B’Twin Ultra 520 AF GF Rival Disc review£1,200.00

An alloy all-rounder worth online browsing for?

BikeRadar score4.5/5

Decathlon’s hypermarché house brand has given us yet another top-value alloy all-rounder that shames a lot more expensive bikes.

Coming in at just under £1300, you might expect some compromise with the alloy chassis, and at a claimed 1470g (M) it is fairly heavy. The only obvious cost-saving elements are the external gear cables and brake hoses, although they are bonuses in terms of minimal friction gear operation and easy servicing.

The full carbon fork aids the Ultra’s accurate steering and handling feel
The full carbon fork aids the Ultra’s accurate steering and handling feel

B’Twin Ultra 520 AF GF Rival Disc frame and kit

The mainframe tubes are triple butted (three different thicknesses in each tube) and the rectangular top tubes and down tubes are smooth-welded onto a short (150mm) tapered head tube. Add the 390mm reach for a potential predatory ride position, if you remove all the carbon-fibre spacers.

It would feel even more speed-focused with a normal bar rather than the stumpy 75mm-reach Deda drops, and SRAM levers that naturally bring your hands in close to the bar. The tall SRAM lever hoods give a good handhold for dropping your elbows and getting aero.

Opening the throttle confirms that the press-fit bottom bracket and deep tapering chainstays give forthright power delivery to the 142x12mm rear axle. A chainstay flat mount for the 140mm rear brake keeps the back-end neat too.

Judging by the space around the 27mm-wide Mavictyres there’s easily room for 30mm rubber or clip-on mudguards. The lack of any proper mudguard or rack mounts is definitely a fail on what could otherwise be an outstanding winter club run/commute/group training bike for the UK.

B’Twin Ultra 520 AF GF Rival Disc ride experience

Wet arse and dirty face aside, the Ultra still managed to distinguish itself on grimmer test days thanks to the sticky compound of £70 worth of Mavic Yksion Elite Guard tyres.

Add a low-slung frame, in terms of standover height, and these give the B’Twin a surefooted feel despite a middling 72.5-degree head angle and metre-long wheelbase.

The quality Fizik Antares saddle makes the Ultra a forgiving place to sit
The quality Fizik Antares saddle makes the Ultra a forgiving place to sit

The stiff Mavic Ksyrium wheels and tapered steerer, full carbon fork and boxy frame give it an accurate steering and line-holding character. 

Where B’Twin wins is that the triple-butted maintubes and single-butted chainstays keep this stiffness just the right side of harsh. The tyres stay tracking well even when the surface is more track than tarmac, and I never suffered from vibration numbness even on long rough rides.

The low frame gives 30mm more exposed seatpost to flex and soak up shock than the Canyon. Add the top-quality Fizik Antares saddle and the Ultra is a forgiving place to sit, particularly if you get caught out by a sudden pothole slam.

The braking is well modulated, the extended lever hoods feel more secure than low, smooth levers like the new Ultegra, and once you’re used to the one-lever-does-it-all actuation, rear shifting is good and front shifting is okay thanks to the Yaw cage angling tech.

The B’Twin Ultra 520 AF GF Rival Disc is an all-round distance package that’ll look after you well while still feeling dynamic and alive enough for shorter, sportier rides, B’Twin has done a brilliant job with the Ultra.

Guy Kesteven

Freelance Writer, UK
Guy started filling his brain with cycle stats and steaming up bike shop windows back in 1980. He worked the other side of those windows from '89 while getting a degree in “describing broken things covered in mud" (archaeology). Dug historical holes in the ground through the early '90s, then became a pro bike tester in '97. Guy has ridden thousands of bikes and even more components the world over since then and can remember them all in vivid, haunting detail. Can't remember where the car keys are, though.
  • Age: 45
  • Height: 180cm / 5' 11"
  • Weight: 68kg / 150lb
  • Waist: 76cm / 30in
  • Chest: 91cm / 36in
  • Discipline: Strict sadomasochist
  • Preferred Terrain: Technical off-piste singletrack and twisted back roads. Up, down, along — so long as it's faster than the last time he did it he's happy.
  • Current Bikes: An ever changing herd of test machines from Tri bikes to fat bikes and everything in between.
  • Dream Bike: His Nicolai Helius AM custom tandem
  • Beer of Choice: Theakston's Old Peculier (not Peculiar)
  • Location: Yorkshire, UK

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