it's a mix of factors as for why heavier vehicles go over bumps better

1 - bigger/taller vehicles generally have more suspension travel which is also softer

2 - heavier vehicles have more inertia (which results in less body movement when going over bumps)

3 - bigger wheels mean a larger radius which means bumps feel softer when hitting them - think pushing a shopping cart versus riding a bike over a crack

4 - the bigger and heavier wheels actually act against the smoothness of the ride here, but the suspension is designed for that and the overall inertia of the sprung mass seems to mostly cancel it out

I will say that I generally hate speed bumps as a concept. I think that they are ineffective and annoying to everybody.

cons of speed bumps:

• annoying to the driver

• annoying to everybody else who has to hear cars and trailers squeak and smash over them

• annoying to drivers behind drivers who crawl over them at a snail's pace

• annoying to cyclists (if they don't have cutouts for bikes)

• they interfere with snow plowing operations

• they distract drivers from paying attention to their surroundings, and have them focused on speeding up and slowing down for each bump because they must get there faster faster faster always

• drivers accelerate and brake between each bump, causing engine tire and brake noise for everybody nearby

• the constant accelerating and decelerating of 4,000 lb vehicles is incredibly wasteful *not just because of fuel but because of tire and brake wear and pollution from that

• some people just drive over them at 'full speed' which makes bouncy car and tire slap noises (this is usually what I do when I come across gentle speed humps in a 40 km an hour zone, I'm not slowing down and speeding up the whole time so I'll just hit it at 35, tap the gas to get back up to 40, and coast until the next one. obviously my speed is appropriate to the surroundings at the time and I don't always do 35 in these situations, I'm just talking about when it's clearly wide open and obviously nobody hiding behind parked cars)

it annoys me so much because like you can get the same result by just narrowing the lanes and designing your streets better instead of having a literal highway-speed-designed road with two lanes each direction and raised median and 6 ft painted paved shoulder until a curb with no sidewalk immediately adjacent to the pavement with a 50 km an hour speed limit slapped on it