Full Speed Ahead, better known as FSA, has been extremely successful making carbon components such as cranks, bars, stems, and carbon road wheels, and they have used their knowledge to produce a line of mountain bike wheels. This line up consists of their XC Race wheel, the K-Force; the XC model, the SL-K; and the trail-oriented Afterburner.
All three of these models are designed with the exact same measurements: 25mm deep x 26mm wide on the outside, and 21mm on the inside. This is fairly narrow compared to most rims as the industry is shifting to a wider rim. This may be a turn-off for some riders but this size works great for FSA’s target market: racers.
The rims are designed with an asymmetrical shape (4mm offset). This design allows them to increase spoke tension by 20%, thereby cutting the spokes from the standard 32 to 24 to save weight, while still creating a very stiff and rigid rim. Despite having few spokes these rims are very tough. I really put the SL-Ks through the ringer here in rocky Colorado and they held up great.
These wheels are laced up to FSA’s “Quick-Draw” hub which has six prawls, three of which are engaged at any given time creating 54 points of engagement. This makes for a very quick transfer of power from the pedals down to the dirt.