Vivi F26FUL 500W Long-Range Fat-Tire E-Bike

Vivi's marketing leads with "1000W peak," but the bike is a 500W rated rear hub. That's the number Vivi's own catalogue tags it with, and it's the number that matters legally: state power caps regulate rated watts, and 500W clears the 750W ceiling used by every state except Oregon's 1,000W limit. 75 Nm of stated torque is a healthy figure for a 500W rated hub. The pedal assist is a 12-magnet cadence sensor: power arrives when the cranks turn, not in proportion to how hard you push. That's the budget standard, and on a 74 lb fat bike it means the surge-and-coast character every bike in this tier shares.

Vivi claims "up to 50-60 miles." The arithmetic: a 26x4.0" fat-tire bike typically burns 20-30 Wh per mile in mixed pedal-assist riding. The 864 Wh Pro pack that Amazon sells ÷ 25 Wh/mi ≈ 35 miles; Vivi's base 614 Wh pack works out at about 25 miles. Hitting 60 miles on the Pro pack requires ~14 Wh/mi: a light rider, PAS 1, flat ground, no wind, on tires this wide. Treat the claim as a lab ceiling and plan on 30-40 miles from the Pro pack.

Vivi's spec table lists pedal assist to 25 mph and the half-twist throttle capped at 20 mph, a Class 3 configuration (throttle-equipped Class 3 is legal in most, not all, states). The Amazon listing we link states 20 mph instead, so check the display settings on delivery to see which cap your bike ships with. Class 3 brings real restrictions: banned from many shared-use paths by default, mandatory helmets in several states, and outright illegal to sell as street-legal in DC, Kentucky, Massachusetts, Montana, North Carolina, Pennsylvania and South Carolina. Check your state's page before assuming the 25 mph mode is street-legal where you ride.

Mechanical disc brakes with 160 mm rotors are the biggest compromise on the sheet. They work, but on a 74 lb bike that reaches 25 mph, 180 mm hydraulics (as on the ACE01) are a meaningful safety upgrade, so budget for pad adjustment every few hundred miles. The 80 mm lockable coil fork takes the edge off broken pavement but is not trail suspension. Shimano 7-speed drivetrain, a 54.6V 2A charger (slow, since a full Pro-pack charge takes overnight), and 26x4.0" all-terrain tires round it out. Certification is the quiet headline: SGS-tested UL 2849 (system) and UL 2271 (battery), the certs New York City's Local Law 39 and California SB 1271 key on. Vivi's warranty runs 1 year on motor and battery, shorter than Kingbull's 2 years, standard for the Amazon-refugee price tier.

Buy the F26FUL if you want a big battery in a certified fat-tire bike (the Amazon listing's 864 Wh Pro pack, for $862.60 (as of Oct 14, 5:10 PM EDT, subject to change)) and your riding is fire roads, gravel, sand, or snow where 4" tires earn their drag. Skip it if you brake late and hard (get the ACE01's hydraulics), want natural-feeling assist (the ACE01's torque sensor), or ride purely on pavement (the C26UL does that job for $415.15 (as of Oct 14, 5:10 PM EDT, subject to change) and weighs 56 lb against this bike's 74 lb).