Educational tools

In this section, you can find detailed description and definitions of all the parameters that make up the racket and it’s playing characteristics. I try to make everything as easy to understand as possible, while also backing up the principles with equations and definitions from the physical perspective. Not all variables are equally important when customizing rackets. For my take on important parameters check this chapter.

Racket variables

First I want to introduce you to important racket variables and principles, that you need to consider before you start modifying your racket. First there are variables that are pretty much set in stone when you select a racket, and that you generally can’t change with modification:

  1. Head size
  2. String pattern
  3. Stiffness and beam construction

And then there are parameters, on which you can have an impact on with modifications:

  1. MR^2 – Mass and balance
  2. Swingweight
  3. Twistweight
  4. MGR/I
  5. AIM – Average Impact Mass
  6. Strings
  7. Grip shape and size
  8. Length

I will describe and define the first group of variables here, while the second group deserves separate chapter because it’s what we can influence through modification.

Head size

Bigger head size equals more power and gives you more margin for error when swinging fast and upwards, meaning you are less likely to shank the ball or hit it with the frame. But against popular belief, head size does not directly equal a more forgiving racket. A forgiving racket is a racket with a big sweet spot and offers high power levels even on the off-center shots. So a big head size alone will not make your racket forgiving. Two players that come to mind with 100 sq. Inch head size and jet unforgiving rackets are Rafael Nadal and Alexander Zverev.

They both have low twist weight, which is the parameter that influences forgiveness the most. But a trade-off is less feel, control, maneuvrability and so on. What is true is that bigger head size means more mass will be further away from the rackets Y axis, meaning it will increase twistweight. But this would only hold true if we compare let’s say a 100 sq. Inches and 90 sq inch racquets, with the same beam construction…the 100 sq. inc one will have more mass further away from the Y axis, and that’s why generally rackets with bigger heads will have higher twist weights. You can read more about this topic in chapter »Twistweight«.

The increased power that comes from big head sizes is primarily because the main and cross strings are longer and can stretch more.

In the early days of so-called tweener rackets, there was a lot of rackets with bigger head sizes and lower twistweights. Nadal’s racket is a good example of that. Today Babolat evolved the Aero line to be more user-friendly and forgiving by increasing the twistweight, but Nadal is still playing with the original version. His racket has a small sweet spot but a very powerful one. That’s why he likes to stand far back from the baseline to give himself a better look of the ball and more time to hit the ball in the sweet spot. That’s also why he is so dominant on clay courts, where he has more time.

String pattern

The most common string patterns are 16/19 and 18/20. There are variations in between, but in general, fewer strings give more spin and power, while more strings or denser string patterns provide more directional and depth control. The string pattern also affects the launch angle of the ball leaving the racket. More open string patterns have higher launch angles, meaning that the ball flies higher above the net. This, of course, holds true if everything else is equal in terms of strings and racket set up. For example, you can make an open string pattern play more like a dense one with thicker strings and vice versa. Denser string patterns also result in a stiffer string bed and less string movement, while more open patterns enable strings to move more and feel softer. String movement is one of the main factors that affect how much spin can a racket impart on the ball.

Other things to consider are for example using a thinner string in a dense string pattern because in a dense string pattern, strings hold their tension better and don’t break as easily and thinner strings generally have better playability characteristics. You can read more about strings and string pattern interaction in the subsection strings.

Stiffness and beam construction

Modern graphite or any other composite racquets are much stiffer than what used to be the standard in the old days – wood. Modern materials are also stronger and can be manipulated in different layups. A layup is how for example, the layers of graphite are put together. While they are stronger, which means the racket can be made lighter and not break or give under the forces that are exerted on it, during the contact.

An important factor is also that graphite racquets are hollow when old wood racquets were solid. If you take any given mass, for example around 300 grams for a racquet, and you make it in to a solid cylindrical shape, it is much easier to bend that 300 grams of the same material in a hollow cylindrical configuration, but in a hollow configuration, the tube will have a larger overall diameter. That’s why with modern materials, the beams of the racquets are hollow and thicker. The cross-section is also not symmetrical or even sided. For example, let’s take a wood or plastic ruler and bend it. It will be much easier to bend it across the narrow part, than edgewise. This is important when designing a beam shape while considering the racquet stiffness. Tennis racquet frames have a hollow cross-section that is longer in the bending direction, that is at the right angles to the string plane. The modern tweener racquets usually with big heads, have a more pronounced asymmetry of the cross-section. The beams are for example 25mm or thicker, which makes them very stiff.

Like mentioned in the previous chapter about head sizes, this principle can be used to create racquets with bigger head sizes and jet lower twistweight, by varying the beam width, for example making it thicker on the sides, so that the stiffness remains the same, but less material is used, resulting in less mass on the sides of the hoop and lowering the twistweight.

Stiff racquets deform less and vibrate with a smaller amplitude (but with higher frequencies) when exerted to the forces at contact. The vibration frequency of racquets is between 80 Hz for a very flexible wooden racquet and 200 Hz for a very stiff modern racquet. If you hit the ball properly in the middle of the strings than the racquet will not vibrate at all and it will not feel stiff or exert forces into your arm, regardless of the frame stiffness. Frame stiffness is a factor only if you mishit the ball. It’s a general misconception that a stiff frame leads to injuries. It actually stiff strings that are much worse. A combination of a stiff string and a stiff racquet on a mishit ball is what lead to elbow and wrist injuries.

Considering all this, stiffer frames also lead to increase of power especially on hits outside of the sweet spot, because less energy is lost during the impact due to the frame flexing and vibrating.

It’s also worth mentioning that lighter racquets need to be stiff, because there is not much mass moving through the contact and the frame would bend too much, leading to a significant loss of directional control.