Folding mid drive conversion options?

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Aug 19, 2023
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Los Angeles
Been looking at some high end fancy folders. I want something with real strength for San Francisco hills.
I emailed the helix titanium 24" guy, he says a mid drive wouldn't fit, or schwalbes. Helix - The New Standard in Folding Bikes. Big Wheels. Titanium Frame. Rides Better and Folds Smaller. Made in Canada.

Luna Folding Ebike These guys have bolted a 750w bafang mid drive to a junky taiwanese 24 lb folder with that bad mid-frame hinge design. And it's sold out currently.

I'm unsure if a brompton can fit one. Maybe a 750w direct drive and a big rack battery, but that might affect the finished size.

Saw this moulton with a small bafang added on. Disassembling it every time might be a pain though, and it doesn't exactly come apart super small, something that could fit in the back of a taxi or trunk would be cool.





I tried that electric brompton, it's junk. Front wheel 350w drive and the battery as a backpack mounted to the front, and the hi-tensile steel frame, it's so heavy and doesn't make it up hills at all, battery drained real fast too. Brompton does make a full titanium frame though that ranges 16-19lb. I do like the idea of a removable battery / battery rack, would help to charge indoors while doing delivery and taking a break.


There's also this pendix drive for a Brompton etc, but the quality looks a little eh, and 250w. 2000$ nearly too. Pendix GmbH l Retrofitting Brompton-bicycles to eBikes



taking a non-electric hummingbird bike and adding a beefier motor might work. but it folds sort of weirdly.




the VELLO looks quality, although the stock only comes with 250w, can be purchased non electric. It has that nice folding style without a bullcrap segmented tube.







MONTAGUE also has a folding 250w mid drive which makes me wonder if their standard bikes could be adapted. So heavy though. and large. https://www.montaguebikes.com/wp-content/uploads/2020/08/M-E1-Folded-800.jpg



Then there's bike friday which is kinda like moulton.


The Tern ECLIPSE series seems like it could conceivably work. https://www.ternbicycles.com/sites/default/files/2021-06/Eclispe-platfom-ElegantlyPortableandCompact-2000*1000.jpg
And supposedly has a well made frame joint. https://www.ternbicycles.com/us/tech/471/ocl-frame-joint


this guy here did something i think with that meh 250w bafang "fun" motor Full suspension mid-drive folding ebike, oh yEs!



I like the idea of using a real high end folder like Brompton, Montague, Vello, Helix, something with a really reliable frame that's not gonna fold up. Was also looking at non folders like the Specialized Creo , Or a regular road bike with a Bikee Lightest or Bafang 750w mid added. Or maybe a folder with a 750w direct drive and some kind of removable battery pack. I wish there was like some kind of almost kid's bike style minivelo with a really low short double diamond frame and a seat and handlebars you could just pop out, would probably be a lot more structurally stable than your average folder.

Can someone also explain to me any good hub/geared hub/mid drive motors that are 250w "compliance" rated but go higher etc as far as kits go, with really low weight around 4 lb
 
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I'm in the market for something like this for my car road trips. I was figuring to buy the bike/frame then adding the ebike stuff. But if there is a factory made one it would be at least worth a look. Wonder what frame would be worth buying too.

Hopefully Chalo will chime in.
 
Since the wheels are smaller, I'd pay close attention to how the downtube meets the bottom bracket, or in some of the linked examples, above the bottom bracket, to the seat tube. Not sure about the Luna frame quality, but that intersection, with the curved downtube, allows the motor to sit much higher. I'd worry about speed bumps with the titanium frame, but the orange bike, the Brompton and Velo all look like the motor will sit higher.
 
Does it have to be a folder ?
Fyi, For many years i used a mid drive , rigid frame, e MTB bike as a “in city commuter” from a outer city car park.
I carried it in the boot (trunk) of a mid sized mitsubishi sedan by removing both QR wheels, seat and stem, and the in frame battery to make packing it in easier.
disassembly and reassembly took less than a minute ( literaly a few seconds with practice) once you learn how to rerig the chain on the cassette.
Obviously, this solution would not help if permanent storage is the issue, but it did eliminate the need for a costly, heavy folder for me.
A “compact” frame , and 26” wheels Make a much smaller unit.
 
I put a motor on a Tern S8i, but differently than you are thinking. The S8i uses a Gates Belt drive to a Shimano Alfine 8 rear hub and none of that is really amenable to a motor - the driveline didn't seem like it would suit the existing mid-drives, and replacing the rear hub with a motor meant only one speed. I used a Grin All-Axle on the front wheel, and it was powerful enough to break traction on steep uphills.

With more research, and some of the newer mid-drives on the market, you may find a way to mount one, and that may be the best solution, if possible.

However, several other Tern folders might work. My Tern P24H has the narrow fork (Grin has a SAW motor just for these forks), but uses a regular 135mm rear hub width. To manage the short chain length, the hub is a combination cassette and 3-speed hub. You will lose the hub gears by replacing this with a motor, but there are several options.

The GMAC I'm running on my tadpole trike now has good torque, and if you want to ensure the 250W limit class, the Shenyi SX2 rear from Grin can probably also do the job (I'm going to try one on my trike soon - it's about half the nominal power of the GMAC). Grin classifies the SX2 as a 250-500W motor, which is what all the motors listed as 250W actually are, I think.

My Tern P24H has a 11-32 cluster. Given the small wheel size, I don't think you can go much larger than that, but with enough motor power, you may not need a wider gear range. However, an option I am using on my trike now is an Efneo 3-speed planetary crankset. That would get you back the 3 ranges you lose from not having the internal gear hub when you replace it with the motor. The Efneo is offered with a stock chainring (28T, 40T, 50T), or a mounting spider for optional chainrings (38T or above, on 130BCD spider). Efneo lists Tern as compatible.

My older P24H is a bit twitchy on corners at high speed, but just different rather than bad. The S8i rode very nicely. I never had problems with the build quality or strength. Tern is known for using standard bicycle components, apart from the Neos compact derailleur on my P24H.
 
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I put a motor on a Tern S8i, but differently than you are thinking. The S8i uses a Gates Belt drive to a Shimano Alfine 8 rear hub and none of that is really amenable to a motor - the driveline didn't seem like it would suit the existing mid-drives, and replacing the rear hub with a motor meant only one speed. I used a Grin All-Axle on the front wheel, and it was powerful enough to break traction on steep uphills.

With more research, and some of the newer mid-drives on the market, you may find a way to mount one, and that may be the best solution, if possible.

However, several other Tern folders might work. My Tern P24H has the narrow fork (Grin has a SAW motor just for these forks), but uses a regular 135mm rear hub width. To manage the short chain length, the hub is a combination cassette and 3-speed hub. You will lose the hub gears by replacing this with a motor, but there are several options.

The GMAC I'm running on my tadpole trike now has good torque, and if you want to ensure the 250W limit class, the Shenyi SX2 rear from Grin can probably also do the job (I'm going to try one on my trike soon - it's about half the nominal power of the GMAC). Grin classifies the SX2 as a 250-500W motor, which is what all the motors listed as 250W actually are, I think.

My Tern P24H has a 11-32 cluster. Given the small wheel size, I don't think you can go much larger than that, but with enough motor power, you may not need a wider gear range. However, an option I am using on my trike now is an Efneo 3-speed planetary crankset. That would get you back the 3 ranges you lose from not having the internal gear hub when you replace it with the motor. The Efneo is offered with a stock chainring (28T, 40T, 50T), or a mounting spider for optional chainrings (38T or above, on 130BCD spider). Efneo lists Tern as compatible.

My older P24H is a bit twitchy on corners at high speed, but just different rather than bad. The S8i rode very nicely. I never had problems with the build quality or strength. Tern is known for using standard bicycle components, apart from the Neos compact derailleur on my P24H.
Oh, and for San Francisco, I recommend a locked clutch and a battery not charged to 100% at the start so there's room for regen braking. The regen braking on my Tern, my Cruzbike, and now my Greenspeed Magnum will bring the machine to walking speed without engaging the mechanical brakes. The mechanicals are still there for urgent stops.
 
Does it have to be a folder ?
Fyi, For many years i used a mid drive , rigid frame, e MTB bike as a “in city commuter” from a outer city car park.
I carried it in the boot (trunk) of a mid sized mitsubishi sedan by removing both QR wheels, seat and stem, and the in frame battery to make packing it in easier.
disassembly and reassembly took less than a minute ( literaly a few seconds with practice) once you learn how to rerig the chain on the cassette.
Obviously, this solution would not help if permanent storage is the issue, but it did eliminate the need for a costly, heavy folder for me.
A “compact” frame , and 26” wheels Make a much smaller unit.
I'm wondering if I could convert a BMX frame into one with a removable long seatpost and long handlebars. That would be tough and structurally stable. Loading an extra 15-30 lb on a folder is a kinda scary. But that pendix Brompton mid drive is interesting, if anything could handle the extra weight it's Brompton or montage or vello id imagine
 
Related question,
Assuming you're using a mid drive for example, on a regular bike your 700c , 26, 29 etc wheels are preserving your momentum. But since you're using electric assistance, would going 16, 20, 24 be more efficient overall? Of course there are a million different variables in terrain, and smaller wheels may be better uphill, but assuming half flats and half hills, or some san Francisco type terrains. No fat tires, just skinny or medium balloon 16, 20, 24. And of course the reduced weight and added torque
 
GMAC in the rear of a 20" to 24" folder, with the highest current the motor will continuously tolerate. Set the system voltage according to the speed you want.

Check out Swift Folder; it's one of the highest structural integrity frames around.
 
mid drive might work great tucked up high, which way does the swift folder fold?
Fold pivot is just forward of the seat tube. Mid drive would get pinched and prevent a full fold, I think.
 
GMAC in the rear of a 20" to 24" folder, with the highest current the motor will continuously tolerate. Set the system voltage according to the speed you want.

Check out Swift Folder; it's one of the highest structural integrity frames around.
Nice. Would it accommodate a front rack idk where you could put the battery, the Brompton does the front. That hub motor is interesting too. I wonder if you could add folding handlebars to the swift also. Add some carbon rims...
Origami Swift 10-speed Folding Bike | Origami Bicycle Company — Origami Bicycle Company
 
I was also thinking hard about finding some way to use a real quality titanium or cromo BMX frame, find a way to easily remove a long commuter seatpost and have totally removable handlebars and stem and wheels, you feel me? Ditching the idea of a fold and using a low frame with perhaps telescoping seatpost and stem. That could accommodate a mid drive and allow you to use high quality BMX rims and hubs also. Maybe a removable fork idk. Chimera Electric BMX Motorized Frame this is set up more for 24" but it sure is powerful , 1000 to 4000w power 8 lb motor
 
Brakes and gears on a BMX will be tricky.

You might be better off with something like this …
 

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Add some carbon rims...
Carbon is a gimmick. Titanium is a gimmick. There's not a lot of fat to trim off a rough-and-tumble city folder without adversely impacting its durability, rigidity, quietness. If you're only looking at quality bikes made of chromoly, aluminum, etc., it's not glamorous materials but rather effective design and implementation that will ensure modest weight and a good ride.

A good folder will always, no exceptions, weigh more than a regular bike of equal quality construction. It doesn't matter that it's physically smaller. It has a harder and weirder job to do. It will always ride worse, no exceptions. It will always cost more, no exceptions. And it will always fit worse, because factors other than fit must be accommodated.
 
This pendix drive that just fits over your crank has terrible reviews and costs 2000 euro, but it does make me wonder what kind of mid drive could accommodate a Brompton fold, if any. Maybe removable or folding pedals would help somehow idk
 

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Direct drive hubs have many good characteristics but one of the main drawbacks is lack of torque when laced in a larger wheel. DD hubmotor in a smaller wheel (like as in a folder or BMX)) naturally improves that disadvantage.

Why try to force a mid drive into a limited space?
 
How does a 750 to 1300w or 1000 to 1600w motor handle on a narrow 20" BMX tire bike?

The 1.2 kg/2.7 lb 200w Q75 motor seems kinda interesting too. Feel like that would be ok on a titanium Brompton, the regular brompton was heavy as hell with regular 350w hub. I tried my first BBSHD today at 800-1600w , I wonder how that would handle on a 20". Or the lighter bbs02. Better than on a 16" for sure . Tern uses an anemic 250w bafang or mid range bosch "250 continuous" on their 50+ lb folders. The tern verge however is only 21 lb base weight, which could make up for the added weight of a BBSHD and maybe some big front rack battery similar to the brompton backpack battery. I think the tern vektron motor already weighs like 8 lb so I would think you could shoehorn in a 9.5 lb bbs02 to the verge without making it self destruct at least. The 26" tern, and the Vello with it's lack of split frame still look interesting too, can't find ISO ratings except for the heavy Bosch clunker vello e cargo
 
Maybe dual removable fork batteries? The vello has a diamond shape but the tern doesnt. Brompton uses a backpack for their 6-7 lb battery on a front rack and it's terrible weight distribution, fork seems like it would be better, but maybe you would need to upgrade to truss fork?
 
These don't fold the smallest, are things like this without a split frame , or disassembling types like other bike Friday or moulton, any safer? Also are there any minivelo non folder frames like this with real low diamond? Converting a BMX seems really too hard
Seems more like hatchback friendly than sedan friendly though. The cargo one starts at 34 lb and supports 440 lb weight
 

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The helix bike is kinda interesting but another one without a split frame that might not accommodate a mid, and seems to have issues. CHANGEBIKE however is isp certified more than Montague, only fullsize bikes though.
 

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No iso rating available as far as I can see, just some en rating for the cargo
 

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Montague m-e1 , no split frame, but overly heavy. Shimano Steps E6100 mid-drive, 54 ish lbs
Certain Shimano motors I believe support third party battery but not this, unsure on peak wattage. The Montague fit however has a carbon fork and weighs about 26 lb. You could probably also find a used Montague mtb on Craigslist, but again they don't have an iso rating like changebije does as far as I have read. The paratrooper elite and highline weigh about 27/30 lb, and presumably you could swap that fork for a super lightweight gravel suspension fork from Fox etc for big bucks.
 

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