Originally Posted by
Hypno Toad
It's
not intended to consider your weight or trail conditions 
where do people get this idea?
Which is what makes it useless chart for most to use. If my bike was stored inside at 70 degrees and my tires are at 10 psi it tells me that at 10 degrees my tires would drop to 7.2 psi. Now lets say I get to the trail and it's soft conditions after recent grooming. If I'm a 225 pound guy I'm probably going to have to lower the pressure so I don't put ruts in the trail. If I'm a 165 lb guy the pressure is probably OK where it's it and then there is everything in between. Now if I get there and the trail is hard packed maybe the tires are ok where they are or a little air could be added.
Then there are other variable that chart doesn't consider...are the tires 3.8" wide or 4.6" wide? Are they 26" fat or 27.5" fat?
Really too many variables between temperature, rider weight, tire width, tire diameter and snow conditions to make that chart worth while. It's easier to pump the tires up to about 10 psi before leaving home and then decide to leave alone or let more air out once the destination is reached.
