Science: It works, bitches! Part 1, Pressure.

So people have been complaining about the use of  Bars as a unit of pressure.  I actually think that it's quite useful, and has more meaning than the arbitrary "psi" that is the standard (at least here in the USA).

"bar" is a unit of pressure equal to 1 atmosphere.  If you're sitting at sea level, atmospheric pressure is pressing inward with about 14 pounds per square inch of surface area.  It's also pressing outward with the same pressure, which is why you don't feel anything.  If you suck the air out of a beer can for example, and it collapses, it isn't because the vacuum is pulling the sides inward from the inside.  There's nothing inside the can to pull.  It's because atmospheric pressure is pushing the sides inward from the outside, and there is no longer and equal pressure inside to balance it out.

  If you inflate a tire to "1 bar," what you're doing is putting twice as much air into the tire than if you had just left it open to the atmosphere.  The difference in pressure between the inside and outside of the tire is 1 atmosphere worth.  2 bars would have a difference of 2 atmospheres between the inside and outside.

Now imagine you have a tire inflated to 2 bars at sea level and you launched it into the vacuum of space.  The difference would be that in space, there is no atmosphere to press back in against the air in the tire pressing out.  This would add 1 additional bar of pressure to the tire.  So 2 bars at sea level is 3 bars if you launch the tire into space.  This is why some people think it's a good idea to deflate tires if you're flying on an airplane.  This actually doesn't matter much, because airplanes are all pressurized to about 8000 feet, so even though you're flying at 30,000, you only have to deal with the pressure at 8000, which is about 4 psi of difference.

That's all.  I'm certainly not going to tell you what pressure you should inflate your tires to.  I'm simply suggesting that if someone decides to recite their pressure in bars, that you trust it as an acceptable unit of measure, and continue on with your ride.  Until it goes uphill.  Then you ask them to explain how atmospheric pressure works and attack.