Shortly after I posted my article on gear effect to my web site, I
got email from Marcel Bal asking about face roll. That was such an
obvious part of what I was doing, I was a little embarrassed at not
having added roll to the article. Kudos to Marcel for understanding
the subject well enough to point that out.
It was a little more work than I had anticipated, but it has been
added. You can see it at <http://www.tutelman.com/golf/clubs/gearEffect.php>.
The bottom line is that face roll is a definite advantage in
enlarging the vertical dimension of a driver's sweet spot. For those
who continue to insist that the sweet spot is a point that cannot be
enlarged (something I consider a silly semantic exercise), let me
rephrase it. If you miss the sweet spot too high or too low, you lose
a lot less distance from a proper roll than from a flat face.
The mathematical model says "proper roll" is about 8" -- slightly
flatter for low clubhead speeds and slightly more curved for big
hitters. But the total range from ball speeds 120mph to 180mph is no
more than 7.5" to 9". Even if the model has significant errors, the
number is most probably no more than 12".
Cheers!
DaveT
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