These two drivers benefit from large, lightweight carbon-fiber sections on the top and on the sole to produce different ball flights and to resolve various performance challenges. The way this works is that the lightweight carbon-fiber panels reposition each driver’s center of gravity. The ST-Z features sections in the sole’s heel and toe that lower the CG to produce a neutral ball flight with lower spin and maximum forgiveness on off-center hits. The ST-X boasts a larger panel stretching across the toe and center of the sole. This leaves a heavier, all-titanium section concentrated in the heel. The heel bias is bolstered by an 11-gram fixed weight screw that helps slicers return the clubface to square at impact. (A lightweight option on the ST-X includes a sub-40-gram shaft.) A forged super-alloy titanium face insert features a new variable-thickness pattern for better flexing on off-center strikes, and the wave shape in the sole extends the hottest area to include impacts lower on the face. Read more >>