The B’Twin Rockrider AM 100S is available with three different wheel sizes. From smallest to largest, the same bike takes 27.5in, 27.5 Plus and 29in wheels

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When the Rockrider first showed up for test we thought we’d been sent the wrong bike by mistake. And it’s easy to see why. We were expecting a 140mm travel trail bike to rival the Calibre Bossnut, but the array of remote cables attached to the fork and shock, combined with the 100S tag on the top tube screamed XC race bike to us.

B’Twin Rockrider AM 100S review

Rest assured, the AM 100S delivers on its suspension promise, as we measured the rear wheel travel at 139mm exactly.

Decathlon even gives you the option to add additional wheelsets for £249 at checkout. As part of its Switch and Ride program the wheels come with tyres, brake rotors and a cassette pre-installed, so you simply plug them in and go ride. Bonus!

This wheel size cross-compatibility is only possible because the dropout spacing on the Rockrider is the wider Boost standard. And it’s one of the very few entry-level full suspension bikes to use the stiffer and more secure bolt-thru 12x148mm Boost spacing on the rear.

With no geometry adjust feature to compensate for the height difference been the three wheel sizes, we opted for the smallest wheels (27.5in with 2.25in tyres) to keep the BB height as low as possible and bring extra stability to what is a relatively short bike. That was the theory at least, but with hindsight we should have opted for the fatter Plus wheels and tyres.

Manitou McLeod shock delivers 140mm of travel

Suspension

Just like with the wheels, the 140mm of travel on the B’Twin is not fixed. A twist grip remote on the handlebar is connected to the fork and shock and it lets you toggle seamlessly between three suspension modes; full open, pedal platform and locked out. It’s similar in concept to the Scott TwinLoc system but instead of the rear suspension always being one step firmer than the fork to offer a better position for climbing, B’Twin’s system seems to favour a stiffer fork, which isn’t ideal.

The range of rebound adjustment on the Manitou Machette fork isn’t ideal either. At 74kg we ran it wide open and it still wasn’t fast enough, so lighter riders will struggle to achieve an optimum set-up. Thankfully the Manitou rear shock has a much more usable range of damping adjustment.

Three remotely activated suspension modes, front and rear

Components

The stock bike comes with a rangy 90mm stem fitted as standard, but Decathlon UK was smart enough to swap it for a 60mm. Granted it’s not short by modern standards, but the frame doesn’t have the length needed to got any shorter. Experience tells us that wide handlebars always makes a bike feel bigger, so B’Twin isn’t doing itself any favours by fitting a narrow 720mm bar.

Other than the cockpit, the specification on the Rockrider is sorted. The in-house dropper post works like a charm, while the 11-speed SRAM NX drivetrain never skipped a beat. Okay so we weren’t crazy about the flat, square profile of the custom Tektro lever blades, but there’s not faulting their stopping power as they easily locked up the skinny Hutchinson tyres.

148mm Boost rear end will fit in 27.5in, 27.5in Plus and 29in wheels

Performance

Throw a leg over the Rockrider AM 100S and it’s like taking a step back in time. The narrow bar, short frame length and skinny tyres, sending out mixed messages that are somewhat at odds with it’s 140mm travel, modern Boost hub spacing and 120mm dropper.

The suspension response jars too. The default position of the Manitou shock and fork being topped out, rather than sat in the 140mm of available the travel. Taken together, the B’Twin Rockrider feels more like a hopped up XC rig than a fully formed trail bike.

And this is where the 27.5 Plus wheels would really improve matters. The extra cushioning would improved small bump sensitivity, while the much bigger contact patch would slow down the steering response and counter the relatively steep head angle.