That's not true, my car scrapes on them at practically any speed.
People with slightly higher cars than mine scrape because they try to brake, forcing their suspension to compress, then go over the bump.
There's so much ceremony to going over a speed bump that I think plenty of people not going that fast are inconvenienced. whether that inconvience is worth the net benefit is a separate issue.
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
People with slightly higher cars than mine scrape because they try to brake, forcing their suspension to compress, then go over the bump.
There's so much ceremony to going over a speed bump that I think plenty of people not going that fast are inconvenienced. whether that inconvience is worth the net benefit is a separate issue.