MOI & MOIG measurement

Dedicated electronic devices allow to measure MOI (moment of inertia) of whole club fast and easy, but their prices are rather too high for occasional, home use.

Dave Tutelman describes the method which bases on the pendulum phenomenon. The value of whole club MOI can be calculated after some measurements that can be done at home. The most difficult task is to mount the club by the butt so that it can swing like a pendulum (see figure below and at the bottom of this page). If it succeeds, the procedure is very easy.

Pendulum for MOI measurement

Measurement method:

There are only four steps needed to compute the whole club MOI. Three measurements:
– the club’s period of the pendulum’s swing (with a stopwatch)
– the club’s total weight (with a postal scale)
– the distance of the balance point (CG) of the club from the edge of the grip cap (with a ruler)
and entering the measured data into calculator below.

Simultaneously, based on the same data, the calculator estimates the MOIG and BMI values that are used in the BioMatch club fitting method.

See the pictures at the bottom of the page. They shows how to measure the distance from CG to butt and how to mount the club to get the pendulum (the holder made at home and used by me for MOI measurements).

 

NOTES:

  • Conversion to other MOI units are available here.
  • The result of the calculation based on correct measurements is the good approximation, but it is still an approximation. Use it at your own risk.
  • A 3 g error in weight, a 6 mm (1/4″) error in distance or 0,01 sec in time will result in more than 3 kg*in² (one point) of error in the result. The accuracy of 1 gram, 3 mm (1/8″) and 0,005 sec is required.
  • Measuring the period accurately enough is hard, but achievable. It can be done by measuring the time of 40-50 pendulum cycles with a stopwatch and divide the result by the number of cycles. The alternative method is to use a smartphone application designed for slot cars lap times tracking (e.g. Mini4WD) and take the average time of one cycle after 50 cycles (it is 100 car laps in the application).

 

Center of gravity of the golf club

 

MOI pendulum holder

 

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update: November 2021