The Science of Spin January 07 2014
As a follow up to the All Wedges Are Not Created Equal blog that measured the variance in performance between a number of manufacturers wedges it's worth delving into the subject of spin generation a little with a brief review of the USGA literature that is freely available and commonly held beliefs.
What are the technological factors that effect spin?
- The roughness of the flat surface between the grooves
- The sharpness of the top edge and/or the type of grooves
- How far apart the grooves are positioned
- The depth of the grooves.
The interaction that creates spin is quite simple, it is one that creates the most friction and therefore the most spin. At lofts of 40º and under the interaction is mostly sticking and no slipping occurs, the friction force is the same with both smooth and rough surfaces according to Chou, Liang and Yang (Science and Golf II: Proceeedings of the World Scientific Congress of Golf II)
This leads us on to the research conducted by the USGA over a period of years prior to the rule change regarding groove technology, available here USGA Research. The interim paper notes that prior research has found that there is no difference made by groove configuration and face treatment and proceeded to test both the U & V groove types in dry conditions concluding that there was no difference once again.
However during the benchmark player testing there was found to be a difference between modern equipment and old V grooves and balata balls that spun more that any modern equipment combination. From the rough however it was found that the U grooves had the potential to spin MORE than from the fairway!
The study also concluded that the edge radius or the 'sharpness of the edge' is a contributor to spin but the closer towards a V Groove shape it became the significance reduced to almost none.
Groove spacing was also found to be a significant contributor regardless of groove type.
The type of milling was found to have no significant influence on spin rate from the rough except for an extremely rough surface.
So the question remains as to what was responsible for the often huge performance gaps for spin generation between wedges included in the testing from the previous blog entry. If all the above were bulletproof it would fair to say the performance should be very similar throughout when using the same player, in the same conditions, even allowing for some technical variance.
We're excited to be planning some testing next month that will include the use of grooved and non grooved wedges from a variety of lies and distances. While it will not be as scientifically sound as the USGA's (expensive) testing it should provide some insight into this fascinating topic in the real world sense.