The 20mph campaign/s and arguments...

That's part of the idea behind 20mph limits rather than zones. Limits don't require vertical deflection (which was always built into 20mph zones to be 'self-enforcing'--obviously, while it's still annoying, it also led to cars with much better suspension).

Any driver with a brain would far rather drive at 19.9mph down a smooth easy road than drive over something resembling a BMX track gone wrong at 10mph whilst getting both their body and motor proper battered. Forget trying to carry fragile cargo as well, such as er…everything!