What is the best tire pressure?

Running them that much more than the recommend pressure will probably ruin them. Usually 3 to 5 pounds is the most you should go over in a winter tire. Nitrogen is better than regular air. It stays in the tire better, extends tire life, and can improve fuel economy slightly.

ok first of all refer to your owners manual for suggested air pressure in your tires. 45 and 51 are way to high even for snow n ice. you are actually supposed to let some of the air out. second no nitrogen is not regular air, its in fact nitrogen. not the air we breath. the air in your tire just doesnt leak out or go away what happens is the when the tire is cold the air inside the tire compress even more so its like you have less air. when your driving down the road your tires heat up and heats the air up inside the tire. which expand causing the pressure to go up. like a ballon. what makes nitrogen special is that is doesnt compress and expand nearly as much as the regular we use. the reasoning behind this is down to the chemistry of nitrogen. not explaingin that. they use nitrogen in aircraft tires because it doesnt freeze and has no water in it. and it doesnt expand under extreme heat. idk if it will imporove your gas milage or not sounds like bs to me. but it wont extend your tire life. do googling you'll understand

Nitrogen will marginally improve gas mileage(only 2-4%) because it leaks out less which will keep the tire at the correct pressure for longer periods. This causes the tire to rotate more easily leading to less fuel consumption. It extends the tire life due to it ability to disperse heat as well as it less oxidizing nature compared to oxygen. Here is a study providing more information about the benefits of nitrogen http://www.getnitrogen.org/pdf/print_articles/Technical%20-%20Why%20Nitrogen%20Inflation%20Extends%20Tread%20Life.pdf