Bike vs. Car Tire Pressure

[canadianliberal]

This is related to my last post, but I figured I should start a new one as it veers of topic.
I bought a Tire pressure gauge and I checked my car tire pressure and they all read between 29-31 PSI. The tires recommend no more than 45 PSI, while the car recommends to stay around 30 PSI. Which is fine.
But my bike tires simply read 75 PSI. Which is more than double what my car requires. So why is it that bike tires require higher level of pressure than my car tires?

[TESTUser111]

I'm not that sure, but I think it has to do with volume. Car tires have a much larger volume and therefore don't hold as much pressure. Here's a similar discussion from <a href="http://www.bikeforums.net/showthread.php?t=448281">bike forums</a> that might shed more light.

[canadianliberal]

Last question is it safe to pump up a bike with a compressed air machine? More specifically a compressed air machine which plugs into my car's cigarette lighter? Like this one here.
<img src="http://www.pumps-manufacturer.com/productsimages/CarAirCompressorMiniAirCompressorAirPump_44564.jpg" alt="Air Compressor" />

[TESTUser111]

Air compressors will work fine... just be sure to watch your pressure gauge so you don't over-inflate your tire.

[canadianliberal]

Sounds good thanks .