On a bike: 46,6 mph
In a car:
Dodge Ram B 250 Van - 1986 model - 3,5 metric tonnes
75 mph (downhill with tailwind)
:D
The engine was close to exploding, and the whole car was shaking violently :P
Other than that, I've driven 75-80 in a normal car. But the maximum speed limit here is 60, and the tickets you get are pretty high. If I would have been caught at that speed, I would probably have lost my licence :/ (you're on "probation" the first 2 years after you get your licence)