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Up next in the series we take a look behind the numbers of the GT Force.
It was exciting times when GT released the Force and Sensor. Their previous bikes were always a bit wacky, and while some of the theories they used were interesting, they were probably best left as theories. Which is why when they quietly dropped all their prior quirks and adopted a proven layout lots of us sat up and looked a bit harder at their bikes.
Force Analysis Details
Travel Rear: 150mm to 152mm
Travel Front: 160mm
Wheel Size: 27.5
Frame Size: L
COM Height: 1150mm
Chainring Size: 32T
Cassette Cog Sizes: 50T, 24T and 10T
Many bikes of today are converging on a similar Horst link rocker layout, and for good reason. It’s naturally a stiff and light layout, it can generate good suspension curves, and amongst the details there’s room for a water bottle. But the Force could be seen as a good example that simply just changing to this layout is not job done. No matter what layout you go for, you have to work hard to position all the pivots well and get good curves, surrounded by good geometry and packaged in a form that is durable, reliable and up to the task of mountain biking.
The Force has a leverage ratio progression of 12.9% with an average ratio of 2.75 in the low chip, and there's 13.4% progression with an average ratio of 2.77 in the high chip. The bike has a similar shaped curve to the Specialized Stumpjumper EVO, with a progressive to linear curve in low chip and a linear/progressive/linear in high chip.
There’s more progression than the Specialized, which is good, but overall the ratios are a bit on the high side, down to their choice of a 55mm stroke shock. For example, a 60mm stroke shock would have given an average ratio of 2.5, and a 65mm stoke would have further lowered it to 2.3.
Lowering the leverage ratio would bring more balance to the spring/damping equation - right now it might be a touch too much in favor of the spring. And longer stroke shocks are easily available. Perhaps design got priority and they didn’t want to push the rocker link farther up the seat tube, but it looks like there was room to do it and line up the seat stays really nicely with the top tube.
To be a fly on the wall in the development meetings would provide the reasons as to why they chose this.
A touch of over-springing might be needed on this bike to provide some support. Again, it’s dependent on the aggression level of the rider and their desired output from the bike, but it’s not as much of a predicament as the Specialized. If the rider wants to use most of their travel most of the time, and never really hucks to flat, then it should all be okay. But the pilot style riders might be looking to add some psi and a volume spacer or two to help hold the bike up.
More progressively damped shocks are going to help out on these lower progression bikes. There would still need to be a bit of over springing, but the amount of Newtons of damping support that can be added with a progressively damped shock will help support the bike and resist its want to over use travel.
The GT is constantly below 100% anti-squat in all settings and gears and even in the least regressive setting, 32/50, it still quite low at sag and only getting worse the more into travel you’re going.
Riding along a smooth climb, with smooth pedaling and this might be okay. But, factor in impacts while climbing and non-smooth pedaling technique on a technical climb, for example, and more of the rider’s energy input into the pedals is going to be wasted rather than being used to push the bike forward.
Again, we have another bike in the enduro category that dips below 0% anti-squat. The industry really isn’t doing much to help Mike Levy’s hate of lockout levers
The anti-rise curve is pretty nice, rising as it goes through the travel. If it was a bit higher up in percentages then this would further reduce any of the vague feeling at the rear wheel that comes from really low anti-rise figures, as well as give a touch more support to the rider.
However, it’s a smooth curve with reasonable numbers and doesn’t drop off the farther into travel you go. That should provide some nice mechanical support when the going gets tough. And given the combo of leverage ratio and anti-squat, you might be spending more of your time at the second half of travel rather than being nicely supported and held up higher in the travel.
The axle path is predominantly forwards in its trajectory. But really only a true high pivot bike is going to show a vast difference here, and then it’s going to have some compromises in other aspects of the suspension.
But, the Force hasn't got the big forwards travel of the Stumpjumper. Among all the bikes analysed so far, the axle path could be the least perceivable characteristic. Someone would have a hard time singling out the axle path differences between the GT, Specialized and Marin on the trail. The combination of leverage ratio, anti-squat anti-rise and geometry are going to have more of a say in the characteristics of this bike, and it’s only when you go to an extreme that the strength of the axle path characteristic flavor is going to be more noticeable
There’s a more pronounced difference between the high and low chip settings, but this also is apparent in the geometry change between the two settings. Due to the long link lengths and the chip being in line with the shock it doesn’t translate into vast differences in suspension characteristics. Final Thoughts
Previous Behind the Numbers Articles:Marin Mount Vision Suspension AnalysisStumpjumper EVO Suspension AnalysisIntroducing Behind the Numbers - A New Suspension Analysis Series