Iron (golf)
An iron is a type of club used in the sport of golf to propel the ball towards the hole. Irons typically have shorter shafts and smaller clubheads than woods, the head is made of solid iron or steel, and the head's primary feature is a large, flat, angled face, usually scored with grooves. Irons are used in a wide variety of situations, typically from the teeing ground on many par-3 holes, from the fairway or rough as the player approaches the green, and to extract the ball from hazards, such as bunkers or even shallow water hazards.
Irons are the most common type of club; a standard set of 14 golf clubs will usually contain between 7 and 11 irons, including wedges. Irons are customarily differentiated by a number from 1 to 10 that indicates the relative angle of loft on the clubface, although a set of irons will also vary in clubhead size, shaft length, and hence lie angle as the loft increase. Irons with higher loft than the numbered irons are called wedges, which are typically marked with a letter indicating their name, and are used for a variety of "utility" shots requiring short distances or high launch angles.
Prior to about 1940, irons were given names rather than numbers. Some of these names, e.g. mashie, niblick, are found in literature of the early twentieth century. Although these clubs and their names are considered obsolete, occasionally a modern club manufacturer will give a new iron the old name.
Design and manufacture
Historically all irons were forged from a flat piece of metal, which produced a thin clubhead that resembled a blade. Modern investment casting processes enabled manufacturers to easily mass-produce clubs with consistent properties. This manufacturing process was first used by Ping, and also made it possible to take weight out of the back of the clubhead and distribute it around the perimeter. These perimeter weighted, or cavity back, irons made it much easier to achieve consistent results even when striking the ball outside the "sweet spot", when compared with traditional bladed, or "muscle back", irons.In 1933, Willie Ogg – who was serving as an advisory staff member for Wilson Staff – created a patented design for distributing weight away from the heel of the club head, moving it towards the "sweet spot" of the blade. This design feature was used in the Wilson "Ogg-mented" irons, the forerunner of perimeter-weighted or cavity back irons.
Although most irons are now produced by investment casting, many high end iron sets are still produced by forging, as the resulting clubhead is easier to adjust by bending to adapt the set to a player's specific needs. The resulting club is also generally thought to have an improved "feel" due to the softer consistency of the forged metal as opposed to cast.
Manufacturers sometimes try to combine the characteristics of both muscle and cavity backed irons, which has resulted in terminology such as "cut-muscle", or "split-cavity" to describe these designs.
There are also many hybrid clubs, so-called because they combine some of the characteristics of irons and woods, that closely resemble standard irons. Many sets of clubs, especially those marketed for beginners, now include hybrids to replace the more traditional 3 and 4 irons.
Muscle back
A muscle back is the more traditional design and consists of a solid metal head, typically made of forged iron. The design of the club typically distributes the metal more evenly around the clubhead, which makes the center of mass of the club higher and the moment of inertia lower as compared to newer cavity-backed designs. As such, these clubs are said to have a smaller "sweet spot", requiring greater skill and a more consistent swing to make accurate, straight shots. Novice golfers with less consistent swing fundamentals can easily mishit these clubs, causing shots to launch or curve off of the intended line of play.A "muscle back" is also commonly referred to as "blade". The name "blade" can give golfers a better understanding of what type of club face they are hitting with. As mentioned with the "muscle back", these irons have rather smaller club faces and smaller sweet spots than cavity back irons. Most people understand a "blade" to be a very flat section of a device, which is why these smaller and "flatter" irons are referred to as "blades".
Cavity back
Cavity back, or perimeter weighted, irons are usually made by investment casting, which creates a harder metal allowing thinner surfaces while retaining durability and also allows for more precise placement of metal than forging techniques. Cavity backs are so called because of the cavity created in the rear of the clubhead due to the removal of metal from the center of the clubhead's back, which is then redistributed, most of it very low and towards the toe and heel of the clubhead. This has the general effect of lowering the clubhead's center of mass, placing it underneath that of the ball allowing for a higher launch angle for a given loft. The perimeter weighting also increases the moment of inertia, making the clubhead more resistant to twisting on impact with the ball. The result is a clubhead with a larger "sweet spot" that is more forgiving of slight mishits.Comparison and preference
Modern clubs generally borrow from both "muscle-back" and "cavity-back" design features and fall into a gradient.Club sets with more extreme perimeter weighting, giving the clubhead a very wide sole, are typically known as "game improvement irons", because they allow novice and casual amateur players to get the ball up in the air more consistently, and make straighter and more accurate shots despite their less consistent ball-striking skill. This generally improves their final score as compared to a round played with harder-to-hit muscle-back designs causing more errant shots and thus more penalty strokes.
However, these same forgiving characteristics can make game improvement irons harder for a skilled golfer to use well. The tendency of the clubs to correct mishits will frustrate a golfer's attempts to intentionally hit a curved shot, for instance to avoid an obstacle lying along a straight flight path, or to counter a rightward or leftward slope to the fairway that would make a straight shot roll into the rough. This lack of ability to "work the ball" can frustrate a more skilled golfer attempting to place the ball more accurately on the fairway than a novice would normally be concerned with. The increased clubhead mass and lower center of mass can also be incompatible with a more skilled player's stronger swing; the higher mass reduces clubhead speed, while the higher launch angle causes more backspin and wastes the golfer's energy sending the ball up into the air instead of out over the fairway.
Clubs intended for skilled amateurs and professionals, while still incorporating some perimeter-weighting characteristics, generally have less extreme weight distribution, instead placing more weight closer to the center and higher, and reducing overall clubhead mass slightly. This allows the golfer to "work the ball" while still giving some advantage based on the lower center of mass as compared to older designs. The slightly reduced mass of some sets also increases clubhead speed allowing for more variation in swing strength and thus carry distance than would be possible with the heavier mass of most game improvement irons.
Components
Clubhead
Investment casting, while allowing for a greater range of design options, produces a very stiff and inflexible head that can be difficult to adjust for a player's desired lie and loft. Forged irons, while they allow for easier and a greater range of adjustments, are limited in the designs that may be achieved.The shaft length of an iron decreases as the iron's number increases; therefore, the iron number is inversely proportionate to its length. This reduced length means that a clubhead of the same mass traveling at the same angular velocity has lower momentum because the clubhead's speed is slower. To combat this, higher-numbered iron clubheads are heavier than lower-numbered iron heads; there is generally a increase in mass between one clubhead and the next higher number.
Due to the average golfer's desire to hit the ball farther, the loft on modern irons is much less than that on irons from even the late 20th century. For example, a modern 9-iron has comparable loft to a 7-iron from the 1990s. Manufacturers have been able to reduce loft without compromising usability, by moving weight into the sole of the clubhead, thereby lowering the center of gravity and enabling the ball to be launched on a higher trajectory for a given loft than a design with a higher center of mass. Tour professionals now use these same de-lofted clubs, and so the gap in skill and thus in distance between a professional and casual golfer remains.
Over the years, groove technology has changed the playability of irons. For the past 80 years, little has changed about grooves. However, a new rule by the USGA and the R&A has changed the way that grooves are to be made starting in 2010. In general, the deeper the groove, the more grass can be dispersed behind the ball at impact. This allows control over the amount of spin, which is crucial to flight characteristics of the shot as well as how well received the ball is on the green. The less that is between the ball and the club at impact, the more spin that will be produced which, while decreasing launch trajectory, allows the ball to stop quicker upon hitting the green due to the spin limiting the balls rolling speed at impact. Better players benefit the most from deep, sharp grooves as the more clubhead speed is generated, the more spin the player is able to introduce. By forcing manufacturers to lessen the depth and cut on the grooves, the new rules will penalize shots from longer grass slightly more and put a premium on hitting the fairway.