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Sunny Health & Fitness Recumbent Bike SF-RB4631

Sunny SF-RB4631

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350 lbsMagnetic,
8 levels
Frame: 3 years
Parts: 90 days

The Sunny SF-RB4631 is one of the recumbent bikes released by Sunny Health & Fitness at the beginning of 2017. As opposed to other Sunny recumbent bikes, it features an arm exerciser with its own friction resistance, along with a magnetic resistance mechanism for the pedals. It’s up to a point similar to the Stamina Elite Total Body bike, but it costs considerably less. Although it’s a trainer designed for home use, it features a durable construction and an impressive weight capacity.

Technical Details and Specifications

  • Assembled dimensions: 53L x 24W x 54H (135L x 61W x 137H cm)
  • Assembled weight: 89.5 lbs (40.5 kg)
  • Supported weight: 350 lbs (159 kg)
  • Handlebars: Recumbent and front arm exerciser
  • Seat: Adjustable
  • Drive: Belt
  • Resistance: Magnetic, 8 levels
  • Fitness meter: Time, speed, distance, total distance, calories, pulse, SCAN
  • Warranty: Frame 3 years / Parts 90 days

Frame construction

This Sunny exercise bike features quite a durable steel frame designed to support users up to 350 lbs (159 kg). It has a one-piece chassis, a feature that considerably improves its overall sturdiness, while the welding points are precision-machined. All the steel parts within the unit’s frame are coated with a corrosion-resistant paint; the color used is light gray with the Sunny logo painted red, these being the only colors available for this model.

Of course, the bike’s construction also integrates several plastic parts. These are the covers of the flywheel, the covers of the arm exercise mechanism, and several other small covers. These don’t diminish the unit’s overall sturdiness, though, as they only have a protective and cosmetic role.

The Sunny SF-RB4631 is not an extremely heavy recumbent exercise bike. However, it does weigh approx. 90 lbs (40.5 kg). This weight adds to its overall stability. Plus, its rear base bar is equipped with adjustable stabilizers which allow you to perfectly level it on any type of floor. On the other hand, transporting the assembled unit is far from being difficult. Its front base has two small transport wheels which facilitate its relocation. By using these wheels to relocate the machine you will basically be handling less than half of its total weight.

Compared to other recumbent bikes, the Sunny SF-RB4631 isn’t an extremely large unit. It takes 53″L x 24″W (135 x 61 cm) of floor space when fully assembled. However, it is recommended to leave at least two feet of clearance on each side, and at least one foot of clearance at the front and rear, for safe operation.

One last aspect to mention here regards the unit’s step-thru design. Due to this type of frame construction, the access to the seat is easy. Thus, entry and exit shouldn’t be a problem even for users with disabilities or elderly users.

Seat and handlebars

The Sunny Health & Fitness SF-RB4631 recumbent bike is equipped with an ergonomic, fairly large seat. Its dimensions are 10.5″D x 15″W (26.6 x 38.1 cm). Both the seat and the backrest integrate a generous layer of foam padding and have a durable, vinyl upholstery. The backrest is contoured; it has a durable steel backbone which results in an excellent, healthy lumbar support.

The seat is adjustable. Its adjustment track offers several inches of travel back and forth. The min/max inseam for this bike is 26″/33″ (66 – 83 cm); it is measured from the furthest position of the pedal, straight to the front edge of the seat. Differently put, this bike can accommodate users between 4’10” and 6’4″ (148 – 193 cm). Also, the seat assembly, as well as its metallic base are rated for a user load of 350 lbs (159 kg).

However, the backrest cannot be adjusted independently from the seat, as for the LifeCore 860RB, for example. It’s directly attached to the seat’s frame assembly and will move along with it on the adjustment rail.

A set of handlebars is attached directly to the seat assembly. They feature ergonomic grips with integrated pulse sensors. In case you’re wondering, the distance between them is 22″ (56 cm). Just as the backrest, these recumbent handlebars cannot be adjusted independently from the seat.

As opposed to many other recumbent bikes, the Sunny SF-RB4631 features an arm exerciser instead of the usual front handlebars. Its side arms are length adjustable. They’re equipped with rotating, large grips as well as horizontal grips. The console mast is slightly inclined towards the seat, so the position of the arm exerciser is not too far from the seat; thus, exercising your arms doesn’t require an awkward position as for other trainers.

Resistance system

This Sunny recumbent bike features two distinctive resistance systems, one for the pedals, and one for the arm exerciser. For the pedals, the bike uses a manual magnetic resistance system, while the arm exerciser integrates a friction resistance system. The two elements are not interconnected and can move independently from one another. In other words, if you only use the pedals, the arm exerciser does not move, and vice-versa.

The pedal resistance system consists of a small magnetic brake attached to the tension lever at the lower part of the console mast via a steel cable. As you move the lever up or down, the magnetic brake position in relation to the internal flywheel changes, resulting in more or less resistance.

There are 8 distinct resistance settings marked on the adjustment lever. The top, 1-3 levels provide a light resistance, great for recovery training. Conversely, the lowest 7-8 settings offer the possibility to achieve a higher burn and execute training routines of superior intensity. But as a general idea, the highest resistance setting isn’t extremely difficult; it can be labeled as mid-range resistance.

The resistance system of the arm exerciser integrates a small wheel and a leather brake pad connected to the knob on top of the assembly. By turning the knob clockwise, the pad applies more friction to the wheel, generating more resistance. You can basically tighten the knob up to the point you can barely rotate the arms. Also, since this is a friction resistance system, it’s not whisper-quiet as the pedal resistance.

Drive system

Since this is a Sunny exercise bike equipped with a magnetic resistance system, it uses a belt drive system. This means you won’t have to worry about transmission lubrication. Also, a belt drive generates less vibration than a chain and delivers a very quiet pedaling motion.

The bike integrates a perimeter weighted flywheel. This type of construction results in a bit more inertia and consistency during pedaling. It also delivers a very steady motion. The weight of the flywheel is not specified. But as a general idea, its weight should be somewhere between 12 – 18 lbs (5.4 – 8.1 kg). This means the lowest resistance settings don’t generate a lot of resistance and the stress on the joints is minimal.

The bike is equipped with a solid crankset with steel crank arms. The pedals are made of durable nylon material, featuring a non-slip surface and adjustable straps. They’re weighted in order to always turn face-up for ease of foot placement. They also have standard threads, so replacements for them are widely available.

Exercise meter

The first aspect to mention here is that the bike’s fitness meter (or console) is not connected to the arm exerciser. Therefore, it doesn’t track the calories burned or any other metrics when you only use the arm exerciser. On the other hand, when using the pedals, it tracks time, distance, total distance, speed, calories, and heart rate. It features an LCD display with large, easy-to-read digits.

The unit is very easy to operate. It only has one (MODE) button which toggles ON/OFF the SCAN function. When the SCAN function is ON, all the workout metrics are rotated, each one being displayed for 6 seconds. This button also fulfills the unit’s reset function; by pressing and holding it for 3 seconds all the values are cleared to zero, except the total distance. To reset the total distance you have to remove the batteries.

The unit is battery-powered; thus, the bike doesn’t require being connected to a power circuit. It uses 2 AA batteries which are included. It has a sleep mode to which will enter after 4 minutes of inactivity on the bike. It automatically starts up when you begin pedaling or if you press the button.

Assembly and Maintenance

The bike’s base frame along with the main drive and resistance elements comes pre-assembled. You only have to add the base stabilizers, the console mast, the arm exerciser, the console, the seat with its backrest, and the pedals. This may take more than an hour, but the process is not complicated. Plus, the manual provides pretty clear assembly instructions, and all the tools needed for it are included.

Once the unit is assembled, maintenance doesn’t require much. If the arm exerciser emits a rather loud noise when in use, the internal friction leather pad may require lubrication. This can easily be done by removing one of the arms and side covers and applying a bit of silicone lubricant on its flywheel. Along with that, it’s recommended to periodically check the bike for loose bolts and parts.

The Pros

  • Sturdy frame – can support users up to 350 lbs;
  • Adjustable stabilizers on the rear base;
  • Transport wheels on the front base;
  • Padded seat and backrest with a contoured design, for maximum comfort;
  • Adjustable seat – can accommodate users up to 6’4″;
  • Recumbent handlebars with pulse sensors;
  • Anti-slip, weighted pedals with adjustable straps;
  • Arm exerciser with friction resistance;
  • 8 levels of magnetic resistance for the pedals;
  • Console that can track time, distance, total distance, speed, calories, and pulse;
  • Smooth and quiet operation, suitable for apartment use;
  • Easy to assemble;
  • Very little maintenance required.

The Cons

  • No bottle holder;
  • Not tablet holder;
  • The console display doesn’t have backlight.


The Sunny Health & Fitness SF-RB4631 is a magnetic resistance recumbent bike equipped with an arm exerciser and a basic console. It has a very sturdy frame, being able to support users up to 350 lbs. It’s an exercise bike designed for light to medium cardio and recovery workouts, great for anyone who wants to tone legs and arms muscles, regain or maintain cardiovascular shape, stamina development, and weight loss. And finally, it’s one of the most affordable bikes with a front arm exerciser available at the moment.

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