I Just lowered my mini cooper s and put 18 inch wheels. Unfortunately the fitment wasn't correct so i had to drill the holes bigger. Is this 100 percent safe?

 

which holes you talking about? the lug holes in your wheels?

 

Did you do this with a hand held drill? Any vibrations while driving?

 

With an existing hole there, and assuming you went from 12mm to 14mm (only 1mm taken off), I'd say you should be fine. It would be really hard to get a hole out of round when removing such a small amount of material, especially given that you already had a starter or pilot hole.

 

I believe it was 12mm to 14mm. Yes he did use a hand drill. But this place has a very good reputation. I used a 18 inch Kyowa KR518 wheels.