Refit your driver after major speed gains
After a major clubhead-speed gain, the shaft, loft, and center of gravity that fit at the old speed may no longer work. The instructor recommends working with a professional to dial the equipment back in; in his own 135-to-155 mph example, loft, center of gravity, weights, and swing weight all changed.
Channel: Club Champion
Watch official source at 8:39Why this context matters
On why gaining speed forces a driver re-fit.