Bafang BBS02 vs hubmotor - Need to climb

hi, awesome forum you got here. i'm new to electric bikes, but not new to lithium-ions (i've got several boxes of NCR18650B sitting here)...

basically i need the bike to go offroad punctuated by steep, sandy hills which are sections where i NEED to use granny gear (22T front, 32T rear)

now my dilemma with the BBS02 is i'll lose the triple chainrings up front. does this motor have enough torque to get me up these obstacles?

on the other hand a hub motor lets me keep the triple chainrings...

what do you guys think? many thanks

Sounds too steep for standard, intended for street use hubmotors. Hubmotors need to keep turning at a certain rpm or they will melt. For street use motors, that's about 15 mph when climbing steep hills.

I haven't tried the through the chain one, but I suspect with a motor going on it, you won't be needing that smallest front ring anymore. But you might want something smaller than a 48 tooth. What does it come with?

dogman, i believe the bbs02 comes with either 46t or 48t

though i could have my machinist make a spider to mount a smaller chainring, like this 32T, i'm not sure how it would affect the chainline

I've no Idea if the Bafang 750 watt is as powerful as the Bosh but the Bosch will easily climb a 16% grade with only the 9 speed cassette on a Raleigh bike, at the expense of top speed of course, but I didn't find it bad at all on my 64 km trip in Germany last summer. I also don't know what tooth chain ring it used.

My own haibike with bosch uses the Sram dual Drive III in the rear hub which gives a great range of gears I found it capable of climbing 20-25% possibly 27% with hard peddling but it did it.

Maybe you could think of a rear gear hub such as the Sram ? It does loose some peddle efficiency though without motor assist.

Maybe try a NuVinci N360 CVT hub ? that's a very popular option on the E.U mainland on the 30 mph Bosch pedelecs. Oh and belt drive.

I would much prefer the good old simple ultra cheap 3 chain ring option. Having said that when I'm just farting around the 3 speed Sram hub is terrific and changes very well under a full load. I would love to try a NuVinci hub.

NuVinci have geared hub options too and Rolhoff have a 14 speed hub, I could imagine climbing walls with that ! The downside to hubs is weight.

Grade is one thing. Sand is a completely different beast. The 750W BBS02 will have no trouble going up a paved (or otherwise solid) 16% grade in with a 48T Front Chainring and 25+T Rear Sprocket. However, anything short of a Hubzilla will die a violent death if making that same grade on a deep sand surface.

this guy made a freewheeling triple chain ring. I did something similar with mine but I only have a double chain ring.

[youtube]tVweIvS81rg[/youtube]

The would need to spider it and then bend the legs in to offset the already likely slightly off (outwardly) chain alignment - my own adapter had to use 130mm BCD because I could not get clearance for anything else with a recessed adapter however it corrected my chainline (with the help of 2MM spacers) and made for much less friction and thus loss of power in the drive train.

That said if the question is really one of BBS-02 vs hubmotor - what you need to answer is can you maintain your top speed using a hub motor climbing this hill, short answer - not without a shit ton of power. On the other hand, if you have a tach on the internal BBS-02 motor, you will find a point in RPM as close to with no load that you will be at maximum efficiency for the motor which means less heat, more power and less electricity needed - you may not go as fast, maybe 14 up a serious climb but the motor will be in peak efficiency the entire time - the same hub motor limited to say 1/2 it's maximum loaded speed is more a space heater and will eventually overheat, demagnatize and possibly melt insulation.

If you have major hills to climb I suggest perhaps (not knowing your wheel size or ratios) determining what no load speed of your motor is at your given voltage (they run without modifications up to 1500w and 15S or 62.25v) - for instance if the 55.5v nominal cadence works out to be 120 is that a cadence you can match to contribute - I can for short whiles, so I can assist up a hill or in increasing the top speed on a flat away, etc.

Hope that helps you a bit !

Regards,
Mike

Also consider a hub motor in a smaller rim like a 20".

If your hills are very steep you may need a more powerful mid drive than the 750w bafang like this build here:

http://endless-sphere.com/forums/viewtopic.php?f=6&t=57337

Agee about the sand. I've melted hub motors in deep sand that was flat. Floaty wide tires are a must.

so i've done some catching up with current bike tech (been away for a long while)...

seems like a 42T rear cog would cut it for me. i'm just concerned that the BBS02 + legs would bend those things

Have you ever considered using dual lighter hubbies? I had such bike for a while and it made a great climber. Also the weight, torque and frame stress was distibuted over 2 wheels, so the bike had awesome traction up steep climbs, although to get the most of it, I was required to shift my weight at the steepest of climbs.

I find the Bosch has enough power to get me up 16-25% but I would be peddling hard after 20% but I can do it where hubs would burn. The Bosch would be hardly warm after such a climb.

The difference though is the Haibike has an S-ram Dual Drive III hub in the rear wheel so you got much greater gear ratios than just the 9 speed cassette.

For 500-700 watts peak it sure can climb.

So I would imaging the Bfang can climb good too , but you'd be lacking the extra gear ratios for the steepest of climbs.

I wish they would not eliminate the good old cheap 3 chain rings at the front.

i'm starting to think that the Bafang BBS02 might not be the right kit for me. perhaps i would be better served by a Cyclone? as i understand it the two smaller chainrings are still usable, right?

miuan said:

Have you ever considered using dual lighter hubbies? I had such bike for a while and it made a great climber. Also the weight, torque and frame stress was distibuted over 2 wheels, so the bike had awesome traction up steep climbs, although to get the most of it, I was required to shift my weight at the steepest of climbs.

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yes i'm also considering dual hubmotors, but for different reasons

was thinking of getting a MAC 12T rear hub for climbing. and a faster front hub for the flats/pavement. or is this a stupid idea?

You want equally fast hubs front and rear, rear only on the flats or both for extra power.

miuan said:

You want equally fast hubs front and rear, rear only on the flats or both for extra power.

Click to expand...

On one of my 2WDs, I have the PAS connected only to the rear motor and the throttle to both. the PAS has a control panel where you can set the level, which gives enough power for normal riding, but when I want extra power for climbing or acceleration, I use the throttle to ring in the extra torque. For tricky off-road stuff, you need the extra traction from the 2WD,which the throttle provided. The throttle over-rides the PAS.

I also have a 2WD with a fast motor on the front and a slow high torque motor on the back with 2 independent throttles. For climbing, the extra torque from the front motor is still enough to make a big difference, but there's a slight efficiency loss like that. All the different configurations work and have their own advantages and disadvantages, but the main advantage is the ability to use smaller motors so that your suspension and handling work better, and your drop-outs suffer much less stress.

d8veh said:

I also have a 2WD with a fast motor on the front and a slow high torque motor on the back with 2 independent throttles. For climbing, the extra torque from the front motor is still enough to make a big difference, but there's a slight efficiency loss like that. All the different configurations work and have their own advantages and disadvantages, but the main advantage is the ability to use smaller motors so that your suspension and handling work better, and your drop-outs suffer much less stress.

Click to expand...

awesome. so it's not a crazy idea after all