Commute over a BIG STEEP hill with a BBS02

[jmw]

I recently built a BBS02 750w using a thin tire street frame. My intention was to get the build experience, then build on an old Cannondale road bike frame and come out with a commuter. The commute is unique, 8 miles each way with an 1800 foot hill in the route. Will this work? The all-up weight will be about 200 lbs. (me plus bike). I am willing to pedal but I am not very strong. Are there some calculations I can do? What happens if the motor gets too hot? I tried the climb with a hub-motor bike (Bionx) and made it about half way up before I was exhausted. Your experience and/or analysis would be appreciated.

 

[cycborg]

I'm trying to wrap my head around the idea of an 1800 foot hill in Central Florida...

What's the grade? How long is it? How fast do you want to go?

You could get an idea of the power required by running this calculator. Apparently the BBS02 is good for 1200-1300 W for several minutes without overheating.

 

[darth_elevator]

Sorry, I don't have any calculations, but speaking from personal experience with now nearly 800 miles on my BBS02, I know a BBS02 can pull 200 pounds up an 1800-foot grade over eight miles. My total weight -- bike, rider, bafang, battery pack -- is 250+. Saturday we went on a 25-mile ride that had 3200 feet total altitude gain.

I doubt that you'll have overheating issues unless that 1800-foot gain is all at once. I am also interested in knowing what the grade is and how long it is. I had some overheating with steep mountain bike climbs that I'm guessing are a lot steeper than anything in Florida. I got a smaller chain ring and haven't had any issues since. My internal temperature on Saturday never went over 100 degrees F, and that was with my pedal assist cranked up pretty high.

How many Amp hours are you planning to have in your battery pack? On Saturday's 25-mile ride, I used approximately 15 Amp hours. (I would have used less, but I roared full throttle on the last 2 miles of downhill just for the rush.) If you go with a smaller pack, like 10 Amp hours or so, you might want to consider charging your battery at work, so you have a fresh pack for the return commute. I remember seeing a calculation somewhere on Endless-Sphere that the BBS02 will use about 15 watt hours per mile on the flat with moderate pedaling and 30 watt hours per mile with throttle only.

 

[KINNINVIEKID]

It has a sensor inside that will cut power to the motor if it overheats to prevent damage.
When it cools it reconnects so no worries there.
All you need is a decent granny gear for steep hills,I live up on the Teesdale moors and find that 44T-34T will allow me to climb anything round here.

 

[Ade]

I'm trying to wrap my head around the idea of an 1800 foot hill in Central Florida...

What's the grade? How long is it? How fast do you want to go?

You could get an idea of the power required by running this calculator. Apparently the BBS02 is good for 1200-1300 W for several minutes without overheating.

My bet is that it's an 1800 foot long hill that's steep.

And to try to answer the OP - I have a shorter commute than you, around 9km/6 mile round trip, but half of it is long hill that is very steep in places - I use a 10ah bottle/frame battery with 25R cells and my 750W BBS02 handles the trip on my 24KG fat bike with ease. After a round trip, the battery indicator is hardly at 80% - I do peddle a bit, though not strenuously and remember, one half of the trip is downhill too.

 

[BaronPils]

That is the perfect user case for a mid-motor above hub motor.... because you can trade in speed for torque...

You should optimize your speed so that the power of the motor defeats gravity. Driving up the hill @40km/hr probably will be to much..
I would expect with lowering the (granny) gear each hill should be possible, only your speed will be limited significantly.

The BBS02 is most comfortable at around 80rpm.. Let's say we want to beat te mountain at 18 km/hr.

then you need front: 44T and at the back 25T @80rpm/27inch tyre...
maybe 25km/hr then you need front: 44T and at the back 18T @80rpm/27inch tyre...

But it should be doable without overheating the motor for sure in the correct gearing.

 

[Ade]

That is the perfect user case for a mid-motor above hub motor.... because you can trade in speed for torque...

You should optimize your speed so that the power of the motor defeats gravity. Driving up the hill @40km/hr probably will be to much..
I would expect with lowering the (granny) gear each hill should be possible, only your speed will be limited significantly.

The BBS02 is most comfortable at around 80rpm.. Let's say we want to beat te mountain at 18 km/hr.

then you need front: 44T and at the back 25T @80rpm/27inch tyre...
maybe 25km/hr then you need front: 44T and at the back 18T @80rpm/27inch tyre...

But it should be doable without overheating the motor for sure in the correct gearing.

I forgot to mention that I have a 36T front chainring and a 9 speed cassette though I only ever use the smallest 5 sprockets. I can do 25 to 30 kph up steep hills without any problem and 50kph on the flat (motor is limited to 50kph). My fat tires are 29 inch in diameter.

 

[jmw]

Thank you for the input.
I should have mentioned that the 1800 foot hill is in North Carolina where we spend the summer.
I don't think that there is a hill over 600 feet in peninsular Florida.