Got to be atleast 60 to look like you've even done anything 
Edit, just to clarify, im 70mm on the back and probably 70ish on the front and i weigh a good 100kg and i dont have trouble with speed bumps anywhere, the only place i catch is a specific car park on a harsh slope where the front bumper hits.

Edit, just to clarify, im 70mm on the back and probably 70ish on the front and i weigh a good 100kg and i dont have trouble with speed bumps anywhere, the only place i catch is a specific car park on a harsh slope where the front bumper hits.
Doesnt even own a 306.