Same hear, Nissan 350Z scrapes most speed bumps even going as slow as is possible.
Also, they don't work for a lot of cars - I see lots of cars (presumably without stiff suspension) fly over the things at quite high speed. It seems that at certain high speeds, if you straddle them just right, you don't have to slow down at all.
Yup, on cars with soft suspensions you can actually get more clearance by speeding up right as you reach the speed bump, since weight transfer will push the front end of the car up
Also, they don't work for a lot of cars - I see lots of cars (presumably without stiff suspension) fly over the things at quite high speed. It seems that at certain high speeds, if you straddle them just right, you don't have to slow down at all.