Alpine passes at low speed with Mid-drive ?

Dear fellow cyclists,

I am an experienced cyclist, but completely new in the ebike market. I have been eagerly reading this forum and I cannot wait to build my first ebike

Objectives:
I often go and ride long climbs, passes in the French Pyrénées. They are usually 10 to 16 km long, averaging 6 to 9 % steep. I usually climb one or two in a row. I usually climb no faster than 7 to 10 kph. Using this link with conservative data, I gather it represents a 450W motor power.
I want to keep doing this on my road bike, and build an ebike for my wife to ride with me.
She would use the motor only for climbing (not descents and flat sections), let's say a maximum of 25km of climbing per day, averaging 7% steep. She would also keep on pedaling to help the bike (I don't know how many watts she can produce, she is a healthy young woman, not a cyclist).

Bike and rider:
I have a nice Cannondale Hardtail MTB with hydro brakes that I will use for my wife's future ebike.
Total weight of bike + motor + battery + rider : 94kg

Motor and batteries:
I understand that for steep climbs and low speeds, Mid Drives are the best.
I also understand that Bafang are the best affordable option.

For batteries, I see that the most affordable and reliable option are 16850 from Samsung or Panasonic. I also undesrstand that Bafang needs 48V to 52V.

MY questions to you:
My biggest concern is to find a setup that allows for VERY low speeds (down to 6kph), on long climbs (up to 25km).

1. Is Bafang a good choice? If so, should I aim for BBS02 or BBSHD? (isn't peak power only about top speed? if so I don't care).

2. Regarding batteries, what do you suggest? I wish I can use a cheap dolphin case (or similar). 48V or 52V? How many Amps/Ah ?

3. Chainring and cassette seem critical in my case. What should I aim to keep low speed and good motor efficiency? What is the smallest chainring we can mount on a Bafang?

Many thanks in advance for your kind help. I look forward to building this!!

It sounds like the 500w would do it, and that says the 750w to me. Will she get the right gear though? She could need more to get going while she finds the right cog.

The dolphin does mean a spare battery can be carried. Then you can carry one or two, depending on the day.

I would build a 20" direct drive hub motor ebike. Use Statorade (Ferofluid) in the motor.

See: https://endless-sphere.com/forums/viewtopic.php?p=868394&display_history=true

With this you can have regen braking on the way down and save brakes. Maintenance is way lower with direct drive hub motors.

You could even do a dual drive bike, front and rear wheels both driven by hub motors. Better heat dissipation and less load per motor.

To climb a 10% grade at 10kmph with 100kg load is about 300 W load.
Assume 60% system efficiency and you need 500 W from you battery.
To climb 25km at 10kmph you need 2.5 hrs.
You need 1250 Wh of battery ONE WAY.
You won't get nominal performance from a battery and you do not want to run 100% DOD so you need like 1250/0.8 = 1600 Wh. This is about 9 kg.

This is assuming 0 W input from the rider.

Smallest chain ring I know of for the bafang kits is the 30tooth. Looks like it says its only available for the BBSHD. That is not a bad thing if you know for sure you are going to be climbing. Overkill but that never hurt anyone.
http://lunacycle.com/parts/bafang-parts/bbshd-parts/luna-mighty-mini-30-tooth-bbshd-chain-ring/

When most people around here talk about overheating things and wearing out drivetrains its because most of us are using many times human leg power on these bikes. Like 10x human leg power! If you are actually building a bike to go human speeds up a hill then the drivetrain wont know the difference between human legs and a motor. Your goals should be very attainable and super reliable if she can resist leaving you in the dust. Is she any good at wheelies?

The only slight challenge is is going to be that lower speed provides the least amount of cooling air flow so you definitely want to let that motor spin hence the 30 tooth chainring recommendation. But again you are talking about the lowest end of the ebike power spectrum.

Personally I would stay away from a hub for this application because the gearing of a hub is determined only by the wheel size. For climbing with a hub you would always want the smallest wheel possible but, put a 20" on a mountain bike and now the geometry is all strange and she will be rubbing pedal on the ground all the time. Just my opinion there.

A Bafang kit is a great way to go to keep it feeling very natural and bike like. Very easy integration with variable human power assist levels right out of the box. It will be light and easy to transport having centralized weight when hanging it on a car mounted bike rack or keeping the rear quick release function for removing the wheel to transport the bike if you do that.

Good luck. This will be an excellent training tool for you trying to keep up with her.

You will get as many different recommendations as answers. I am a big proponent of mid-drives, and specifically the BBS02 crank drives. I installed a 48V 500W BBS02 on a bike for my 60 year old sister over two years ago. She has significant hills that have up to 20% grade, but only about 3/4 mile. She loves the bike.

You can not use regen with a BBS02, so good brakes are necessary.

One reason I really like my BBS02 drive trike is my lack of range anxiety. I can easily pedal it for multiple miles with no assist on flat to moderate terrain. On other bikes, such as the LWB recumbent I had a few years ago with a DD front hub, I could only pedal without assist for relative short distances, even on fairly flat roads.

Welcome to the forum and good luck with your project no matter what system you decide to use.

I say BBSHD with smallest chain ring 30T.
As far as battery, Dolphin case is perfect get the most capacity you can afford, and 52v is ideal.


BBSHD will make it easier because it already has gear sensor included with it, so it's easier to use for your wife.

BBSHD with 30t and a 38 to 42 big ring on the back depending on how fast you can climb. All she has to do is be comfortable at slow speeds while pacing you uphill. You should be able to find a gearing combination that will allow her to match your speed in one of the PAS settings.

diff_lock said:

I would build a 20" direct drive hub motor ebike. Use Statorade (Ferofluid) in the motor.

See: https://endless-sphere.com/forums/viewtopic.php?p=868394&display_history=true

With this you can have regen braking on the way down and save brakes. Maintenance is way lower with direct drive hub motors.

You could even do a dual drive bike, front and rear wheels both driven by hub motors. Better heat dissipation and less load per motor.

To climb a 10% grade at 10kmph with 100kg load is about 300 W load.
Assume 60% system efficiency and you need 500 W from you battery.
To climb 25km at 10kmph you need 2.5 hrs.
You need 1250 Wh of battery ONE WAY.
You won't get nominal performance from a battery and you do not want to run 100% DOD so you need like 1250/0.8 = 1600 Wh. This is about 9 kg.

This is assuming 0 W input from the rider.

Click to expand...

DD is not for slow and hard. Switching to a 250w geared hub motor would be 30% more efficient and not overheat with the same 36v 15A. Neither would match his speed as well as the mid drive with the same controller flexibility plus lots of gears though. Keeping it efficient at any speed likely

It seems to me you have done alot of reading yet, and you're fairly right with your assumptions.

I live on a steep volcanic island, let me share my experiences.

Before I bought my BBS02 I test rode a direct drive from BionX. It became hot very fast and drained the battery almost instantly, so going DD is the worse you can do IMHO. Middrive is the way to go.

Concerning power output your wife will be satisfied with 500 or 750 Watts. There's a 36V version with 500W that spins not that fast as the 48V 750W. The BBSHD spins even faster, you can hardly keep up with it.
I don't know the preferred cadence your wife is pedaling, but the motor should fit to it. As one of the main advantages of a middrve is, that you can let it spin in its sweet spot, you shouldn't spoil it with a mismatching cadence. I would go for 36V next time for myself, but I'm quite lazy though.

Regarding batteries I recommend you to buy the best you can get, as all batteries lose capacity sooner or later. So the more WH you have at the beginning, the more it can lose while it still stays usable. There's dolphin style batteries from various suppliers, mostly chinese vendors, with 3400mah and 3500mah cells. This ends up in 36V 17.5Ah or 48V 14Ah nominal. For example, I go 100km and 2500 height meter with two 48V 11.6Ah packs. I'm 80kg with a Fullsuspension MTB weighing roughly 25 kgs.

There's cheap and helpful wattmeter available for less than 10€ that tell you about total and consumed Ah/ Wh. I would never ever dispense with this little dongle, as I stranded once before with an empty battery. The battery gauge on the Bafang display is shitty inaccurate.

When buying cassettes, go for steel cassettes. They can handle the torque of your middrive without falling apart. And they are really inexpensive.
Make use of a genuine E-bike chain like the KMC 9e. It is more durable and long enough to fit your drivetrain without patching together a normal 112 link chain plus a few additional links.
Front chainwheels are available from aftermarket supplier with 42T and 41T. I stayed with my OEM 46T from Bafang. Combined with a 12-36 cassette and 26" wheels it gets me everywhere with no effort at all. And yes, I'm talking about 20% and more at 8-10km/h. Plus I can gain speed in the flats. It costs 22€ shipped from china, and it is the only component of my middrive I replaced yet. That was at KM10.000.

If you get a BBS02 with the most common C961 display you'll never see that high mileage on the screen. Everytime you reach 5161km the mileage counter flips to zero.There's a software bug somewhere.
So, do you need to reprogram your kit? Some say you must, some say you should. Some don't care too much what people say, keep on pedaling and make some use of throttle now and then. That's me. Of course you can improve the performance of your middrive by changing the basic setting, as well as you can fry your controler quickly. Maybe just try without at first.

In my case there was some heat issues at the beginning. The motor even started to smell a little bit. Especially on hot summer days with me pedaling real slowly. I ordered some CPU heatsinks 14x14x5mm and two round LED heatsinks with 73 mm diameter and glued them onto the housing . Now the Bafang still gets hot, but not too hot to worry about. And it looks awesome.

Good luck with your build.

friendly1uk said:

DD is not for slow and hard. Switching to a 250w geared hub motor would be 30% more efficient and not overheat with the same 36v 15A. Neither would match his speed as well as the mid drive with the same controller flexibility plus lots of gears though. Keeping it efficient at any speed likely

Click to expand...

Which geared hub motor can survive a two hour climb at 10% grade? I do not have experience with geared hub motors, but they seem setup for failure with their moving parts. Also regen braking might be of use on decent.

On Ebikes.ca 's motor sim, the Bafang G01 will overheat at 350 W continuous (10 kph / 10% / 100 kg) and be less efficient. Could be their motor data though.

Alps & Pyrenees, you may want to stay within the EU law & steer clear of systems advertised as 500W & over. a 100kg person an a 10% grade at 10kph is using 10000 * 10% * 9.81 * 100kg /3600 W = 272W. If you just pedal 72W, that's a totally legal motor power output and I suspect it's way more than you need.
Or you may want a rip snorting tarmac burner Your choice!

WoodlandHills said:

BBSHD with 30t and a 38 to 42 big ring on the back

Click to expand...

+1. try to get the lowest gearing you can find, because if she uses the motor she will be MUCH faster than you are, and it will be not that easy to maintain a low speed if don't have the correct gearing for it. capacity is not that much of a thing, because if you both ride very slowly, she will burn a lot less energy. my little daughter can ride 50km+ with a 400Wh battery in all electric mode alone.
i bought my customer's kits from paul/cellman. a lot of battery options and battery bags/cases to choose from, and top service.

Dear friendly1uk, diff_lock, DanGT86, Rassy, fredfire, WoodlandHills, Speady, bobc, izeman, and future helpers,

[for those who don't want to real all my post, my questions are in red below]

I'm amazed with your quick and detailed answers. :wink:
Some of my questions seem already settled... while other emerge...

Let me sum things up.

Motor:
There is a consensus around mid-drive, and BBSHD in particular. Not because of the power, but because it can be bought with a 30T chainring and because of gearsensor.

DanGT86 said:

Smallest chain ring I know of for the bafang kits is the 30tooth. Looks like it says its only available for the BBSHD. That is not a bad thing if you know for sure you are going to be climbing. Overkill but that never hurt anyone.

Click to expand...

Rassy said:

One reason I really like my BBS02 drive trike is my lack of range anxiety. I can easily pedal it for multiple miles with no assist on flat to moderate terrain.

Click to expand...

friendly1uk said:

It sounds like the 500w would do it, and that says the 750w to me.

Click to expand...

fredfire said:

I say BBSHD with smallest chain ring 30T. BBSHD will make it easier because it already has gear sensor included with it, so it's easier to use for your wife.

Click to expand...

Batteries:
Battery is tricky. Let me do the calculations.

Speady said:

There's dolphin style batteries from various suppliers, mostly chinese vendors, with 3400mah and 3500mah cells. This ends up in 36V 17.5Ah or 48V 14Ah nominal. For example, I go 100km and 2500 height meter with two 48V 11.6Ah packs. I'm 80kg with a Fullsuspension MTB weighing roughly 25 kgs.

Click to expand...

bobc said:

a 100kg person an a 10% grade at 10kph is using 10000 * 10% * 9.81 * 100kg /3600 W = 272W. If you just pedal 72W, that's a totally legal motor power output and I suspect it's way more than you need.

Click to expand...

diff_lock said:

To climb a 10% grade at 10kmph with 100kg load is about 300 W load.
Assume 60% system efficiency and you need 500 W from you battery.
To climb 25km at 10kmph you need 2.5 hrs.
You need 1250 Wh of battery ONE WAY.
You won't get nominal performance from a battery and you do not want to run 100% DOD so you need like 1250/0.8 = 1600 Wh. This is about 9 kg.
This is assuming 0 W input from the rider.

Click to expand...

Let's say we have some input from the biker, , we downsize the grade to 8% or 9% and shorten the trip a bit, all resulting in 800Wh (50% downsized).
800Wh can be attained either via 52V x 15ah or 48V x 17ah.
I will keep on eye on the market for this, hoping that 16850 batteries will keep on improving over the next few months.

Miscellaneous:

Speady said:

When buying cassettes, go for steel cassettes. They can handle the torque of your middrive without falling apart. And they are really inexpensive.
Make use of a genuine E-bike chain like the KMC 9e. It is more durable and long enough to fit your drivetrain without patching together a normal 112 link chain plus a few additional links.

Click to expand...

Duly noted. I will do this.
Is it the same chain that goes from the cassette to the chainring to the motor? Or are there two different chains?

...
And now, my pending questions (still need your help guys :wink: ) - in red below

Overheating:

diff_lock said:

On Ebikes.ca 's motor sim, the Bafang G01 will overheat at 350 W continuous (10 kph / 10% / 100 kg) and be less efficient. Could be their motor data though.

Click to expand...

What makes a motor overheat? Too much power input? Too low spinning?
What are the names of the BBSHD and BBS02 on the ebikes.ca simulator?

Gearing:
Gearing seems to be THE one issue I need to tackle.

WoodlandHills said:

You should be able to find a gearing combination that will allow her to match your speed in one of the PAS settings.

Click to expand...

izeman said:

+1. try to get the lowest gearing you can find, because if she uses the motor she will be MUCH faster than you are, and it will be not that easy to maintain a low speed if don't have the correct gearing for it.

Click to expand...

Speady said:

As one of the main advantages of a middrve is, that you can let it spin in its sweet spot, you shouldn't spoil it with a mismatching cadence. I would go for 36V next time for myself, but I'm quite lazy though.

Click to expand...

Do we have any detailed information of the good cadence / spinning for an efficient BBSHD? For every PAS mode? (I don't think she needs a thumb throttle, but I want to make sure that she is pedaling for real and that the motor is in its high efficiency zone.)
Then I could do some calculations.

Let's say I have 34T cassette (need to check that) and a 30T chainring. That is 1.88 meters per spin of pedals (30/34*2.133). With a cadence of 60 spins/minute, that is 6.8 kph. Looks good to me, but I am unsure on how BBSHD works (only dealing with cadence?)


Crazy idea

diff_lock said:

I would build a 20" direct drive hub motor ebike...With this you can have regen braking on the way down and save brakes.

Click to expand...

Because she would only use the motor uphill... this gave me a (silly) idea.
Is it possible to use a very light hub motor who would freewheel uphill... and charge the battery dowhill? She would never use it as a motor, but only as a generator and brake saver?


And then, the last question, maybe the more important one :

DanGT86 said:

Is she any good at wheelies?

Click to expand...

We shall see

Is it the same chain that goes from the cassette to the chainring to the motor? Or are there two different chains?

Click to expand...

There's only one chain, from crankset to rear hub, as you know it from normal bike.
With a BBSHD I strongly recommend an E-bike chain like KMC or Connex.

.What makes a motor overheat? Too much power input? Too low spinning?

Click to expand...

Both, but low spinning is worse. With BBSHD that's not an issue. He's got huge coolingfins.
But BBS02 is not that bulletproof.

.Let's say I have 34T cassette (need to check that) and a 30T chainring. That is 1.88 meters per spin of pedals (30/34*2.133). With a cadence of 60 spins/minute, that is 6.8 kph.

Click to expand...

Then in the highest gear with 11T you top out with some 20km/h. Keep in mind that the middrive plus battery adds serious weight to your bike. You'll ask for a litte electric help even in the flats.
In addition the 30T chainwheel gives you the worse chainline you can think of.

.because of gearsensor

Click to expand...

You can power gearsensor on the plug of one brake switch of a BBS02 as well.

hoping that 16850 batteries will keep on improving over the next few months.

Click to expand...

We all do that. But 3500mah for a 18650 cell will stay the best option for while.

. Looks good to me, but I am unsure on how BBSHD works (only dealing with cadence?)

Click to expand...

Bafang says 120 to 150rpm. Of course you can pedal slower with lower efficency.

You won't get nominal performance from a battery and you do not want to run 100% DOD so you need like 1250/0.8 = 1600 Wh. This is about 9 kg.
This is assuming 0 W input from the rider.

Click to expand...

Yep. It's a worse case scenario. But you undestood why I doubled up my battery for decend 2500+ m uphills in the canaries.

I had neglected to consider cadence when jumping right to the HD and 30 tooth. I still think that is going to cool more effectively being overkill in the power handling department. I would ask the vendor for an opinion on the different rpms and heat and power capabilities. You are a pretty easy customer considering you have very realistic expectations and you have done your homework.

Motors work just like legs. Just think of cadence as voltage and pedal pressure as current. You can conquer any hill with enough gearing to crank it out but try it in the wrong gear and your muscles start screaming. Motor feels it the same way but wont get naturally stronger over time. High load/current kills efficiency so more power going into the motor comes out as heat. Power doesn't have to equal heat if you gear it appropriately. The right gearing keeps the current down and the efficiency up allowing for higher power with less heat produced.

Don't bother with the hub motor regen idea. The great cosmic accountant of the universe is really good at her job. You will have to input an amount of energy to lift that hub up the hill just for chance to recover some of that on the way down through regen. Its not worth it. Regen is a cool native feature of a hub when you already plan on using one but not worth it if you are mid drive.

I recommend regen primarily as a way to save brakes, not recapture energy. I recommend direct drive hub motors for the lack of maintenance vs geared systems (hub and mid drive).
I never looked into the price of the BBSHD till now, looks like it is over 600 USD. For that price you could get two professionally built hub motors from Ebikes.ca which would handle your climb, and much more, "maintenance free". You can save 60 USD per wheel if you lace the wheels yourself.



At 600-700 usd for motors, get John in CR 's hub-monster instead, does 20 kW peak easy.

The Bafang G01 is a geared hub motor, not a mid-drive unit. The motor is pretty small (less copper) and the thermal path from the coils to the environment I would assume to be pretty terrible, so it gets hot.
I do not know how to simulate BBSHD units on the Ebikes.ca sim.

If you think you need 800 Wh to complete the climb, spec the (any) battery at least 125% of that as you do not want to completely discharge the battery, and you will not get rated capacity at higher discharge rates.

You can find a very lightly used electric moped with a 1500-3000 W hub motor for under 400 USD locally and it comes with all the electronics you need to run it. Use the motor+electronics off that and build it into a bike.

http://www.hs-escooter.com/sdp/1012764/4/pd-4958252/16970055-2261356/2000W_48V_60V_10inch_QS_Hub_Motor_with_Disc_brake.html

Der fellow ebikers,

Your comments have been more than helpful.

I ordered a BBSHD, a 30 tooth chainring, a 48V 13a shark battery and started installing this on my mountain bike. Approx €1100 (without the bike).
The set up is temporary, I just wanted to try the beast.

Needless to say I'm having fun with this bike. I understood what was the "e-grin" and my friends enjoyed it also this weekend.

I took a picture to share my joy with you


Inevitably, I have encountered one major issue :

Speady said:

In addition the 30T chainwheel gives you the worse chainline you can think of.

Click to expand...

Because of chain alignment, I cannot use the last 3 cogs of my (9sp) cassette. However, that's the all point of my build to use 30x34 cogs for my wife to climb passes at low speed... When I use one of these larger cogs, the chain rubs/scrapes against the BBSHD metal body.

What are the available options for me?

I have been thinking about building a custom 9 speed cassette where the 34 cog would be already at the 6th position (and then not use 7, 8 and 9), but I don't know if it's possible.

I also read that some people use a 7 sp cassette on a 9 sp body with spacers. But I am not sure it is reliable (how about deraileur indexation?)

Do you have any ideas on this? I would be more than grateful.


Another (smaller) issue : when the engine is shut down, the cranks are not fluid. It's very sticky when pedaling forward and backward. Is this normal? I would like to be able to use the bike as a non ebike from time to time, without this extra effort. Maybe Have I tighten the BBSHD bottom bracket too much??

Thanks in advance.
a happy ebike noobie