I have a 3rd gen vios, and most of the time I have full passenger (5 total) and sometimes full load on trunk. Most of the time my bottom part hits speed bumps when I am full, even when entering speed bumps on an angle.
I searched and searched the internet but can't find what should I change to prevent this. Most of the topics online are for performance with a single person not for everyday family use.
I'm using all stock Vios 2015 Base J, 14" wheels.
If your car is old, then possibly the shocks/springs/dampers are worn/old so the car is both lower than it should be and not responding to the bump as it should.
Otherwise, the Vios is pretty small, and loaded with 5 people it will sit low to the ground, so you may just have to accept that speed bumps are better avoided. I'd suggest you look under the car to see what is actually hitting the ground. It is often part of the exhaust system hanging lower than it should, so this is easy to fix - simply sort out the hook and rubber support.
If it is part of your chassis or the underside of the sump - your only options are to either raise the car - by replacing shocks, springs and possibly other parts of the suspension - or avoid the speed bumps.
try to put rubber stopper on the springs, ask your mechanics about this. We have the same car but im using 15", All stock, VIOS e 3rd gen also.
