Whatever you think you have in there, you could probably run a little less!
With more and more people getting on fat bikes, heading out the door and enjoying the trails, perhaps the single biggest issue isn't who is using what trail, or when, but how much air is in their tires when they're on it.
It almost feels counter-intuitive; how can tires as low as 2 psi be faster? Think of a dune buggy, which only stays on top of the sand by running very big tires at very low pressures. The higher the pressure, the more any tire holds it shape, and when the tire holds shape on snow, it not only digs in deeper, but looses traction and slides over snow instead of gripping it, no matter what tread you've got. Even if it feels supple to the touch, 6 or 7 psi is very high and is only useful on days where the trail is almost iced over and hard as asphalt, which doesn't happen all that often.
We've been in the fat bike game for years, and each and every one of our racers, friends and employees have a psi-story to tell. For JW, the gospel came from Chris Kushman, who had JW comedown from 7psi to 3 on a blustery day on the Leelanau Trail. Suddenly, instead of spinning out and sinking in, JW was staying on top of the snow, going faster, and having way more fun.
My own tale of over inflation was at the New Year's Day Ride three years ago. I was on a Surly Moonlander with wide Bud and Lou tires. After struggling behind people for the first few miles, I let some air out in frustration....too much, I thought initially. No hand pump, no co2, I hopped on the bike in a panic to catch up with Ryan Kennedy and the rest of the guys before they got too far ahead to air me back up. I was surprised how fast I caught up with them. Before, I'd barely been able to keep pedaling; now, I made up ground in a few minutes that would have been a massive effort even a few psi higher. The rest of the ride, I was making it up and over almost everything, even after some of the others were forced to walk.
Tire pressure isn't just a part of the fat bike experience, it's the key element for fun, for trail maintenance, for true versatility, and even for speed. It's not always easy to keep up on, either. Just as snow can change dramatically with just a degree or two change in temperature, so can your tire pressure. Where you keep your bike can change your tire pressure by as much as half. Taking warm tires into the cold can cause them to lose half 3 or 4 psi if it's below 20 degrees.
The easiest way to check your tire pressure is to have a gauge the can read such low pressures. If you don't have a gauge yet, there are some more organic ways to see if your tire pressure is low enough. You should be able to push your tire in a good centimeter with just your thumb. Alternatively, you should be able to sit on the bike, look down at your rear tire and see it 'puddle' out under your weight a good centimeter or two.
Low tire pressure is more fun, more efficient, and faster, while being much better for the trails. And if you aren't sure, ask your fellow fat bikers to see if you're in the ballpark before heading out on the trail!