Fig 1

Fig 2

Fig 3

Fig 4

There have been a number of studies showing that (assuming a player can maintain the same bat-swing speed) using a bat with a larger moment-of-inertia (MOI) will enable the player to hit balls faster and farther. So it is not surprising to find that another popularly used technique is to alter the weight distribution; either by adding weight to the barrel end or by moving weight from the knob to the barrel without altering the total weight so that the balance point moves further out from the handle and the moment-of-inertia increases. According to some Senior Softball discussion groups, one of the more popular high performance bats (Miken Ultra 2) is often end-loaded by simply removing the iron rod in the handle.
The bar chart above shows the batted-ball speeds measured for four bats (single-wall aluminum, wood, multi-wall composite, and multi-wall aluminum) before and after the moment-of-inertia had been increased by 20%. The increase in moment-of-inertia was obtained by adding weight to the barrel end of the bats in a fashion similar to that used by some of the more popular bat doctors. In all four cases, the increase in moment-of-inertia resulted in an increase in batted-ball speed, usually by about 3 mph.

Science of End Loading

COR versus Compression
Both baseballs and softballs come in a variety of stiffnesses. Softer balls are often used for younger less experience players because if a player is hit with a softer ball it doesn't do as much damage and the game is thus a little safer. More experience players usually don't like to play with these "dead" balls and prefer harder, more lively balls. Sometimes, the weather conditions,especially the temperature, may dictate choosing a certain type of ball over another. Weather conditions can be a problem since the elastic properties of baseballs and softballs change significantly depending on the temperature and humidity of the environment in which the balls are kept. When you pick up a softball you will usually find two numbers printed on the ball as ratio, something like 375/.44. These two numbers represent the compression and Coefficient-of-Restitution (COR), respectively. The compression is simply the amount of force in pounds that is required to compress the ball a quarter of an inch, and it represents the "hardness" of the ball. Compression is measured by performing a static compression test on the ball. A compression value of 375 means that if 375-lbs of force were applied to the ball it would compress by 0.25-inches. If you held a 375/.44 softball in your hand tried to squeeze it as hard as you can, and then try the same thing with a 575/.44 ball, the 575 ball would feel harder because 200 more pounds of force are required to compress the ball the same amount. The second number stands for the coefficient-of-restitution, or COR, and represents the elasticity or springiness of the ball. The COR is measured by firing a ball from an air cannon at 60-mph (or 90-mph) towards a rigid surface and measuring the ratio of rebound speed to initial speed. You could compare two balls by dropping them from the same height onto a flat cement floor. If you compared a 375/.47 ball with a 375/.40 ball you would find that the .47 COR ball would bounce slightly higher.

Science of Softballs and the Effects of Temperature

Fig 5

But, it cannot be disputed that shaving a bat to make the barrel wall thinner does indeed improve performance. The two graphs below were provide to me by a manufacturer and show the measured batted-ball speeds for an aluminum bat (left graph) and composite bat (right graph) for which the walls were successively shaved. Removing 0.01" of material in the aluminum bat increases the batted-ball speed by 4-mph. If the original bat had the ASA certification stamp (indicating batted-ball speed below 98-mph), the modified bat now well exceeds the ASA performance limit and is now illegal. The change in the composite bat is even more dramatic. Starting with a production model bat and shaving off 4 plies on the inner diameter increases the batted-ball speed by 6.5-mph. This bat, which originally came in just under the 98-mph limit now drastically exceeds the limit, with a measured batted-ball speed of 104-mph.

Science of Bat Shaving

The bar chart at right shows the measured change in performance for several aluminum and composite slow-pitch softball bats both before and after sending them to a bat doctor for shaving. The bats labeled "MAxx" are multi-walled aluminum bats and those labeled "MCxx" are multi-walled composite bats. The batted-ball speed for very single bat improved by at least 2-mph, with some bats improving by almost 8-mph. The ASA performance limit is 98 mph, and every single one of these doctored bats exceeds this upper limit after being shaved. In other words, every one of these altered bats is now illegal.
Just to put an 8-mph increase in performance in performance in perspective, the difference between a softball leaving a bat at 98-mph and a softball leaving a bat at 106-mph is about 62 feet in additional distance travelled.

Composite Bats are made by pressing layers of resin and fiber together (see video). The resin can be broken up in between each layer of composite by Bat Rolling. The bat is placed in between 2 rollers and pressure is added to flex the bat in order to break up the resin. As the resin breaks up the fiber is free to flex which gives the bat more of a trampoline effect. This trampoline effect equates to greater batted ball speeds. This effect can also be achieved with aluminum or alloy bats also. The metal becomes more malleable which also causes a trampoline effect and more distance to the batted ball.

What Exactly is Bat Rolling?

Perpendicular bat rolling was the first type of bat rolling machine to be manufactured. Perpendicular bat rolling was the industry standard in the infancy of rolling. The Perpendicular method breaks the resin up in 1/4 of an inch stripes along the barrel at maximum pressure (see fig 1-2). As bat rolling evolved so did the machines and the parallel roller was created. The parallel roller is able to put consistent pressure along the entire circumference of the barrel to break up resin completely (see fig 3). For this fact perpendicular rolling followed by parallel rolling has become the bat rolling standard.

Parallel rolling is optimized with a 6 inch roller. Most slowpitch softball bats have a 9 inch sweet spot (see fig 4). Parallel rolling will cause the barrel to flex about 1 1/2 inches past the roller at maximum pressure (see fig 5). The flex should not extend into the end cap area or the taper area for risk of damaging the integrity of the bat. The 6 inch roller will not damage the taper area or end cap area but a larger roller has the potential to flex the composite material in these areas and cause structural problems with the composite.

What are the effects of perpendicular and parallel bat rolling?

Recently, several bat manufacturers and some scientists have suggested that a better (and safer) way to control the game would be to regulate the balls used in a game (i.e., choosing a deader or softer ball) instead of banning bats as is the current practice.

Here is a brief synopsis of .52 core balls vs. regular balls.

Most polyurethane cores are VERY sensitive to temperature, especially those with little flexibility (ie low cor. balls). Tests have shown that classic M balls can have compression fluctuations of 400 lbs. going from 40 degrees to 90. In cold temps the M balls can get to 600+ PQI while dropping all the way to 175 in 90 degrees. That is why softballs feel so much harder when you hit them in cool temps vs. hot. It is also why an M ball feels like a pillow and goes nowhere in very hot weather. The .52 275 is different from almost every other ball in that it has a very high cor. (flexible or bouncy core) and a very low compression. This combination makes the core pretty much impervious to temperature change. You'll essentially be hitting the same ball at 40 degrees as you do at 90. With that said, the .52 275 starts soft and stays soft.