Available with 39/27, 40/27 or 42/27-tooth chainrings, 170mm or 175mm crank arms, and to fit BB386 or BB30 bottom brackets, the K-Force Light Compact is one of FSA’s lightest cranksets.
It boasts wide-profile carbon composite crank arms that flare into a three-armed spider with a wide chainring contact area, all designed for a combination of minimum weight and maximum stiffness. The splined axle is tough chromoly steel, the chainrings are CNC-machined 7075 aluminium with profiling to ensure super-smooth shifting, and the chainring bolts are Torx headed aluminium. It's compatible with nine- and 10-speed chains.
Durability of FSA’s superlight MegaExo bottom brackets is good. If you really want carbon cranks these are among the best available, but we've always had a problem with the way composite cranks quickly look scruffy on the surface. Cheaper and lighter alloy doubles are available that stay looking good for a lot longer and perform on a par.
Also consider: FSA SL-K Compact 386 MegaExo, £520. FSA also produce a lightweight SL-K crankset for about £80 less that uses carbon arms with an aluminium skeleton. Its weight and durability is almost identical.