Via John Graham's blog (http://johngrahamgolf.com/blog/) -- the following data courtesy of Trackman based on their own experience.
Found several things interesting. One was the relatively small variation in optimal backspin for widely different swing speeds. Less than 300rpms at any AoA between a 75mph swinger and a 120mph swinger! When you think of all the time spent obsessing over "spin-killing" shafts and driver heads on Internet golf forums...
Another was the spin loft numbers. As I understand it, spin loft is dynamic ("actual") loft at impact less the angle of attack. So, if we take the flat hits (0 degree AoA) in the chart, then the optimal spin loft in those cases should roughly equal the theoretical optimal face loft for the driver itself, surely? And those seem way high? Nine to 13 degrees for a 120mph swinger? (In practice it might be even more because if we assume hands ahead at impact, that will be additionally delofting the club a degree or so.) Maybe I'm reading this wrong or not understanding the basic relationships correctly?
(EDIT: Realized I wasn't including the shaft bend contribution to the dynamic loft, but pretty sure that rarely adds more than about 1.5 degrees.)
Anyway, at minimum probably also some useful reality-check numbers for all those discussions about driving distance.
Edited by Stretch - 5/21/11 at 10:18am