Originally Posted by Mithrandir

Basically, the more air pressure that's in a tire, the more the bike vibrates. It gets transferred into your arms and seat, and can leave you pretty sore.

Less air pressure in a tire means it sucks up more of the road static.

Likewise, the same effect follows with tire width. Wider tires suck up road static, while thinner tires are more "hard".

This comes at a speed tradeoff; the thinner/higher pressure your tires are, the less rolling resistance they create, and let you go faster. Personally, I would rather have a softer ride than going negligibly faster.