The 4.0 is the cheapest of GT's four-bike Sensor line-up. It shares a frame with the £2,699 Sensor 1.0, so it’s not surprising that a few component compromises have had to be made to get it in under £1,000.
The Sensor is a lesson in how spec listings, geometry tables and weights don’t tell the whole story. If you were choosing a bike from catalogues you could easily discount the GT, but it’s a great deal more entertaining than you might expect.
Ride & handling: Trail-munching suspension and rewarding handling deliver a fun ride
On paper the GT doesn’t look like it has much going for it. At 32.4lb (14.7kg) it’s heavier than a lot of its price rivals, largely thanks to a component selection in which every part is a notch or two down from the best of the competition.
Transmission is Shimano Alivio throughout, without even a Shadow mech to draw attention, brakes are Tektro Dracos, there’s an FSA square-taper crank and lots of GT-branded bits. But you quickly forget all that out on the trail.
The Sensor is a whole lot of fun, thanks largely to conﬁdent yet agile geometry combined with a very contemporary short-but-wide cockpit. It’s also got GT’s Independent Drivetrain suspension, the latest incarnation of the venerable i-Drive setup.
Being effectively a high single pivot, you get a useful bit of rearwards wheel movement that makes the Sensor super-smooth over smaller obstacles like sets of roots, but the i-Drive gubbins stop the pedals kicking back at you on bigger hits.
It works very well, delivering benevolent cat-like landings off drops and uninterrupted pedalling through chop. The downside of minimal pedal feedback is a degree of mushiness under aggressive pedalling that the simple X-Fusion shock is ill-equipped to control, but keep things smooth and it stays well behaved.
Frame & equipment: Occasionally twangy back end; poor spec compared to the competition
The Sensor has a distinct family resemblance to GT’s all-mountain Force and Sanction bikes, but it’s an altogether more slender bit of kit, especially the back end, which is distinctly slimline. Tucked away around the bottom bracket area are the linkages and pivots that make the Independent Drivetrain suspension system work, with an articulated bottom bracket connected to the mainframe with a forged rod.
This unique suspension design gives the supple rearward axle path of a high single pivot while moving the bottom bracket around to minimise chain growth and hence pedal feedback. A mostly-straight down tube gets a little ﬂare as it reaches the head tube, while the top tube gets the full swoopy hydroforming treatment to give it that GT look.
The shock placement right in the middle of the front end forces the bottle bosses to the underside of the down tube, which isn’t the most convenient spot for them. The shape of the frame allows a particularly direct route for the fully-enclosed rear gear cable which is secured alongside the brake hose by bolt-on clips.
The Sensor forgoes the usual RockShox Recon forks found at this price in favour of Suntour’s Raidon fork. It’s a budget option but we were pleasantly surprised by its smooth and quiet performance. They might be anonymous unbranded parts, but the Sensor’s short stem and 28in low-rise bars play a big part in the bike’s ready-for-anything feel.