Another reason why people speed, is because all modern cars are so sound proofed, that when your doing a ton, it doesn't sound any louder than if you were doing 30. My old Golf was unbearable at anything over 90mph on the motorway.

As proved in this thread, people associate a loud noise with going quickly. So if their car is quite, they think they can't be going that fast.

 

I remember being on a sunny Supermeet in the fast group and as we went through one town a butcher or similar ran out of his shop, gesticulating at us wildly and telling us to slow down. I looked down at my speedo and we were doing 20-25 mph