In a previous article, “How Many Games will a Pickleball Last?”, we determined that the stiffness of the ball is not the primary factor that governs the height to which the ball will bounce. Therefore, balls of different stiffness can meet the USAPA bounce height standard of a 30-34” rebound from a hard surface when dropped from a height of 78”. We also demonstrated that when a Franklin X-40 is new, it is at the peak of its stiffness.
These findings have generated a considerable amount of discussion and questions among our readers. We all know from experience that a newer (and stiffer) ball will rebound from the paddle face crisper, with greater velocity, and with more “pop” than an older or softer ball. How then, can a softer ball rebound to the same height as a stiffer ball? If the rebound heights are the same for a soft or stiff ball, then why doesn’t a soft ball have the same amount of “pop” as a stiff ball? Let’s look at the science for answers to these questions.
Ball Stiffness
The stiffness of a pickleball is regulated by USAPA, where the ball must undergo no more than 0.25” of displacement under a load of 43 lbs. This standard was developed for baseballs and softballs and implies that the maximum stiffness of a pickleball is 172 lbs/in, which seems very stiff. Using our digital force gauge that we used in a previous article (“How Many Games will a Pickleball Last?”) we determined that a new Franklin X-40 ball has a stiffness of about 93.5 lb/in, or almost half as stiff as the standard. After about eight games, the stiffness of the ball reduced to 75.2 lb/in, almost 20% softer than a new ball (Figure 1).
Paddle and Ball Interactions
When you strike a pickleball with your paddle, the same amount of impulse force is applied to the ball whether the ball is stiff or soft. What is different, though, is that a stiffer ball will put more stress on the paddle face and cause it to deform like a trampoline. In a previous article, “How Large is the Sweet Spot?”, we performed a vibration test of a paddle to identify the so-called trampoline vibration mode (Figure 2).
Figure 2. Paddle Trampoline Mode
A harder hit or stiffer ball will cause a deeper trampoline deformation of the paddle face, which will spring back and add energy to the ball on rebound, giving the ball greater velocity. The trampoline deformation mode will not be as pronounced on a lightly hit or softer ball, and therefore less energy is added to the ball on rebound, giving it less velocity. This is the fundamental reason why a newer or stiffer pickleball will have more “pop” than an older or softer pickleball. This cannot be demonstrated in the USAPA drop test on a hard surface, as it is necessary to examine the interactions of the ball with the paddle face.
Players who use paddles with stiff faces (control paddles) will not notice a significant difference between a stiff or new ball verses a soft or worn ball. However, players who use paddles with soft faces (power paddles) may notice some degradation of their games when softer or worn balls are used. When playing a soft dinking game, neither of the paddles will have an advantage, as the ball is not being hit hard enough to create the paddle trampoline effect.
Why Does This Matter?
Competitive or advanced players who may prefer to hit the ball harder, with lots of spin and more speed may benefit the most from using newer or stiffer balls. These players should therefore select pickleballs with the highest stiffness out of the box that do not degrade or become softer with use. While these balls will provide the fastest play, they will (usually) come at a premium price.
Recreational or intermediate players who play for fun or exercise may not need to pay the added expense for high stiffness or high durability balls. These players may also prefer to play a slower game and/or they may not hit the ball sufficiently hard to gain a benefit from the trampoline effect. Intermediate players might also be working to improve their skills, where a slower or softer ball will offer a greater opportunity for learning. A medium-stiffness ball may therefore be ideal.
Beginners or players with limited mobility may want a slower ball and might pick one with a low stiffness out of the box. These will provide the greatest opportunity to learn their strokes, exercise the proper footwork, and improve their skills.
Future Articles
We have reached out to USAPA for an explanation of the ball test standard and have not yet received a reply. On face value, it doesn’t make sense for a pickleball to be as stiff as a baseball. A more realistic specification that would preserve the integrity of the game might be a displacement of 0.25” under a load of 32 lbs or less. This would yield a maximum stiffness of 128 lb/in.
Pickleball manufacturers might also define “competition” balls with high stiffness, “recreational” balls with medium stiffness, and “beginner” balls with low stiffness. In the coming weeks we will analyze and test several different balls to determine the feasibility of classifying them according to their stiffness and to define what these stiffness limits might be.
