Smash Factor

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lder
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Smash Factor

Post by lder » Fri Jan 28, 2011 11:44 pm

I was wondering if there are any other factors besides where the ball contacted the face, which influence smash factor. For example, if i nail a drive and an imprint is left on the center of the face, can i assume the sf is very close to 1.5. I realise excesive spin could lower this number, or maybe not?? Thanks in advance

dtutelman
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Re: Smash Factor

Post by dtutelman » Sun Jan 30, 2011 7:01 pm

lder wrote:I was wondering if there are any other factors besides where the ball contacted the face, which influence smash factor. For example, if i nail a drive and an imprint is left on the center of the face, can i assume the sf is very close to 1.5. I realise excesive spin could lower this number, or maybe not?? Thanks in advance
Here are things that could influence smash factor, besides where on the face impact occurs.
  • Face angle - This is negligible for the face angles we usually encounter; 3* is a lot, and that would only make a 0.2% change in smash factor. But wait! Face angle works vertically as well as horizontally. In the vertical direction, loft shows up as face angle. And a 12* loft could take more than 2% off the smash factor.
  • More face angle - The loft of the club is effectively the loft at impact only if you have a zero wrist angle. If you come into impact with a cupped wrist, it could be more than that. I've played with guys who add considerable loft with their wrists.
  • Clubhead mass - Making a driver head 10g heavier increases the smash factor by almost 1%. Making it lighter hurts smash factor by the same amount.
  • Coefficient of restitution - The COR of your driver may not be right at the USGA limit. There are manufacturing tolerances; I suspect most manufacturers have about a 2% range of COR, but it might be better or worse.
None of these makes a BIG difference (unless effective loft gets out of hand). But they add up.

Cheers!
DaveT

lder
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Post by lder » Sun Jan 30, 2011 10:44 pm

Thanks a lot for the answer. The head weight point you made is very interesting. For a long time in long drive, lder's were obsessed with getting clubheads as light as possible, some believed cobra staffers had access to extra light heads. But obviously there are diminishing returns with regards head weights and smash factor. Is it generally agreed that a 200g head is the best blend of speed with enough weight for a high SF?

dtutelman
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Post by dtutelman » Sun Jan 30, 2011 11:02 pm

lder wrote:...For a long time in long drive, lder's were obsessed with getting clubheads as light as possible... But obviously there are diminishing returns with regards head weights and smash factor. Is it generally agreed that a 200g head is the best blend of speed with enough weight for a high SF?
Oh my! You are asking almost the same question that got me into golf physics in the first place, more than twenty years ago. It turns out there is nothing new under the sun. And the answer was known to golf scientists way before the question ever occurred to me.

Look at Cochran & Stobbs' book, which was first published in 1968. You don't have it? Run out right now and buy it. And read it. Anybody who asks questions like this should first be familiar with all of that book.

Look at Tables 32:2 and 32:3 and the accompanying text. And look at the equation referred to in Appendix I. (Hint: It's a slightly simpler version of the equation I used to answer your original question.)

That should tell you more about the answer to this question than I could by trying to summarize it.

Good luck!
DaveT

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