Even though a fat ski may have greater weight-distributing surface-area measurements, the skinny ski still wins in a glide race because there's less resistance perpendicular to the direction of travel. More simply: The fatty creates more drag. That's true only on hard snow, though. In soft snow, all that width lets fat skis float more easily through powder and crud so you can open up the throttle a bit. That same soft snow will swallow (and thus slow) a narrower ski. So why can fat skis feel like Speedy Gonzalez underfoot? Their relatively shallow sidecuts are straighter than those found on hard-snow skis, which insist on turning all the time. Remember: "Turning" is just another term for "braking." Fat skis, like old-school GS boards, barely bother with sidecut, and thus sprint downhill.
Since fat skis have more surface area than regular skis, are they faster?