Anyway:

Tyres. They make a huge difference to a bike's handling and even add considerably to speed, but very few people understand anything about them other than bicycle folklore that is usually wrong. Read up on them on wikipedia and study the docs and tyre ratings on Schwalbe's site. Low hystereis rubber and advanced antipuncture systems that let a tyre wall stay thin (necessary for speed) while not being being easy to blowout are where it is at.