With the possible exception of the ball itself there is no more tightly regulated piece of equipment in golf than the driver. Since 1998 the USGA and R&A have capped the Coefficient of Restitution (COR) for drivers at .822. That means that since 1998 driver faces haven’t gotten any hotter. Since 2002 the maximum allowable head size has been 460cc. That means drivers haven’t gotten any bigger.