I can most assure that they do given the right conditions and course. We did the Copper En Fuego Winter Mountain Bike race this weekend. While not all the top finishers were on fat bikes it sure made a HUGE difference. Only two or three of the top 15 were on "skinny" tired mountain bikes. Was able to hang with the pros/former pros on my moonlander even though I am just a Cat 4 rider. It was amazing at the mass start of 162 riders to watch those with fat bikes just motor ahead. There was even a difference between those on Moonlanders and 3.7" tire bikes. Granted, this was on parts of the course where the snow had been gone over with a groomer and you could punch through knee deep in places.
My teammate was on a bike with Nokian studded tires. We are at the same fitness level and he wished he had a fat bike as he was amazed at where racers could ride and where they had to walk/run their bikes depending on how fat their tires were.
Whenever anyone asks if it really makes a difference, I respond that it depends like everything else in the world. I did ride a good way up the ski slope that other bikes could not due to the larger tires. But then again most of us do not ride at ski resorts...
Some highlights of the race:
Having the starting gun be fireworks.
Racing at night in the Colorado Mountains with head/bike lamps and steam rising from all the racers.
A super steep downhill next the tubing hill (superior crashes at the 90 degree corner at the base of that!)
180 degree corner off icy pavement down a short steep hill onto the ice skating pond then cross style dismount and run up two flights of stairs.
Two way traffic on part of the course in the dark with blinding headlights coming at you.
Jack Frost screaming in your ear as your heart and lungs are almost exploding
Free Dale’s Pale Ale and a G’Knight (8.7%) with a free pint glass after the race!
Hearing dudes complain after the race about riding regular mountain tires and that is was no fair.
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