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CAROL vs. Sunny Exercise Bike: Which one to buy?

Delve into a comprehensive comparison between CAROL Bike and the Sunny Exercise Bike. Both are designed to cater to distinct fitness goals and requirements.

While the Sunny Health & Fitness Indoor Exercise Bike offers an affordable initiation for indoor cycling newbies, CAROL Bike is a premium investment for those seeking a scientifically-backed, time-efficient training approach.


To the uninitiated, the world of indoor cycling can appear overwhelming, with countless models that seem identical. Your fitness goals, experience level, and workout preference will guide your choice. We’re here to help you navigate these options, contrasting 2 distinctly targeted exercise bikes: the Sunny Health & Fitness Indoor Exercise Bike and CAROL Bike.

Sunny Exercise Bike: Overview

Affordability & Design


A budget-friendly choice ideal for beginners, this model boasts a robust steel frame with a minimalist design.


Performance Features


The hefty 49-pound flywheel guarantees stability even for heavier users. The belt-drive system ensures a quiet and smooth ride with minimal maintenance.




The seat and multi-grip handlebars of the bike are fully adjustable. The seat adjusts vertically within a 28-39 inches range and the seat-to-handlebar distance can be adjusted from 18 to 22 inches. The bike fits inseams from 27 to 42 inches. Some users complain about the seat being too narrow and rigid so they had to buy a special padded seat cushion to make their rides more comfortable. The bike comes with cage pedals that don’t require cycling shoes in order to ride it.




This no-frills model doesn’t require a power source and lacks Wi-Fi or Bluetooth capabilities. The primary extra feature is a bottle holder.


All you need to do to get going is to turn the resistance knob on and start pedaling. The bike shows a smooth and solid performance during low-intensity active recovery rides, high-intensity interval training sessions, and long endurance rides.


The lack of a cadence monitor and resistance indicator allows you to perform only basic workouts. If you want to get a better insight into your progress, you can buy these items separately from a retailer or opt for a different model—the Sunny Evolution Pro II Magnetic Indoor bike. This model has a performance monitor that tracks speed, cadence, distance, calories, and pulse. You also can take a look at the upgraded model Sunny Health & Fitness Indoor Cycling Exercise Bike Pro II which has a performance monitor, pulse sensors, and a device holder.


Price Point


At $400, it offers an economical start to indoor cycling, inclusive of free shipping.

CAROL Bike: Overview

CAROL Bike stands out by offering unique protocols that consist of the shortest, most effective high-intensity workouts — backed by science.


Design & Set-Up


CAROL Bike has a sleek minimalistic design with a polished frame sturdy enough to sustain supramaximal exercises. It comes as a single unit and doesn’t require any setup. The bike has an adjustable seat and a five-grip position handlebar allowing you to lean deeper during the all-out sprints.


Advanced Metrics


CAROL Bike provides you with more detailed information about your training sessions. Workouts are displayed on the 11-inch display as a series of simple graphics including your ride progress, power, cadence, and heart rate. You also receive a chest-worn heart rate monitor with your purchase for more accurate tracking. 


Training Programs


Unlike broad-spectrum cycling classes, the CAROL Bike hones in on 20+ science-backed indoor cycling workouts. CAROL Bike has an AI-controlled magnetic resistance that automatically tailors resistance levels to keep you working out at your maximum capacity throughout the training.


3rd Party Apps


While riding, you can make the most of CAROL Bike’s built-in integrations with training and fitness apps. If you use cycling apps like Zwift, Kinomap, Rouvy, BKool, and FulGaz, CAROL Bike will automatically adjust the resistance and simulate different outdoor cycling conditions, like road gradient and wind speed. You can enjoy live and on-demand classes through Peloton Digital or Apple Fitness+ and watch entertainment shows on Netflix, Disney+, and YouTube. Wi-Fi and Bluetooth connection makes your options almost endless.


Price Point


Retailing at $2,595, CAROL Bike might be steep for some. However, for those seeking a time-efficient and scientifically-backed workout, it offers tremendous value.

CAROL offers the shortest, most effective workouts—backed by science. On top of this, it is the most versatile bike on the market, with a wide range of third-party integration.

CAROL Bike: Training experience

CAROL Bike riders get a completely different training experience than the one you can get at a spin studio. Instead of sweating for a prolonged period of time, it offers you an extremely short supra-maximal workout.


CAROL Bike’s signature REHIT (Reduced Exertion HIIT) workout consists of 2×20-second sprints performed at maximum capacity, as well as a low-intensity warm-up and cooldown.


It is based on research that has shown that 2×20-second all-out sprints are enough to deplete up to 30% of the body’s glycogen stores and trigger metabolic changes that increase calorie afterburn and significantly improve aerobic fitness. More or longer sprints don’t have a greater effect. According to studies, a 5-minute CAROL Bike ride achieves the same cardiovascular benefits as a 45-minute run. You will also burn more calories on a 15-minute CAROL ride compared to a 30-minute run, with 66% of calories being burned after the training.


CAROL Bike is the only bike fully optimized for REHIT— making it simple, effective, and safe. Its AI-personalized workouts learn to push you to your limit, so every second matters.


On top of REHIT, CAROL Bike offers other workouts for different training goals:


If your main objective is to lose fat, the Fat Burn ride was designed to efficiently burn calories. This HIIT training consists of 60×8-second sprints with 12-second recoveries in between each as well as a short warm-up and cooldown. It has been shown to induce the longest excess post-exercise oxygen consumption (EPOC) compared to steady-state moderate and vigorous workouts—you burn almost 50% of calories after the ride.


If you prefer low-intensity endurance training, Zone 2 rides are performed at a level of effort where holding a conversation is still possible. You can choose between the 3 options: Zone-Based Free Ride which keeps you automatically in a specific training zone, Constant Power Free Ride which allows you to select a target power, and Regular Free Ride which lets you directly control resistance.


All workouts have several custom variations with a different number and duration of sprints depending on your fitness level.

CAROL vs. Sunny Exercise Bike: Summary

The CAROL and Sunny bikes cater to different fitness segments. Your decision hinges on your objectives, experience, and budget.


Sunny: A budget-friendly and basic bike suitable for those dipping their toes into indoor cycling. It’s quiet and smooth, though advanced users might yearn for more in-depth workout control.


CAROL Bike: Provides the shortest, most effective workouts suitable for any age and fitness level – while offering greater versatility and choice than most other smart bikes. Its price tag is justified by its unique, scientifically-supported training method. Its high-efficiency workouts are unparalleled in the industry.

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All our experts have MSCs in Exercise Science, and they’re here to answer your questions. Whether it’s about the science behind CAROL Bike, or general fitness advice, whatever’s on your mind—we’re here for you.

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