Please help me make some decisions...

[StoneTower]

I purchased a Fat Bike from a family member that has a Bafang M620. It needs some work. I got 2 new inner tubes and got the tires to hold air. I was able to bleed the rear brake and get it to work. I bled the front brake for good measure. I now have a charger (which I did not before) and most things are working well. It has been years since I worked on bikes. I noticed that the derailleur looked a little off. I made a derailleur hanger alignment tool to see it the hanger was bent, and I was amazed and how far off it was.

I was able to straighten the hanger without any issues, but I think the derailleur may be bent.

Aside from this, I am not sure I like the gearing. I would like to be able to pedal the Fat Bike if I run out of battery and even in the lowest gear, it is brutal to pedal it up my driveway.

The bike has a Shimano CS-HG50-10 rear cassette and probably a 42-tooth front chain ring on the Bafang Ultra. With motor assist, there is no problem getting around, but what if I need to pedal back home. In looking up those cassettes, they are a 11-36t. With the wide rear hub on the Fat Bike, the chain line sucks (in my opinion).

I thought about reducing the front chainring size, but the chain is very close to the top of the chain stays on the rear suspension.

What about a new derailleur and a new (maybe) 8 speed cassette (along with a new shifter and chain that would be required. Do they make any 8 speed cassettes that will hold up to the Bafang M620 that have maybe a 48 or 50 tooth ring on the cassette?

I am looking for ideas. I would have probably never purchased a e-Fat Bike but this one had the Bafang M620 which I wanted, and the price was too good to turn down. This bike frame is the same as this one, but the rear suspension and front fork is set up to be a Fat Bike.

Thanks for your help in advance.

 

[m@Robertson]

I think you have to do a couple of things here:

First, forget about being able to comfortably pedal a bike like this without power. Its just not practical to do with a bike that is probably in the range of 60 lbs or more. The reality of owning an ebike is you figure out very quickly what your range is, and you make a point of not exceeding it. Usually this is not a handicap. Especially on emtb's where you just naturally use less power on trails (you are riding unpowered down every hill you climb up, and your pedaling up a hill is slow and not particularly power-consuming).

With that said, changing the gearing to better suit your riding terrain certainly is both do-able and a common practice. But not with an 8-speed., which is antiquated technology largely resurrected by Far East low-cost DTC ebike manufacturers. In the West its only found on junk bikes sold in department or discount stores.

There are a couple of colossally expensive 8s options from SRAM that are meant for downhill bikes, but the SRAM clusters are small because thats what downhill bikes need. Same for tooth capacity. That leaves, by and large, junk remaining in the 8s category. Shimano Tourney and similar. Up from the 'factory junk' category and maybe the only 'up' is the Box 4 group from Box Components. You would need the derailleur, cassette, shifter and a chain. I'd pick the SRAM EX1 chain as it is mid drive stressed and 8s compatible.

If you want to take things up a notch, I'd go 10-speed. Same SRAM chain would be fine. I am really fond of the Microshift Advent X 10 speed system for super high stress hills and loads. And its inexpensive. Can it fit on your bike? Good question. The deciding factor is the rear frame spacing and of course you'll have to either have a Shimano mtb-compatible cassette freewheel (sounds like you do) or build a compatible wheel with a new, strong rear hub that has a steel cassette body (DT Swiss 350 Hybrid - or the standard 350 Classic with steel cassette upgrade - is the DIY favorite but be warned you pay for that indestructability).

Lets hope your cassette body is already steel. If it is, the next risk is under the body at the pawls. If its a 3- to even a 5-pawl body, then the risk is of the motor torque tearing those poor pawls off. Thats the next failure point that the ratchet engagement hubs like DT Swiss, Mavic, Hope or the low-cost ZTTO overcome. I hear SunRingle also makes even stronger hubs that are not so expensive but I have no details.

 

[StoneTower]

So, the bike currently has a Shimano CS-HG50-10 rear cassette. It is a 10 speed cassette now. The idea of an 8 speed came from reading that 8 speed chain is stronger. As I said, I have not ridden in quite a few years but I was extremely supprised at how hard it is to pedal the e-bike Fat Bike.

Where I am at, if the Shimano Deore derailleur is bent (I straightened the hanger with the tool I made) I could either try and straighten the derailleur or I could buy a new. If I was going to go that far, I was wondering if I should have a larger cog in the back than a 36 tooth which is what the Shimano CS-HG50-10 rear cassette has. Is a 42 tooth chainring with and 36 cassette gear too high high a ratio and not low enough? I just like to make the best choices when I fix something. The other idea was to run fewer but more cogs on the larger side and use spacers to move the gears into the center of the chain line to make a better chain line.

Thanks.

 

[m@Robertson]

So, the bike currently has a Shimano CS-HG50-10 rear cassette. It is a 10 speed cassette now. The idea of an 8 speed came from reading that 8 speed chain is stronger.

That is baloney You can google around some chain tests and you'll find that 10 and 11s chains test to be stronger than the older 8s and even 9s, and the stated difference is simply that chain manufacturers have gotten better at their jobs. My 10s hill-climber cargo bike actually uses an 11s ebike chain - 11s chains have the same internal dimensions as 10s, just a hair narrower on the outside dimensions. The extra fudge room makes for a drivetrain so quiet you'd think you were riding a belt drive.

As I said, I have not ridden in quite a few years but I was extremely supprised at how hard it is to pedal the e-bike Fat Bike.

Yeah just take that in stride. In practice you will learn your bike's limits and learn to go nowhere near them. Just part of the game and the end result is no need to go bananas coming up with or worrying about out-of-power solutions.

Where I am at, if the Shimano Deore derailleur is bent (I straightened the hanger with the tool I made) I could either try and straighten the derailleur or I could buy a new. If I was going to go that far, I was wondering if I should have a larger cog in the back than a 36 tooth which is what the Shimano CS-HG50-10 rear cassette has. Is a 42 tooth chainring with and 36 cassette gear too high high a ratio and not low enough? I just like to make the best choices when I fix something. The other idea was to run fewer but more cogs on the larger side and use spacers to move the gears into the center of the chain line to make a better chain line.

Thanks.

The HG50 cassette is, if I remember correctly, pinned-together into a single piece, so thats perfect for a mid drive because a pinned-together monolithic cassette distributes its force all across a cassette body, so it doesn't dig into the body like its a block of cheese, which a single cog will do very quickly. So if you have an HG50 and you find it is pinned together... leave it if you are happy with the gear range. If you are not, since you have a 10s system I'd strongly recommend the Microshift Advent X derailleur, shifter and the 11-48T steel cluster. Especially if the derailleur is already screwed up some. I would not try and fart around with bending the cage, the hanger etc. If it breaks you are walking home.

Here's a look at mine on that same hill-climber cargo bike... and to answer one of your questions indirectly: That is a 42T front chainring and a 11-48T cassette. I did once have a 40 on the front and it fit fine as well, but the tooth profile was not aggressive enough. For my use, which includes up to 130 lbs of cargo plus my 230 lb self, plus steep hills, you have to take steps to ensure complete reliability.

I can get up on that 48T cog, but chain line is so bad on a bike with such a short rear triangle (thats even a 26" tire so very small) I don't use it. The thing that matters is not the chainring/cog tooth differential. Its chain alignment. If its too skewed on a 160 Nm motor you turn the chain into a chainsaw that will chew right thru your chainring teeth. So on this 10s cluster, I really have 8 usable gears as I also don't like the alignment on the 11T either (these are choices I am making ... the bike will shift onto them and the gears will work, but I know from experience that using them carries a penalty I am not willing to pay).

If you are going to be screwing around with re-gearing a powerful mid drive, read this:

How To Build a Mid Drive Ebike That Doesn’t Break

Mid drives up the ante on the required competence of the builder. Read this so your bike lasts without things breaking or wearing out early.

talesontwowheels.com

There's more there than you need since you are not starting from scratch, but it will give you a lot of background you lack coming into this new. Once you are done with it, follow up with this:

How To Ride a Mid Drive Ebike Without Breaking It

If you can ride a bicycle you already know how to ride a hub drive ebike. Not so a mid drive. Particularly a powerful one that can tear your chain apart. Fear not. The rules are simple.

talesontwowheels.com