum solution is the one that best fits your requirements and personal preferences.

The 'simplest and most reversible' conversion is a front hub motor (complete with wheel, tire and tube) and removable battery (rackmounted, handlebar bag, etc).

... and regards to the opinions (everyone has one) that you receive here and elsewhere: a pinch of salt is sometimes in order.
 
There's no real advantage in a mid drive if you only have one gear ratio. You might as well use a geared hub motor like the Q100 or Q128; it will weigh less and cost less than most mid drives, be easier to install, and not add stress and wear to your chain drive.

The only attraction of a mid drive in a single speed application is being able to use whatever hubs you like.

If I were building a bike with your modest power and speed requirements, I'd use a Q100 front hub, with a suitable size battery and controller on a dainty front rack. That would minimize complication and wiring, while allowing the rear wheel to be the stronger conventional type.
 
Yes, people put a bike in high gear and leave it all the time,,,,with hub motors. so we suggested a hub motor.

You can put one gear on it,,,, after you fiddle around with spacers to get the chain straight so it won't throw off constantly. I just thought a 7 gear freewheel would make the initial setup easier. You do take the derailleur off, or never have it. You use one gear. The one that lines up good.

Single gear mid drives are also fairly common, but more in the frankenbike category, with the second chain and gear driving on the left side, not the crank. In a lot of those cases, one gear is plenty,,,,with a motor capable of driving the thing 60 mph!!

For a bafang mid drive,,, sure you could put it on a single speed bike. But it's going to cost you more in efficiency, and risk of burning it up on the steeper hills, if you choose a high gear. I suppose it would work fine in a lower gear. But that would limit your speed much much more than any hub motor would.

A front hub motor is definitely the best option, if you want to keep the rear wheel and it's gears or whatever, intact. That's what fronties are for really, bikes with rear wheels you cannot swap out for whatever reason.
 
It seemed that your riding environment was a flat commute. Any hills and a one speed mid-drive would be a poor choice. I have a 750w BBS02 with 11-17-28 gearing spaced for an 8-speed derailleur and basically keep the rear in the 11 for flat to mildly hilly areas. Of course, this is a much more powerful system, but I think the smaller motor would still function adequately for FLAT COMMUTES. Its advantages would be better weight distribution and if you ever get a flat Of course, you need to determine the appropriate gearing to keep the motor in an optimal range.
 
This bike is very light at about 13kg. It has a tiny geared front hub-motor at 24v and no gears. The battery is hidden in the frame. It goes up steep hills pretty well with a 100kg rider on board and is surprisingly pleasant to ride around. The only down-side is the maximum speed of 12 mph and range of about 12 miles.

I've built several bikes with small wheels. They all climb well with small geared hub-motors. One could also reach a speed of 35km/h without pedalling. The small motors can make a lot of torque and speed if you make them spin fast, which requires small wheels. You can't get the same climbing ability in 700c wheels because they spin too slowly.

 
If you want something simple and reliable a hub mounted motor is the best. As you have to stay within the 250W unit, you won't have to worry about extreme power.
 
If you want lightweight stealth and to preserve the fixty look-you would have to build a friction drive I guess. Or for a cool 80grand you could do the tour de france thing and get one popped down you're seat tube. Friction isn't the most practical but better than a mid drive with no gears ( which will suck ).
K
 
I'll throw one more opinion in here.

A BBS01 mid drive's only advantage over a hub motor is it's ability to use gears. There is no regen, and a coaster brake isn't possible.

If you want regen, you need a direct drive hub motor. unfortunately, those are big, powerful, heavy, and illegal for you... Also a lot of fun. :mrgreen:

Your best match for your needs is a geared hub motor like the Q100. Mounting one on the front wheel would solve any issues with matching it to the rear gearing or brakes, though my preference is for a rear mounted motor for both performance and handling. At this power level, it really makes no difference.

I'd never encourage you to do something illegal... but the real fun starts at around 350 watts.
 
(I have a 250w Bafang unit, which I commute with extensively).

Seems like there are three debates in this thread:

1. Is it possible to use a 250 Bafang mid drive?
2. If yes, is it a good idea with no gearing?
3. Is there a viable alternative?

1. Depends mostly on you frame and the budget. See the Bafang section of the es wiki for fitment check instructions, tools and general knowledge.
Be aware, BBS01 are gen 1 bbs units may be phased out going forward. Again, read the wiki.
Depending on you frame and your budget, most likely = yes.
2. There are still benefits without gears. All your wheel parts can remain standard bicycle (I. E. No custom spokes or wheel builds)
And the kit is very simple and clean- most work straight away each plug only goes into where it's meant to and it's pretty waterproof and the controller is part of the motor unit. Very straightforward.

Is it a good idea? Sort of. It's like removing a key attribute and wondering whether it's still good. At the end of the day... you can always change it. Note it's only a 250 motor which will overheat and or strip the nylon gearing in it if the gearing is too hard. For this reason, I would want gearing in the rear, 7 to 9 is cheap on parts and pretty straight forward.

3. Yes. As eluded to by everyone else, a hub motor, usually geared (internal gearing, lighter and more for the weight) is better. Why? Because you no longer have increased drive train wear, you can still have single speed and it can be done cheaper.

The rest is up to you. .. personally I would keep your nice fixie nice and put together a separate ebike. That way you start the collection and don't ruin something you already enjoy.
 
Then there is the Cyclone 3000W mid drives, I think Luna is selling those for ~380 bucks... and there is a lot of knowledge spread over the Cyclone 3000W thread at E-S on the non-hub section of the forum...

Those can be really good.

G.
 
True enough,, a 3000 w mid drive will need no shiftable gears. It will merely have issues with burning the rubber off your rear tire all the time.
 
About coasterbrakes.. any one tried the CB model or tsdz2 ?

http://www.szbaf.com/en/components/component/motor/mm-g310250-1.html
 
Back
Top