Choosing a new fat e-bike, but which one?

Hello everyone. I recently joined this forum and, not surprisingly, you have met another person interested in purchasing an e-bike.

I used to be an intense mountain bike rider, but now in my 50s trying to do that kind of mountain biking is too difficult for me. Now we have e-MTBs – a game changer. I also had the opportunity to ride a few different fat bikes (not electric) and absolutely loved how they ride. With my new bike and electrical assist, I want to go deep into the forests for a casual ride, maybe some overlanding, as well as ride on the road and bike paths alongside my wife with her e-bike.

I have a philosophy when buying these machines: save your money, make a huge investment, and keep that investment for decades. I only recently had to let go my 27-year-old mountain bike as it was too costly to repair (i.e., I am better off buying a new bike).

I want an “everything” fat bike. That is, good for overlanding, good for trail riding (although not the most technical or toughest trails), good for road riding, and good in all types of weather as I enjoy riding in rain and snow. As I age, comfort has become an extremely important concern. Traditional MTBs have a more aggressive riding posture that my back would not react well to. A more upright, relaxed position is preferable, and I can usually achieve this by installing an adjustable stem. I also require dual suspension and strongly prefer a mid-drive motor as I will be climbing hills on roads and trails often. I am also only 5 ft 4 in tall. With shoes on I may gain about ½ inch, but a small frame would be preferable if I can find one. Otherwise, I will have to get a medium-sized frame (which is meant for people at least 5 ft 6 in tall).

I have narrowed down my options to two bikes, but I am open to other models if anyone has something better:
  • QuietKat Ibex
  • Rambo Venom
QuietKat Ibex
The QuietKat Ibex is a great e-bike. I will be test riding a comparable model soon to make sure I am comfortable with a medium-sized frame. Apparently, they do not make small frames in this model although their Rubicon (no longer available) had all the same specifications and was available in small (sigh).

Another limitation of the Ibex is the gearing. I would prefer more gearing options, especially the Rohloff 14-speed hub. I am not certain if the Ibex (or any of the QuietKat models) could be upgraded with that hub. I have sent them an e-mail asking that question.

Rambo Venom
This bike is amazing and has everything I want in an e-fat bike including the Rohloff 14-speed hub. However, it does not have dual suspension (the QuietKat Ibex does). The Venom’s battery has less capacity than the Ibex, but I can live with that. Conversely, the Venom supports mounting dual batteries, which doubles the range. This bike also has a removeable throttle button in case you go to an area where throttles are not allowed (not sure if the Ibex has this function). The Venom is only available in one size: medium.

How do I Choose?
As long as I can use the controller to set the bike as class 1, class 2, class 3, or unlimited, then I can stay within the legal limits of almost anywhere I go. Right now, if I buy one of these bikes, I have to sacrifice dual suspension (Venom) or the Rohloff speed hub (Ibex). I want both. I have e-mailed QuietKat to see if a Rohloff upgrade is possible, as well as Rambo Bikes if they intend to create a future version of the Venom that has dual suspension.

Assuming both responses above are negative, which bike would you choose? Or, does anyone know of an e-fat bike that combines the best of the 2 bikes above? Or maybe a different bike I have not considered? Your feedback is *greatly* appreciated. Thanks!
Ever since I converated my 29er Mountain Bike to mid drive BBSHD, I never ride my Juiced EFat Bike. If I could do it over I woulda converated a quality Fat Bike. That's my advice...you can do the whole coversion, with lekkie chain rings, for around $1200...so just look for a decent used $400-$600 fat bike (hydro disk breaks) and have at it is my advice. For less than $2K it'll be superior to the overweight tanks you mentioned.
 
I own 2 Bafang Mid Drive Hard Tail Mountain Bikes I built myself by converting Trek Bikes. Had about 2k in each after going completely through them & putting in the biggest down tube EM3EV batteries available, I have also put together 5 Hub drive Fat tire "Juiced " hard tail E Bikes for family. My biggest Neg on those is the Incorporated Battery. On the Plus side Fat tires provide a form of suspension cushioning on your rear by flexing that I wish I had w/my 2'1" rear tires. They are adjustable & Fit most Pleasure riders short or tall. They go good off road & come w either 750 or 1000 w Motors & a 19.2 AH 52V battery. Abt 2K will get you one. That being said , I sure like the set up and looks of "Mr Spocks " bike ! Its obviously not his first rodeo building something like that.
 
I am considering buying a fat non-e-bike and make it a fat e-bike. There is so much to learn, though and I will have time to spend considerable time studying how to go about this kind of build.

If I go with a hardtail, I like the Surly Ice Cream Truck with 4.8-inch tires as long as I can install a front suspension fork, but I would be limited to installing a rear hub rather than a mid-drive motor. I much prefer full suspension and mid-drive. That combination is much harder to do with an existing fat non-e-bike frame.

If anyone has suggestions for a full suspension, fat non-e-bike that can accommodate 4.8-inch tires I am very open to suggestions.
 
Why would you have to do a hub motor with a Surly ICT? Its a great donor bike. FYI the ICT fork is suspension-corrected, meaning its got longer fork blades. I have used just the fork in a couple of projects for my 2wd bikes and it is a jewel. For your purposes, that means you can add a suspension fork and not change the bike's steering or geometry.

It has a 100mm bottom bracket , but thanks to the chainstay width, you are going to want a 120mm BBSHD. That gets you a 160 Nm motor. The ICT frame is ideal for a conversion mid drive because of the size of the triangle that lets you fit a battery inside, and the straight down tube that lets you tuck the HD up against it so you don't lose ground clearance.

You use the 120mm axle length to move your secondary housing out to the right so it clears the ginormous chainstay... something you'll have to deal with on any truly fat frame. Here is a pic of what I did on that white Stormtrooper I pictured earlier. This is during the build so the locking clamps have not yet been applied. The spacer on the left is actually a metric drill bushing you can have made @ McMaster-Carr to your exact specs (ID, OD and length, down to a millimeter) for about 40 bucks. On the right are my dual-inner-lockrings, that on their own will keep the motor from ever moving post-install. At that time when that pic was taken in 2018, I had not yet figured out that using the bottom bracket spacer as a washer between them ruined the jam nut effect of the two parkerized lockrings fit directly together.

Anyway, that spacer puts the secondary housing about two business card-widths clear of the chainstay root. If it touches it will eventually break the frame at point of contact. So... 120mm motor and a big spacer.

IMG_20180517_184524.jpg


And here it is after final assembly. Note the dual interlocking hose clamps that lock the motor into place. A $5 solution. That was June 2018. The motor is still in place today with no adjustments or re-tightening.

IMG_20180609_090732.jpg
 
Why would you have to do a hub motor with a Surly ICT? Its a great donor bike. FYI the ICT fork is suspension-corrected, meaning its got longer fork blades. I have used just the fork in a couple of projects for my 2wd bikes and it is a jewel. For your purposes, that means you can add a suspension fork and not change the bike's steering or geometry.

It has a 100mm bottom bracket , but thanks to the chainstay width, you are going to want a 120mm BBSHD. That gets you a 160 Nm motor. The ICT frame is ideal for a conversion mid drive because of the size of the triangle that lets you fit a battery inside, and the straight down tube that lets you tuck the HD up against it so you don't lose ground clearance.

You use the 120mm axle length to move your secondary housing out to the right so it clears the ginormous chainstay... something you'll have to deal with on any truly fat frame. Here is a pic of what I did on that white Stormtrooper I pictured earlier. This is during the build so the locking clamps have not yet been applied. The spacer on the left is actually a metric drill bushing you can have made @ McMaster-Carr to your exact specs (ID, OD and length, down to a millimeter) for about 40 bucks. On the right are my dual-inner-lockrings, that on their own will keep the motor from ever moving post-install. At that time when that pic was taken in 2018, I had not yet figured out that using the bottom bracket spacer as a washer between them ruined the jam nut effect of the two parkerized lockrings fit directly together.

Anyway, that spacer puts the secondary housing about two business card-widths clear of the chainstay root. If it touches it will eventually break the frame at point of contact. So... 120mm motor and a big spacer.

View attachment 10103

And here it is after final assembly. Note the dual interlocking hose clamps that lock the motor into place. A $5 solution. That was June 2018. The motor is still in place today with no adjustments or re-tightening.

View attachment 10104
Wow! A mid-drive on a Surly Ice Cream Truck would be awesome!

The reason why I assumed a hub motor was my lack of knowledge on the kind of frame needed to install a mid-drive. I am very, very new at this and am still uncertain about building a bike of my own. Obviously, not every frame can accommodate the motor. Still learning little by litte.
 
I was thinking about installing a Rohloff speed hub onto an e-bike, but learned that the speedhub is limited to 130 nM of torque when the more powerful Bafang motors produce 160 nM of torque. I e-mailed Rohloff directly and asked them whether they will ever create a speedhub that can handle torque, such as 180 nM.

Below is my original e-mail:
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Rohloff Design Team:

I am interested in installing your Rohloff speed hub into my e-bike. Upon reading the specifications, your hub can handle 130 nM of torque. Many e-bikes today, including mine, produce 160 nM of torque, thus upgrading my e-bike with a Rohloff is not a good idea.

In the future, would it be possible to design this hub that can withstand more than 160 nM of torque? I am saying “more” because I would never want the motor to reach the hub’s maximum. For example, could you design (or upgrade) the hub to handle 180 nM of torque?

The 130 nM torque limitation is the only reason why I am not purchasing one at this time. I was hoping your engineers would consider this, especially for the US market. I see 1000W Bafang mid-drive motors everywhere and many people like me who would really benefit from having your hub installed.

Thanks.
________________________________________________________________________________________________________________________________________________


Below is Rohloff's response:
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Good morning,

Many thanks for getting in touch.

I believe, like many other customers, you are confusing two points. As such, just for clarity:

The 130Nm input torque value is exactly that, input torque at the SPEEDHUB sprocket. The 160Nm and/or higher motor torque values are output values measured at the crank. Every bicycle, regardless of chain or belt, has a primary transmission ratio created by the crank sprocket and hub sprocket. Generally, this is a 2:1 or 2.5:1 ratio and reduces the torque from the motor accordingly. 180Nm motor output put through a 2:1 primary transmission ratio is only 90Nm at the SPEEDHUB sprocket - well below our 130Nm max. (180/2=90).
________________________________________________________________________________________________________________________________________________


If my interpretation is correct, the torque produced by a mid-drive motor is limited to the torque generated at the crank sprocket location, but not all of that torque is transferred to the rear hub. The Rohloff speedhub can handle a maximum of 130 nM of torque. A 1000W Bafang mid-drive motor produces 160 nM of torque at the crank sprocket, but only transfers about half that torque to the speedhub, i.e., 2:1 ratio, or 160 nM / 2 = 80 nM. 80 nM of torque is well within the Rohloff speedhub's specifications of 130 nM. Therefore, Rohloff speed hubs can be used on e-bikes with mid-drive motors that can produce as much as 130 nM * 2 of torque, or 260 nM.


I found a web page that explains this in detail, although I did not realize that calculating torque using an internal hub is much more complicated: https://sheldonbrown.com/twist-internal.html
 
Their response was very interesting:
That is VERY interesting. I've heard of queries to Rohloff being unanswered. This is the first time I've heard of a response and it makes sense. This explains why reported Rohloff failures on Bafang motors are so rare. You can always expect someone to find a way to break stuff.

With that said, I've heard of lots of problems with one particular manufacturer who used them in production bikes paired to an Ultra. I don't want to say who until I look it up and make sure my memory on who it is, is accurate.
If my interpretation is correct, the torque produced by a mid-drive motor is limited to the torque generated at the crank sprocket location, but not all of that torque is transferred to the rear hub.
I think we're talking about the secondary gear reduction which is still inside the motor itself. "I think" means I am guessing since I have not invested the time to get serious about this subject. EDIT: Nope the primary-to-secondary internal gear ratio is 21.9 to 1 so thats not it.
Therefore, Rohloff speed hubs can be used on e-bikes with mid-drive motors that can produce as much as 130 nM * 2 of torque, or 260 nM.
I think since we already know of $1400 Rohloffs dying in use with 160 Nm motors, you would do well to just be happy with trying it on a 160 Nm motor and let some other pioneer take the arrows in the back by going big. Note that the similarly-priced Kindernay is rated for 160 Nm.

You've shared your response. Can you also share your exact question to them? A lot of times there can be details hidden in an answer based on how the question was phrased.
 
I think since we already know of $1400 Rohloffs dying in use with 160 Nm motors, you would do well to just be happy with trying it on a 160 Nm motor and let some other pioneer take the arrows in the back by going big. Note that the similarly-priced Kindernay is rated for 160 Nm.
I think I enjoy changing gears manually more than I would like to have an automatic transmission. When I was younger, I preferred cars with a manual transmission (remember the clutch and stick shift?) rather than an automatic transmission.

My interest in Rohloff is more for my wife than me. My wife will eventually buy a class 1 or class 2 bike, and I will be able to upgrade the hub at a later date. The bikes she is interested in have much smaller motors and produce far less torque - much less than 130 nM.

As for me, I want to push my bike to the limits. :) To get started in e-bikes, I recently found a demo model of an Okai Ranger on sale and decided to purchase it. After riding it every day for over a week, I can say my interest in fat bikes has not changed. I love it!

My wife knows that the Okai is my starter bike. Breaking into this new hobby has additional costs: (1) the cost of two e-bikes for my wife and I, (2) the cost of a new bike rack that can carry multiple, very heavy e-bikes, and (3) the cost of purchasing and installing a class IV hitch with a 675 lb tongue weight (completed earlier this month). We could not afford to purchase the ultimate e-bike for me (or possibly build) this year. I am grateful, though. I can enjoy riding my new Okai Ranger (which I highly recommend to anyone as a starting fat e-bike) with my wife on roads and light trails. On my own, I can take that bike on more serious trails once we receive our new bike rack that we ordered (in about 10 weeks).
 

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I think I enjoy changing gears manually more than I would like to have an automatic transmission. When I was younger, I preferred cars with a manual transmission (remember the clutch and stick shift?) rather than an automatic transmission.
I used exactly this analogy when I first built my Cyclone-powered Stumpjumper. It had no display at all. Just an inline wattmeter giving me watt output (peak around 4kw) and charge level. It being my first mid drive, I learned real fast with that kind of power that I had to row thru the gears. No pedal assist. All throttle-feathering to go with pedaling. It was primitive, hands-on ... and I absolutely loved it.
 
Have a comment I am 5’5” and bought a Eunorau step thru. Don’t think any one else mfg one. Mid drive 1000 watts full suspension with ok quality. 140 mm front Very unique bike 17 ah battery and can add a second 17 ah for 34 total. Scram 11 speed for 3700? I hear they make many other brands?
 
I have never heard of Eunorau, thus cannot comment on their quality. Their Specter-ST step through looks impressive based on the specifications.
 
I have question regarding the battery. I noticed on Bafang's web site they have two models I am interested in:

Whale Shark 48V, 24.5 aH (1176 Wh)
Whale Shark 52V, 21.0 aH (1092 Wh)

Which would perform better on a fat bike? The greater voltage or the greater watt-hours? Both batteries cost the same, have the same dimensions, and have the same weight.
 
Which would perform better on a fat bike? The greater voltage or the greater watt-hours? Both batteries cost the same, have the same dimensions, and have the same weight.
Neither. These batteries are proprietary to the new CAN bus Bafang motors that are essentially clones of the BBSHD and BBS02 (or the CAN bus Ultra). But they are not perfect clones. Internally both motors are the same as their older cousins. However they are just different enough that parts are not interchangeable except MAYBE for chainrings. Most importantly the controllers are no longer editable so you cannot customize the motor's settings. Also since the motors demand a proprietary battery, you are right back to being stuck with one vendor.

Worth noting: Bafang advertises these batteries as "50.4v" which could make you think it is a 12S battery until you find out that 50.4v is the nominal value (50% charge) for a 14S pack (what is known as a "52v" battery), and thats what they are. This is the same thing as seeing a 48v (13S) pack, but a 48v pack is really fully charged at 54.6v. 48v is only the nominal charge value.

And... where did you see these batteries? (link). the ones I have seen were not called whale sharks and they were both listed as 50.4v. I thought the whale shark name was something the aftermarket came up with. Scroll down on this link and you will see the only two batteries they put on their web site that are of the whale shark type. Their web site NEVER is up to date with everything they sell so I am not surprised there are differences.

 
Oh and another thing: On the whole whale shark concept on a bike that will get overland duty: You are putting a big, heavy battery into a triangle that will end up being held down by two water bottle bosses in its cradle. A 17.5ah whale shark pack at Bafang USA Direct (which is not Bafang at all they just use the name) is 12.5 lbs, so figure a 21.0 to 24.5ah pack could end up being 15 lbs easy... all supported on two M5s. Breakage is not uncommon. EM3EV has created a reinforced shark type pack to address this but they are the only ones. If you want a battery that is able to take a beating with a bike that takes a beating, then you need to use a triangle pack, sized and braced with closed cell foam (not enough to insulate in heat) so the battery doesn't become a UFO.

On a bike where I couldn't (and didn't want to) do this, I took extra steps. The pack you see below is only 13ah, but its still pretty heavy at 9 lbs since its potted inside for durability. Its a Luna Wolf pack I used because it fits like a glove in the available space. In addition to the very strong magnets that hold it into its 2-bolt cradle, I supplemented that hold with two hose clamps threaded thru slots meant for this purpose in the battery's base. Then on top of that I took 3" velcro cinch straps and used them to basically clamp/cradle/smother the entire battery. The risk still exists that a bad thing could happen given the nature of the connection, but I've done all I can. I did in vact try and figure out a way to put a small rectangular bag in there and couldn't get it done. Not enough room around the edges.

PXL_20220418_225028195.jpg
 
I had no idea about this web site. I was going to BafangUSADirect.

I was hoping to mount the battery on the tube, as well as strap it onto the tube similar to your recent photo. Having a battery inside a triangle bag with padding seems insecure to me, but that's my bias about having to secure everything on a bike before riding.

With the URL link you provided, now I see the different motor options including the M620. I am glad I made this mistake publicly so other novices can learn from our discussion. All I can say is...wow. The deeper I dive into this the more complicated it gets. Right now, I have no clue what components I would buy if I were to purchase today.

Given your experience, I am becoming more and more convinced to go with a custom battery when the time comes. I wish Bicycle Motor Works had a mounting accessory. How much foam do you use inside the triangle bag? I can see 1-inch padding on the bottom, but if I wrap the battery too much then it will overheat due to lack of ventilation. The battery housed inside a bag also reduces ventilation.

A new NYC law requiring e-bikes to meet UL certification will go into effect within the next six months. I live in New Jersey and when NYC passes a new law, New Jersey (the entire state) tends to do the same. Thus, people building e-bikes in NYC (and most likely NJ) will have to buy UL certified motors & batteries going forward. I understand the rationale behind the law, but that makes buying or building an e-bike more complicated in the short term for NYC residents - and urban populations are more likely to buy or build an e-bike.
 
I had no idea about this web site. I was going to BafangUSADirect.
That explains it. Thats just a reseller using the Bafang name. Not the best source from what I have heard. I have used them for small parts but have heard of people having bad experiences with big orders.

I was hoping to mount the battery on the tube, as well as strap it onto the tube similar to your recent photo. Having a battery inside a triangle bag with padding seems insecure to me, but that's my bias about having to secure everything on a bike before riding.
What you want to do is less secure than putting it in a bag, believe it or not. 15 pounds of battery secured by two little screws. And the mount itself is plastic tabs holding onto a 15 lb battery. Put a pack designed for your frame in a bag and there won't be much room to move to start with in the first place.

IMG_20181017_190525.jpg


Given your experience, I am becoming more and more convinced to go with a custom battery when the time comes. I wish Bicycle Motor Works had a mounting accessory. How much foam do you use inside the triangle bag? I can see 1-inch padding on the bottom, but if I wrap the battery too much then it will overheat due to lack of ventilation. The battery housed inside a bag also reduces ventilation.
Part of the idea of buying a custom pack that is really big is it doesn't get hot, because the load is shared among many more cells than a typical commercial pack. You also want to pay attention to the cells you use, although this is not really a thing in 2023 like it was in 2018. In 2018 you could pick Samsung 30Q cells which were powerful, but they ran hot. You could instead choose Samsung 25R's which were nowhere near as energy dense, but you could flog them like a rented mule and they never even got warm. So 25R packs were best for high output and you lived with the lesser energy density meaning your pack had to use more cells and be physically larger. No longer an issue in today's market using 21700 cells.

I don't use much padding. First I remove all bottle boss socket cap bolts on a downtube, and seal the frame holes with rubber mastic tape. This removes hard bumps on the frame that will wear into the battery over time, even if you think button caps will solve the problem instead (they won't). Then I put a single layer of MinicelT-600 down as a spine for the base of the triangle pack. Maybe two if I can. Then a single square or triangle cut of padding, one for right and left sides. This is plenty of protection even if there are gaps. I'll also usually use a 2" or so wide strip over the top because batteries can bounce, and a top strip will secure the pack.

Its a different job every time, sinc eyou are always working with a different frame, and a different pack. Since you are zipping the bag closed there will never be open ventilation so this is also where having a big pack made that doesn't heat up by design solves the problem by not letting it happen in the first place.

A new NYC law requiring e-bikes to meet UL certification will go into effect within the next six months.
Yup. No help for that, although if you do your part and your chosen battery builder does theirs, the end result is going to be a better product than what is made on an assembly line.
 
I understood that the NYC law regarding UL listing was ONLY for someone who is SELLING an ebike. No restriction on what you build for yourself.
From my understanding the New York UL2849 requires all ebikes & batterys to be UL listed. Any bike/vehicle not UL listed will be banned or fined.

Supposedly they are talking about a ebike buy back program to help replace people with non UL listed bikes/vehicles.

They said extra officers would be employed & Saturday they planned executing the new law in full force.
 
Supposedly they are talking about a ebike buy back program to help replace people with non UL listed bikes/vehicles.
Buying back the battery of a DIY e-bike will be very problematic. Now they have to buy a new battery that may not be compatible with their motor or not be the correct size to fit in the triangle or their rear rack. Also, can you imagine someone who had bought a bike with an integrated battery and motor having to return the entire bike? I have not heard of any major manufacturer like Specialized, Trek, etc., having a recall like the car manufacturers do.
 
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