What?

 

Atmospheric pressure at sea level is like 14.7 lbs, so even a flat tire isn't really flat. If I add 40 PSI to my tire, I'm actually measuring the differential pressure between outside the tire and inside. Since ambient is already 1 bar, the tire actually has 54.7 Lbs.

 

Atmospheric pressure is 14.7 PSI.. 40 + 14.7 = 54.7.

 

A tire gauge reads the difference between outside and inside pressure. If you put a gauge on tire before it is inflated, the outside and inside pressure will be the same, there will be no differential so the gauge will show zero. If that tire is sealed and taken to 18,000 feet, it will show about 7 psi, sea level pressure is about 14 psi. Adding your desired tire pressure to 14 psi (sea level pressure) will give you the same differential you would have if you took your properly inflated tire to the space station (outside of the station) it would show your desired pressure PLUS 14 psi, if you inflated at sea level before the flight. Since we don't ride our bikes in space, just put in the recommended pressure and don't over think it.

 

Don't forget to let the winter air out of your tires and put new summer air in.

 

I am lazy, I put the pressure at the "with passenger and baggage" figure so I don't have to pump up the tire before taking someone for a ride and then let air out when I am solo. You may be far more OCD than I am and have no problem making frequent adjustments. Low pressure causes excessive tire flexing and that generates heat. A hot tire is softer than when that tire is cool so it wears faster when hot. If it gets hot enough, it will fail so a couple EXTRA psi is better than a couple psi below the spec.

 

I'm not at sea level, so your nerdy calculations are useless to me

 

My 'nerdy' calculations are based on a 78% nitrogen concentration anyway, so they may not apply to you.

 

I would think the tire manufacturer, the tire pressure gauge manufacturer and the moco have taken all this into consideration when calculating the recommended PSI.

That way, I don't have to...

 

Uh ho, I didn't change last summer air to winter air, I hope I didn't void my warranty...