Gear 101: What is a CT test, and how does it differ from a COR test?
In 2020, CT (characteristic time) tests on drivers are discussed more than ever due to increased testing on the PGA Tour. In this edition of Gear 101, we wanted to explain what CT testing actually is, and how it relates to the previous COR (coefficient of restitution) tests you’ve likely heard about in the past.
As you may remember in 2019 ahead of The Open Championship, Xander Schauffele had a run-in with the R&A after his driver failed a CT test. During the aftermath of that ordeal, the PGA Tour implemented mandatory driver testing for the 2019-2020 season. Ahead of the 2019 Safeway Open, five PGA Tour players reportedly failed the CT test conducted by the USGA Equipment Standards staff. Drivers continue to be CT tested at each event, and of course, all retail drivers are thoroughly tested before they hit shelves.
Prior to 2004, the R&A and the USGA tested drivers using a COR test, which tests for the spring-like effect of a club head. To measure COR of a golf club, tests were conducted by firing a golf ball from an air cannon at a club head and measuring the velocity at which the ball bounced off of different areas on the face. It’s a measure of energy transfer, so the lowest reading would be 0.000, where all energy was lost at impact, and 1.000 would be the highest, where all energy was transferred.
According to the USGA, COR couldn’t exceed 0.822 with a tolerance of 0.08, so any driver measuring over 0.830 was deemed illegal.
“The COR test was really accurate to the physics of what happens with a golf club hitting a golf ball,” said Tom Olsavsky, VP of R&D at Cobra, on our Fully Equipped podcast. “If you have a COR test and you hit it off-center, [the face is] going to be slow because of the inertial effects and the speed effects.”
The problem with the test is, according to Olsavsky, is that it’s time consuming, taking about 45 minutes to map each club head.
In 2004, the USGA moved to a different test, called the CT test. The CT test also measures the spring-like effect of a club face, except it uses a small, portable pendulum system that strikes the face with a steel ball. Sensors then read the amount of time the two objects stay in contact with each other. The limit of time placed on golf clubs is 239 milliseconds with a tolerance of 18 milliseconds. Therefore, any golf club that measures higher than 257 milliseconds on the CT test is deemed illegal.
The CT test, being that it’s just a small pendulum device, is “really easy to use,” according to Olsavsky. Actually, some OEM Tour Trucks that travel to PGA Tour events each week have a CT testing setup right in their truck.
Due to the differences in how the tests are setup and measured, however, the CT test is not a perfect replacement for the COR test, according to Olsavsky.
“What we do find is that CT testing off-center is not as accurate as COR,” Olsavsky says. “CT testing will read high, because it’s really a mechanical response versus the actual impact physics.”
Olsavsky’s gripe is that the CT test doesn’t always accurately mimic the response of a golf ball.
“When you’re pinging [the steel ball in the CT test] a half-inch or more off-center, you get a higher response,” Olsavsky says. “When you hit it out there [with a golf ball], it’s a really bad, slow shot and it’s going sideways.”
Regardless of which test is better, the current rules of golf club conformity are based around CT testing. Therefore, that is the test that PGA Tour players must pass each week to continue using their gamer drivers, and that’s the test retail drivers must pass to hit shelves.
Hear more opinions and insights from Olsavsky on a number of gear topics in the Fully Equipped podcast below.