Because the Whiskey 50 course has such a wide variety of conditions, bike choice is all about weighting the pros and cons of different bike setups.
Because of the significant amount of climbing and the relative steepness of it, bike weight plays a more important role than it would on a flatter course. Thus, the long pavement climb off the start and the 15-mile climb out of Skull Valley would favor a lightweight hardtail.
On the other hand, the descents are rocky, rooty, and loose, catering to those running full suspension. Full suspension also helps reduce overall wear and tear on the body, a factor that becomes important after several hours of racing.
While it’s often accepted that races are won on the uphill sections of a course rather than the downhill, the descents in the Whiskey are technical enough that a good rider piloting a bike with slightly more suspension could make up a significant amount of time on the downhill sections on a rider on a bike with less suspension.
Wheel size also presents a similar dilemma on the Whiskey course. The road sections, and especially the descent to Skull Valley and the flatter parts of the climb back up favor 29 inch wheels, but much of the singletrack is either turning right or left and is peppered with tight switchbacks which would swing the advantage back to 26 inch wheels.
Tire choice is also a balancing act. The dirt roads and paved sections, in addition to the never ending uphill, cry for a fast rolling, light weight desert tire that corners well in loose conditions. But too light of a tire is asking for a sidewall slash, especially on the descent of trail 260. A tire with strong sidewalls and fast rolling tread seems to be the ideal compromise.
In the end, bike set up will be rider specific. A lighter rider would probably benefit the most from the weight savings of a hardtail for the climbing and could get away with lighter tires while a more aggressive, heavier rider would appreciate the added security of a full suspension rig and sturdier tires.