With a course consisting almost entirely of fire roads with only a handful of sections of singletrack, most riders will be seen on hardtails with 29 inch wheels. Full-suspension would be excessive on this course.
Because the majority of the course is fairly smooth without any excessively steep climbing, there is always the temptation to ride a cyclocross bike to save a little bit on weight and reduce the rolling resistance with narrower tires, but some of the rocky sections act as a deterrent.
Even with the mellow profile and smooth roads, the course has a history of causing flat tires, mostly through sidewall tears, so those choosing to run ultra lightweight tires are definitely running a risk. An ideal compromise would be a tire along the lines of the 1.9 Kenda Karma or a 2.1 Maxxis Crossmark, both of which are fast-rolling and lightweight but will hold up clattering over some rocks.
Riding a bike without front suspension would also be an option for this course to save a little weight, but due to the length of the race and the fatigue caused by the rockier sections, Maines says that “There are enough bumps over 104 miles to merit front suspension for most folks.”