Considerations for building mid-drive e bike from scratch/frame up?

Tortoined Grower

Tortoined Grower

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Hello, I am currently in the theoretical stage of my first e bike conversion/build.

Originally I was going to buy a relatively cheap $400-$700 CAD brand new mountain bike to convert using a mid drive kit such as the Bafang BBSHD. Then I realized that most of the stock parts on those bikes were not what I wanted and would need to be replaced with parts that fit my needs (better tires, cruiser handlebars, hydraulic disk brakes with hoses long enough for said handle bars, etc). Sort of like a Frankenstein's monster of bike parts. With my priorities being that it can handle a 170lb man + groceries on the rear rack going 40km/h.

My questions are:
1) Is it a good idea to build an e bike from scratch/frame up? (Probably by buying a used bike and replacing most things except the frame itself)

2) If so, what should I look for in a decent, reliable bike frame.

3) Is it also a good idea to buy a used/old bike frame instead of a new one.

I would greatly appreciate anybody's insight, experience or even just online resources that are relevant. Thank you.
 
The most important bit of a good frame is the space for a battery. For ebikes, full suspension frames are preferred for obvious reasons, but they're often heavily disadvantaged when it comes to the main triangle area. If you can pick out anything, then either:

- a decomissioned mid-drive e-bike such as Haibike to put then new drive unit via an adapter
- a frame with as big of a triangle opening (without suspension interference) as possible

will make a decent starting point. Virtually all of the other parts can then be picked individually.

That being said, if you want a really nice mid-drive, I personally found the LightCarbon kits very enticing, and would likely be building one if not for the fact i have another project going on. You get a frame with a mated Bafang motor, and can get a set of carbon wheels from them. Put appropriately bling components on it and you get a bike beating most factory units on price and performance.
 
Tortoined Grower said:
Hello, I am currently in the theoretical stage of my first e bike conversion/build.

Originally I was going to buy a relatively cheap $400-$700 CAD brand new mountain bike to convert using a mid drive kit such as the Bafang BBSHD. Then I realized that most of the stock parts on those bikes were not what I wanted and would need to be replaced with parts that fit my needs (better tires, cruiser handlebars, hydraulic disk brakes with hoses long enough for said handle bars, etc). Sort of like a Frankenstein's monster of bike parts. With my priorities being that it can handle a 170lb man + groceries on the rear rack going 40km/h.

My questions are:
1) Is it a good idea to build an e bike from scratch/frame up? (Probably by buying a used bike and replacing most things except the frame itself)

2) If so, what should I look for in a decent, reliable bike frame.

3) Is it also a good idea to buy a used/old bike frame instead of a new one.

I would greatly appreciate anybody's insight, experience or even just online resources that are relevant. Thank you.
Click to expand...
You provided enough information to start with, but a little more info could result in better guidance.

Building from the frame up is great, but is an expensive route compared to buying a bike that has most of the components you want. I built my first bike with an old mountain bike I wasn't riding, but later got a nice frame and transferred the e stuff over.

Buy a bike that fits you well, like shopping for any bike. As mentioned, you want a frame that makes it easy to mount components on, which in the case of the BBSHD is only the battery (and bottom bracket dimensions to match the BBSHD).

With a mid drive, it would be good if you are familiar with working on bicycles, and replacing chains and cassettes, since those will be normal wear items.

You didn't mention terrain or range requirements. Depending on those, you may consider a hub motor conversion as well. The lowest maintenance option is a direct drive hub motor, since the only moving/wear parts at the wheel bearings. No internal gears or clutches to deal with like a geared hub or mid drive motor.

I wouldn't buy a new bike for your first build. You will find things you like and don't like as you get more miles under your belt, which allows you to make a better informed decision for yourself when it gets time to upgrade. Initially, you just want to get your feet wet and have fun.

You can check out the build thread subforum to see how others have approached their builds. The thread for my bike is below. You'll see what the first $650 investment looked like at the time and how it evolved over the years (the first pic in the thread is always my current configuration).
endless-sphere.com

My econo-e-bike

Current Configuration (04-18-24) of my e-bike: Motor: Previous: MXUS 1000W slow wind 9C clone, 26" generic rim Current: Leaf 1500W 5T, 24" Halo SAS rim Controller: Previous: 18 FET KT 30A Sine Wave 18 FET 7kW PowerVelocity controller Current: No name "80A" Sine Wave w/3-speed switch, cruise...
endless-sphere.com endless-sphere.com
 
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bananu7 said:
The most important bit of a good frame is the space for a battery.
Click to expand...
Hmmm... I don't think so. I only ever had one e-bike setup with a battery in the frame (an ordinary Hailong "Shark"pack), despite all of the bikes I ever used having tons of room in there. All the better, bigger batteries I've used since then would negatively affect my ability to pedal effectively if I put them in the area swept by my legs within the frame

The OP specified being able to carry groceries. Any bike that can carry groceries, can carry a battery. For me, rack attachment options and agreeable dropouts are more important than space in the front triangle. I use the top of the rear rack, or a front (frame mounted) cargo box, or occasionally a handlebar basket, to carry my battery.
 
Chalo said:
Hmmm... I don't think so. I only ever had one e-bike setup with a battery in the frame (an ordinary Hailong "Shark"pack), despite all of the bikes I ever used having tons of room in there. All the better, bigger batteries I've used since then would negatively affect my ability to pedal effectively if I put them in the area swept by my legs within the frame

The OP specified being able to carry groceries. Any bike that can carry groceries, can carry a battery. For me, rack attachment options and agreeable dropouts are more important than space in the front triangle. I use the top of the rear rack, or a front (frame mounted) cargo box, or occasionally a handlebar basket, to carry my battery
Click to expand...
Oh, I totally missed the groceries part. For commuter bikes I agree it's less critical, but for a tourer or specifically a mountain bike, none of the options you mentioned are great.

Especially if you want to fit a large battery for e.g. 100km range, the weight on the bars or the rack affects handling significantly.
 
For 40kmh and a light rider you probably can stick to stock brakes.
You can use something half the size of a BBSHD to achieve the top speed you want. Unless you're climbing mountains.

Look at some of my builds. All are either used or extremely cheap mountainbikes. You don't need any kind of special bike for a low power ebike like you're describing.
 
I have built 3 mid-drive bike's a battery in the triangle is what you want keeps the weight centered. A hardtail mountain bike is probably the easiest to convert something with a cassette rear wheel will give you gearing options. Walmart was closing out Schwinn AL comps for 180 it's a decent frame with usable 27.5 wheels.
 
Thank you all for your replies, it has definitely been eye opening. I feel like I have learned a lot from looking at some of the suggested builds as well.

I tried to keep my original post brief because I wasn't sure who would even reply. To elaborate a bit, I do not do any mountain biking; I mostly like exploring my city on long rides, commuting to work (distance changes based on where I live and work from year to year) and doing food delivery (as a recreational activity not a reliable source of income lol).

The initial idea I was proposing is geared towards having a bike capable of handling more power if I find myself needing that in the future. That is why I suggested the BBSHD even though I might not even need it at all, it is confusing to see what I might need when the range of power in e bike builds is so huge.

I am assuming that a mtn bike frame would be better for putting an amount of stress greater than intended with just pedaling. In truth I would absolutely love a frame with that super low dip in it for easy mounting (walk through, commuter or dutch style I guess), but I am unsure if any would be a good idea for long term stress and the ability to upgrade every part of it (tires, drive chain, durable rear rack or maybe even a small bike trailer).

I also have assumptions about my need for hydraulic brakes because my first e-bike had them and failed to stop with enough force after replacing the front brake with a cheap mechanical one, but that was an 80lb dual battery fat e-bike.

The reason I wanted a mid-drive motor is mostly because I have a lot of trouble keeping up with traffic that constantly starts and stops at every light, especially in streets that often funnel traffic into single lanes because the right lane is full of parked cars. I was hoping that more torque could help me stay at pace with cars that constantly need to pass me and don't always do so very safely. Also, it just seemed like a better idea to me because I think it would be worth the maintenance for more power and efficiency.

(Long rant about my terrible experience with Store bought E-Bike)
To give some context of my experience: I've been riding bicycles to get around different cities for most of my life. In 2023 I made a decision that has been one of the best and worst decisions of my life when I bought this fat tire e-bike from Movin' Mobility Pulse Fat Tire E-Bike | Best All-Terrain Electric Bike – Movin' Electric Bikes
I was amazed at how much fun I was having and how much easier it was to get around, having an e-bike itself was the good part. However, after a few months all of the problems started to become apparent. Even with 2 batteries (20+10 AH) I was finding the range to be extremely poor in comparison to their scummy marketing which said it could do 120KM to 200KM per 2 battery charges. I also thought that the fat tires would be better for me in the winter, but I didn't know that they were more suited for actually riding on pure snow instead of roads that are usually plowed with only a little slush and spots of ice. Having 4.0" tires (+probably this huge frame) actually just decreased my range/efficiency, made it impossible to ride above 7km/h when the battery died and worst of all made it impossible to utilize transit bike racks which could have saved my ass dozens of times when the bike stopped working or had a flat.
 
If you don't have hills and lots of stop and go traffic build a hub. A geared hub will be more efficient in stop and go traffic than a direct drive but I prefer the silence of a DD hub.
 
hillslayer@ said:
If you don't have hills and lots of stop and go traffic build a hub. A geared hub will be more efficient in stop and go traffic than a direct drive but I prefer the silence of a DD hub.
Click to expand...
Thanks I'll be looking into the difference between DD and Geared to see if one of them works better for me.

I was kind of deadset on mid-drive due to several convincing videos by JohnnyNerdOut, but then as I tried to dig a bit deeper I was seeing more and more people speaking up for hub motors and now I feel a little wishy washy.

If my understanding is right, mid drive motors seem to be much better for torque and climbing hills when it's a relatively low watt motor (under 1000 watts I guess). While hub motors become a better idea at higher wattage because they are powerful enough to compensate for the lack of a drive chains efficiency.

Does this sound right at all or is there still something I'm missing?
 
I wouldn’t use YouTube videos to make decisions, except by extracting the facts presented. YouTubers tend to lean in one direction or another, like anyone else, so it’s better to form your own opinions rather than be influenced by a YouTuber or anyone else. I have an affinity toward hub motors, others have one toward mid drives. Most folks on the forum recognize the merits of one vs the other, so although they may have strong opinions, you will generally be guided toward what you describe as your requirements.
I wouldn’t recommend a mid drive for stop and go; just too much time and effort shifting. Like on a pedal bike, if you have to stop quickly due to a light, you may not have time to get it shifted down. I’d like to build a mid drive some day for slow steep single track riding, since that’s the one thing I can’t do with a hub. Any climb that allows the bike to ride over 10mph, I’d go with a hub motor. You need to decide what you need based on the facts and how you’ll be riding.
Remember power required for climbing is relative to speed, almost linearly, except for wind resistance. You need to take into account efficiency of the system at those speeds as well. But generally, you use less power when climbing slower.
If you need range, stay away from fat tires.
 
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fwiw I too was initially sold on a mid drive due to many advert-articles my google searches spat out. However 2 years on with a hassle free hub drive, Im very glad i read a bit further..
 
E-HP said:
I wouldn’t use YouTube videos to make decisions, except by extracting the facts presented. YouTubers tend to lean in one direction or another, like anyone else, so it’s better to form your own opinions rather than be influenced by a YouTuber or anyone else. I have an affinity toward hub motors, others have one toward mid drives. Most folks on the forum recognize the merits of one vs the other, so although they may have strong opinions, you will generally be guided toward what you describe as your requirements.
I wouldn’t recommend a mid drive for stop and go; just too much time and effort shifting. Like on a pedal bike, if you have to stop quickly due to a light, you may not have time to get it shifted down. I’d like to build a mid drive some day for slow steep single track riding, since that’s the one thing I can’t do with a hub. Any climb that allows the bike to ride over 10mph, I’d go with a hub motor. You need to decide what you need based on the facts and how you’ll be riding.
Remember power required for climbing is relative to speed, almost linearly, except for wind resistance. You need to take into account efficiency of the system at those speeds as well. But generally, you use less power when climbing slower.
If you need range, stay away from fat tires.
Click to expand...
Very well said, thank you for giving me some excellent advice that is very well suited towards my situation. It's very hard to sidestep the bullsh#t of online articles/videos so I'm very happy to hear practical information based on experience from people who are less likely to generalize things or have some motivation to sell a specific product.
 
Yeah.. if you have flat land generally, a mid drive is mostly pointless, will be more expensive than a hub, less efficient, and less reliable.

The only plus being:
- easier rear wheel swap
- weight balance / reduction of unsprung weight ( in the case that you have a full suspension bike )

Conversely if you live in very hilly place like i do, a mid drive makes way more sense than a hub.
..but i still chose the hub motor anyway most of the time :)
 
Stop reading JNO and look at Grin (ebikesca). IMO, a 1500w direct drive (DD) rear hub system (maybe even a 1000w) in a steel 90's hardtail MTB would suffice for your needs. Depending on the size of the frame, you could put the battery in the triangle or rear rack.
 
As an update to my journey of trying to find the frame that works best for me, I have tried 2 different used frames (a hard tail bike with 29 inch wheels and a full suspension with 27.5 inch wheels. I didn't buy either because I realized that the seat was way too high even when bottomed out and I was not comfortable when standing idle over the seat. At this point I've come to the conclusion that part of my goal on top of everything will be to have a bike with a low seat and lower center of gravity.

An obvious first step is to use 20 inch tires which will lower the height at least 3 inches, but in terms of really low riding frames that are disk brake compatible, I'm having a hard time looking for one that might work. Would a youth bike be a bad idea even if I somehow find one that has a steel frame with disk brake mounts? Either that or a bmx frame which are also rarely disk brake compatible. I know the inner triangle would likely be too small for a decent battery so I was planning on just mounting it on the top of the triangle instead.

The last idea I have is to take the cheap 16 inch wheeled "Isinwheel U1 Electric Bike" that I have been using for the last few months and replace the rear wheel with a 20 inch 1kw hub motor in addition to the controller, display etc (whole new kit using this e bike as a frame). I would remove the 36v 7ah batteries that are inside the frame so that I can mount a 48v 20 ah battery pack on the top of the tube frame and see if I can make a diy rear rack for the back portion of the tube frame. Some real madman sh#t, I know, maybe it should be a last resort if its too far fetched. I am also unsure if having a mismatch with the 16 inch front wheel and 20 inch rear wheel would be a real problem.
 

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How tall are you?

Bike height is dependent on frame size, not wheel size. There's bikes that have 29 inch wheels that fit 5 ft. tall people.

The smaller the wheel, the worse the ride quality, the slower you will actually want to go.
The shorter the wheelbase, the more likely a wheelie is to happen, the more hard to control as the speed goes up, the less power you can run.

On a 16 inch wheeled bike i wouldn't run 1kw, you won't have a good time, ride quality at high speed is going to be unacceptably bad.
 
neptronix said:
How tall are you?

Bike height is dependent on frame size, not wheel size. There's bikes that have 29 inch wheels that fit 5 ft. tall people.

The smaller the wheel, the worse the ride quality, the slower you will actually want to go.
The shorter the wheelbase, the more likely a wheelie is to happen, the more hard to control as the speed goes up, the less power you can run.

On a 16 inch wheeled bike i wouldn't run 1kw, you won't have a good time, ride quality at high speed is going to be unacceptably bad.
Click to expand...
Thanks again for some information I wouldn't have considered, I'm 5'9 and my leg inseam is around 30" or so. I also have a suspension seat post I forgot to mention that adds 4 inches to the bike seat height. The mountain bike I tried had exactly 30" of seat height when it was bottomed out with no suspension seat post. It was just low enough, but I would prefer lower. The 16 inch bike just felt so convenient and handled well at 32km/h max. I loved the fact that I could mount it easily and that if I slipped on ice or something I would fall such a short distance that it was like nothing even happened.
 
amberwolf said:
You could build one of these, but I'd recommend a 26" rear wheel (or larger) for sufficient ride quality, instead of the 20" I used.

https://endless-sphere.com/sphere/t...-recycled-parts-cargo-ebike-crazybike2.12500/
View attachment 367334
Click to expand...
This looks absolutely boss and so relaxed which I love, but an important factor for me is being able to take my bike home on a bus rack for the many occasions I may need to do so (flat tire, low battery, really far destination beyond range).

I am so picky, it really is a pain.
 
You could ride a bike with up to 32" wheels :)
I run a suspension seat post - just need to buy a bike that's almost 1 size down to fit it - no problem.

If you like lower in the back, put a 27.5" rear on a 29er bike.. this will drop your center of gravity and improve the standover problem greatly.

Consider that a 1kw motor will take you up to 48kmh or well beyond that with additional voltage.. that's really fast for a 16 inch wheeled bike.. you hit a bump and you are going flying on those tiny wheels... wouldn't recommend it!
 
If you are looking for a cheap bike that comes in all kinds of different sizes, check this company's bikes out:
Save up to 60% off new Mountain Bikes - MTB - Front Suspension Gravity BaseCamp LTD

If you are using a big suspension seat post and you'd normally buy a 19"... i'd get a 17" to accommodate it..

..then change the rear wheel to a 27.5" to lower the stand over height... now you can rest on the ball of your foot at a stop at least :)

Bonus from this change: your fork will have a more slack angle and therefore feel a tad bit more stable at high speed.
If you were to use a hub motor on this bike, the motor would produce a bit more torque thanks to the smaller wheel than stock.
 
Wow, thank you very much. Hopefully I will be successful with my search after all of this updated information. I spent the whole weekend looking at a computer screen and feeling like I was getting nowhere.
 
I spent half of today looking at new bikes at Canadian Tire and Sport Check just to try out different sizes. After trying out a 14 inch frame with 27.5" tires, I found that size to be probably as good as it gets for my purpose. I will also probably need to switch to using a front rack since the rear rack bag just seems impossible with any traditional bike frame that I need to step over to mount. I will continue looking for more used frames, but I have bookmarked the "GT Women's Laguna Pro 27.5" from sport check for $450 CAD on clearance as a backup up plan.
 
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