The Face – Bulge and Roll

The team at Diamond Golf discuss the issues of horizontal bulge and vertical roll in modern golf clubs.

There is no single club specification which determines a consistently tight shot dispersion patterns, it is the golfers’ playing skills which will have the most significant impact on shot direction.

Club fitting techniques can sometimes help golfers though by building equipment which assists them in finding a more repeatable straight club head position through impact. Once achieved, a golfer with a reasonably consistent repeatable swing should take note of the sometimes subtle but no less important face specifications of horizontal bulge and vertical roll.

Because of the nature of modern metal woods it is not possible to specifically use vertical bulge and horizontal roll as fitting factors. Both elements are now ‘built-in’ through the manufacturing process

Horizontal bulge is the radius of curvature across the face of a wood head from heel to toe. It is intentionally designed to counteract hook or fade ball flights when impact occurs on the toe or heel.

Bulge came about as a club spec in the late 1800’s and exists now as offering ‘gear effect’ to the ball at impact. Wood heads previously were flat faced or even concave. By adding a convex radius, East to West across the club face, 19th century club makers discovered that off-centre hits would stay more on-line because of the spin created by the toe or heel curvature. Off-centre impacts cause the head to rotate slightly around its centre of gravity. The friction created by this movement causes the ball to slide towards the centre of the face, creating a hook when hit out of the toe and a fade when hit out of the heel.

Vertical roll is the curvature of a wood head in a North to South direction. Whilst existing as a spec for as long as ‘bulge’, its primary benefit in club design is its significant impact on carry distances – a factor affected by the height of the club face.

The effect of vertical roll is such that on some modern drivers the face can be so deep that the loft can actually vary by as much as three degrees from top line to centre and centre to bottom of the club. This means an average driver head actually offers a loft range of as much as six degrees difference depending on the depth of the face which in turn then affects launch angle. Where the ball leaves the face of the club will determine its launch trajectory and subsequently just how much forward roll there will be.
Since there is no significant performance advantage from adding vertical roll in the design of a club it makes sense to design clubs without this feature – something Wishon Golf have done in some of their wood head models.