THROWBACK THURSDAY: GT’S FULLY ACTIVE LTS

Too much is never enough

GT didn’t stun the world when the company put the RTS full-suspension bicycle on the market in ’91. After all, this was a manufacturer that had made a living from off-center, cutting-edge designs that flew in the face of tradition. With the acceptance of front suspension, it was only a matter of time before the braver bike brands would delve into rear shocks. While most rear suspension designs (at least the good ones) sprang from the minds of ex-motorcycle racers (e.g., Robert Reisinger, Horst Leitner, Doug Bradbury, etc.), GT’s RTS was a rising-rate linkage system designed by a race car designer. So far, so GT.

The RTS was a good first shot at the full-suspension market, but it had some genetic weaknesses: Its rising-rate linkage made the shock less effective at singletrack speeds; its high-pivot swingarm caused considerable wheelbase change and created a chain-length problem; the suspension was immobilized under braking and pedaling forces—it was non-active. Remember when front suspension was new? Everyone cranked up the spring pressure way high to keep the fork from moving under pedaling pressure. After a while, riders began to soften the forks as they adopted new riding techniques to take advantage of suspension. Well, the same is true with rear shocks. GT fell into the intellectual trap of designing a new concept around old thinking and experience. Its race team, accustomed to rigid bikes, wanted their suspension bikes to feel like rigid bikes under pedaling loads. So, the RTS delivered the feel the racers wanted; however, active suspension was catching on, and once RTS owners realized the benefits of full suspension, they were sure to want a more supple ride—a feel the RTS is incapable of providing.

So, how did GT go about solving this dilemma? They didn’t change the RTS, which had a strong following; instead, they built a totally new bike—the LTS. Its purchase order had two requirements: (1) Fully active rear suspension and (2) overall weight light enough to allow it to be raced in cross-country events. The LTS is a parallelogram, scissor-link suspension attached to a straight-laced, alloy-diamond front section (which surprisingly bears no resemblance to its RTS sister ship). The LTS does display GT’s penchant for the bizarre and its reputation for bombproof reliability. If you can judge a book by its cover, the LTS should be the perfect second-generation full-suspension bike from the blue-and-yellow team.

The MBA test crew spent a couple of months hammering the GT LTS. Here are the test riders’ most common questions and answers.

 

QUESTION ONE: WHAT IS PARALLEL-LINKAGE?

If you don’t mind a little grease, look under the family sedan. Chances are the front suspension is a parallel-link setup. The seatstays on the LTS and the front wheels of most midsize autos have a swingarm on the top and bottom. This allows the suspension to travel in a different arc from a single link. A rear wheel attached to a conventional swingarm orbits around the swingarm pivot on the frame and the rear axle, period. By using links of different lengths and shuffling the location of the pivot points, a clever suspension designer can cause the rear wheel to scribe a vertical line, an “S” curve or even an arc opposing the swingarm’s radius. An example of this phenomenon is the rear derailleur’s parallelogram, which tracks the rear cogs in a negative arc. For auto designers, the parallelogram setup keeps the tire level with the pavement as the car leans over in a curve. For GT’s LTS, the dual links make the rear wheel travel on a vertical plane so the wheelbase remains more constant.

QUESTION TWO: IS THE LTS SUSPENSION ACTIVE?

Yes, Virginia, the LTS is an active system. The greatest advantage of the LTS’ linkage is its ability to isolate braking and pedaling torque from the suspension. Chain tension, the nemesis of bicycle suspension, tugs on the seatstays. Because the swingarm and upper member pivot at 90 degrees to the seatstays, there is no resistance to vertical movement. Braking pushes on the upper link and pulls the swingarm, but the results are similar. The shock is free to do its thing on the vertical plane, unaffected by braking forces.

If this reads too tech for your diet, ride the LTS and bounce up and down while ascending a paved hill and the shock will operate easily (the same will be true on the way down under braking).

Mismatch: There are two camps in the linkage army. One believes in rising rate and the other in straight rate. The LTS’ rising-rate rear end was in constant disagreement with the relatively linear Rock Shox fork. Take the time to dial in the LTS and the ride can be harmonious.

 

QUESTION THREE: WHAT’S WITH THE FUNKY SCISSOR SHOCK?

To reduce weight without sacrificing strength, the LTS’ Fox air/oil shock is compressed between the seatstays and the upper link. This eliminates the extra bracing and triangulation that would be necessary if the shock were mounted on the frame. The LTS suspension feeds stress into the frame at the intersection of the bottom bracket and the top tube, which requires little extra reinforcement beyond the amount of metal necessary for a standard diamond frame.

QUESTION FOUR: WILL THE LINKAGE GET SLOPPY?

In time, all suspension bikes will wear out (except Allsop beam rear ends). The more moving parts, the quicker a small amount of wear will add up to a wiggly bike. GT’s engineers have taken great care to extend the life expectancy of the LTS. Working against them is the fact that the LTS’ parallelogram linkage requires 10 bearings (twice as many as a MacPherson rear end). Special Kevlar-reinforced composite bushings at each pivot and a unique taper-lock system to eliminate end play in the bearing shafts are GT’s main weapons against premature aging of its rear end.

Room for less: The Horst Link dropout is one hefty unit. In the modern world of CNC-tortured aluminum components, GT’s larger-than-life dropouts have the look of a car bumper. GT’s designers don’t care; they didn’t want flex at any cost.

 

QUESTION FIVE: CAN A MULTI-LINK SYSTEM BE RIGID?

GT’s image in the fat-tire world is strength. To maintain this reputation, the LTS is way overbuilt. The upper link is investment cast from titanium for extra rigidity; the seatstays are ovalized and the shock mount is actually a long gusset that reinforces the curve in the upper section. There are no larger Horst Link dropouts on Earth. Both the swingarm and upper link pivots are also larger than life.

To further ensure that the LTS will track a straight line, the frame’s front triangle uses a 1.75-inch-diameter downtube, a 1.25-inch seat tube and a 1.5-inch top tube. The frame is overbuilt and oversized but not necessarily overweight. The complete bike weighs 24 pounds, which places the frame at just about 5 pounds even.

Riding the LTS proved that GT’s efforts were not wasted. The bike could be sprinted or hammered in a big gear without a hint of lateral flex. To be sure, the suspension could be felt as the bike was accelerated. It is an active system, but the movement wasn’t accentuated by chain torque or linkage slop. In this aspect, the LTS is one of the MBA test riders’ top-rated full-suspension bikes.

Another secret: To offset chain-tension-induced suspension action, the LTS’ swingarm pivot is elevated above the bottom-bracket center line. Variations in swingarm pivot location allow designers to fine-tune the degree of chain torque. The GT was spot-on, because it soaked up a bunch of punishment under full climbing power.

 

QUESTION SIX: HOW DID THE SUSPENSION PERFORM?

The GT LTS was a top performer in the suspension department, but there was a glitch that reared its ugly head. There was an imbalance between the straight-rate spring and damping up front in the Rock Shox Judy SL fork and the LTS’ rising-rate linkage and Fox air shock. The Judy fork has a micro-cellular foam spring, which has a compression rate similar to a coil spring. The LTS has a Fox air/oil shock. Air springs have a progressive spring rate (this means the air pressure increases in proportion to the amount of shock travel). The linkage is designed to be slightly progressive also. There is no doubt in the test riders’ minds that the LTS would work better with a coil spring shock, like the Noleen NR-1 shock off of the RTS.

The result of this imbalance is that the rear end forces the front to do all the low-speed, small-impact work, and it feels like the Judy is being overtaxed in medium-sized bumps. To compensate, MBA switched the Judy’s bumper stack to the stiffest ones, which forced the rear end to work harder over the bumps. We then added speed and small-impact work, and it felt like the Judy was being overtaxed in medium-sized bumps. We then added 5 pounds more air pressure to the shock to keep the suspension operating on the least progressive initial part of its travel. The MBA mods helped balance the LTS well enough that we were able to enjoy the bike’s active suspension without having the fork blow through its travel on every impact.

Climbing traction was greatly increased over the RTS due to the active rear end’s ability to closely follow the earth’s surface. This was a great benefit, especially considering that the Psycho Racing K rear tread and steep, 75-degree seat-tube angle were negative factors in the traction department. The rear tire and forward rider position made out-of-the-saddle efforts a bit of a hassle up sketchy climbs. Extra care was required to prevent wheelspin. The LTS was at its best at speed, especially over rolling terrain. The LTS leveled any trail surface and felt like a time-trial road bike. Test riders would simply steam away from the pack the moment a long stretch of rough double-track appeared. This was especially true up long sections of middle-chainring ascending.

To reduce weight without sacrificing strength, the LTS’ Fox air/oil shock is compressed between the seatstays and the upper link. This eliminates the extra bracing and triangulation that would be necessary if the shock were mounted on the frame.

 

QUESTION SEVEN: HOW WAS THE OVERALL FEEL?

GT has learned from years of pro racing that fluff belongs in pillows. The LTS was equipped with the venerable Shimano XTR group. The only upgrade on our test bike was a pair of White Industry hubs and GT’s new ball-and-socket alloy quick-releases. No squeaky CNC-machined cranks, no stupid compact drive! Nope, just a well-thought-out XTR—the stuff racers use. Syncros made the seatpost and zero-rise 135mm alloy stem, and the handlebar came from Keith Bontrager (titanium, of course).

Astride the LTS, the rider felt at home. It was roomy. The controls were in the right place, and the geometry kept enough weight on the front tire to keep it carving around turns while relaxing in an efficient cycling position. In a word, the LTS felt “right.”

In the air, this was a bike with wings.

 

QUESTION EIGHT: HOW DID THE LTS HANDLE?

Typical GT. No fancy dancer, but the bike wasn’t a plow horse, either. The LTS went where it was pointed and favored fast going over a slight reluctance to carve twisty singletrack. In the air, this was a bike with wings. Even traditionalist Felix Unger was attempting a set of double jumps. For new racers searching to purchase some confidence, try your local GT dealer. The major complaint from the MBA crew was poor out-of-the-saddle climbing traction—such a shame on a bike that loves to be hammered.

QUESTION NINE: HOW DID WE LIKE IT?

Some test riders raced the LTS to victory; the rest simply enjoyed the ride. If they would have asked us before they built the RTS, we would have told them that this is the bike GT should have built in the first place. If you are entertaining the thought of racing or are a full-time dirt rider, the LTS is a true second-generation, cross-country-capable suspension bike.

If we had our druthers, we would opt for a coil-spring shock absorber and swap to a more aggressive rear tire. Purists had to ask if all of the LTS’ parallel-link-suspension monkey-motion is necessary. It could have been achieved with fewer parts. The Syncros stem outdoes the Answer Attack unit for the largest-hunk-of-aluminum-for-no-apparent-reason award. While the Syncros’ size doesn’t detract from the 19-inch LTS’ performance, it looks like it should be a cannon support on a Hummer. If any company has a future in fat tires, GT does. The LTS tells us that the fastest-moving bicycle company in the USA is headed in the right direction. 

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