Sunny Synergy Pro SF-B1851 Review & Comparison with Schwinn IC4 & SF-B1805

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By Robbie Ferri, Cyclist, Personal Trainer, and Group Exercise Instructor.

If you have been looking into Spinning Bikes or Exercise Bikes, you would have come across the name Sunny. They make incredible bikes, and the Sunny SF 1851 Synergy Pro is an excellent example of this. The SF B1851 Synergy Pro is one of their most popular models, but is it worth it? In this article, we will put it up against the other popular indoor cycle from Sunny (SF B1805) and one of the most popular indoor cycles, in general, the Schwinn IC4.

Quick Comparison Table

BikeSunny SF B1851Schwinn IC4Sunny SF B1805
Resistance SystemMagneticMagneticMagnetic
WarrantyFrame: 10 years & Mechanical Parts : 180 daysFrame: 10 years & Mechanical Parts : 3 yearsFrame: 10 years & Mechanical Parts : 180 days
Weight Capacity300lbs330lbs300lbs

Detailed Review

-$300 OFF + Free Cadence Sensor ($70 Value)
Sunny Health & Fitness Synergy Pro Bike

Includes a 40lb inertia-ready flywheel belt drive mechanism to provide a smooth & quiet ride. Its magnetic resistance provides quick, easy, & reliable resistance changes.

  • Use SAVE10 coupon code on Sunny Official Site for 10% OFF!
  • Free Cadence Sensor to Sync with the SunnyFit App! Applied to your Cart!
Buy from Sunny Health Amazon Reviews


  • 40 lb flywheel
  • 300 lb weight capacity
  • Magnetic tension system
  • Adjustable inseam: Min 29 in / Max 39.5 in
  • Caged/SPD compatible pedals
  • Warranty: 3 year structural frame 180 days other parts and components
  • Product dimensions: 49L x 22W x 46.5H

Things I liked:

  • Magnetic Resistance System
  • 40lbs Flywheel
  • SPD Clip in Pedals
  • Belt Drive
  • Large Flywheel

Things To Consider:

  • Limited Warranty 

The Sunny SF B1851 Synergy Pro is a beautiful bike to look at. It has a classic spin bike style and would fit any home gym well. I like that they have gone for a pale gray on this bike and not a Matt black like many other bikes on the market. It has a standard front facing flywheel. I like it because not only does it look good but you can always see it from a safety point of view. If you have a pet or child run across the front, you can quickly hit the emergency stop. 

sunny synergy pro easy transport

The layback seat design looks excellent, and it has a classy look to it with oversized tubing. It’s a sturdy and robust bike and will handle any sprint you give it. If you are concerned about moving it, don’t be, it has wheels at the front, making it easy to move around.

Flywheel and Drive Chain

It’s a belt drive system, and this has enormous advantages compared to other systems on the market. Using a belt gives you a better connection to the bike. It also takes much longer to wear than a chain, so much less maintenance will be required on this bike than many other bikes available. 

The flywheel is a perfect weight and sits at 40lbs. The flywheel is the big wheel at the front that you must drive around. Having a heavy flywheel makes the bike feel much sturdier and gives the bike a lot of stability. 

It has a magnetic resistance system which is very impressive. Magnetic resistance systems are what they call frictionless. A Frictionless system doesn’t require a brake pad like many spin bikes do. This will use magnetic force to create resistance on the flywheel. To increase the resistance, all you have to do is turn the dial in front of you while on the bike. This brings the magnets closer to the flywheel creating a heavier resistance the closer it gets. 

It is a fantastic system and again removes the need for maintenance. The bike’s drive chain makes it extremely quiet, and if you live in a flat or terrace house, your neighbors probably won’t even realize that you have a spinning bike in there. I wouldn’t tell them they might ask to use it, and you’re not going to want to share this bike as it will be your pride and joy.


The Sunny SF B1851 Synergy Pro is full of great accessories, and I feel they have done well here to add to the user experience. The bike has a performance monitor to give you metrics about your ride, and it will tell you average speed, max speed, cadence, time, distance, calories, and more.

Alongside this great monitor, you also have a heart rate monitor on the handlebars. Where you see the silver metal pads on the bar, hold this, and it will give you a heart rate reading. This is great to see how hard you are working or to ensure you are not working with too much intensity on those longer sessions.

The next is the pedals. Instead of running ordinary toe clips, the Sunny SF 1851 Synergy Pro has toe clips on one side and SPD clip ins. These are the pedals where you can clip in and use special spinning shoes. Having these pedals will save you money and time when upgrading your footwear on the bike. The saddle is of excellent quality and very comfortable. I have been on many bike saddles, and this one felt pretty cozy quickly and looks like it is built to last.

You also have a bottle cage on the fork, which I thought was a lovely touch as it keeps your drink out the way, but easy to get to while riding. On the other side of the fork, you also have a holder for dumbbells. The handlebars have a mount in the center. This is a device monitor, so you can use a tablet and spin to an application or even watch a film if you can keep up the pace till the end. 


The bike is very adjustable. Firstly the seat is four way adjustable, and the handlebar is two way adjustable. This will help you get a perfect position, and that’s going to help you on those longer rides. It can fit a rider with an inseam of 29.5” to 39.5”. This is a great range and will get the majority of people on.

sunny synergy pro dimensions

Assembly and Set up

It’s not a challenging bike to assemble. Like most exercise and spinning bikes, you will find them to come in a few parts. You will need to add the base and attach the seat and the bars. The total time to get this done should take 30 minutes but allow an hour and don’t rush it. Top Tip, make sure the pedals are tight, or you will damage the thread while riding.

The Sunny SF B1851 Synergy Pro vs. The Sunny SF B1805 Indoor bike

Sunny Health Magnetic Bike SF-B1805

Priced usually under $600, this model offers users an experience often reserved for higher-priced options. This quiet belt-driven model includes a heavier front flywheel weighing in at 44 pounds.

Amazon Reviews

A great bike to compare the Sunny SF B1851 to is the Sunny SF B1805. They are both in a similar price range and have very similar specifications. They are incredibly different bikes though, so let’s go into that.

  • Firstly design, as I discussed before, the Synergy Pro is a much sleeker design. It is bigger and has oversized tubing. This makes it look like a much more expensive bike than it is and does give it a nice edge. The Sunny B1805 does look much more basic and a little cheaper than the B1851. They both still look good, but I feel the B1851 would suit a pro gym better. Internally they are very similar because they are both belt drive and magnetic.
  • One of the most significant differences is the handlebars. They both have a tablet holder, but the B1805 is missing the monitor. It does make it much easier to see what you’re doing when you have a monitor. Also, not having a heart rate monitor makes it difficult to know where your body is while training.
  • The next big difference is the quality of the saddle. The B1851 has a much more stealthy quality saddle than the B1805, which has a larger, more basic saddle.

They are both great bikes, but the B1851 does come out on top, in my opinion.

The Sunny SF B1851 vs. The Schwinn IC4

Schwinn IC4 Bike

Comes equipped with Bluetooth connectivity, allowing you to link to several apps such as Peloton® and Zwift®. The Schwinn really does offer excellent quality at a very affordable price.

Buy from Schwinn Holiday Sale ▶▶

Let’s come away from Sunny bikes, and let’s compare the B1851 to another branded bike for a similar price. One of the best value for money bikes on the market is the Schwinn IC4, and Schwinn is known for unbelievable quality and very reliable bikes.

The Schwinn IC4 is an excellent bike and looks great too. Many people commonly use the Schwinn IC4 as an alternative to a Peloton because of its connectivity via Bluetooth. Although it looks great, the Sunny B1851, in my opinion, looks a bit more solid and has a more attractive exterior to it. Internally, as with the other bikes, they are very similar because they are both magnetic and belt drive.

The monitor on the Sunny does give similar data fields to the Schwinn, but the Sunny has an inbuilt Heart Rate monitor. Unfortunately, with the Schwinn, this is separate and has to be worn. The Schwinn monitor does supply Bluetooth connections and also a power function. The power function is only an estimate, but it can still measure your progress. Overall the Schwinn has a better monitor.

I feel the Sunny has a better look to it and is a solid, simple bike that looks great. The Schwinn is a little more advanced with its all singing all dancing monitor, but they are both fantastic bikes.

Alternatives to the Sunny SF B1851 Synergy Pro

Sunny Evolution Pro 2

Sunny Evolution Pro II Magnetic Indoor Cycle (SF-B1986)

The 40 lb flywheel provides momentum while you ride on this low impact cycling machine. The smooth and silent belt-drive mechanism guarantees your cycle exercise will be quiet, particularly in shared spaces. 

Price & Reviews Buy from Sunny Health

The Sunny Evolution Pro 2 is an excellent bike and has a fantastic space-age look, and it also has the clout to back it up with its technology.

Sunny SF B1879 Synergy 

Sunny Health Synergy Magnetic Bike

This belt-driven bike includes a 30-pound flywheel and performance monitor. It offers pulse-sensing handlebars.

  • Use SAVE10 coupon code on Sunny Official Site for 10% OFF!
  • Free Cadence Sensor to Sync with the SunnyFit App! Applied to your Cart!
Buy from Sunny Health Amazon Reviews

If your budget doesn’t quite stretch to the Sunny SF B1851, then this is the bike you want. It’s a watered-down version of the B1851, which is brilliant. 

Sunny SF B1877

Sunny Health & Fitness Magnetic Indoor Bike (SF-B1877)

In addition to the quiet ride, this model includes a battery-operated performance monitor that displays cadence, speed, distance, calories, time, and heart rate.

Amazon Reviews

Another great alternative to the B1851 is the Sunny SF B1877. It has a lesser monitor and the same technology as the Sunny SF B1851 and is well worth looking into.

How does the Sunny SF 1851 review by others?

The Sunny SF 1851 Synergy Pro gets excellent reviews online. We get some people who don’t take to it too well, but most people love it. One common issue is that if you are below 5ft 3”, you might find it harder to get the proper position, besides that, glowing reviews.


Sunny doesn’t offer an excellent return policy. They offer 180 days on parts and labor and 3 years on the frame. This is ok, but the normal on other spinning bikes is about a year. The Schwinn has a better warranty, and I hope Sunny will change this in the future.


Sunny SF 1851 Synergy Pro
-$300 OFF + Free Cadence Sensor ($70 Value)
Sunny Health & Fitness Synergy Pro Bike

Includes a 40lb inertia-ready flywheel belt drive mechanism to provide a smooth & quiet ride. Its magnetic resistance provides quick, easy, & reliable resistance changes.

  • Use SAVE10 coupon code on Sunny Official Site for 10% OFF!
  • Free Cadence Sensor to Sync with the SunnyFit App! Applied to your Cart!
Buy from Sunny Health Amazon Reviews

Whatever bike you pick, you’re going to get a lot of value out of it. I personally love the Sunny SF B1851. The Schwinn is great, but I love the design and the simplicity of the Sunny. It’s a great bike well worth the money.

Robbie Ferri CPT

Robbie from “Riding with Robbie” is a Personal Trainer living in in Norfolk, UK. He has bikepacked all over the World, and also raced ultra distance at a top-level. He has worked closely with industry leaders such as Shimano.

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