MarcusT

I want to mount a Bafang mid drive to my fat bike. I see that pretty much all the motors come with chainrings from 42-52 teeth. These are much too high for my riding (mtn trails). Am I missing something? Is the drive coupled down?
Presently have 22T-36T X 11-36.
Or do I have to buy a smaller aftermarket chainring?
Thanks

andychrist

Yes you are.

E-assist multiplies your own power so you don’t need such small chain rings.

I run 40/32/22 x 11-40 on my unassisted bike, and barely make it up the steepest hills in the lowest gear combo. On the same model bike with assist, 50/42 x 11-32 more than suffices and I zoom up the same hills over 12.8mph

KPREN

The Bafang is geared down considerably and will pull the hills just fine. Get an aftermarket Liekie Bling Ring 42 tooth and forget about your problems. If you want to have better gearing for no power use then go with 11-46 or so in the rear. The minimum number of teeth on the chainring for a good chain line is 42 unless you purchase some expensive stuff. Then you can get down to 40.. The stock chain ring is okay on a bike path but not mountain biking. .

andychrist

You might also consider upgrading your chain to something like this one designed for electric bikes. It will resist snapping and should last about twice as long as a standard chain on a mid drive.

2old

I use a 30 tooth Luna on my BBS02, but like to pedal and never use higher than level 3 PAS (of 9). The hills in socal are steep enough that it's a good workout. However, I've transitioned back to mostly MTB.

MarcusT

I appreciate the replies, but I don't believe we're talking about the same riding. When I say mountains, I mean 1,000 meter climbs of trails and fire roads. 20-25% grade. 42X36 even with a motor is not going to cut it. Maybe 28X36
KPREN, you say it's geared down. Can you express that in gear inches?
Cheers

2old

1,000 meters in what linear distance? There are trails in CA with a lot steeper climbs (surveyed at 37 - 40%) that I've climbed without a motor (22 front, 34 rear gearing). Haven't tried with a motor since e-MTB's are prohibited there. However they wouldn't be difficult with my BBS02 and 30 front, 32 rear gearing.

Pop N Wood

Lots of people run smaller than 42 tooth chainrings with their bafangs. Especially on fat bikes, especially ones ridden in the snow

Lots of options to choose from as well

https://electricbike.com/forum/forum...g-offset-guide

About half way down this link there is a bunch of links to chainrings. Shoot, forgot this site blocks links to red dit

andychrist

Marcus, which Bafang mid drive are you planning to install, a BBSO2B or BBSHD?

Still don’t think you’d understand the nature of e-assist. Those motors can continuously put out 3-4x more power than you.

I live in mountainous terrain myself and have no problem climbing the steepest hills with road gearing, while loaded down with over a hundred pounds of cargo. Never even use the three innermost cogs of the 11-28T cassette while on the inner chainring.





Edit: The TSDZ2 from EcoCycles is available with multiple chainrings.

Also, if you’re concerned about not having the oomph to make it up 25% grades, maybe consider adding a front hub drive as well. Bafang makes them for fat bikes in 20”/26”, 500/1000W. With dual drive you’d have no problem negotiating the steepest gravel roads. Only issue (other than cost!) would be mounting a second battery, but a pair should easily fit in panniers hung from a rear rack.

MarcusT

Thanks Pop, that answers the question.
As for the trails, 1,000 meters is the altitude gain (in mtn speak). It's not the power of the motor of concern, but the trails and roads have switchbacks, rocks, logs, etc. Riding with a 42x36 would have me approach these obstacles at +20kmh. Does not make for safe riding.
I presently have a Bosch EMTB, I want to sell it and convert my fat bike because it is more sure footed.

Looking at this model:
https://bafang-e.com/en/products/motors/m-series/m600/

2old

Better look at the BBSHD. The M600 requires a dedicated frame.

MarcusT

Meant to say the M625. Was not too sure, need to check the DIY videos to ensure the motor will fit.
As usual, the Bafang website is not very informative.

2old

The 325 and 625 look like new DIY units and available now.

Chuckles1

20-25% grades? Man, you need a mountain bike! Can you put an MTB cassette on the rear? I run an 11-36 on my road bike, but 12% is probably the steepest I do with 39/48t chainrings. I don't know how big they go, but I've seen posts about MTB cassettes with a lot more than 36t. Ive heard of aftermarket spiders that go on Bafang mid-drive that might allow for a smaller chainring. Good luck. I'll be interested to hear how you make out.

KPREN

From reading this statement it is clear that you do not understand e bike power.
I sounds like you are confusing motor output in watts with the ability to climb as slow speeds and thinking in terms of gasoline motors for power. Electric motors work opposite of gasoline motors. Your above statement would be correct for a gasoline motor, because max torque is achieved at about 2/3 of maximum rpm and you would be haulin. With an electric motor, maximum torque (the power to turn the pedals) is achieved at zero speed. Zero speed is also where the electric motor is not putting out any power. Just because the electric motor is technically not producing any power a zero speed does not mean that the bike will not wheelie you over backwards if you give it full throttle with 42 X 36 gearing..
The BBSO2 Bafang will pull a 25% grade with a 42 front chain ring and a 36 rear gear at slow speeds IF you can keep the front wheel down and only apply enough power to get the job done. If 25% grades is your normal mode, then think about a BBSHD. The bigger motor will not overheat as much on the same climb.

KPREN

Maximum chainring speed on the Bafangs is about 130 rpm. The motor itself is turning around 5,000 plus rpm.

Everyone here is right about the chainring size. You can go below 42 teelth. If you do, your chain line will suck and you will have short drivetrain life and may not be able to run high count cassettes. A Bafang will do it regardless of what you may think.

I am running a Big F

at Titanium bike with a BBSHD setup with an 11 speed drivetrain. I have a 42 tooth Lekkie chain ring and 11X46 cassette. I am running 4-52 volt batteries in parallel for a total of 2,538 watt hours. The only time I get into the cogs above 36 are when I am climbing at very low or no power applied. My bike weighs 82 lb and I weight 200 lb. I often pull a trailer up to 150 lb.



On this bikepacking trip I was pulling 25% grades

Pop N Wood

KREN is the man, very knowledgeable and always gives good advice. he also owns a fat bike where I don't

But Karl is a bit of cult guru and really likes small chain rings and big motors when riding his fat bike in the snow.

https://www.electricbike.com/all-i-w...e-in-the-snow/

A for large rear cogs I've seen posts of people who have taco'd the rear cogs on ebikes. Make sure you get a strong one and that the chain line isn't too bad.