Single speed cargo bike feasibility

[Klingejonas]

Hi,

I'm thinking of converting my Bullitt cargo bike to electric drive. My major concern is to keep it as simple as possible as it is used year-round as a commuter - snow, rain, sun etc. the less parts the better.

I'm currently using a internally geared hub (Shimano alfine 8 speed) but would like to dispense with the complexity of gears if possible.

My thinking was that a sufficiently "torqueye" direct drive hub motor could to the job. However as I have no experience whatsoever I hope that I can ask you advice and recommendations.

I'm looking for a max assisted speed of 35 km/h
I'm doing roughly 35 Km per day and would like the battery to last for that Distance
I would like to arrive at work without breaking much of a sweat in the 17 km up there
The bike weighs in current configuration some 28 kgs and never carries a load higher than 110 kgs total including me
We have no hills worth the name. Longest is 600meters at 6% max incline
I'm in decent shape, race in the c class in national road racing series
Budget - not critical, but 1200 use is better than 2500 usd

I've been looking at the 750w solutions from Falco and from Bafang. I know these are fundamentally different but can't figure out what he best solution is - if any.

Any ideas, suggestions, input etc is very welcome! Is it even possible - and a good idea?

Be Jonas

 

[dogman dan]

Ok, the key thing here is the weight. Under 300 pounds, you should have no major problem using just about any hubmotor that has 750-1000w of power.

IMO, you would be better served though, by choosing one with a lower rpm, vs one built for speed. So if you get an rpm choice, pick the slower one, and then get some speed back by running it on 48v.

Though you might prefer a single speed, the question is how do you find your ideal gear in the first place? It will depend on the size of your front chain ring, and the speed you ride. I have done this trick. Use a 7 speed gear and derailleur, partly because I just need a tensioner.

Then using a piece of baling wire on the derailleur, I can lock it down in whatever gear I end up choosing. No shifter, but if I stop, I can change gears if I need to. Once I find the gear I like, it just stays there. Tends to be the 14t gear anyway, the smallest cog. But not always.

The hill should be no problem to get up, in for example 14-48 gear. Which should be about right for 30 kph.

Best solution for me, for a cargo bike is something in the 2000w ballpark. Just nicer when you do have a stop sign, on a hill, and you need to get going again. More able to carry more than 300 lbs up more than 6%.

But 1000w will do what you explained as your needs.

 

[dogman dan]

Links to your bike can help.

I see now that you wont have a long chain, that has to have a tensioner.

https://thebullittbike.wordpress.com/bikes/169-2/

Front hub might be an option. Then you keep your rear IGH.

 

[littleskull99]

I have a friend with an electric bullit. He has a majic pie in the front wheel. It does around 18-20mph on 48v. Il see if I can find a pic..

 

[dogman dan]

Pie on the front does sound yummy. Small wheel up front, so a regular speed motor will do beautifully.

 

[littleskull99]

Torque arms have since been added. It goes up hills like a goat with the majic pie.

 

[Klingejonas]

Thanks for all your answers - very fast and informative

The magic pie sounds attractive and looks great on the Bullitt in the picture. Not sure about channeling 70nm of torque through the front wheel though - wouldn't take much water on the road in a bend to take a spill. Is that a problem for your friend?

It doesn't strike me as very plug-n-play though and as I'm a n00b with this I don't know if it gets a bit too complicated. That aside I have a few questions about the magic pie that I couldn't quite find on the golden motor.ca website.

Is it a pedal assist system or only throttle based?
If pedal assist, how does it determine the level of assist - cadence, torque or how?
Brake cutout - does a sensor exist that would allow be to use my own brake levers to cut power (as for e.g. Bafang)?

Thanks!

Br Jonas

 

[littleskull99]

Yes it does get slippy in the rain but no more than a pedal only bullit imho. I believe it is throttle only. My friend bought his kit with battery and we had to solder a connection to the battery. Other than that the kit was straightforward to install.

 

[1000w]

I have a steel cargo bike, which I'm sure is heavier than your aluminium Bullitt, and I run a rear 12 turn Mac. This set up has given my about 2000 km of faultless service, pushes me, two children and shopping up hills no problem. I have the controller programmed for 1400w.
Cheers,
Matt

 

[Drunkskunk]

The Magic pie is about as close to plug-n-play as Ebike kits get. There may be ways to adapt a pedal assist sensor to one, but that's not the default, and not exactly plug-n-play. In General, I've found using a throttle to regulate the amount of assist my motor gives much better. Your brain will always be better at deciding how much power you require at any given instant, and respond much faster than some sensor can.

The consequence of lost traction in a front tire is higher than the rear, so there is some risk. However, your bike's aluminum frame and 120mm rear hub spacing aren't good candidates for a rear motor, so a front or a mid drive are your only real options. You have the advantage of front cargo, so a front motor makes sense when hauling an actual load. You can minimize slippage risk by choosing a wider front tire with good tread for wet weather.

 

[Klingejonas]

This forum is a goldmine - thanks for all your time so far!

The bullitt can officially be dealer-converted to Bionx hub-drive so hub it can be done. That being said I don't know which ones fit.

The magic pie front drive seems more and more interesting, I love the simplicity! In Denmark, however, only pedelecs are legal so I'm not familiar with throttle-based systems. Just so that I'm sure how the it works:

- there's a throttle so basically your bike is turned into an electric motorcycle. No need to pedal unless you want to?

There's no real freewheel on the magic pie, so if your battery dies you're in for a long slog home?

No fiddly torque-, speed or cadence sensors are necessary for the operation, just hub, battery and throttle?

There's no brake-interface so if you panic-hit the brakes and forget to loosen the throttle you might cook the engine - or will the throttle zero when released?

Br Jonas

 

[littleskull99]

- electric motorcycle. - Pretty much.

- freewheel. - There is no freewheel on the front magic pie motor but a rear motor will have threads for a screw on cassette and freewheel. You would have to change the drop outs for derailer compatible ones. Larry n harry sell these. If you mean the freewheeling of the motor when not powered, yes there is magnet resistance with direct drive motors like the pie and yes its a bit of a bear unpowered. Maybe you could look at a geared motor which effectively disconnects the motor when not in use.

- just motor, batt and throttle. - There are ebrakes in with the kit that cut motor power when brake is pulled. Is your alfine a pedal back/coaster brake? As this may mean rear dropouts are narrower than 135mm and may mean you cant run a standard rear hub. I guess the bionix is narrower or specific to the bullit. Also you could melt something if you pedal back brake whilst motor is on but the front ebrake can be used.

Hope some of this helps.

Matt.

 

[Klingejonas]

Good stuff Matt, thanks for that. I meant freewheeling of the motor so that's also answered. I'll talk it through with my lbs, but already have most answers from here.

Be Jonas

 

[Drunkskunk]

I did some research. Since Pedelec is a legal requirement, there is an option. The Cycle Analyst is a great add-on for any Ebike, and among all kinds of information it can display, it can also accommodate the THUN pedal sensor. It's a fairly straightforward conversion, but does take some wrench skills as you would need to replace the crank and possible the crank arms during the install. It's also not cheap, but it makes for a much better system than most of the commercially available ebikes use. Golden Motor Canada recommends it for the Pie, and offers this explanation as to why the usual system doesn't work.

Any direct drive motor like the pie will have drag when not under power. But it's not much. The drag is often called Cogging, and can be calculated using this simulator by placing the throttle at 3% and sliding the speed line out to your actual pedal speed. I ride one of the worst cogging motors ever build for a bicycle, and I ride it often with no power. it really doesn't cause that much of a problem. At the very worst, it's about like trying to ride a street bike with knobby tires.

A geared drive motor has an internal freewheel, so you won't any cogging.

 

[melodious]

I understand the way folks feel about keeping things simple in a bike, and that translates to single speed mentality (kudos if you don't don't freewheel & brake, that's serious balls). Personally, I enjoy the different cadence options that gears provide to relieve the monotony.

Why remove the IGH Alfine8 to a SS in a cargo bike? Personally, it doesn't "click" for me. I understand that a slow torquey motor and lots of watts will do the trick. An unloaded SS electric cargo bike I can see. A loaded down SS electric cargo bike I can't see.

Gearing to a high cadence allows one to make pedal/leg position for technical maneuvers easier. That's my 2¢. Anyways, with a front motor you can always change between a SS and IGH easily, then make a decision which riding style you prefer.

I love those front loading cargo bikes. If the goal is to carry huge loads under pedal power and sacrifice as little handling as possible, a front loading cargo bike is where it's at. 8)

 

[Klingejonas]

Thanks guys!

I saw the thun on the golden cycle site and found it very interesting. However, the price quickly gets to about 1500 usd with this and the cycle analyst and then we're in Falco-territory- and that seems like an even more plug-n-play product with a 5 year warranty. I think I'd splash those extra 500 use for that - without knowing anything about the falco solution.

The Ss- idea came because I was so new to this that I didn't even consider a front hub, only rear hub - and I didn't want to maintain a dérailleur, cassette, cabling and shifters throughout a loooong winter. If I go with a front-hub I'll definitely keep the rear igh, no need to sacrifice that.