HKM-3921107 Fat Tire E-Bike Runs a 750W Hub on 20 x 4.0 Tires With Seven Speeds and 360 Degree Lights and a Brown Saddle

750W · 624Wh · 25 km/h · 20 x 4.0 · 7-speed · front and rear shocks · 360 degree lights · 264 lb

Twenty Inch Tires Seven Speeds and Lights That Guard the DarkA Brown Saddle and Night Lights Out

A 20-inch fat bike with a 750W hub, a 48V 13Ah pack worth 624Wh in the frame and seven speeds. Front and rear shocks, mechanical discs at both ends, a brown saddle and a 360 degree lighting set that puts a wide floodlight up front and a brake-flashing tail lamp behind. It is listed at 25 km/h and 20 to 37 miles, and it weighs 78.7 lb with a 264 lb load rating. The battery is a lockable canister on the down tube, so it comes off for charging indoors.

The frame is a black loop with an exposed battery canister on the down tube, a brown sprung saddle and a high-rise bar. It is the classic fat-tyre scrambler silhouette: small wheels, a long seat and a headlamp mounted high enough to clear the front tyre. The brown saddle is the one warm colour on an otherwise all-black bike.

The lighting is the feature that separates it. The front unit throws a wide flood rather than a spot, and the rear lamp flashes continuously under braking, which is the difference between being seen at dusk and hoping you are. If a lot of your riding happens after work, that matters more than another 100W of motor.

At a Glance

• 750W Rear Hub — 48V system, single motor
• 48V 13Ah Pack — 624Wh on the down tube
• 20 to 37 Miles — Listed range
• 25 km/h — About 15.5 mph, listed
• 7-Speed Drivetrain — Derailleur at the rear wheel
• Front and Rear Shocks — Sprung fork and twin rear springs
• 360 Degree Lights — Flood headlamp and brake-flash tail
• 20 x 4.0 Tires — Pneumatic knobbys on spoked rims
• 78.7 lb — Mid weight for the class
• 264 lb Load — 120 kg rating
• Brown Saddle — Sprung, over the rear wheel
• Mechanical Discs — Front and rear, cable actuated

Frame Saddle and Lights

The frame is a black loop with a battery canister bolted to the down tube, a brown sprung saddle over the rear wheel and a high-rise bar with a cross brace. The headlamp sits on a bracket above the front tyre rather than on the crown, so it clears the fat casing when the fork compresses.

The wheels are 20 x 4.0 pneumatic knobbys on spoked rims. Twenty inches is the size that keeps a fat bike stable at low pressure without making it a two-person lift, and spokes can be trued at home after a hard knock. Run them at 15 psi on pavement and 8 on sand.

Suspension is a sprung fork up front and twin springs under the saddle at the rear, which is enough to take the edge off a curb or a rutted track without adding the weight of a linkage. Brakes are mechanical cable discs at both ends, with a barrel adjuster at the lever for pad wear.

• Frame: black loop, battery canister on the down tube
• Battery: 48V 13Ah, lockable
• Wheels: 20 in spoked, 4.0 pneumatic
• Fork: sprung
• Rear: twin springs under the saddle
• Brakes: mechanical cable disc

Fitted as shipped: the 360 degree lighting set, front and rear fenders, the brown saddle, a kickstand and the pedals. The bars carry the throttle, the assist switch and the brake levers, and the battery canister has its own lock and charge port on the side.

750W and 624Wh

The motor is a 48V 750W rear hub driving through a seven-speed derailleur, which is the arrangement that lets you pedal with the motor on a slope instead of letting it do all the work. The listed top speed is 25 km/h, about 15.5 mph, so this is a bike built for paths and tracks rather than the road.

The pack is 48V 13Ah, 624Wh, in a canister on the down tube. It is the smallest battery in this group, and the listed range is still 20 to 37 miles because the motor is modest. Take the lower number for throttle use and the higher one for pedalling at low assist.

A lockable canister is worth having: it means the pack comes off for charging indoors, and it means the bike is not dead if the battery ages. Check that the lock engages fully every time you refit it, because a canister that rattles will wear its contacts.

Who It Fits and How It Rides

The saddle is low and sprung, and the bars are high, so it suits riders from about 5 ft 4 in to 6 ft 2 in. The 264 lb rating covers most adults with a pack, and at 78.7 lb the bike is manageable to lift onto a rack. A very tall rider will find the cockpit short.

On gravel and packed dirt it is stable and the twin springs keep the saddle from kicking, and the fat casing rolls over sand. On pavement it is slow by design and the knobbys hum, so it is a path and track bike rather than a commuter. The lighting set is genuinely useful after dark.

• Paths, gravel and campground loops
• Dusk and night riding on known routes
• A second bike that fits in a shed
• Not for traffic or long road rides

What's in the Box

Before the first ride: fit the front wheel and torque the axle, set the bars square to the fork, check the battery canister locks fully, bed the cable discs in with ten firm stops and charge the pack. Budget 35 to 50 minutes, and check the brake cables after the first ten miles.

Color and Finish

Black covers the frame, canister, fenders, fork, bars and rims, and the brown saddle is the only colour on the bike. The lighting set adds a white flood up front and a red tail behind, and the frame lettering is a muted grey rather than a bright decal.

Touch-up paint in satin black is available on request. The wear points are the canister where a boot rubs it, the saddle edges and the fork lowers.

Battery Care and Maintenance

Because the pack comes off, the routine is simple: charge it indoors between 20 and 90 percent for daily use, take it to full once a month, and keep it above freezing while charging. Store it around half charge if the bike will sit for a month, and refit it with the lock fully engaged.

Check tire pressure before every ride at 15 psi on pavement and 8 on gravel, check the spokes and axle nuts after the first 50 miles, and check the canister contacts for corrosion if you ride in the rain. The cable discs need the barrel adjuster turned as the pads wear, and the pads are a five-minute swap.

Specifications

Frequently Asked Questions

Service and Policies

Coverage that lasts beyond the box. Orders ship free with a tracking number in 2 to 5 business days. From delivery, the product is protected for 180 days against manufacturing defects and transit damage, returnable within 30 days for a full refund, and covered by a 24-month parts-and-labor warranty on manufacturing defects. Four policies, one idea: ship it free, protect it for 180 days, take it back for 30, and stand behind it for two years.

HKM-3921107 · fat tire electric bike · 48V 750W rear hub with a 7-speed derailleur · 48V 13Ah 624Wh lockable canister on the down tube · 20 to 37 miles listed range · 25 km/h top speed, about 15.5 mph · mechanical cable disc brakes front and rear · sprung fork with twin springs under the saddle · 20 x 4.0 pneumatic knobby tires on spoked rims · 360 degree lighting with a flood headlamp and a brake-flash tail lamp · brown sprung saddle, fenders and a side stand · 78.7 lb with a 264 lb load rating · charger in the box · UL listed · built for paths, gravel and dusk riding rather than traffic · lockable canister so the pack charges indoors · the tail lamp flashes under braking so traffic behind you sees it