By Paul Kendrick, Cardio & Endurance Editor · Updated 12 October 2026
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Sunny Health & Fitness
The Sunny Health & Fitness Premium Magnetic Exercise Bike (model SF-B1805) is a very good spin bike to ride and a so-so one to own at UK prices. You get a 20kg flywheel, silent magnetic resistance, a belt drive and a 136kg user limit in a 57kg frame that doesn't shuffle about when you sprint. What you don't get is a screen, Bluetooth, numbered resistance levels or clip-in pedals, and at £461.53 on Amazon UK that's a lot to leave out. I'd score it 4.0: buy it for the ride, not the spec sheet.
It's also the bike that already sits at the top of our best spin bike UK guide, so this review goes into more detail on why it earned that spot and where the cracks show.
How we review
We haven't ridden this bike. This review is built from Sunny Health & Fitness's published specifications and user manual, the Amazon UK listing, recurring patterns in verified owner feedback, and direct comparison with the other exercise bikes we've reviewed. Where Sunny doesn't publish a figure, we say so rather than guess.
This bike suits someone who wants a heavy, quiet, studio-feel ride and is happy to supply their own entertainment. If you follow YouTube or app classes on a tablet, ride mostly by feel and want a frame that won't wobble under a 100kg-plus rider, it fits well.
Skip it if numbers matter to you. Anyone working through a structured plan with target cadence, watts or repeatable resistance levels will find the SF-B1805 frustrating, because it gives you nothing to measure against. You'll also want to look elsewhere if you're tight on budget, since £460 buys a lot more features from other brands.
Sunny's official product page lists the SF-B1805 with a 44lb flywheel, magnetic tension, a 300lb maximum user weight, a 28 to 38 inch inseam range and a 3-year frame warranty (Sunny Health & Fitness SF-B1805 product page). The spec list doesn't include a monitor, which matches what owners report.
| Model | SF-B1805 |
|---|---|
| Flywheel | 44 lb / approx 20 kg |
| Drive | Belt |
| Resistance | Magnetic, micro-adjustable twist knob (no numbered levels) |
| Console | None listed |
| Connectivity | None |
| Seat adjustment | 4-way (up, down, fore, aft) |
| Handlebar adjustment | 4-way |
| Seat to handlebar distance | 17 to 21 in |
| Inseam range | 28 to 38 in (approx 71 to 97 cm) |
| Max user weight | 300 lb / approx 136 kg |
| Pedals | Steel toe cages with straps |
| Dimensions | 48 L x 23 W x 45 H in (approx 122 x 58 x 114 cm) |
| Unit weight | 125.7 lb / approx 57 kg |
| Extras | Tablet holder, bottle holder, transport wheels, emergency stop brake |
| Warranty | 3 years frame, 180 days parts and components |
The flywheel is the reason to buy this bike. At 20kg it's heavier than most home spin bikes at this price, and that weight carries you through the top and bottom of each pedal stroke instead of letting the cranks go dead. On a light-flywheel bike you feel a slight hitch twice per revolution; here the stroke is round and continuous, which is the closest a stationary bike gets to rolling on a road.
Magnetic resistance pairs well with it. Nothing touches the flywheel, so there's no squeal, no felt pad to glaze over and no dust. It's the main mechanical difference from the cheaper Sunny Pro SF-B1002, which uses a friction pad on a slightly heavier 22kg flywheel. The friction bike feels a touch more like grinding up a hill under heavy load, but its pad wears and eventually needs replacing. The SF-B1805 asks for none of that upkeep.
Stability is the other strong point. A 57kg machine on a wide base with floor stabilisers doesn't rock when you stand to climb, and that mass is what backs up the 136kg rating. Heavier riders tend to feel the difference between this and a 30kg budget bike within a few pedal strokes.
Sunny lists an emergency stop brake; on studio bikes like this it's operated through the resistance knob. Learn to use it in your first session, because with 20kg spinning beneath you the pedals will keep turning if you simply stop pushing.
Both the seat and the handlebars adjust four ways, and that matters more than most buyers realise. Fore and aft handlebar movement lets shorter riders bring the bars closer without cramping, while taller riders can push them out and avoid a hunched back. Sunny quotes a 28 to 38 inch inseam range (about 71 to 97cm), so measure your inseam rather than going by height if you're unusually short or tall.
Set the saddle so there's a slight bend in your knee at the bottom of the stroke. Our guide to exercise bike seat height walks through the heel method if you've never fitted a bike before; getting this wrong is the commonest cause of sore knees on any spin bike.
The saddle is a firm, narrow studio shape, and saddle comfort is a common complaint with this style of bike. A gel cover is a cheap fix, though padded cycling shorts usually help more.
There's no monitor. Not a basic one showing time and distance, nothing. For some riders that's fine: they prop a tablet in the holder, follow a class and judge effort by breathing. For anyone who wants to see whether this week's ride was harder than last week's, it's a real gap.
The cheapest fix is a clip-on cadence sensor and a chest strap paired to a phone app. A decent heart rate monitor gives you an objective effort measure that's arguably more useful than a cheap console's calorie guess anyway. Budget £40 to £80 on top of the bike for that setup.
The micro-adjustable knob gives a smooth, stepless range, and that's genuinely pleasant to ride. The trouble is repeatability. If a session calls for four minutes hard and two minutes easy, you can't write down "level 14" and hit it again next week. You end up counting quarter turns of the knob, which works, but only roughly. If you plan to follow an exercise bike HIIT workout with set targets, pair the bike with a heart rate strap and steer by heart rate zones instead.
The steel toe cages with straps are sturdy and work with any trainer, but they don't hold your foot as securely as clipless pedals at high cadence. Experienced cyclists will want to swap them for dual-sided SPD pedals, which adds cost and a spanner job. The Sunny Premium Smart Bike (SF-B1805SMART) ships with dual clip-in and cage pedals as standard.
Sunny is an American brand, and the SF-B1805 reaches Amazon UK as an import. Sunny's own US store has listed it at $599.99, and the £461.53 UK price is roughly that figure converted at current rates. It isn't gouging, then, but it also doesn't adjust for the fact that UK rivals at this price routinely include a screen and Bluetooth. Measured against what else £460 buys here, it's expensive.
This is the comparison that hurts the Sunny most. The JOROTO X4S is £399.99 on Amazon UK today, around £60 cheaper, and it adds a backlit LCD console, Bluetooth with app support including Kinomap, and a readable numbered resistance dial. Its user limit is higher too, at about 150kg.
What the X4S doesn't do is publish a single flywheel weight to match the Sunny's 20kg figure; JOROTO describes a dual flywheel system instead. If ride feel is your priority and you'll never look at a number, the Sunny's heavy flywheel is the known quantity. For nearly everyone else, the X4S is the better buy, and we rate it higher (4.4) for that reason.
Check JOROTO X4S price on AmazonThe smart version shares the same 20kg flywheel and frame, then adds a digital monitor (calories, distance, odometer, pulse, speed, time), Bluetooth to the free SunnyFit app, 16 marked resistance levels and SPD-compatible pedals. When we reviewed it, it was £599.99 on Amazon UK. That's about £140 more for fixing every complaint in this review. If you were going to buy a cadence sensor and SPD pedals anyway, the gap narrows to well under £100, and the smart bike is the more sensible choice.
The SF-B1002 costs roughly £300 and has a heavier 22kg flywheel, but its friction pad resistance wears over time and it also has no console. Its user limit is lower at 125kg. If budget matters most, it delivers a similar ride for £160 less; if you want silent, maintenance-free resistance and a higher weight limit, the SF-B1805 justifies the step up.
Yes, if you ride consistently. A 2019 systematic review of 13 studies found that indoor cycling may improve aerobic capacity, blood pressure, lipid profile and body composition, with the strongest weight and blood pressure results when it was combined with diet changes (Chavarrias et al., Medicina, 2019). The authors flagged a lack of randomised controlled trials, so treat those findings as promising rather than settled.
For a practical target, the NHS recommends adults get at least 150 minutes of moderate activity or 75 minutes of vigorous activity a week (NHS physical activity guidelines for adults). Five 30-minute rides at a conversational pace hits the first; three 25-minute interval sessions gets you to the second.
Sunny supplies tools, hardware and a user manual in the box. Allow an hour and get a second pair of hands, because the main frame is heavy. Once built, the transport wheels at the front let you tip and roll it, though at 57kg you won't want to move it daily.
Maintenance is light. Wipe sweat off the frame after each ride, check the pedal and crank bolts every few weeks, and keep an eye on the belt tension. There's no chain to lube and no pad to replace.
Check Sunny SF-B1805 price on AmazonNo. Sunny's own specification for the SF-B1805 does not list a monitor or console, and there is no Bluetooth. You get a tablet holder instead. If you want speed, cadence or calorie numbers, add a cadence sensor or a heart rate strap and use a phone app, or look at the SF-B1805SMART, which adds a digital monitor and the SunnyFit app.
Sunny rates the frame to 300lb, which is about 136kg. That is a generous limit for a home spin bike, and the 57kg unit weight helps it stay planted when a heavier rider stands up out of the saddle.
Not numbered ones. The magnetic resistance is set with a micro-adjustable twist knob, so you can nudge the effort in tiny steps but there is no level 1 to 16 printed anywhere. That suits riding by feel and following classes, and it makes repeating an exact interval session harder.
Not out of the box. It comes with steel toe cages and straps. The pedal threads are a standard size on most spin bikes, so many owners swap in dual-sided SPD pedals, but check the thread before you buy any, and remember the smart version already ships with clip-in and cage pedals.
For ride quality, yes: a 20kg flywheel, silent magnetic resistance and a 136kg limit is a strong mechanical package. For features, it's poor value. The JOROTO X4S costs less on Amazon UK and adds a console and Bluetooth, so the Sunny only makes sense if you specifically want its heavier, simpler ride.
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