CUBE Bikes Reaction GTC SL 29  2016 Mountain Bike Review

CUBE Bikes Reaction GTC SL 29 2016

Reviews / Hard Tails

CUBE Bikes 402,599

At A Glance

The Reaction SL is a race ready full carbon 29er with speed on its mind and not much else. Aimed at the rider looking for a fast XC bike that isn’t going to break the bank it sits just below the Elite models in their XC race range. Two sizes are available in 27.5 wheeled guise, 16” and 18” and then there is a full range of sizes for the 29er version that we have on test here.

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If you are looking for a carbon race machine, a marathon tamer or just a fast bike for long days in the saddle, the Reaction should be on your shopping list!

Tech Heads

Cube has been at the forefront of carbon frame technology for some time now and that shines through. The Reaction uses their Grand Turismo Composite for which they use a twin mould method that creates a smooth internal frame surface that helps keep weight down and strength up.

The down tube is a monster, which shouts stiffness, the top tube is a broad flat affair that is super comfortable should you end up shouldering the Reaction for any reason. The chain stays are beefed up and the seat stays are more about rigidity than flex. A tapered head tube ensures accurate steering and a bolt through rear hub keeps the back end taunt.

Kit wise Shimano XT takes care of the braking and drivetrain, the latter being a 2 x 11 set up. There is a Fox 32 FIT4 100mm fork plugged in up front; the three modes can be toggled through via a bar mount lever. Wheels are Fulcrum Red 66, with Schwalbe Rocket Ron and Racing Ralph tyres complete the package.

Finishing kit includes a Cube seat post topped with a Stella Italia saddle. Cockpit wise, Cube provide a 100mm stem, 720mm flat bar and lock on grips.

Cube GTC Reaction SL 21’’

Seat tube 515mm
Effective top tube 628mm
Head tube 125mm
Chain stay 435mm
Front triangle 692mm
Wheelbase 1127mm
BB height 305mm
Head angle 70°
Seat angle 73°
Reach 434mm
Stack 637mm

Weight w/o pedals 24.1lbs

On The Trail

Jumping on board the Cube I was relieved to find that the bike was not as stretched out as I had feared it might be. For a 21” frame the effective top tube length is 628mm, which is fairly short for a bike of this size.

I'm on the bike and I have dabbled with the fork, which is excellent by the way, and I start to ride…this is the moment it begins.

Wow, it is fast.

I take off up the fire road from where I park and I just don't stop. 14 miles later and my regular training loop is done, the light is fading, I make a snap decision and stamp hard on the pedals, the Cube GTC Reaction SL bursts forwards and I give it everything I have for the next 14 miles.

At 24lbs, I expected the Cube to climb well and it did not disappoint.

The Reaction SL comes with a 2 x 11 drivetrain sporting 36T and 26T front chainrings. I can only imagine the 26T is there for the Marathon guys that spend hours riding up Alpine fire roads. I never even came close to using the 26T and at times, I was scurrying up some near vertical wet and muddy climbs, the amount of traction I was able to find with racing tyres on beggared belief.

Get the Reaction onto woodland singletrack and general trails and it is like the speeder racing scene from one of those War Stars movies, mind-bogglingly fast and quite frankly addictive. Again grip was better than I would ever have dared hope from the Rocket Ron up front, yes I found its limits but they exceeded my expectations.

But what about when the going gets steep, the Achilles Heel of XC orientated bikes… The Cube GTC Reaction SL handled moderate downhill sections very well; the fork is well controlled, and the longer reach due to the large size gave predictability that meant I managed to clear sections at a greater pace than expected. Obviously, it’s a racer at heart, so it isn’t going to be comfortable smashing its way down Fort William. It is however surprisingly capable, and that is a testament to the bike's design and cockpit layout!


It is fast.

Great value, I was amazed when I found out that this model retails for around £1600 in the UK. For that, you get a great frame, an excellent fork and a very solid kit list.

It is light but could easily be lighter, go to 1 x 11 for no cost and lose a chunk of weight. Then you can work on switching carbon with the finishing kit.

Tyre clearance is good, meaning some bigger rubber could be fitted for comfort or grip. I even managed to get 27.5+ 2.8 tyres in there, which made the Cube a real hoot.


I have just sat and looked at the Reaction SL for 5 minutes trying to find fault. At this price point, I can find none; each piece of the bike worked flawlessly and the whole comes together as more than the sum total of the parts. I would probably lose that 26T for the type of riding I do though.


What my time on the Cube showed me more than anything else is that I need/want a lightweight short travel hardtail in my life - soon! Wow… Oh, and did I mention that the Cube GTC Reaction SL is fast?

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This review was in Issue 39 of IMB.

For more information visit CUBE Bikes


By Nigel Garrood
Nigel Garrood was one of the instigators of the IMB project and has been with us since the very beginning. This loveable rogue has more stories than the Bible and is known to enjoy a beer or two. On the bike, he’s fast and loose and often puts younger riders to shame. Equally he’s been known to suffer from the odd crash and carries the scars to prove it. He was once referred to as being a robot sent from the future to save us all!

Tried this? What did you think?