Sunny Health & Fitness Premium Smart Bike Review: Heavy Flywheel, Manual Resistance

The Sunny Health & Fitness Premium Smart Exercise Bike, model SF-B1805SMART, is the brand's attempt at a proper studio bike rather than another cheap upright. It sits at £599.99 on Amazon UK, verified in stock on 3 August 2026, which puts it in an awkward and interesting spot: roughly double the price of the £300 magnetic bikes that fill the category, and roughly half what a Keiser or a top-spec Schwinn will cost you. The pitch is heavy hardware for the money, and on that count it mostly delivers.

The headline numbers are a 44lb (20kg) flywheel, a quiet belt drive, magnetic resistance across 16 micro-adjustable levels, dual-sided pedals that take SPD cleats or ordinary trainers, and a 300lb frame rating (Sunny Health & Fitness SF-B1805SMART official product page). That is a lot of bike per pound. The word doing the heaviest lifting in the product name, though, is "smart", and it needs unpacking before anyone spends £600 on the strength of it.

What "smart" actually means on this bike

Resistance is adjusted by hand. There is a tension knob under the handlebars, you twist it, and the magnets move closer to the flywheel. The app has nothing to do with it.

This is the single most common disappointment with bikes marketed as smart, so it is worth being blunt about. On this Sunny, the Bluetooth connection is one-way in the sense that matters: the bike sends your cadence, speed and distance to the SunnyFit app, and the app displays them, logs them and plays a class over the top. When an instructor says "add two turns", you add two turns yourself. Nothing happens automatically, no virtual hill will make your legs suddenly heavier, and no class will hold you at a target power number. Bikes that do that use electronically controlled resistance and start well above this price.

Whether that bothers you depends entirely on how you train. Plenty of experienced riders prefer a knob, because it is instant, silent and never lags behind the instructor. If you have come from a gym spin class you will find it completely familiar. But if your mental picture of a smart bike involves the machine adjusting itself while you concentrate on your legs, this is not that bike, and no amount of firmware will make it one.

Who it is for

The SF-B1805SMART suits someone who wants the feel of a studio bike, will ride it several times a week, and does not want a monthly subscription attached to it. Riders stepping up from a wobbly budget machine are the obvious audience, along with anyone who mainly rides to their own plan or a YouTube class and just wants the hardware to be solid underneath them. If you ride twice a month for gentle cardio, this is far more bike than you need and our best exercise bike UK guide has cheaper, lighter options that will do the job. If you specifically want app-controlled resistance, skip straight to our best smart exercise bike UK guide, because that is a different shopping list.

Build and ride feel

The flywheel is the reason to buy this bike. At 44lb it is heavier than almost anything else at £600, and you feel it within about thirty seconds of getting on: the pedal stroke carries through smoothly rather than stalling between downstrokes, and standing efforts do not set the frame rocking. Cheap spin bikes with 8kg or 10kg flywheels feel skittish and hollow by comparison, and that difference is what separates a bike you keep from one that ends up under a duvet in the spare room.

The belt drive is quiet enough for early mornings in a flat, and unlike a chain there is nothing to lubricate or re-tension. Magnetic resistance helps here too, since the magnets never touch the flywheel; there is no felt pad to wear out and replace, which is the standard failure point on friction bikes at this money. Sunny quotes 16 micro-adjustable levels, running from level 1 up to level 16.

One honest gap: Sunny publishes the 16-level figure but does not publish a numbered readout on the knob or the console, and the monitor tracks calories, distance, odometer, pulse, speed and time without showing a resistance number. That makes repeating an exact effort from one session to the next harder than it is on a bike like the Schwinn 800IC, where the numbered dial lets you return to the same setting every time. You end up going by feel and cadence, which is fine for general fitness and less good for structured progression.

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The SunnyFit app, and what it does not do

Sunny states on its own app page that SunnyFit is free to download and free to use, with no subscriptions and no hidden fees, and the app FAQ repeats it in the same words. That is not a trial or a stripped-back tier; the trainer-led sessions, the scenic World Tour routes, the workout history, the challenges and the leaderboards all sit behind no paywall at all. Set against a Peloton subscription, which runs into hundreds of pounds a year, this changes the real cost of ownership more than any hardware spec on the page. Sunny's app page also mentions links to Apple Health and Google Fit, with Samsung Health listed as in development.

The content itself is decent rather than special. Class production values, instructor charisma and music licensing are all a visible step below Peloton, and if you have ridden both you will notice within one session. Volume is not the problem; polish is.

On third-party apps, be careful. Sunny does not claim Zwift, Peloton or Kinomap support anywhere in its published material, and its SunnyFit FAQ specifically says non-Sunny equipment is not officially supported by the app, which tells you how narrowly the ecosystem is drawn. We could not verify that this bike broadcasts to third-party training platforms, so we are not going to imply that it does. What you can always do is prop a tablet on the holder, play whatever class you like, and turn the knob yourself. Since the resistance is manual regardless, following a Peloton class by feel works about as well here as it would on any other knob-controlled bike.

None of that stops the bike doing the actual job. The NHS asks adults for at least 150 minutes of moderate activity a week, or 75 minutes of vigorous activity, and cycling counts in both columns depending on how hard you push (NHS physical activity guidelines for adults aged 19 to 64). That target is achievable on this bike, and the payoff is measurable: a 2025 study in the European Journal of Sport Science found that around 150 minutes of cycling a week over 10 weeks raised relative VO2max by 10.5% in the cycling group while the control group dropped 2.8% (Effects of Commuter Cycling on Physical Activity, Cardiometabolic Health and Body Composition).

Fit, footprint and the assembly problem

The adjustment range is one of the bike's quieter strengths. Seat and handlebars both move four ways, the quoted inseam range runs from roughly 29.9 to 40 inches, and the seat-to-handlebar distance spans 17 to 21 inches, so two people of different heights can share it without a fight. The 300lb rating is more generous than most rivals at this money and speaks to how the frame is built.

The pedals deserve a mention because they are frequently misread. One face takes SPD cleats, the other is a caged pedal with a strap for ordinary trainers, so you can start in whatever shoes you own. If you want the clip-in side, budget separately for cycling shoes and cleats; nothing suitable comes in the box, and that is easily another £60 to £100 on top of the bike.

Assembly is the part owners grumble about most. The machine weighs 125.7lb, most of that concentrated in the frame and flywheel, and getting it out of the box and upright alone is genuinely awkward. Set aside an hour, clear the floor, and find a second pair of hands if you possibly can. Once it is built, the transport wheels let you tilt and roll it, but the footprint of roughly 50.8 by 23.4 inches means it wants a permanent home rather than a corner you tuck it into.

Where £600 puts you

This is a bike that competes on hardware and loses on electronics. Against the £300 to £400 magnetic bikes, the Sunny wins clearly: heavier flywheel, higher weight rating, better adjustment, dual-sided pedals, a free app that is more than a stopwatch. Against the tier above, it is outclassed on precision and consistency. The Keiser M3i is a different class of machine in ride quality and durability at a much higher price, and the Schwinn 800IC gives you numbered, repeatable resistance levels and broad third-party app support for a meaningful premium.

So the calculation is simple. Pay £600 here and you get most of the physical experience of a serious studio bike and none of the subscription. Pay more and you buy repeatability, app integration and finer control. Neither answer is wrong; they suit different riders. If you want to compare across the whole price range first, our best spin bike UK guide lines them up side by side, and the exercise bikes hub covers uprights and recumbents too.

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