MGR/I: the value that says whether the racquet arrives on time
Mass, balance and swingweight each describe part of a racquet, and none of the three says whether it arrives on time. That is the first thing a player feels, though: either the racquet sets itself up, or it has to be dragged.
MGR/I is the value that describes this. It is not a score, and it is not a sales argument. It is a ratio, and it is worked out from three numbers you can have measured.
What we are talking about
Held at the end of the arm, a racquet is a pendulum. Like any pendulum it has a natural period: a speed at which it wants to swing, which depends only on how its mass is distributed.
MGR/I is the ratio between the racquet's gravitational moment — what makes it fall — and its inertia — what stops it. In other words: how fast it naturally swings at the end of the arm.
When that speed matches the stroke, the racquet arrives on time without being pushed. When it does not, the arm corrects — early or late — and that correction is exactly what tuning sets out to remove.
The formula
It is worked out from mass in grams, balance in centimetres from the butt, and swingweight in kg·cm².
MGR/I = ((Mass / 1000) × 980.5 × Balance) / (SW + 20 × (Mass / 1000) × Balance − Mass / 10)
The 980.5 is gravitational acceleration in centimetres per second squared. The rest of the denominator converts swingweight, measured about a conventional axis 10 cm from the butt, into the inertia about the point where the hand actually holds the racquet.
One example, end to end
Take a common frame: 310 g strung, balanced at 32.0 cm, swingweight 320.
Numerator: 0.310 × 980.5 × 32.0 = 9,726.6
Denominator: 320 + 20 × 0.310 × 32.0 − 31.0 = 320 + 198.4 − 31.0 = 487.4
MGR/I = 9,726.6 / 487.4 = 19.96
Nothing mysterious: three measured numbers, one division, a result around 20.
What four grams do to it
This is where the value becomes interesting, because it does not behave like swingweight. Take the same frame and add four grams, once at the tip, once in the butt.
Four grams 66 cm from the butt: mass goes to 314 g, balance to 32.43 cm, swingweight to 332.5 — +12.5 points. MGR/I falls to 19.78.
Four grams 12 cm from the butt: mass goes to 314 g, balance drops to 31.75 cm, swingweight stays at 320.0 — unchanged. MGR/I rises to 20.03.
The same material, two places, two unrelated effects. Swingweight moves twelve and a half points in one case and not at all in the other; MGR/I moves a quarter of a point one way and a twentieth the other.
That is precisely why you do not tune a racquet by "adding weight". A gram has no value in itself: it only has one in a place.
Why it moves so little, and what that means
Anyone new to tuning expects a value to react strongly. MGR/I does the opposite: it is remarkably stable under small additions of mass.
That is not a flaw, it is its nature. MGR/I describes a family of racquets, not a fine setting. It says whether the frame in your hand belongs to the group that follows your stroke or to the group that fights it. Once you are in the right family, it is swingweight, recoilweight and twistweight that do the detailed work.
Put another way: MGR/I is a constraint, not a dial. You check that you stay inside it while you move everything else.
What it does not say
Three things, and they are worth knowing before you get attached to the number.
It says nothing about stability at contact. A racquet can have an ideal MGR/I and still get pushed back on every heavy ball. Recoilweight and twistweight describe that, and they are tuned elsewhere.
It says nothing about the string. And string decides an enormous share of what you feel, at fifty times less than the cost of changing a frame.
It says nothing about stiffness. Two frames at the same MGR/I, one at 62 RA and one at 72, do not send the same thing back up the arm.
A value "around 20", not a score
On common adult frames, MGR/I most often falls between 19 and 21. We do not turn it into a mark out of twenty, and we publish no universal ideal: the value that suits you depends on your racquet-head speed and the length of your arm, not on a scale.
What we do with it is use it as a decision criterion: when the same mass could go in two places, MGR/I is what settles it. The full reasoning is in the Matcheur method.
Working it out on your racquet
You need three readings, and the third is the problem.
Strung mass comes off a kitchen scale, overgrip and dampener included. Balance is found by resting the racquet across a table edge until it holds on its own, then measuring from the butt.
Swingweight, no. It cannot be measured at home: it needs a bench. That is the honest limit of the exercise, and it is also why no product sheet gives it to you.
If you have all three, the division above is enough. If you only have the first two, the configurator places your setup from your physique and your racquet-head speed, and the workshop records all three on your frame when it goes on the bench.
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