- sleek looks
- caveman-easy to install
- smooth, precise shifting
- stiff, efficient power transfer
- works with 9-speed drivetrain as well as 10
- long-term durability yet to be determined
Source: bike shops, catalogs
Warranty: two years
Weight: 710g with MegaExo bottom bracket for compact and standard; 750g for triple
Chainrings: 34/50 (compact), 39/53 (standard), 30/39/53 (triple)
> Crankarm lengths: 165, 170, 172.5, 175mm
How obtained: sample from company
RBR advertiser: no
Tested: 40 hours
Carbon cranks have been with us for a while. The technology continues to evolve with lighter, stiffer versions that employ increasingly advanced technology. FSA’s 2008 SL-K Light crankset is a case in point, employing new manufacturing processes to give a roadie every advantage possible.
The SL-K Light uses the same Hollow Carbon Crank design as FSA’s more expensive K-Force Light. That crank weighs a scant 660 grams, but the SL-K Light is barely 7% heavier while saving $250.
The SL-K Light is part of an FSA crankset family that has shown unmatched stiffness in independent testing. In fact, FSA says its top-of-line K-Force Light has the highest stiffness-to-weight ratio of any crank on the current market, including the Campagnolo Record Ultra Torque, Stronglight Compact Pulsion and the SRAM Force GXP.
In order to create a crank of similar stiffness, yet at a lower price point, FSA incorporates fiberglass in the SL-K Light’s monocoque construction. There is no internal metal skeleton. The arms also have a slightly different mold shape and surface layup. The chopped-carbon-fiber look is more like that of the Campagnolo Record Ultra Torque than the fiber weave found in the K-Force Light.
The SL-K Light crankset includes a MegaExo external bottom bracket with oversized cartridge bearings. This BB significantly increases the stiffness of the crank/axle unit thanks to two significant design improvements:
- The hollow axle is 24 mm in diameter rather than 22 mm as used by the ISIS and other bottom brackets. This may seem minor, but according to FSA stiffness increases as a square of diameter and torsion goes up exponentially.
- The bearings are farther from the center to shorten the lever arm, which further reduces possible flex in the axle.
One of the best features of an external bottom bracket is the simplicity of installation. It could not be more straightforward. Simply thread each bearing unit into the frame, push the axle through (the right crankarm is connected), and attach the left crankarm with an allen wrench.
One catch: You need a special external BB installation tool. I used the one made by Pedro???s, which accepts a socket wrench or adjustable wrench and has a textured surface to make initial threading by hand very easy. Make sure to put the specified torque on the bolt that holds the crankset together. It requires an 8-mm allen wrench and that’s larger than you probably carry on a ride. You don’t want the crankarms loosening miles from home.
On the Road
The SL-K Light crankset is 10-speed compatible, but it ran smoothly and shifted crisply when mated to my 9-speed drivetrain. In fact, it shifted better than the 9-speed Dura-Ace crankset it replaced.
Switching from the D-A crank also shaved about 118 grams (4.2 oz.). This difference was noticeable while riding. The SL-K Light crank spun up quickly and felt stiffer during sprinting and climbing. I especially liked the crankarms’ smooth contours and ample ankle clearance.
The SL-K Light is available with standard, compact or triple chainrings. The 34/50-tooth rings in the compact option produce a wider gearing range, but I opted for standard 39/53 rings like my old setup so I could focus on the crankset rather than the gearing change. The chainrings are CNC machined and use Torx bolts.
One reason roadies like carbon frames and parts is the material’s ability to smooth the ride. Although the evidence is anecdotal, carbon seems to absorb high-frequency vibration while remaining stiff against low-frequency, propulsive forces. Does this apply to a carbon crankset? Perhaps it could if you are coasting over rough roads while standing on horizontal crankarms, but I tend to pedal most of the time. Stiffness is more important to me, and the SL-K Light is plenty stiff.
FSA offers a two-year warranty against defects in materials, and a crash program that knocks 35% off the MSRP of a replacement crank if you break the original in a wreck.
The SL-K Light will definitely add bling to your bike. But that’s not why I would recommend this crankset. More important is the fact that it can significantly reduce rotating mass and improve drivetrain function and efficiency. At an MSRP of $450 (smart shoppers can do better by at least $50) it’s a relatively affordable upgrade that you’ll feel — and begin appreciating — on the very first ride.
Joshua Cohen is a physical therapist and designer of the Kontact Saddle. He wrote his graduate thesis on male ergonomic bicycle seat design. Then, distilling his voluminous scholarly research, he wrote Finding the Perfect Bicycle Seat and, more recently, The Illustrated Guide to Bicycle Seats. Both eBooks are available in the RBR eBookstore.