At 03:16 AM 3/3/2008, Paul Glazier wrote:
I recently got my copy of Sean Fister's new book on long drive.
There was some information contained in the 'Equipment' section that
I found quite interesting. Sean states that the shaft frequencies of
his 2005 WLDC winning drivers were 250 cpm and 251 cpm and that
'they're so stiff that the average guy couldn't even get them
airborne' (p.127). However, in Jeff Summitt's manual 'The Modern
Guide to Shaft Fitting', a 250 cpm shaft comes out at little more
than an A-flex or R-flex.
As you know, Jeff's ratings are based on a driver length of 43".
My question is: Why are long drive shafts rated so highly (XX, XXX,
etc.) when their frequencies are so low? Is it because when these
shafts are trimmed to the length of a normal driver they would be
rated as XX, XXX, etc.? If so, how does shaft frequency change when
you butt trim and/or tip trim? Is there a ball-park figure of cpm
increase per inch of tip/butt trim?
There are indeed ball-park figures. Specific models of shaft will
depart from those figures, but FWIW...
The butt-trim sensitivity of a "typical" shaft (whatever that is) is
about 8-10cpm per inch. That means that if you took Fister's 48"
driver and trimmed it to 43" from the butt, the frequency would
probably go up 40-50cpm. That puts it at 290-300cpm. Since Jeff's
ratings have 278cpm at X-flex, this is indeed XX or XXX.
As for tip trim, that is much more variable, but the sensitivity is
always higher than the sensitivity for butt-trim for that particular
shaft. The NET sensitivity, tip-trim minus butt-trim, is what
clubfitters use to trim for flex.
Hope this helps,
DaveT
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