2000 Ford Focus

There can be many things causing the vibration you are experiencing.

If you have not done so, you really should visit a qualified tire shop or mechanic.

You could be looking at a tire problem (slipped belt, out of balance, uneven tire wear.)

You could also be looking at suspension problems such as shocks/struts, broken coil springs, etc.

If it is vibrating like you are in a washing machine, this may be a very serious issue.