Trail Test - GT Sensor 9er Pro
These days there’s no shortage of 29er bikes on the market, however the majority of them are pegged at the cross-country crowd, with steep-ish geometry and travel that tops out around 100mm. That’s all starting to change however, with the brave few pushing big-wheeled bikes into the hands of more aggressive riders by offering slacker geometry and more travel than previously thought viable for a 29er.
The Sensor 9er Pro from GT is one of these bikes, offering 120mm of travel front and rear and a reasonably slack (for a 29er) 69.6-degree head angle; its full intention is to tempt riders away from their 130-150mm travel 26-inch bikes and into the world of big wheels. One of the strongest temptations is certainly value for money, with Fox suspension at both ends and a full XT drivetrain, combined with Formula’s RX brakes, seeming almost too much bike for the $3,699 asking price. There’s also a cheaper ‘Elite’ version available with X-Fusion and Marzocchi suspension, a basic FSA/Shimano Deore drivetrain and Avid Elixir 1 brakes for $2,399. Our large-sized test bike weighed 12.68kg without pedals, of which 3,016g was comprised of the frame and shock; not bad at all for a well-priced longish longish-travel 29er.
The Sensor 9er’s ‘Speed Metal’ (aka 6061) aluminium frame uses a combination of post-dressed and standard welds and there’s nothing wrong with the overall construction quality. GT have made a conscious effort to keep things colour-coded with plenty of blue anodised bits to match the frame decals and this works to an extent, although depending on your tastes it could be a little over the top. Definitely a case of form over function is the seatpost quick release, which wraps so far around the post that it’s difficult to both open and close; there’s a reason why the majority of clamps use a relatively straight blade, and that’s because it works. The stem top cap is meant to be cool-looking, but in truth it’s reminiscent of a miniature circular saw blade, and almost as sharp. Do what we did and get this thing off the bike before you ride, lest part of your anatomy suffers the unpleasant consequences.
The Sensor 9er’s cable routing looks relatively clean and it’s good to see full length outer casing on all cables to keep things shifting smoothly in adverse conditions. Unfortunately all three of the cables rubbed heavily into the seat tube of our test bike, and without disassembling the bike it’d be difficult to put frame patches where they need to be in order to adequately protect the frame (you’d be replacing them frequently, too). Without some effective frame protection, we could easily imagine the seat tube incurring some serious wear within 12 months.
GT have been using their patented I-Drive suspension system, in various forms, for over a decade. It’s been constantly refined to the point where it performs as well as any other suspension system on the market, and better than many. The high main pivot gives the back wheel a very pronounced rearward axle path, which provides the Sensor 9er with about the best square-edged bump absorption you’ll find. Combine this with the excellent roll-over performance of a 29-inch wheel and the big GT is virtually unstoppable when it comes to rough terrain.
The other side of the GT’s suspension is that, because the bottom bracket ‘floats’ between the front and rear triangle, there’s minimal chain growth and pedal feedback, so even under power the back wheel keeps on sucking up the bumps without unduly interrupting your pedalling rhythm. Plenty of people in forum-land bag the I-Drive system without having ever ridden it; take one for a spin and, understand it or not, you’ll become a firm believer in the quality of this design. On buff trails it doesn’t really have the chance to show its full potential, but in the rough it truly shines.
It’s safe to say that 29-inch wheeled mountain bikes are still in their developmental phase. They’ve changed a lot from the early generation bikes that were built before designers and manufacturers had figured out what works and what doesn’t. This is even more the case for bikes like the Sensor 9er, which are forging into new territory in terms of 29er wheel travel and geometry.
Whilst all bikes and designers will have a slightly different set of priorities, there are a few things that seem universally agreed upon when it comes to bikes with big wheels. Firstly, handlebar height and head tube length needs to be kept down in order to compensate for the longer axle-crown length of 29er forks. Secondly, oversized frame tubes and tube junctions are your friend when it comes to countering the higher lateral and torsional forces applied by bigger wheels. And thirdly, nothing boosts rear end stiffness like a thru-axle.
It’s curious then, that the Sensor 9er sports none of these things; the quick release drop-outs and spindly rear triangle seem quite out of place, and no doubt contribute to the significant twist and flex you can feel both off the bike and once you get it on the dirt. It’s at the front end, however, where things really buck the trend. The head tube measures 140mm, which makes it 20-30mm taller than most other 29ers of this size. Compounding this, GT has spec’d a headset with a 15mm top cap rather than the lower 5mm option, and instead of using a tapered head tube and fork to increase stiffness at both the head tube/down tube junction and the crown/steerer interface, they’ve chosen to go with a straight 1⅛-inch steerer and 44mm inner diameter head tube. The icing on the cake is the 90mm long high-rise stem.