Blades VS Cavity Back

Mon, 06/15/2009 - 11:00 -- Don Trahan

The big time world of golf club iron marketing is primarily focused in selling the cavity back/perimeter weighted iron club head design to the golfing masses, rather than the muscle back blade club head. The main advertising concept of the cavity back is that the weight has been taken from the back center of the club head and moved to the outside and perimeter of the club head, hence the terms cavity and perimeter. (Note: The following explanation and points I will elaborate on in this article, relative to the engineering and physics I will discuss, are, as I interpret them, from my discussions with my engineer mentors as they have explained them to me. Also included are what I have read and interpreted in the marketing material of the club manufacturers, and how I have compiled the two sources of engineering and marketing information to come to what I decipher as reasonable conclusions on the subject. )

The selling point to perimeter weighting by creating the cavity in the back of the club head is that it builds more stability into the club head to resist twisting when the ball is hit off center or the '€œsweet spot.'€ This is critical, as the more the head twists, more side spin is added to the ball, which will add more slice or hook curve, sending the ball more sideways ( also called ball flight dispersion) and likely into trouble. This twisting also means less energy is being transferred from the club head to the ball and it will fly less far, which may be good in that the ball will go less deep into the rough or woods, but if it is a lake it is still wet and gone and now fish food.

To further enhance the perimeter weighting selling point, the '€œsweet spot'€ becomes the center of focus of the selling campaign. There have been advertising points claiming a club has a '€œbigger'€ or '€œexpanded'€ sweet spot, or even '€œmultiple'€ sweet spots. Lately, the sweet spot has also been called the center of gravity or just plain center. (Note: I will discuss sweet spot in an upcoming article.'€
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The perimeter weighting concept was originally the main marketing campaign aimed toward the mid to higher handicap golfer which compromised the majority of players. (Note: on average, only one tenth of one percent of all golfers are scratch or better.) Now, perimeter weighted clubs are made and marketed to the lower handicap players in forged steel and slightly smaller heads to try and gain the acceptance of these lower scoring players. The stability and playability of the bigger sweet spot and less twisting are still the main selling points.

And, with over 40 years of marketing and advertising of perimeter weighted, cavity back clubs and their benefits to resist twisting and hit better (less ball flight dispersion) shots with off center hits, the better players, including Tour professionals, now have them in their bags. I think that making them in the softer forged metal makes the impact sound and, more importantly, feel softer. The softer feel of the ball off the club is critically important for the touch and feel needed and demanded for these finesse shots around the green, and is the key issue fueling the transfer to perimeter weighted clubs by the pros and lower handicap players.

Many Tour pros and top low handicappers resist changing to the perimeter weighted/cavity back using the '€œI am a traditionalist'€ or '€œI am old school'€ slogans. Well, the manufacturers got a lot of them to switch with the development of what they called '€œCombo Sets,'€ and even now make these in forged, softer steel. A combo set is one where the wedges thru the eight iron are '€œmuscle back blades.'€ The rest of the set has a mild cavity back and may have what manufacturers call a mild, modified or progressive offset in the shaft, with the offset increasing as the irons get longer.

Whatever the reason, the switch is on, from muscle back blades to perimeter weighted cavity back irons. The Tour players and low handicappers are still the main, if not the only holdouts still playing muscle back blades. There are enough of them to still warrant most of the top manufacturers to keep the pure muscle back blades in their lineup of clubs. I think this is just fine. Now let me elaborate a little on my reasons why.

There is no doubt that with perimeter weighting, the center of gravity/sweet spot can be moved more up or down the club head, as well as from the center to closed to the toe, to get it closer to the toe where slicers, who swing outside to in, contact the ball more often. They even build the heads bigger to give you more room or clubface to hit the ball. They say that the sweet spot is bigger or enlarged because of the bigger face. They say this will give a more solid impact with less twisting and thus a straighter and likely longer hit because of the bigger face and sweet spot. And, maybe this maybe true, but I like to deal in fact. So, let'€™s look at the flip side of which most everything has one. My thoughts on this bigger is better is for one point, a bigger club gets hung up or slowed down more in the rough or with deep divots. And second, what about the simple logic of a bigger face means '€œmore room to miss'€ the sweet spot and thus hit a worse shot! On both of these points, I take the smaller club head blades.

Because of this built-in compensation of moving the sweet spot toward the toe, I believe golfers are forced to repeat their less than Peak Performance Golf Swing, because the weight of the head will respond best to that outside-in swing path. Just like you can'€™t take the stripes off a zebra, so can'€™t you not take the weight responding to the design out of the clubhead.

Another vital issue I like to point out, the major reason I play muscle back blades, is the physics of weight and energy transfer, from the club head to the ball, at impact. The physics of energy transfer is Mass X Velocity Squared. With perimeter weighted cavity back clubs, the weight is removed from the back of the club and placed around the perimeter for stability to reduce twisting of the head in off center hits. Well, by taking the weight from behind the impact point means there is less weight there transferring energy to the ball. It is what I call hitting someone in the nose with a pie plate versus your fist, or hitting the ball with a pie plate versus a steel frying pan. These may be an over exaggerations, but I believe they easily and accurately explain the concept of energy transfer from the club head to the ball. The muscle back blade, like your fist, has the mass tight and right behind the sweet spot for maximum stabilization and energy transfer.

Smaller and compact, with the weight distribution in the muscle back right behind the sweet spot, is the optimum energy transfer. And with the smaller and compact head, the rotation around the shaft of the head into impact, is tighter and with a smaller head hitting the sweet spot or closer to it, twisting is reduced and better controlled.

My radical revelation for today is if you want to play better golf, hit better and more solid shots with a tighter flight pattern, then give muscle back blades a shot. You won'€™t really ever know if bigger is truly better than smaller and compact. I will add that if you can swing and hit a big head you can hit a small head. I vote for, play and recommend blades. But I will also be the first to admit that taking a stance against marketing is a tough sell. But as the saying goes, '€œthe truth of the pudding is in the tasting.'€

Shortly, I will discuss the sweet spot and will add a few more points to add credence and legitimacy to my, '€œTry blades, they may be better and you may like them'€ prophecy.

The Surge!

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Comments

Mark Lipton's picture

Submitted by Mark Lipton (not verified) on

With the proper stroke, I believe, it is better to drive a nail into wood with a hammer instead of a similar weighted skillet. The weight concentrated behind the impact point, rather than around the perimeter. This is my favorite analogy.
    Once a repeating swing is developed, or developing, a serious golfer could and should
move to blades. IMHO.

T Medley's picture

Submitted by T Medley (not verified) on

Mark,

I hear you, BUT, I still think it's better and less effort to use a nail gun.

PMG

Steve Smith's picture

Submitted by Steve Smith on

Ha ha! There was a guy on the course today that accused me of using a gun for one of my shots.

I hit my tee shot way out of position into a different fairway and was left with a second shot the whole way over the lake from 187 yards and the guys in that fairway waited for me to hit my shot so they could finish playing their hole.

I hit a great 7 iron on the green and one of them asked me what I hit. I told him a 7 iron and he said "are you sure it wasn't a shotgun?"
I just laughed and told him even a blind hog finds an acorn every now and then.;-)

Carlos's picture

Submitted by Carlos on

Dear Surge,
I am an old time follower of PPGS and for years I've adopted the 3/4 vertical swing with better than average results. I really love your system, videos and your knowledge. But as an engineer and scientist, I am sorry to tell you that you are humongously wrong about blades and cavity backs. Let me try to be simple in my explanation. In Physics studies the collision of two bodies there is only one thing that counts, is the Center of Gravity COG of the bodies. The COG of the club will impart force in the COG of the ball, period. Other important variables of the equation are the Coefficient of Restitution COR and mass of the body. To determine the Ball Speed there is an equation : BS = SS (1 + e)/(1 + m/M) where BS is Ball Speed, SS is swing speed, e is COR, m is mass of the ball and M is mass of the club head. COR is limited by USGA on all clubs in 0.83, mass of the ball is 46 g, mass of a driver head is 200 g. If you put these figures in the equation it will result, for 100 mph swing speed in 149 ball speed. Therefore, the smash factor for a driver is 1,49 max. Assuming that you hit it in the sweet spot. In irons, no matter if it is forged or cast, the face will not spring as in a wood, so the COR is much lower, around 0.75.
Here comes the great benefit of the cavity backs, the so called forgiveness. What is forgiveness? It will not cure a bat shot, but if you hit a blade in the sweet spot you will get the 0.75 COR. Let's put in the equation these numbers, 80 mph SS, 0.75 COR, 46 g ball mass, 255 g iron mass, and you will get 119 mph Ball Speed. BUT IF you miss the sweet spot of a blade iron by 1/4 of an inch you will get 0.55 COR, that put in the equation gives you 105 mph ball speed. 14 mph loss, that is approximately 28 yards that you lose. If there is water in front of the green on a par 3, you will hit the 3rd shot from the drop zone. On the other hand, if you miss the sweet spot of a cavity back GI iron by the same 1/4 of an inch you will get 0.69 and your ball speed will be 115 mph, only 4 mph loss, and a comforting 8 yards miss, on the same hole you will likely be putting the next shot. So if you do not have Rory McIlroy swing, put your ego out of the bag and game cavity backs.