Originally Posted by
daoswald
You would need tires with a capacity of 371 liters to put 30 pounds worth of air in them.
PSI is pounds/square inch = force density, not a weight. If it was a weight few would be able to lift their road bikes with two 100+lb tires.
The best way I've found to think about tire pressure is this. The air pressure in your tires is supporting the weight of you, your bike, and your gear. The tire will deform on the bottom based on the pressure in the tire and the weight it's supporting. If you are 180lbs, have a 35lb fat bike and 10 lbs of clothing and gear, that's 225lbs. Roughly speaking, if your tires have 10psi in them they will deform to create 22.5 inch^2 of ground contact to support that weight. If you run 5psi the tires will deform to create 45 inch^2 of ground contact.
If you are riding on loose or new snow, the lower the pressure you can run in your tires, likely the better your bike will perform. It varies with snow conditions of course. The pressure in your tires (PSI) roughly equates to how much force your tires are putting on the snow/inch^2. The example above is basically me when I ride in the winter, so at 2psi my 4.8" tires are getting flat enough on the bottom to create a total of ~112.5 inch^2. And yes, the tires look ridiculous and it is a heck of a lot of work to pedal, but it's pretty impressive when you are grinding your way through 10" of fresh snow.