Review: GT Marathon Carbon Expert

By Shannon Mominee

Tester: Shannon Mominee
Age: 37
Height: 6′
Weight: 180lbs.
Inseam: 33"

Vital Stats
Country of Origin: Taiwan
Price: $3200
Weight: 27.3lbs. w/pedals
Sizes Available: XS, Small, Medium, Large (tested), XL
Contact: www.gtbikes.com

In 1973, Gary Turner began making BMX bikes in his garage for his son to race, and in 1979, he teamed up with BMX racetrack operator, Richard Long, and formed the brand GT. Together they manufactured and marketed chromoly steel BMX bikes, then in 1984 they entered the mountain bike scene. In 1999 GT introduced the i-Drive Independent Drivetrain technology and produced a new breed of rear suspension.

As a kid, I marveled at GT’s freestyle and BMX bikes, with their mag wheels and cool frame designs, and longed to have one. My interest in bouncing around on one wheel steadily switched to skateboarding and then to mountain biking. Now to come full circle, GT’s 2010 Marathon Carbon Expert came to me for testing and I’m still marveling at their engineering.

The Marathon Carbon Expert, the base model of the four-bike Marathon line, features 100mm of front and rear travel. The Expert component package is built on the same carbon fiber, monocoque frame as the other Marathons and uses GT’s i-Drive suspension design. Internal cable routing, two bottle cage mounts, and a metal guard plate over the bottom bracket are standard.

Since the introduction of the i-Drive, the system has undergone improvements and re-designs (see Dirt Rag issues #135 and #110 for past reviews). But the heart of the i-Drive has always been its isolated bottom bracket. With help from the dogbone-shaped i-Link, the isolated BB minimizes chain growth to reduce pedal feedback, but maintains just enough chain growth to tune in some pedal-induced anti-squat for better power transfer to the rear wheel. The Marathon’s two stout pivot points are stacked above one another and each slightly more forward of the bottom bracket. The pivots use 1-1/8" angular contact headset bearings that easily adjust for proper bearing preload.

Setting up the suspension was hassle-free. GT recommends 20% sag, so I pumped 140psi in to the Fox Float RP2 (with Boost Valve) to achieve 10mm of sag. I settled on three clicks from fastest rebound and toggled between ProPedal settings. Rockshox’s Recon Race handles front shock absorption with 100mm of air-sprung travel, compression and rebound adjustment, and lockout. A guide on the left lower helped with determining correct pressure and I settled on 100psi in both positive and negative chambers. I was surprised and relieved that I didn’t have to tinker further with air pressure settings once I left the garage and could concentrate on just riding. A Mavic Crossride wheelset with Kenda Karma 2.0" tires; Shimano SLX drivetrain, shifters, and hydraulic brakes with 160mm rotors; Ritchey Pro bar, stem and post; and a Fi’zi:k Gobi XM saddle completed the parts package.

After a city ride to set up the controls and saddle, the maiden dirt voyage was an epic six-hour grinder on the Pinhoti Trail system in northern Georgia. Once my riding friends and I got over the novelty of the tube shapes, 5-6 miles of climbing was the icebreaker. With the ProPedal turned on, the Marathon is a steady climber on mostly smooth logging roads with just a small amount of movement from the RP2 (only noticeable if I looked down at it). The rear wheel maintains traction over trail debris with slight shock compression, and overall the i-Drive seemed efficient.

When ProPedal was off, the bike still climbed really well, but the RP2 compressed further when rolling over trail features. Pedaling in any of the front three chainrings had the same smoothness, with minimal effect on the suspension and no chain growth to interrupt my cadence. Standing to climb, the front bounced around more than the rear, so I would lock the Recon out and sit to transfer as much power to the rear wheel as possible. At 27.3lbs. the Marathon is a pound or so heavier than other 4" full suspension carbon bikes I’ve tested, but it didn’t feel like it, nor did I get ping-ponged around in the rough.

Heading downhill, I switched the platform off and let the Marathon rip. The i-Drive maintains ground contact superbly, and there were times at speed when I should have caught air, but instead, the shock moved through the travel and the wheels barely broke contact. Set up as such, the Marathon sticks so firm that it required more effort than normal to bunny-hop. I never noticed any harsh feelings, weirdness, clunks or bottoming out of the suspension, even though the dust ring was always 3-4mm from the end of the shaft after riding.

On dry trails, I could hit the corners hard, tilt back upright and be back on the gas without any ghost shifting. I’ll credit that to the isolated BB. The 73° seat tube and 71° head tube angles made the riding position aggressive and placed my weight forward in the cockpit. Handling is fast and the 16.9" chainstays track quickly, but the bike always felt squarely under me. The Marathon went where I wanted and the stiff carbon frame added to the prompt point-and-go characteristics. At 13.1" the BB is plenty high, so clipping the pedals wasn’t an issue. Actually, I don’t think I even crashed this bike or flatted. Woohoo!

I would have liked the steerer tube to be about 10mm longer, because after two hours in the saddle my back began to hurt, even with the stem in its highest position. The Kenda Karma tires left traction to be desired when the trails were wet and I often wished for sintered brake pads for more stopping power, but I got used to braking earlier and keeping the speed in check for traction. The Gobi XM saddle doesn’t fit my anatomy and I dreaded sliding forward on steep climbs. Sitting for 2-5 hours didn’t help my arse either, but the saddle must fit someone or it wouldn’t be made.

The Marathon Expert is a good offering for the $3200 price. The components are race-worthy, and should prove durable. It shouldn’t be a problem finding replacements for the suspension bearings after they wear out, and GT’s website has video instructions for dismantling the suspension if need be. I had fun riding the Marathon and enjoyed its easy setup and smooth suspension. If you’re looking for a 4" travel bike to race and ride all over the backcountry for hours at a time, this could be the bike for you. The frame is warranted for three years.