Why Safety Belts Work
When you ride in or on anything, you go as fast as it goes.

Take the simplest vehicle. Suppose it is just a seat on wheels.

Put someone on it.

Get it up to speed. Then stop the vehicle. The rider does not stop.

The person keeps going until stopped by something. In a real vehicle, it could be the windshield...

or the instrument panel...

or the safety belts!
With safety belts, you slow down as the vehicle does.
You get more time to stop. You stop over more distance, and your strongest bones take the forces. That is why safety belts make such good sense.
See also:
Different Size Tires and Wheels
If you add wheels or tires that are a different size than
your original equipment wheels and tires, this may
affect the way your vehicle performs, including its
braking, ride and handling charac ...
Following Distance
Stay at least twice as far behind the vehicle ahead as
you would when driving the vehicle without a trailer. This
can help to avoid situations that require heavy braking
and sudden turns. ...
Adding Equipment to the Airbag-Equipped Vehicle
Adding accessories that change the
vehicle's frame, bumper system,
height, front end or side sheet
metal, may keep the airbag system
from working properly. The
operation of the airbag system ...
