adidas · Exercise Bike Review

adidas C-21x Review 2026

By Chris Linford · Updated June 2026 · Rated with FitRank

The adidas C-21x is a proper indoor cycle wearing the three stripes. A heavy 16kg rear-drive flywheel, an 8-level manual resistance paddle and Bluetooth for Zwift, Peloton and Kinomap, with a chest strap in the box, for £699 down from £900. It is the stronger of adidas’s two bikes and a genuinely capable spin bike.

adidas C-21x

Bluetooth indoor cycle

4.0/5

FitRank

Very good

Performance4.1

Build4.1

Value3.7

Features3.9

£699£900

Save £201 Check price at Sweatband

Price and any sale applied at Sweatband

The verdict

The C-21x gets the fundamentals of a spin bike right. The 16kg rear-drive flywheel is genuinely heavy, on a par with our top spin picks, and it stores enough momentum to give a smooth, road-like pedal stroke that lighter bikes cannot match. The 8-level resistance paddle adjusts manually and instantly, the way a gym spin bike does, so you can stand up and crank the load mid-sprint without clicking through electronic steps. With a sprint saddle, SPD-compatible Jendel pedals and fully adjustable bars and saddle, it is built for committed training.

It backs the ride with sensible connectivity and a few flourishes. Bluetooth links it to Zwift, Peloton and Kinomap with no subscription of its own, a chest strap is included for accurate heart rate, and there is a dual bottle holder and a tablet shelf. The honest caveats are that resistance is manual rather than app-controlled, so it will not auto-adjust in a class, there are only four onboard programmes, and the £900 list price leans on its frequent discount to £699 to make sense. The Ultra Series LED lighting that glows as you pedal is pure gimmick. But as a heavy, quiet, well-made spin bike, the C-21x delivers.

Ride feel and real-world experience

On the bike, the C-21x rides like a serious spin bike, and the heavy flywheel is why. At 16kg it matches our top spin picks, and that mass carries real momentum, so the pedal stroke is smooth and road-like rather than light and choppy. It feels planted and stable under a hard, standing effort, and owners consistently describe it as reassuringly heavy and very quiet, which it is.

Resistance works the traditional spin-bike way, and that suits some riders more than others. Rather than stepped electronic levels, you shift an 8-level paddle by hand to add or shed load, which is instant and intuitive for sprints and intervals, you just push and go. The trade-off against electronic systems is that it will not auto-adjust to follow a class, and the eight broad steps offer less fine granularity than the C-24c’s 32 electronic levels. For hard, self-directed spin work, the paddle is arguably better; for app-controlled training, it is a limitation.

The setup is built for proper riding. The streamlined sprint saddle adjusts horizontally and vertically, the handlebars are fully adjustable with armrests, and the Jendel pedals take SPD cleats or trainers with toe straps. A chest strap is included for accurate heart rate, there is a dual bottle holder and a tablet shelf, and the signature Ultra Series red LED lighting glows as you generate energy, which looks striking but adds nothing to the workout.

Assembly, size and setup

The C-21x arrives boxed for home assembly, and being a heavy spin bike it is a more substantial build than a light upright, so a second pair of hands helps with the flywheel end. Most people will have it together in around 45 minutes to an hour with the supplied tools. Once built it is heavy and stable, and it sits on transport wheels so you can tip and roll it into place. Check the pedals and bolts are fully tight after the first few rides.

Living with it: noise, footprint and storage

The heavy flywheel and belt-style rear drive make the C-21x quiet and smooth, so it suits a flat or shared home, and its weight keeps it planted during hard efforts. It is a full-size spin bike rather than a folder, so it wants a permanent spot, though the transport wheels help you reposition it. Upkeep is minimal beyond a wipe-down and a periodic bolt check, and the dual bottle holders are a practical touch for longer sessions.

Apps and connectivity

The C-21x connects over Bluetooth to Zwift, Peloton and Kinomap, so you can ride virtual routes, follow live and on-demand classes and gamify your sessions on your own tablet in the integrated holder. There is no adidas subscription: you bring whichever app you like on its own pricing, and a 60-day Kinomap trial is included to get you started. The one thing to understand is that, because resistance is manual, the apps cannot control it for you, so when a class calls for more resistance you shift the paddle yourself rather than the bike adjusting automatically. The included chest strap feeds accurate heart rate into the apps.

How it compares

At £699 the C-21x lines up against the Reebok Z-Tech Sprint, also £699, which counters with electromagnetic, app-controlled resistance that auto-adjusts in a class, where the adidas uses a manual paddle. Our top spin pick, the JTX Studio Pro, matches the 16kg flywheel for £799 and adds a stronger warranty, also without a subscription. Within adidas, the C-21x is the spin-focused alternative to the upright C-24c: choose the C-21x for harder, athletic training and the C-24c for comfortable steady cardio.

Similar spec, different brand: you may want to consider the JTX Studio Pro, another no-subscription spin bike with a matching 16kg flywheel, for £799.

Who it is for

Buy the C-21x if you want a serious, heavy-flywheel indoor cycle, you like manual paddle resistance for sprints and intervals, and you want Zwift, Peloton or Kinomap without a subscription, with the adidas design as a bonus. If you would rather the resistance adjusted itself in a class, the Reebok Z-Tech is the electromagnetic alternative at the same price; if you want our top-rated spin bike, the JTX Studio Pro is the step up; and if you would rather have a comfortable upright, look at the C-24c.

Specifications

Warranty and after-sales

adidas covers the C-21x with a 2-year home-use warranty, which under the brand’s licensed terms is typically on-site (including the drive) in the first year and bring-in in the second. It is sold through Sweatband and Decathlon, so register on arrival if prompted and keep your proof of purchase. That is a reasonable term, though specialists like JTX sometimes offer longer cover on comparable spin bikes.

FitRank breakdown

Frequently asked questions

Chris Linford · Fitness equipment reviewer
Chris writes the home fitness reviews across our sites, including our sister site HomeTreadmill.co.uk. He compares every machine against its rivals on UK pricing and specs, and scores each one with FitRank.

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