Easy to hit: why?

[Open-Faced Club Sandwedge]

I know it's an accepted rule that a cavity-back is "easier to hit" than a muscle-back, and that a multi-material wide-sole deep-cavity technologically-enhanced cavity back is "easier to hit" than a forged cavity-back, and that according to many a hybrid is "easier to hit" than a long iron of comparable length.

Why? Physically, what is it about the "game improvement" aspects of clubs that actually makes them more forgiving? Why would a 4-hybrid be easier to hit than a 4-iron? What's actually going on during the club-ball interaction that magically forgives (or at least mitigates) your mistakes?

-Andrew

[Shorty]

In a cavity back club, the weight is distributed around the perimeter of the club so that there is more "weight" behind shots that aren't hit in the middle. With more traditional clubs, or "blades" as so many wannabes are apt to call them, (even though most of them aren't blades at all) the mass of the club is right behind a shot struck in the middle - good players pretty much only hit the middle, so they don't need forgiveness to the degree newer or unskilled players do, but the majority of top players do not use clubs with a tiny sweet spot, they generally use clubs with some GI weight distribution features. Effectively, with a GI club, you could hit the ball an inch or more away from the middle and you'd likely still get a reasonable result - depending on your expectations and skill level.
A lot of GI clubs have a lot of weight at the bottom of the club, which helps get the ball up in the air, something that new players have difficulty doing.

That being said, because so many golfers who frequent sites such as this are interested in golf equipment rather than golf, they persist in using clubs that don't suit their abilities.

[Open-Faced Club Sandwedge]

So what actually happens differently when a perimeter-weighted club hits the ball slightly off-center, as opposed to when a uniformly-weighted club hits the ball off-center? Does the clubhead actually twist more in the uniformly-weighted one, due to the lower moment of inertia?

-Andrew

[James_Black]

So what actually happens differently when a perimeter-weighted club hits the ball slightly off-center, as opposed to when a uniformly-weighted club hits the ball off-center? Does the clubhead actually twist more in the uniformly-weighted one, due to the lower moment of inertia?

I don't think so, have you ever hit a true blade?

If you don't hit it in the middle the ball flies a lot shorter. I think it's because less mass is near the toe/heel of the blade than in the middle, cavity backs have more weight in these area's so that you'll still hit a good shot.

[sean_miller]

I know it's an accepted rule that a cavity-back is "easier to hit" than a muscle-back, and that a multi-material wide-sole deep-cavity technologically-enhanced cavity back is "easier to hit" than a forged cavity-back, and that according to many a hybrid is "easier to hit" than a long iron of comparable length.

My experience is mixed. I don't have a problem with getting consistent distance or height out of my long irons, so there is no distinct advantage for me to go with a hybrid - up to the 3 iron that is. There are studies that show however, that once an iron gets lower than 23 or so degrees loft it's exponentially harder to hit consistently. I honestly have to really put a good strike on the ball to hit my 2-iron. My 19* hybrid on on the other hand, is about as hard to hit as an 8-iron. Whether it's the lager effective sweet spot, or the weight distribution, I don't care. It took a season, but the 2-iron is on the shelf (unless we play in gale force winds). With wedges and irons I think the main advantage for a mid handicapper like me would be distance control - not worried about leaving the ball short, but I do hit the odd one flush that goes too long. I suspect cavity back players don't have that problem. At least not so severe. Regarding direction control, if your clubface is going wide of the target, your F'd no matter what, but the higher the MOI (as you mentioned) the greater the resistance to twisting in your hand. I can hit a ball off the heel of my MP-11 4-iron and be pin high, but over on the right apron instead of on the flag. During impact, I can feel the club trying to twist in my hands and as I fight it, I'll push the ball to the right. With a GI iron that ball might still be on the putting suface. Over the course of 18 holes that would probably mean more birdie putts. I've considered GI irons, but they're expensive (at least the ones that I like are expensive) and this is just my hobby so who gives a shi+ what I have in the bag?!?

[iacas]

I don't think so, have you ever hit a true blade?

Not necessarily. The guys installing the wood flooring are about done so I don't have the time right now but I remember seeing an article fairly recently that talked about how on certain kinds of hits (heel, I think) the blades outperformed the cavity backs on both distance and accuracy (IIRC).

[jamo]

Cavity backs have a center of gravity that is lower and farther from the face, which result in a higher MOI, giving you increased ball speed on mis-hits due to a higher COR outside of the sweet spot. Cavity backs also tend to have thicker sole, which help people who chunk the ball.

[delav]

Why? Physically, what is it about the "game improvement" aspects of clubs that actually makes them more forgiving? Why would a 4-hybrid be easier to hit than a 4-iron? What's actually going on during the club-ball interaction that magically forgives (or at least mitigates) your mistakes?

http://en.wikipedia.org/wiki/Moment_of_inertia http://en.wikipedia.org/wiki/Center_of_gravity

[Open-Faced Club Sandwedge]

http://en.wikipedia.org/wiki/Moment_of_inertia

Believe me, wiki-level definitions of general physics concepts is not what I need.

How do these concepts come into play during the club-ball interaction? -Andrew

[James_Black]

Believe me, wiki-level definitions of general physics concepts is not what I need.

did you bother reading them?

moment of inertia, also called mass moment of inertia, rotational inertia, or the angular mass, (SI units kg·m2) is a measure of an object's resistance to changes to its rotation

SGI clubs have a higher moi than players clubs.

with golf clubs a lower center of gravity will launch the ball higher, that is why SGI irons have lower lofts, they launch the ball higher.

[Leftygolfer]

Toe misses are much shorter with smaller player cavities in my experience. That is my miss and why I moved to a more forgiving iron. There is just less mass out there so less energy is transferred and it flys shorter.

[double_j]

Said simply - a high MOI on the clubhead means that it's not as easy for the clubface to twist when hit off center. This means that a shot off the toe will act very similarly to a shot off the middle. This is actually undesireable for those people who like to 'work' the ball, since they need the ability to move the clubhead around at will.

And a lower CG just makes the ball go higher for any given loft. This helps the amateur with a slower swing speed get the ball up into the air more consistently. Players who like to control their ball flight (high/low, etc.) and/or with swing speeds fast enough to generate adequate spin on the ball don't necessarily want or need this.

[boogielicious]

Heres an extreme analogy: Think of the club as a pendulum on a wire. Imagine the head of the pendulum is shaped like a rod the size of a dime in diameter and 3 inches long. You are trying to hit the ball with the dime sized end. If you are off by just 1/2 of the diameter from the center at impact, most of the weight will be off to one side of the impact center. The rod will deflect to that side at impact and try to turn. The ball will not receive full impact during contact with the rod (the ball compresses and is on the face for a small amount of time) because the rod is turning during impact.

Now imagine another rod that is the same weight, but the diameter of a silver dollar. It is also 3 inches long but we've hollowed out the area behind the center on the back side to keep the weight the same as the first rod. Now if we hit the ball 1/2 dime width off center, we still have almost all the weight evenly distributed behind the ball. The second rod will not want to turn as much and we will hit the ball farther.

For golf clubs, the difference is not as extreme, but the principle is the same.

[sean_miller]

Heres an extreme analogy: Think of the club as a pendulum on a wire. Imagine the head of the pendulum is shaped like a rod the size of a dime in diameter and 3 inches long. You are trying to hit the ball with the dime sized end. If you are off by just 1/2 of the diameter from the center at impact, most of the weight will be off to one side of the impact center. The rod will deflect to that side at impact and try to turn. The ball will not receive full impact during contact with the rod (the ball compresses and is on the face for a small amount of time) because the rod is turning during impact.

To me, thinking about head of a blade v. CB golf club is pretty straighforward. At least, more straightforward than the swinging rod analogy - especially since the ball is now being struck with a round surface instead of a relatively flat surfaced club head.

[Open-Faced Club Sandwedge]

did you bother reading them?

I did not read them (although I did scan them to see if there was a section for "applications in golf"). I know what moment of inertia means. I know what center of gravity is. I don't need my intelligence insulted when I ask a question, with a response that assumes the reason I'm asking is that I don't understand what wikipedia can tell me about basic physics concepts.

What I didn't understand when I asked (which I now do understand), is why moment of inertia matters so much during the incredibly brief club-ball contact, during which there is not time for the clubhead to rotate more than a few nanodegrees. Instead of asking "why" for the umpteenth time in this thread, though, I tried putting some real effort into relating club MOI to ball velocity in an off-center hit. I think I've now figured out I really needed to be thinking of it in terms of momentum transfer. The collision with the ball transfers some amount of the club's momentum to the ball. Some amount of this momentum is retained by the club (follow-through). Some amount becomes the ball's spin. And some amount transfers as torque on the clubhead. Higher club-head MOI means more resistance to this torque, means less of the pre-contact energy becomes rotational energy of the clubhead, means more energy actually transferred to the ball. -Andrew

[delav]

I did not read them (although I did scan them to see if there was a section for "applications in golf"). I know what moment of inertia means. I know what center of gravity is. I don't need my intelligence insulted when I ask a question, with a response that assumes the reason I'm asking is that I don't understand what wikipedia can tell me about basic physics concepts.

Basically, yes. The negative effects of off-center hits are reduced by high-MOI clubheads, due to the resistance to twisting and deflecting during impact. Low CG clubs apply the same principles of energy transfer discussed above, and help generate higher launch angles.

I wasn't trying to insult anyone. However, an understanding of MOI and CG should make it fairly obvious why GI clubs are "easier to hit."

[WUTiger]

I know it's an accepted rule that a cavity-back is "easier to hit" than a muscle-back, ... Andrew

You actually have three or four questions in your thread. Since you're interested in the details, try out club designer Ralph Maltby's web site. Do a search on some of your terms, and you'll get the engineer's description plus diagrams:

http://ralphmaltby.com/ Maltby did a book in 2005 called The Maltby Playability Factor . It's 272 pages spiral bound, and has full color engineer' drawings about historic development of golf clubs. It's out of print, but you can sometimes find a copy for $2 or so in golf shop clearance bins.