Technical Tips

August 2009

New Revelations About COR/CT Testing
-- by Tom Wishon

While attending clubfitting seminars for the UK and German PGA in Europe last month(June), Tom Wishon and Matt Mohi met for three hours with Steve Otto, the Technical Director of the Royal & Ancient of St. Andrews, to discuss various matters related to the methodology used to determine the spring face conformity of clubheads.
A truly nice man with an engaging personality and a superb sense of humor, Otto left his previous position as a professor of engineering at the University of Birmingham in England in 2001 to lead the R&A’s commitment to elevate their in-house technical capability. Prior to this time, the R&A had a minimal technical base to perform their own equipment testing and relied almost exclusively on the USGA for such investigative matters.

Working from offices adjacent to the 18th green on the Old Course at St. Andrews with rooms full of the latest and most sophisticated testing equipment, Otto leads a staff of technicians who handle a wide variety of technical projects from equipment conformity testing to conducting golf equipment research projects commissioned by the R&A.
TWGT requested a meeting with Otto to discuss issues related to the correlation between the Coefficient of Restitution and the USGA/R&A’s current CT test protocol for determining clubhead spring face conformity. Over the past year in its testing, TWGT had noted some unusual results from CT testing of various clubheads which indicated a possible lack of correlation between CT measurements and COR.

Otto told TWGT that the current CT test is able to correlate to COR only for driver heads. Spring face conformity for other clubheads such as fairway woods and irons is not able to be done using the CT test equipment. When the USGA or R&A receive clubheads other than drivers which they feel may have a face design that warrants an investigation of the head’s spring face capability, an initial CT test is performed on the face followed by an actual COR test done with the old air cannon COR test equipment originally invented by the USGA to determine COR conformity.

The current CT test was developed to shorten the time required to determine spring face conformity and was implemented by the USGA and R&A to replace the old air cannon COR testing procedure in 2004.

What brought about the meeting with the R&A was the fact that TWGT had noted a significant CT measurement difference between its model 770CFE and 870TiCOR thin face iron designs. In testing with CT equipment, the 770CFE resulted in a CT measurement of 249 µsecs, while the 870TiCOR showed a measurement of 298 µsecs.
Working with 770CFE and 870TiCOR iron head samples TWGT had brought to the meeting with Otto, the R&A recorded the same CT measurements as had TWGT for both iron heads. Moving to the COR air cannon test equipment, the 770CFE head showed an actual COR of 0.810, while the 870TiCOR test resulted in a COR measurement of 0.824.

While very little seems to have been publicized about it at the time, in 2006 the USGA and the R&A extended the spring face conformity requirement beyond drivers to include all clubheads. Prior to this, only drivers of 15* loft and lower were compelled to pass conformity testing for the limit on spring face performance. The difference is that drivers are compelled to pass only the CT test while the conformity decision for other clubheads is determined from the air cannon COR test.

Thus the limit for driver heads is a CT measurement of 257 µsecs while the spring face conformity limit for other clubheads is a COR of 0.830. Seems odd to have two different tests for different clubhead types, but this is what happened as a result of the fact that the CT test only correlates to COR for driver heads. It appears because of the inability of the CT test to correlate to COR for any head other than a driver, the once retired COR test has found itself a vital part of equipment conformity testing in the game.


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