Why...?

less air in the tire = more tire contact = more traction in snow

TRACTION! BRILLIANT!
im really into those guiness draft commercials suddenly. BRILLIANT!

from like a scientific point? Or is that it... lol

both?

i know in the winter the air pressure used in my durango is lowered.

Ok im good.... thanks caring freinds

less tire pressure = more traction BUT worse gas milage... so in the summer when traction isn't as needed as in winter, get better gas milage with higher pressure tires.

i'm going to say warmer weather means the air in the tires will expand so they need to lessen the pressure for the summer?

Yeah. When it's cold you need to put air in because the cold makes the air shrink, then warm temps make it expand.

True, but lowering your tire pressure to accomadate for temperature change isn't what this pertains to (I think).  By doing that you would just be adjusting for a different temperature, not altering air pressure. 


By lowering pressure for snow, mud, etc you will increase the tires ability to grip that surface.  Conversely, you will also increase the contact patch, which will decrease your ability to dig down for traction--this is why WRC cars use super narrow tires on snow courses. 

For dry surfaces like asphalt or tarmac you will want to have higher pressure to decrease rolling resistance.  However, you also want to have the biggest contact patch possible, which is why race/autocross/whatever cars will use wider tires. 

So to sum it all up:  small contact patch and low pressure for low grip situations, large contact patch and high pressure for high grip.  I know this brings complications into a simple question, but you can't take out a factor that important.

arround here the cool thing to do is put nitrogen in your tires.

more air pressure in the tire = less tire pressure and better gas mileage during the summer when prices go up :p