The majority of the time, self-tapping screws are installed with no pre-drilling. However, for some applications, it is helpful to pre-drill a hole.
At least three European studies (cited in RInghofer, 2017) comparing the withdrawal resistance of self-tapping screws in pre-drilled and non-pre-drilled holes using self-tapping screws have shown that any difference can be considered negligible. This was confirmed in a recent North American Study as well (for further discussion, see our White Paper, “Screw Withdrawal Resistance in Near-Edge Applications”). Ringhofer, A. (2017).
Axially loaded self-tapping screws in solid lumber and laminated timber products. Verlag der Technischen Universität Graz.