The Force and the Sensor are GT’s all-mountain/trail platforms, sporting 150mm and 130mm travel respectively. GT has totally redesigned both, and the new versions could hardly be more different from the old. Read on to discover how and why the brand has done this, and more importantly, how the bikes ride.
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Out with the old
The previous Force and Sensor both used GT’s I-Drive suspension system.
I-Drive is, in a sense, the last vestige of the once-popular URT (Unified rear triangle) arrangement, where the bottom bracket is mounted on the swingarm, rather than the mainframe.
In GT’s I-Drive layout, the bottom bracket was mounted on a link such that, as the suspension compressed, it moved away from the mainframe, but not as fast as the swingarm.
This increased pedalling efficiency relative to a true URT design by introducing chain-growth, but allowed a more rearward axle path than a conventional (non-URT) suspension system. It was a kind of hybrid.
Now though, GT has dispensed with I-Drive altogether. It’s been replaced with a more conventional Horst-link design (where the rear axle is connected to the chainstay via pivot bearings). Interestingly, GT was one of the earliest adopters of Horst-link in mountain bikes with its LTS (linkage tuned suspension) system back in the mid-90s, but phased this out in favour of I-Drive.
Now LTS is back. It’s no secret that GT has a prototype Horst-link downhill bike (albeit with an idler), being raced successfully on the world cup circuit. What’s more, the GT enduro team have already been using the new Force all this season in the EWS instead of the Sanction. From this it looks like I-Drive may soon be consigned to the history books
The theory
GT cites reduced weight and improved reliability as key reasons for this move, but there’s more to it than that.
By going to a Horst link design, it can more easily control the levels of anti-rise (the amount by which the rear suspension tends to 'squat' into its travel due to rear braking forces) in the system. It says it's tuned the Force’s suspension to have around 40% anti-rise at sag, which is moderately low – far lower than the anti-rise figure on the old Force.
In theory, this should help the bike sit higher in its travel under braking. And, as the suspension is softer in the beginning of its travel, this should, in theory, help with sensitivity over repeated bumps when braking.
In a change of tack from the old bikes, GT openly admits the new Force and Sector are not designed to be especially pedal-efficient. There is a relatively low level of anti-squat (though not the lowest), meaning the bike will bob when pedalling; but this approach should make for suppler suspension especially under power.
The suspension is slightly progressive all the way through its travel. GT recommends setting the sag measured on the shock shaft to just under 25% when measured standing up. This corresponds to a little under 30% when measuring sag seated. The progressive leverage ratio means the sag measured on the shock stanchion will be a lower percentage than the true sag at the wheel.
Also, according to GT’s frame engineer, Luis Arraiz, the bike needs to be set up with relatively little sag. According to him, “you don’t need negative travel” (like you’d get with a lot of sag). “We feel that…with a small amount of sag, we still get that same grip and small bump sensitivity… it’s still soft enough off the top.” He went on to say that “if you set it up with more than 25% sag, it’s just going to be too wallowy”.
GT geometry
Both bikes have been made a little longer and slacker than their predecessors. That may sound like bandwagon jumping, but it’s a welcome change in my book.
There is a fashionable flip chip, which alters the head and seat angles by half a degree and the bottom bracket height by about 6mm. I left the bikes in their low setting, as usual, and in this position, the Force’s head angle is 65 degrees, and the bottom bracket sits at 339mm. The Sensor, meanwhile, is one of the slackest short-travel 29ers around, measuring 65.5 degrees in the low setting, though it’s a little higher, at 349mm.
The Force’s reach measures 440mm in Medium, and 490mm in the XL size I tested. The Sensor’s reach measurements are around 5mm longer. The Force and Sensor use 40mm and 35mm stems respectively.
According to GT, reliability was a key design consideration. While both Force and Sensor have carbon and alloy models, all use an alloy back end, which GT claims is done for better longevity (though cost must also come into play here).
Double-row pivot bearings are used throughout, along with a threaded bottom bracket in order to improve reliability and serviceability. Cable routing is external only for easier servicing, and is routed down a neat grove above the down tube.
Riding the new GT Force and Sensor
I rode the 27.5in wheel Force in Trysil bike park, Norway. The trails here are rather odd – either continually lumpy and natural or manicured smooth, with little in-between. This makes it difficult to judge the bikes comprehensively at this stage. Nevertheless, some interesting ride characteristics stood out.
The first thing to strike me about the Force was the handlebar height — it was simply too low for me even set to highest. At 190cm tall, I like a high bar, but the Force’s low stack height was confounded by a steerer tube cut very short.
The low bar undermined confidence and comfort so much that it’s hard to say too much more about the bike’s handling. I’ve spoken to GT’s Luis Arraiz about this, and he agrees it could be higher — Luis runs a 30mm-rise bar on his personal Force, along with a generous stack of spacers. Hopefully, GT will leave the fork steerer tubes longer for production bikes.
It’s also worth noting that the short stack height makes the reach feel shorter than it looks on paper because bringing the bars up to the correct height will effectively shorten the reach due to the backward slope of the steerer tube.
As for the suspension, once I had fully opened up the compression adjuster on the FOX DPX2 shock, the rear did track well over bumps, especially when pedalling. It does bob a fair amount when pedalling out the saddle though, so I toggled the shock’s lockout switch regularly when climbing.
As for the braking performance, Luis is convinced that the low anti-rise helps the rear wheel grip the terrain under braking, but I’m not so sure.
Having ridden bikes with very high anti-rise – such as Commencal’s Supreme SX – I’m of the opinion that anti-rise actually helps the rear wheel to grip better, by hunkering the bike down into its travel and better preserving its geometry in steep sections.
In my opinion, it’s anti-squat (and the associated pedal-kickback) that numbs suspension sensitivity, not anti-rise. Fortunately, at least when descending, the Force has fairly low levels of both, which helps it to track the ground even when the rear wheel is locked up. The trade-off is reduced pedalling efficiency, though this can be side-stepped with the shock’s lockout lever.
Sizing-up the Sensor
The 130mm travel Sensor 29er felt instantly more comfortable to me. The bar is a little higher (though still pretty low) and the reach is a touch longer. The 65.5-degree head angle and short, 35mm stem make it steer smoothly like a modern enduro bike, but the overall ride is surprisingly cross-country feeling.
As with the Force, the Sensor is not the most naturally pedal-efficient platform in terms of anti-squat, but it feels like there’s a decent amount of low-speed compression damping in the shock; it doesn’t bob much but feels firm over small bumps.
The Schwalbe Nobby Nic tyres use the Performance compound, which is far from sticky even on dry rocks, but rolls really fast.
The low bar again puts the rider in a fairly forwards position. This does benefit out of the saddle efforts, but compromises confidence on technical terrain. It’s more cross-country feeling than the head angle alone might suggest.
GT Force and Sensor pricing and availability
GT’s pricing is impressively aggressive for non-direct brand.
As is the custom with press launches, GT provided its top-spec Carbon Pro models to test. These cost £4,000 / $5,000 / €5,500 apiece, but the range starts at just £1,600 / $1,800 for the Sensor alloy Sport model.
The Sensor is due in bike shops around mid-August, the Force is expected around the end of August.
