Speed Demon

One of my friends recently bought the Polarna M4 Foldable Electric Bike that came with a very powerful, 750W motor, 8-speed gear shifter, and 20″ fat tires. I took it for a test ride and over the span of two blocks in my neighborhood, it went from 0 to 30mph without breaking a sweat! It was both exhilarating and nerve-wrecking to go that fast. Mind you, federal, California State, and local city laws all limit electric bicycles to 20mph! Compared to the excellent Jasion EB7 I reviewed half a year ago, the Polarna was a MONSTER! Here is my review of the M4 model after taking it for a spin for a day.

Key Lock, LCD, USB Charging Port

Why An eBike?

Electric bicycles have enabled our family to travel longer distances and visit more places even though many riders still shun them. They feel that motor assistance is cheating and I agree! Biking is as much a sport as it is recreational: on one hand, there are those who want to challenge their physical abilities, and on the other, it is a more leisure way to explore and bond with family and friends. Two children have steered the competitive me towards the latter as seeing the joy on their faces has even trumped the thrill I used to seek on the mountain trails. Towing them in our Burley D’Lite 2-Seat Trailer (with 45-100 lbs extra) was no joke: cramping up during a trip made for a PAINFUL ride home! That was when I really started to appreciate electric bikes — the motorized assistance on the uphill climbs and during the final return miles with tired legs had been a welcome blessing!

Googo SY26 with Burley D’Lite (25 mi)

Bike or Scooter?

Electric scooters are more nimble to move around with — and in some cases, more fun — but local laws may prevent them from going onto the same paths as electric bicycles. Most can also be carried around more easily due to their more compact size and lighter weight. Personally, I prefer bikes because they are safer to operate, can (usually) go onto the same places that mechanical bicycles can operate, are (generally) allowed to carry an additional passenger, and if the battery runs out or fails, you can still pedal around. A scooter would stop to function without a battery.

Analysis

Polarna’s 20″ Foldable Electric Bike (M4) came in the most well-protected packaging I had ever seen for a bicycle. Jasion EB7’s was done well, but Polarna took it to a whole new level. It was obvious from that moment on that the company meant business and took quality seriously. Indeed, it did. There were no scratched components, everything was already pre-assembled and tuned, and all I had to do was attach the two pedals, and the bike was ready to go! I did not even have to fine tune the disc brakes! The bike’s 68 lbs made it THE HEAVIEST electric bicycles I had ever tested, but there was a reason for that: largest battery I had seen yet, VERY strong motor, and quality material.

Assembly, as I previously shared, was simple: attach the two, collapsible pedals and done. Well, it was not that simple. Neither was marked “Left” or “Right” so you would know which crankset to screw onto. No, the manual had you look at the threading on the pedal to figure out which was which. That was a first for me, but after a few tries, both screwed right on.

Ride performance was clean, smooth, and very comfortable.

Ride performance was clean, smooth, and very comfortable thanks to its fat tires and front AND rear suspension to smooth out bumps and rocky terrain. Shock absorption level could be adjusted for the front fork for increased pedaling efficiency. Fat tires (with low tire pressure) perform better on snow and sand than road or mountain ones by not sinking as much. Furthermore, the motor’s 750W of (nominal) power was strong, holding an unfair speed advantage over both my Googo SY26 and dad’s Metakoo Cybertrack 100 mountain eBikes.  Not even the excellent Jasion EB7 could not hold a candle. That meant a very sudden, rapid speed increase that could feel out of control at times — so much so, that just slowly pedaling on Power Assist (PAS) Level 1 was enough to propel me to 15mph! Let that sink in… FIRST of five gears!

M4 Dimensions /Polarna

Height-wise, my friend at 5’1″ height was comfortably seated on the lowest seat position, but the handlebar could not be lowered. She looked like a motorcycle gangster on a Harley-Davidson cruising in style! Mounting and dismounting was easy for her, and she also had commented how comfortably the bike rode. I fully agreed with her.

Shifting between the 8 gears was effortless with a thumb and finger control mechanism, and the fat tires gave a very satisfying sound while zipping around the neighborhood park and up a few climbs on local mountain trails. Power Assist (PAS) was available in 5 levels by default, and speed topped at a FAST 39.4mph (63.4 km/h) without a rider. YES, nearly 40mph! With myself on it, I was able to get to 33mph. Legally, electric bikes cannot go faster than 20 mph to fall under the United States Class 2 designation, and in California, only Class 2 can ride on Class 1 bike paths. What does that mean? This bicycle’s motor was too fast to legally operate in California. Be sure to check with your local and State laws before you push the Polarna to its top speed.

Fork and Headlight

The fat 4″ tires and strong 750W motor conquered our local, offroad hills with ease, gliding over cracks and sailing over gravel, sand, and rocks. It was quite fun to zip around both uphill and downhill.

Fat tires, when deflated to a low pressure, perform better on snow and sand than road or mountain ones because they do not sink as much.

Electronic controls found on the left side of the handlebar were easy to use and managed the headlight, horn, PAS level, power, and color display. The screen was easily readable under direct sunlight and provided a nice set of information, including battery and Power Assist levels, speed (current, average, max) in mph or km/h, trip time and odometer, and more. A covered USB cable port below the LCD allowed a mobile device to be charged, such as a phone used for map navigation.

Polarna M4 Electric Bike

The Polarna, like the Jasion, had a very clean, streamlined look with cables tucked away nicely. That bike screamed toughness with authority!

Powered by a 672Wh-capacity, Li-Ion battery (14Ah @ 48V), the largest I had ever tested on an electric bike, gave the Polarna a very significant range advantage, although also with more weight: 29-56 miles on fully-electric and 53-69 miles with pedal assist (the manufacturer did claim more conservative numbers of 24-35 and 30-32 miles, respectively.) My past experience found that it should theoretically be able to handle at least 140 miles with PAS only used for short uphill climbs. I prefer pedaling most of the time for exercise/health purposes and only invoke the motor just enough to get up a hill. This can be done by switching PAS from 0 to one of 5 levels, or pushing the thumb throttle on the left side handlebar while in PAS 1 or higher. That leads me to some of the things I did not like about this bicycle.

Unlike the Metakoo Cybertrack 100, every bike I had tested could not activate the throttle while PAS was turned off or set to level 0, the Polarna included. This perhaps is a safety feature to prevent accidental acceleration when power assist was disabled, but I really enjoyed Metakoo’s implementation because it allowed me to pedal unassisted at all times and ONLY power on the motor when I turned the throttle. The Polarna (and all other bikes) required changing the PAS to level 1 before the throttle could temporarily be activated. One would then have to change PAS back to 0 for non-motorized operation. It is a very minor gripe that I got over very easily with my Googo, and it perhaps is best for the rider’s safety to NOT allow on-demand assist with PAS off.

Ignition: Key Positions (Jasion EB7 eBike)

Two keys were included and required to operate the bike’s battery. So, do NOT lose them! The “ignition” could very annoyingly be found below the down tube over which some cabling ran, and the bicycle could not power on without leaving the key inside. That made me a bit upset even though the lock also served to secure the battery. If the key needed to be left in the ignition, then moving it to the handlebar or another accessible location instead would have made for easy insertion/removal (like the Evercross H5 eScooter). Having it at the bottom required one to crouch to align the key with the insertion hole, and if the key was in the incorrect locking position, it could potentially fall off and leave you scrambling to find it. I attached a velcro to it and the cable to prevent that from happening. Most riders would likely just decide to leave the key in at all times. Furthermore, the key positions were NOT labeled on the Polarna. I have included a picture from the Jasion EB7 bike for reference.

Warning: Do NOT lose the keys. You cannot operate the bike’s battery without one!

The battery was housed within the down tube and removing it was inconvenient: first, turn the key to the unlock position, then fold the frame in half to allow the battery to slide out. On the flip side, this mechanism kept the battery safely protected within the tube and also helped to keep the bike compact.

Battery Removal, Locking Mechanism

Front wheel skewer unfortunately was not the quick-release type. This made it harder to steal the tire, but also less convenient to fix flats without bringing a wrench to undo the bolts.

The serial number was etched onto the frame by the left crank.

Polarna included a 109W AC brick to charge the battery within about 4-6 hours. The battery could be left charging within the down tube or removed for energizing by your desk.

AC Charging

Despite the shortcomings I had mentioned — particularly the frustration of needing to leave the key inside the ignition underneath the down tube — this electric bicycle made is a BEAST. It was a joy to spin for both my friend and I, and the build quality and riding comfort were top-notch. For me, personally, the 750W motor provided for a very smooth, strong acceleration, but keep in mind that it could scare a beginner rider for the first time when that initial power kicks in. I felt solidly in control and the suspension worked well in conjunction with the fat tires to even out the effects caused by rocky or shaky terrains. Like Jasion, if Polarna could figure out how to move the ignition to the handlebar, I would have been an even happier rider. Very solid, foldable bicycle.

What’s Good? What’s Bad?

Pros

• Very strong, smooth acceleration with brushless motor
  • Nominal (average) power: 750W. Rated (maximum) power: 1,000W
    • Jasion: 500W (700W peak?)
    • Googo: 350W (560W peak) / Metakoo: 350W (500W peak) / Ancheer: 500W (700W peak)
    • 750W may give beginner riders an initial scare the first time the motor kicks in with a very sudden, rapid speed increase
  • Top speed: 39.4 mph, tested without rider / 33 mph with rider. California speed limit: 20 mph
• (4) Power modes
  • Fully electric: No pedaling necessary
  • PAS – Pedal Assist System: Get assistance while pedaling
  • Motor off: Move bike with the power of your own legs ;-)
  • On demand: Turn handlebar thumb throttle to manually increase speed and motor assist level

Key Lock, LCD, USB Charging Port

• Battery: 672Wh Li-Ion (48V @ 14Ah) (Model: FZZ006/X1)
  • Detachable with Lock and one of 2 keys for more convenient, off-bike charging
  • Only used about 20% on a 32-mile trip
    • Motor was only activated to assist with uphill climbs, and the rest of the time was pedaled manually
  • Housed within the down tube and accessible by folding the bike in half
  • These types of batteries have a 500+ cycle lifespan and lose about 20-25% capacity after every 500 cycle
  • Automatic power off

Warning: Two keys are included — do NOT lose them! Bike cannot be powered on without one, and they also lock the battery to prevent its theft.

• Range: 24-35 mi on fully-electric, 30-32 mi on pedal assist modes (according to manufacturer)
  • Our own tests found the range to be more like 29-56 mi on fully-electric, 53-69 mi on pedal assist modes
  • Approx. 140 mi with occasional pedal assist based on our 32 mi ride with motorized help only on uphill climbs
• 109W wall charger (2A @ 54.6V)
  • Manufacturer claimed empty to 100% in 4-6 hours. My tests agreed
• IPX4 water resistance – “Resistant to water splashes from any direction”
  • Bikeable in rain but do NOT go through water that is high enough to reach the motor or battery!

Shimano Derailleur, Rear Suspension

• Shimano 8 speeds
  • When the battery is out, the higher number of gears will allow easier, more effective, manual pedaling
• Dual, mechanical disc brakes for faster, more controlled stopping
• Front AND rear shock suspension for smoother, comfortable handling
  • Front level is adjustable for increased pedal efficiency at the expense of comfort
• Large, color LCD Control Panel
  • Displays speed (mph by default) (current, average, max) / battery level / motor assistance amount (PAS 0-5) / odometer / trip distance and time / and more
    • When motor assistance level is set to 0, motor does not turn on, and you will pedal fully manual
  • Covered USB cable port below the display for charging devices (0.5A/ 5V)
  • Backlit and readable in bright daylight

Serial number is etched into the frame by the left stem for registration with local police to aid with recovery.

• Arrived practically fully assembled
  • Should take 5 mins to finish build by simply screwing the collapsible pedals onto their respective crankshafts
    • Make small tuning adjustments to the handlebar and seat post height as needed
    • Surprisingly, neither the front nor rear disc brakes needed any adjustment (this rarely happened with any bike I had previously built — Jasion was the other exception)
• Electronic headlight and horn

Folded Bike

• Foldable, aluminum alloy frame with rider support for up to 360 lbs
  • Excellent built quality and compact
    • Folded: 37″ L x 33″ H x 22″ W / Unfolded: 67″ L x 48″ H x 23.2″ W
  • Can accommodate 5’1″ – 6’5″ biker height with its quick-release seat post
    • Seat height: 25.5″ minimum
  • Adjustable handlebar height: 46.5″ minimum

Foldable Head Tube

• Streamlined cabling along the bottom of the down tube
• 20″ Fat Tires (20 x 4.0 tube) for more controlled, comfortable rides
  • Jasion EB7’s tubes were 20 x 3.0
  • When deflated to a low pressure, fat tires perform better on snow and sand than road or mountain ones by not sinking as much
  • Uses Schrader valve with recommended pressure of 30 psi (max)

Tip: Fat tires, when deflated to a low pressure, perform better on snow and sand than road or mountain ones because they do not sink as much.

Excellent Packaging

• Weight: 68 lbs. Heavier than our previously-tested Jasion/Googo/Metakoo/Ancheer and a non-electric Santa Cruz Heckler
  • Extra weight due to a larger battery and stronger motor
• Electronic Taillight
• Excellent packaging with heavy-duty cardboard and foam padding
• Rear Rack with 150 lb load capacity (Consider rear rack seat cushions)
• Built-in kickstand
• Rear skewer long enough for mounting Burley trailer hitch
• Tools included

Cons

• Ignition is at bottom of the down tube
  • Very inconvenient to insert key to power the bike on or to lock/unlock battery because it requires you to crouch down considerably
    • Cabling running across it adds to the frustration
  • Key is required to stay inserted to power bike on. It also serves to lock the battery against theft
    • May accidentally lose the key during a ride if switched to the wrong position
    • Key could get damaged if down tube hits a hard object. It could also get dirty from mud
    • Key may not be replaceable
  • This is the BIGGEST complaint I have with this bike. I wish it was relocated to the handlebar or another, more easily accessible place

Rear Tire and Rack

• No on-demand pedal assist while PAS is off (set to level 0). Minor gripe but would have been a nice-to-have
  • Googo and Ancheer were the same way. Only Metakoo’s Cybertrack 100 had the option to temporarily kick on the motor by turning the handlebar throttle
• 750W motor acceleration may be too powerful for some
  • Top speed went well past the 20mph federal, California State, and local laws
• Battery takes some effort to remove because it requires you to first fold the bike
  • Could not find where to purchase an extra battery, not even on manufacturer’s website at polarnaebike.com
• Pedals were not labeled “Left” or “Right”
  • Printed guide had you look closely at each pedal’s threading to determine which crankset to screw onto

Pedals

• Front wheel skewer is not quick-release
  • Cons: More inconvenient to fix flat tire, especially if a wrench was not brought for the bolts. Takes more time to attach/detach wheel
  • Pro: Slightly better theft deterrent. Casual thieves do not like to spend more time than necessary
• Handlebar height may be too tall for shorter riders
• LCD screen may get damaged from a fall
• Headlight does not work without turning on the LCD, but the Electric Horn does
• No fast-charging of battery
  • Metakoo included a 168W wall charger (4A @ 42V) that allowed its battery to go from empty to 100% in as little as 3 hours. Polarna’s 109W charger took 4-5 hours
• Keys to lock/unlock battery were not numbered
  • May not be possible to get a matching replacement. So, do NOT lose them!

Warning: Do NOT lose the keys! Battery does not work without one!

• Some may prefer a handlebar throttle instead of the thumb throttle
• Heavy at 68 lbs due in part to a larger battery

Tips

Maintenance

• Before first use, charge the battery fully
  • Covered charging port is on the removable battery itself
  • AC charging brick LED: Red = Charging. Green = Full
  • Lithium Ion batteries are known to be volatile and could catch on fire
    • Do not charge overnight or unsupervised for prolonged periods of time. Stop charging once full
    • Do not leave the bike in full sun or below freezing
  • Keep battery charged at 50% or more to prolong battery’s 500+ cycle lifespan. Try to never let it drain completely
    • Lithium-Ion batteries lose about 20-25% of capacity after every 500 charging cycle
• Before riding, check the tire pressure (30 psi max) and tighten any loose screws
  • Ensure seat post is locked and tight

Operations

Polarna M4 Electric Bicycle

• Motor: Switch battery on and turn on display by long-pressing the Power button on the controller
  • Set Pedal Assist to level 1 or higher by pressing “+” button. Motor kicks in as you pedal
  • Throttle the thumb accelerator by the left-side handle, and the motor will fully take over (Power on demand)
    • The more you push, the faster the bike will go
  • To power off the motor so you would only be able to pedal manually, press Power button (Pedal only), set PAS to level 0 on the display, or turn off the battery
• Headlight: Press the Light button. Display does not need to be turned on
• Electronic Horn: Press the Horn button. Display does not need to be turned on
• Data display: “i” (Info) button toggles Odometer, Trip mileage, Trip time, etc.
• Walking power assist: Press and hold “-” button for 2 secs to activate motor at low speed
  • Helps with walking the bike uphill at 3.7 mph (6 km/h)
• As battery neared empty, I noticed that maximum speed gradually lowered
• Do not brake hard. Doing so could make you painfully tumble, skid, and/or wear out the tires
  • Be aware of unexpected obstacles. I tumbled once while mountain biking and was hurt quite badly. It was not fun

Aircraft Transport

Most, if not all, airlines prohibit electronic scooters and bikes that do not meet specific criteria. United Airlines, for example, allows collapsible ones whose battery is both removable and below 300 Wh. Southwest Airlines is more restrictive at 160 Wh. This bike’s battery is 672 Wh. Lithium-ion batteries are known to be volatile, and the higher their capacity, the more risky they are. Check with the airlines, TSA, and FAA for more details.

Bike Assembly

Here are some installation tips for those assembling their first bicycle. There is a diagram below to identify the major bike parts.

Bike Repair Stands

I use a repair stand to help with assembly and maintenance. SereneLife SLBKRS3 has a maximum load capacity of 66.7 lbs — enough to carry most electric bikes without falling over.

SereneLife Bike Repair Stand, Metakoo Cybertrack 100 mountain eBike

For easier maintenance or assembly, a bike repair stand can save a lot of time and back pain. Be sure to get one that can hold up your bicycle’s weight.

Bike Parts

Bicycle Parts /Al2 (CC by 3.0, Wikimedia CurID 2995998)

Motor Bike Laws

I first learned about laws governing motorized scooters when reviewing the Joyor X5S, and unfortunately, they were (and still are) not straight-forward. There had been a number of accidents involving scooters hitting pedestrians or riders hurting themselves. I get it. Laws are there to protect people from each other and themselves, especially from irresponsible individuals.

Electric bikes can result in severe injuries or death with their high speeds.

Surprisingly, the laws governing electric BIKES are much more lax. They are very similar to non-motorized bikes, in fact! There are different classes of eBikes. This Jasion falls under the lower-speed Class 2 with a maximum of up to 20 mph, and as such, can be used on Class 1 bike paths in California. All 3 classes can ride on the protected, one-way Class 2 bike lanes found on streets and highways. Be sure to check with your local regulations. Some States categorize eBikes as mopeds or motor vehicles.

• Class 1: PAS-only with no throttle. Max assisted speed: 20 mph
• Class 2: PAS and throttle. Max assisted speed: 20 mph
• Class 3: PAS-only with no throttle. Max assisted speed: 28 mph

California Law

Disclaimer: I AM NOT A LAWYER. Please consult your local city, police department, and/or legal professional for advice.

The following is my interpretation of how I understand the law. It has been shortened to only point out parts that I found interesting or noteworthy.

Mountain biking with Cybertrack 100 /Metakoo

• Does NOT require riding with a Driver’s License or Instruction Permit (eScooters require them!)
• No license plate required
• Passengers are allowed as long as the bike was designed for it
• Can ride on existing bike infrastructure
• Speed limited to 20 mph
• Follow most of the same laws as non-motorized bicycles
• Helmet required for riders 17 years and younger
• No minimum age limit

Accessories

Some accessories I recommend for this bike for added convenience and safety:

• Molik Bike Handlebar Bag
• Salzmann 3M Spoke Reflectors: For increased visibility in the dark
• Bar End Bike Mirrors (like BriskMore, Tagvo, or Zacro): To see behind you
• Rear rack seat cushions
• Burley Trailer Coupler: So trailer can be switched to another bike (ie. bike failed or ran out of battery)

Final Thoughts

I thought the Jasion EB7 was one heck of a Fat Tire electric bicycle, but then my friend brought her Polarna M4 along, and I was blown by its sheer power and workmanship. Granted, the latter sold for $260 more and was considerably heavier due in part to a heftier 750W motor and larger battery. Topping at an unmanned 39mph and 33mph with me sitting on it, its speed was exhilarating, dangerous, and potentially illegal due to federal, California State, and local city limit of 20mph.

Polarna M4 Electric Bike

Overall, the Polarna handled hills exceptionally well on some steep mountain trails, and the larger battery capacity should provide plenty of power to help the rider not cramp up the thighs on longer trips.

My family and I had very much enjoyed exploring town together instead of idling around in the car. It is both a healthy activity and a great way to bond with one another while building up the children’s confidence and endurance. I have not found myself going back to a non-motorized bicycle for daily rides, although I would still only take out my trusty Santa Cruz Heckler for more advanced mountain thrills.

Having the option to dynamically turn on or off electronic pedal assist is GREAT — that way, you can go manual, motor assisted, or all motorized.

Where To Buy

• Polarna M4 Foldable Electric Bike
• Accessories
  • Molik Bike Handlebar Bag
  • Salzmann 3M Spoke Reflectors
  • Bar End Bike Mirrors: BriskMore, Tagvo, Zacro
  • Rear rack seat cushions
• Burley D’Lite 2-Seat Bike Trailer/Stroller
  • Additional Trailer Coupler so Burley can be switched to another bike (ie. bike failed or ran out of battery)

Related Posts

• Reviews
  • HeyBike Cityrun: Beautiful, 26″ electric cruiser bike with 500W motor, 7 speeds (21mph)
  • Jasion EB7: 20″ foldable, electric, 7-speed bike with fat tires, 500W motor, 20mph max
  • Googo SY26: 26″ electric mountain bike with 21 speeds, large informative LCD, electronic headlight and horn, and solid build
  • Metakoo Cybertrack 100: 26″ electric mountain bike with 21 speeds and a clean look
  • Ancheer AM001907/AN-EB001: 26″ electric mountain bike with 21 speeds, electronic headlight and horn, and powerful, rapid acceleration
  • Macwheel Ranger 500: Comfortable, 7-speed, electric cruiser for city commutes
  • Gyroor C3: Single speed, electric, semi-foldable, and priced fairly low
• How to Quickly Teach a Child to Ride a Bike (Balance With No Training Wheels)
• Bike USA Stabilizer Wheels for Adult Bicycles