Surface 604 Big Sky Review: This E-Bike Will Fit Almost Everyone!


We’re here with the Surface 604 Big Sky e-bike, and it’s the larger sibling of the Big Sky and Sunny Day models. Both of these models are cruisers and offer great value at a price of $2,199. While they are stripped down a bit, Surface 604 is known for using higher quality parts, making them semi-affordable options.

The Big Sky is classified as a Class 2 e-bike by default, but it can be unlocked to Class 3 if you prefer a higher speed. It features a trigger throttle, torque sensing pedal assist, and a torque sensor located at the rear. Let’s dive into the details.


This particular model comes in one frame size and style, which is the high-step design with stylish tubing. The swept-back handlebar adds to the classy appearance. The bike has a matte gray finish with bright orange and blue accents, creating an eye-catching look. Let’s watch a video review of this e-bike, and then you can read a full and detailed review!

FRAME MATERIAL:6061 Aluminum Alloy
MOTOR TORQUE:45 Newton meters
TOP SPEED:20 mph (32 kph)
DRIVE MODE:Torque Sensing Pedal Assist, Trigger Throttle
ELECTRIC BIKE CLASS:Throttle on Demand (Class 2), Speed Pedelec (Class 3)
GEARING DETAILS:9 Speed 1x9 Shimano Alivio Derailleur
BRAKE DETAILS:Tektro Auriga Hydraulic Disc with 180mm Rotors
WHEEL SIZES:27.5 in (69.85cm)
SADDLE:Selle Royal Gipsy
HEADSET:Integrated, Sealed Cartridge, Straight 1-1/8"
BATTERY AMP HOURS:12 ah (Optional 14ah or 20ah)
BATTERY WATT HOURS:576 wh (Optional 672wh or 960wh)
ESTIMATED MIN RANGE:25 miles (40 km)
ESTIMATED MAX RANGE:80 miles (129 km)
TOTAL WEIGHT:55.5 lbs (25.17 kg)
GEOMETRY MEASUREMENTS:19" Seat Tube Length, 29.5" Stand Over Height, 29.5" Width, 78.5" Length, 49" Wheelbase

Design and Build Quality

The Surface 604 Big Sky e-bike features a thoughtful design that combines functionality and aesthetics. One notable design element is the internal routing of the cables. The cables pass through the frame, creating a clean and streamlined appearance. However, at the bottom bracket area, the cables become slightly exposed before emerging along the right side of the bike. This routing arrangement may not be as visually tidy as the internal routing throughout the rest of the frame.

The Surface 604 Big Sky e-bike features an aluminum alloy frame, which strikes a balance between strength, weight, and affordability. However, it is worth noting that the chain cover is made of steel, which adds a bit of weight compared to plastic covers. While steel is sturdy and reduces the chances of rattling, it may be prone to rust if scratched. Applying touch-up paint can help prevent rust formation and maintain the bike’s appearance.

The bike incorporates modular quick disconnects, making repairs and updates convenient. Components such as the display, brakes, trigger throttle, and button pad can be easily accessed and replaced if needed. The presence of quick disconnects simplifies maintenance and ensures efficient troubleshooting.

The Surface 604 Big Sky e-bike offers various possibilities, including an open port for an optional headlight. This feature allows riders to customize their riding experience by adding a shiny 120 headlight that can be mounted conveniently.

The front wheel utilizes a quick-release system with 100-millimeter hub spacing and a 9-millimeter quick-release skewer, which is a standard configuration. In contrast, the rear wheel has a width of approximately 138 millimeters and employs a 12-millimeter slotted threaded axle. While there is no torque arm on this e-bike, it incorporates a torque washer and a torque sensing plate on the other side of the rear dropout. This design enhances strength and stability during high torque situations.

Notably, the bike showcases paint-matched rims that complement the frame color, creating a visually cohesive and attractive appearance. This attention to detail adds to the overall aesthetics of the Surface 604 Big Sky e-bike.

Regarding the motor, it is identified as being manufactured by an off-brand, as opposed to the more recognizable Buffet motor found on some of Surface 604’s other models. The motor features the brand’s name printed on it, indicating its origin.

The placement of the kickstand at the rear of the bike is worth mentioning as it offers convenient support when parking the e-bike. This position allows for easy deployment and ensures stability when the bike is stationary.

The Big Sky e-bike is equipped with a 42-tooth steel chainring and a square-tapered spindle. While some other Surface 604 models may have a stiffer and more advanced hollow spindle from Samox, the square-tapered spindle on this model gets the job done at a slightly lower price point. The branded crank arms measure 170 millimeters in length, and the wellgo BMX pedals are made of durable aluminum alloy. These pedals not only provide ample surface area and traction but also complement the frame’s aesthetics.

The bike features a nine-speed 11-36 cassette, offering a wide gear range. This range is particularly important because while the Big Sky e-bike is initially set to a top speed of 20 miles per hour, it can be unlocked for higher speeds, reaching up to 26 or 28 miles per hour. The availability of extra gears and a smaller sprocket ensures a comfortable riding experience at higher speeds. The Shimano Olivio derailleur performs adequately in maintaining smooth gear transitions.

Located on the handlebars, the nine-speed trigger shifters of the Big Sky e-bike include an optical display window, allowing riders to monitor the selected gear. While the low gears can be easily controlled using the thumb, shifting to the high gear requires the use of the pointer finger. It is worth mentioning that Shimano Dior shifters allow for both thumb and pointer finger operation, offering more flexibility. This detail is particularly relevant for riders who prefer using their pointer finger for braking.

Speaking of braking, the Surface comes equipped with Tektro hydraulic disc brakes. These brakes deliver excellent stopping power, ensuring reliable and controlled deceleration. The hydraulic disc brakes offer enhanced modulation and responsiveness, providing riders with a confident and secure riding experience in various conditions.

The 604 Big Sky e-bike is equipped with large 180-millimeter rotors and dual-piston calipers, ensuring powerful and reliable braking performance. The brakes are designed with motor inhibitors, meaning that whenever the brakes are engaged, the power to the motor is instantly cut off for enhanced safety. Additionally, pulling the brake lever activates the optional rear light, causing it to blink, further improving visibility and safety. The bike is pre-wired for lights, allowing for easy installation of additional lighting accessories. While this model may not come with lights included, the wiring is already in place for convenient upgrades.

The Big Sky e-bike provides mounting points for fenders on both the front and rear, allowing riders to add fenders for protection against splashes and debris. It also features a mounting point for a rear rack, offering the option to attach accessories such as a trunk bag, picnic basket, child seat, or any other cargo-carrying needs. This makes the bike versatile for commuting or recreational purposes.

In terms of comfort, the Big Sky e-bike comes with a larger and more plush saddle compared to many other Surface 604 models. The saddle used is the Cellar Royale Gypsy, featuring elastomer bumpers for added cushioning. The seat post diameter measures 30.4 millimeters, providing stability and compatibility for various seat post options. Riders have the option to swap out the seat post for a suspension seat post, which would offer additional comfort by absorbing vibrations and bumps. However, it is worth noting that the absence of a suspension fork in this model helps reduce weight and cost, while maintaining the bike’s purpose-built design.

The tires on the Big Sky e-bike are Inova branded and feature reflective sidewall stripes, adding an extra element of safety by increasing visibility in low-light conditions. These tires are designed in the 650b standard and offer a decent tire pressure range of 30 to 65 PSI. Adjusting the tire pressure towards the lower end of the range, around 30 to 40 PSI, can enhance comfort by providing a smoother ride with increased damping of vibrations. However, it’s important to note that lowering the tire pressure may slightly decrease efficiency and range.

The Big Sky e-bike I weighed earlier came in at around 55.5 pounds. The weight is positioned centrally and low on the frame, which enhances the bike’s handling and stability. Notably, there is no suspension fork on this model, but the high-volume 27.5″ x 2.4″ tires compensate for it. These wide tires provide stability, a touch of comfort, and a larger wheel diameter, enabling a smoother ride over cracks and bumps with a lower attack angle.

Overall, the Surface 604 Big Sky e-bike’s design includes thoughtful features for safety, versatility, and comfort. With its powerful braking system, pre-wiring for lights, mounting points for fenders and a rear rack, comfortable saddle, and reflective tires, it is well-suited for various riding situations and preferences.

Motor and Battery

The Surface 604 Big Sky e-bike offers a solid performance with its 500-watt nominal and 750-watt peak motor. While the exact torque measurement is not easily determined, it is estimated to be between 45 to 60 newton meters. During rides, the motor noise is slightly more pronounced, indicating its engagement, and the bike feels zippy and responsive. The motor performs well, providing the desired power and acceleration.

Getting started on the Surface 604 Big Sky e-bike is made easy and convenient, especially when carrying a heavy rack, loaded bags, or a child trailer. Using the throttle to initiate movement is simpler than trying to stand up and push the bike forward. However, the presence of a torque sensor on this e-bike ensures a responsive and natural riding experience.

With the torque sensor, the bike detects the amount of force you apply to the pedals and provides assistance accordingly. Demonstrating this responsiveness, even at Level 2 assistance, the bike delivers power smoothly and naturally. The harder you push on the pedals, the more power you receive from the motor. Increasing the assistance level to Level 5 showcases the bike’s ability to kick in with significant power when you exert more force. This feature not only enhances the bike’s performance but also encourages riders to put in more effort, enabling them to go faster and potentially extend their range, which is beneficial when using a more efficient battery.

Even with the responsive motor assistance, the Surface 604 Big Sky e-bike still maintains the feel of riding a regular bicycle. The torque sensor ensures that the motor support complements your pedaling, making it a more intuitive and enjoyable experience. Changing gears seamlessly while riding uphill is possible, allowing you to find the optimal gear ratio for tackling challenging terrain.

One notable advantage of the e-bike is the ability to utilize the throttle to assist when needed. For instance, if you’re struggling on a hill or experiencing discomfort in your knees, a gentle push on the throttle provides an instant boost, helping you ascend the incline with ease. In fact, the throttle can propel the bike to significant speeds, offering a thrilling and efficient means of transportation.

Also, one aspect to consider when choosing the Big Sky e-bike is the battery capacity. The base level battery, included at a price of $2,199, is a 48-volt pack with a capacity of 12 amp hours. The 48-volt system offers improved efficiency and power. However, Surface 604 also offers optional battery upgrades, including a 14 amp hour and a 20 amp hour pack. The 20 amp hour battery protrudes slightly on the side, affecting symmetry and adding some weight. The weight of the e-bike is approximately 55.5 pounds, considering the included components.

In order to provide better visibility of the display, we moved the Surface 604 Big Sky e-bike into the shade. With a simple press and hold of the power button, the display comes to life, showcasing its vibrant color and stylish branding. The display offers a range of useful readouts to enhance the riding experience.

One of the standout features is the percentage battery indicator, which displays the battery level with one percent increments. This level of precision is far superior to traditional battery indicators with a few bars that disappear one by one. With the percentage indicator, you have a more accurate understanding of your remaining battery capacity, ensuring you don’t get stranded unexpectedly.

The e-bike offers five levels of assist, and the display allows you to easily adjust the level using the plus and minus buttons. If your battery is running low, you can reduce the power assistance to conserve energy and make it back home comfortably. Taking it down to zero turns off the pedal assist, but it’s worth noting that the throttle will still be inactive. However, the walk mode is functional, activated by holding the minus button for a brief moment. This feature allows the rear motor to engage at a slow speed, making it useful in situations such as walking the bike through crowded areas or tackling steep terrain with a flat tire.

The display also provides various other readouts, including trip distance, odometer, maximum speed, average speed, and time. Cycling through these readouts is as simple as pressing the “I” button. Additionally, there is a dedicated light button on the display, indicating the presence of an optional light accessory. Although there were no lights connected during the demonstration, Surface 604 offers a compatible light that can be seamlessly integrated into the system, providing enhanced visibility and safety.

The charge port is positioned relatively low near the crank arms, which can be vulnerable if the pedals are cycled backward and accidentally bump the port. Although the e-bike is designed to be water-resistant, without fenders, the port may be exposed to moisture and dust. While the bike’s battery and components are generally durable, this particular design aspect should be noted as a potential trade-off.

The battery is easily accessible by inserting the included wrench and turning it to release the battery pack. The pack weighs around 6.5 to 7 pounds and features a convenient USB charging port at the top. Additionally, another USB charging port is located at the base of the display, allowing users to connect additional devices such as aftermarket lights or smartphones for GPS purposes. The color display on the Big Sky e-bike is visually appealing and provides a wealth of information, which will be discussed further shortly.

The included charger is a two amp charger, which is suitable for the base level 500-watt-hour battery pack. While there are four amp chargers available for faster charging, the two amp charger is sufficient for the base level battery’s capacity. It is lightweight and cost-effective. However, for the optional higher capacity batteries, Surface 604 offers a faster charger as an upgrade, allowing riders to quickly recharge their e-bike between multiple rides in a day.


In the end, the Surface 604 Big Sky e-bike presents itself as a versatile and well-designed electric bicycle. Its internally routed cables provide a clean and streamlined appearance, while the modular quick disconnects make repairs and upgrades straightforward. The aluminum alloy frame, combined with the steel chain cover, offers a balance of durability and weight savings, although the steel cover may be prone to rust if scratched.

Performance-wise, the Big Sky e-bike demonstrates its capabilities with a 500-watt nominal and 750-watt peak motor, delivering a zippy and responsive ride. The torque sensor system adds to the natural and smooth riding experience, providing more power as the rider applies greater force. The option to choose different battery capacities allows for customization based on individual needs, with the display offering precise percentage battery indicators to prevent unexpected battery depletion.

The inclusion of Tektro hydraulic disc brakes with motor inhibitors ensures reliable stopping power, prioritizing rider safety. The bike’s pre-wired setup for lights and additional accessories, such as fenders and a rear rack, adds versatility for various riding scenarios and practicality for commuting or carrying cargo.

The comfortable cruiser-style design, complete with sweatback handlebars, a plush saddle, and high-volume tires, prioritizes rider comfort and stability. The upright body position and potential for adding a suspension seat post enhance the overall riding experience, although it comes at the cost of added weight and potential frame flex.

The user-friendly display provides essential information, such as battery level in percentage increments, trip distance, average speed, and more. The option for walk mode further demonstrates the bike’s practicality in different situations, offering a slow speed assist for maneuvering in challenging terrain or crowded areas.

So, the Surface 604 Big Sky e-bike impresses with its combination of performance, design, and practicality. Whether riding for leisure, commuting, or tackling various terrains, this e-bike offers a versatile and enjoyable experience for riders of different preferences and needs.


Alternatives of Surface 604 Big Sky



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