A mid-drive folding bike?

It all started back in the ’80s when Dr. David Hon, a leading expert in laser technology, decided to change careers and focus on something he was passionate about. That passion was green transportation, and he specifically wanted to make a great folding bike. 

His first project was to create a bike that fit under a train seat. In the decades since he’s filed over 300 patents, and Dahon has expanded into a line of both non-motorized and motorized folding bikes. What’s really interesting with the Unio E20 is that, unlike most folding e-bikes where the motor is located in the hub, this one is a mid-drive. 


The Unio E20 is a truly unique folding bike. It folds much like any 20-inch folding bike, but the battery is integrated into the seatpost instead of the front half of the top tube, and the motor is mid-mounted instead of a rear or front hub. As we got more into the bike, it became clear that these design features held distinct advantages to the bike’s ride and performance. The frame is so low that it’s easily a step-through. With the quick release, getting the right seat height is a cinch.

“Silly us, but who reads the manual? Apparently, we should have.”

The construction of the aluminum frame as just a single, hinged top tube keeps the step-over and stand-over height super low. Completely folded, it has a small-enough footprint to fit at least two in a trunk easily in a back seat, under a desk at work, etc. It’s a better folding bike than a regular bike when it comes to putting it on a bike rack, especially tray racks. With the 20-inch tires and low top tube, it’s harder to get hooks that low.


Thanks to the great tool-free adjustability in the handlebar/stem, the handlebar can easily be rotated and also raised or lowered for better ergonomics and comfort. The aluminum wheels are quick release, which is convenient yet potentially risky if you’re going to lock the bike up. In fact, you’d want to lock the rear wheel through the frame, and hopefully run at least a cable lock through the front wheel and perhaps the seat rails. Or, take the seat/battery when you leave the bike.

The big 52-tooth front chainring drives a SRAM X5 9-speed rear cassette that offers just the right range of gears. The Dahon-branded V-brakes offer plenty of stopping power, and they’re easily adjustable. There are no brake cut-off switches. 


The motor is branded Dahon, but they actually partnered with Tong Shen to develop it. It puts out 200 watts nominal on a 36-volt system. The great thing about a mid-drive is that it puts out the power up front, and you add to that while pedaling and control
the overall torque output with the 9-speed drivetrain.

What do you never see in a folding bike? If you answered a mid-drive motor, you’d be correct! The Dahon is unique with this feature.

The 313Wh battery is what is used as the seat tube, with the saddle rails clamped to the top. It’s a long, thick tube that can adjust for a surprisingly large range of heights, from sub-5 feet to well over 6 feet tall. The back of the battery is marked, so the desired height can be set after collapsing the system when folding the bike. Because of the battery setup, the bottom of the battery is where the power cable extends to plug in under the frame. 

The monochromatic display has all the information you need at a glance. You can see the mode, battery level, power-assist level (1-5) and speed in mph or k/h, as well as total distance traveled.

When you put the seatpost into the seat tube, this squiggly wire comes out of the bottom and is plugged into the motor case under the bike.


Folding bikes in general are great last-mile transportation to get you home from the train or bus, but also to take in your car when you travel, so you can run short errands without giving up your parking space or burning any fuel. As an electric bike, however, the Dahon is more than just a last-mile choice, since it has enough range to get you farther faster than a traditional bike.


The battery port is at the top of the battery near the saddle and easy to find at any height. After a full charge, we tried to turn the bike on at the display, and it wouldn’t power on. Why? Well, we found out after giving the whole bike a once-over, checking the connections, etc., it turns out that the master power switch was on top of the battery. Silly us, but who reads the manual? Apparently, we should have.

Mechanical V-brakes are not fancy, but they do the job.

Selecting a low pedal-assist power to start off, the motor still kicks in powerfully. Smaller wheels, like these 20-inch wheels, help accentuate the tremendous torque compared to larger wheels. Where almost all folding bikes have hub motors, most also have only cadence sensors. That is, a sensor (usually in the bottom bracket area) that just wants to know that the pedals are moving, then the motor outputs you at the amount of power allotted by that particular selected power level. If you “ghost pedal,” or barely turn the pedals, on a system like that, the bike will still zip up to the speed offered at that power level.

This bike has a torque sensor. We love that, because it then matches your power input at the pedals and gives you more as you pedal harder. It’s a much more natural, controllable feeling. Also, hub motors are known to overheat on long, steep hills, shutting off when you may need them the most. Mid-drive motors don’t do this. We took the bike on some long, steep hills, and it never blinked. 

Because of the small wheels, the derailleur cuts it close on ground clearance. Be aware if you ride off curbs.

The Kenda tires are marked 20×1.75 inches and are fairly low volume, so they like higher tire pressure. This lowers resistance and makes them ride nicer, but they also offer zero protection from bumps in the road. Any shock there will go straight up the aluminum frame and/or fork and directly to you. Something to keep in mind if you do have lots of bumps on your roads. That said, the tires offered plenty of grip, even in cornering. You can feel how well-balanced this bike is while riding it. All the motor and battery weight is in the center, not toward the front or the back. 

The Unio E20 folds into a very compact package for storage or transportation.

It has a very quiet ride, the only sound you really hear is when you shift. Shifting is smooth and accurate. We found it overall a very comfortable ride even on longer rides. The relatively light weight makes it easy to carry up and down stairs. When folded, it has magnets to keep it together until you are ready to unfold it and ride.


The Unio E20 rides so well that you forget you’re riding a folding bike, and the overall ergonomics are great. This is a great choice if you want a bike that rides well, has very natural power delivery, and you don’t mind paying extra for that. Some people won’t care; others, particularly avid cyclists, probably will. You could easily take two or three of these along on road trips and you wouldn’t even need a bike rack to carry them.



Price: $2599 

Frame: Aluminum

Fork: Aluminum

Motor: Dahon mid-drive, 200W, 60 N/m

Battery: 313Wh

Controls: Dahon

Charge time: 4–5 hours

Top speed: 20 mph

Range: 15-20 miles (tested)

Rear derailleur: SRAM RD 9-speed

Chain: KMC Z

Brakes: Dahon V-brake

Saddle: Dahon

Rims:  20”, double-walled aluminum

Hubs: Dahon

Tires: Kenda, 20×1.75”

Weight: 35.4 lb.

Color choice: Jet Black or Mars Red 

Sizes: One size