You won't lose your wheels going at the posted limit, if it is a 30kmh road. For comfort you probably do want to reduce down to 15-20 in an average car.

If you encounter a warning sign for speedbumps on a 50kmh or 70kmh road you better start braking if you dont't fancy getting airborne.

There are some weird deadlocks in Swedish road regulations that make it unreasonable difficult to change the speed limit in some situations. They sometimes work around that by actively making it impossible to drive the posted limit.