By Frank Thomas July 18, 2008

Our equipment guru, Golf Digest Technical Advisor Frank Thomas, has the answers to your questions. Click here to submit a question for possible use in this column and you could receive a signed copy of Frank's latest book, "Just Hit It: Our Equipment and Our Game." For more from Frank you can visit his site franklygolf.com. [Note: Each week submitted questions will be reviewed and the best one will receive a signed copy of Frank's book, "Just Hit It."]

BOUNCING GOLF BALLS FOR DISTANCE

Frank, is it possible to determine if one golf ball will go farther than another when hit at moderate club head speeds, by dropping them from shoulder height and watching which one bounces higher?

--Werner

Werner,

Unfortunately there are only two things you will find out about a ball, by bouncing it from a height of about 5 feet. One is, how high it bounces from this height, and two, how fast it will come off a putter.

Before we get into this topic we should explain COR (Coefficient of Restitution). COR is a measure of the efficiency of the transfer of energy between two colliding bodies. Imagine a ball being thrown at a brick wall at 100 mph. If it bounces back at 75 mph then the COR of the brick wall is 0.75. The lower the impact speed the higher the COR. The COR of a putt will be about 0.90 or more, but when using the same ball off a super driver at 110 mph the COR will be about 0.83.

All balls do not have the same fall-off rate as impact speed increases, so bouncing balls from five feet is not a good indicator of how fast the ball will be projected off a clubhead at a swing speed of 90 mph. We also need to recognize that ball speed alone is not enough information to predict how far a ball will travel.

The aerodynamics of a ball are extremely important. For example, a ball without dimples will travel about 130 yards compared to an otherwise identical ball with dimples -- launched at the same speed, spin, and launch angle -- which will travel 260 yards. The dimple configuration and the spin rate therefore play a very important role in distance and you will not be able to determine how a ball will spin or its aerodynamic lift and drag properties by bouncing it.

However, I would like to assure you most balls today are very good and the selection of a ball should be based on your swing speed, control around the green, and what you can afford. But in the end the differences in performance between the most popular brands is minimal and certainly smaller than our ability to take advantage of the subtle design differences. Most manufacturers of premium balls have a ball in their line designed for slower than tour swing speeds and these are not only good balls but cost considerably less than the premium balls which do a lot for our ego, but little to enhance our performance.

For example, the new NXT Tour ball from Titleist, the Bridgestone E6, the Nike Ignite, the Callaway HX Hot, and the Srixon AD 333, just to name a few, are all very good balls for 99% of us and don't cost a premium price.

Werner, bouncing balls is fun but is of limited value in deciding how they perform off a driver.

Hope this helps,

Frank

EXCEEDING USGA MOI LIMITS?

I recently put expanding foam inside a high MOI driver head, and am now wondering if this might increase the MOI past the USGA limit?

--Tom

Tom,

This is a very interesting question, which I don't believe the USGA carefully considered when adopting the MOI rule. Please bear with me for a minute while I give you some background.

First, understand that the MOI is the resistance to angular acceleration or simply, twisting during impact. The higher the MOI (within practical limits) the less it will twist during impact and the more forgiving the club will be of mis-hits.

If you hit the club in the center of the face -- on the sweet spot and opposite the center of gravity -- it will not twist during impact and the need for a high MOI becomes unimportant. Therefore, a high MOI is for us mortals, who miss the sweet spot more so than the superstars. The elite spend all their time perfecting their swing and are able to adjust to hit the ball on a particular spot, high, low, center/high, center/low or any where else on the face they wish. Whereas, most of us are lucky to hit the ball somewhere close to the center every now and again.

With this in mind you may ask, why has a limit on MOI -- which helps the average golfer more than the super stars -- been adopted? Is this really a conspiracy against the rest of us who love the game and need as much help as possible?

The real concern is that the first MOI proposal from the USGA was to limit it to 4,800 gm-cm². This was then adjusted up ward to 6,000 gm-cm² after the manufacturers pointed out that the original proposal was inappropriate.

"After careful consideration of the comments received from equipment manufacturers, the USGA has approved the implementation of a clubhead moment of inertia..." (of 6,000 gm-cm² which includes a test tolerance) The justification for the change of heart -- tap dance -- was that 'the difference between 4,800 and 6,000 was not significant.'

Why, we may ask, is there any need to set a limit at 6,000 if the difference between 4,800 and 6,000 has little to no real effect on performance? Surely anything above 6,000 is just as insignificant. The logic behind adoption of this rule is very questionable.

BUT now that the limit has been adopted, reaching it has become something of a challenge to the manufacturers, especially because there are dimensional and volume constraints which were also adopted a year or two earlier.

The closer the product is to the USGA limit the better it is, or so manufacturers imply and many golfers believe. This is just not true.

Wow! Tom this is quite a journey to get to your answer but I hope it gives you some background about the club you have, the silly restrictions you have to live with, and what the USGA is doing for you -- or should I say to you.

So, let me breathe, if you fill your club with foam it will certainly increase the MOI and if it was right at the limit of 6,000 gm-cm² before the foam job, you will now have a non-conforming club. Similarly, if you add lead tape to the back of the club you will increase the MOI. So it all depends on how close to the limit the club was originally when you bought it off the shelf. This is quite a nightmare for you but just imagine how a USGA official will react on the first tee when you tell him you have foam in your head.

Frank

TIGER'S DRUG TEST: REVISITED

I received so many comments about my answer to Jerry regarding drug testing, that I feel obliged to revisit it one more time.

My answer to the question about "Tiger's Drug Test" last week, was in essence suggesting that an adopted rule, which states that "performance enhancing substances are not permitted" (or something similar), should be enough without the need for testing.

I maintain that the essence of the game based in part on a code upon which the game is built, is at stake. Once we turn over the responsibility of self-monitoring of any rule, to a referee, we are fracturing the very foundation of our game.

It is the responsibility of the golfer alone to call any infractions on him/herself. Introducing a second party -- which implies "we don't trust these guys" -- is a personal affront to the profession and it in turn relieves the individual of a fundamental responsibility unique to our game.

Why can't we treat this drug rule like any other rule in the book?

If there are drugs which truly enhance a golfer's performance -- which is still in question -- then surely the best golfers in the world will know this sooner than anybody else. However, without a rule, there is no violation. But with a rule -- where the intent is unambiguous -- the golfer knows, and soon his fellow golfers will learn of any intentional violation. Peer pressure has proven to work very well in resolving intentional and/or repetitive rules violation problems.

If I tightly close my eyes for a few moments, maybe when I open them drug testing will be something that has gone away and we can again trust our elite golfers.

Patrick, Scott, Clyde, John and many others, I cannot thank you enough for your thoughtful e-mails. It is very clear that you too want to protect the integrity of our game but find it difficult to come up with the right formula.

Frank