3 More Golf Equipment Terms Explained and How They Can Help Your Game

Centre of Gravity (COG)

Centre of Gravity heights, photo by @kirkoguri on Twitter

Centre of Gravity (CG) is a point in the head that represents all the mass of head. The above photo shows the position of the centre of gravity in 4 different heads by height. Only minimal differences but enough to make the heads perform quite differently.

The CG is sometimes referred to as the sweet spot of the club. The sweet spot is the projected position of the CG from inside the club on to the club face. It is quite a small spot and is not bigger in some clubs then other.

When the ball is hit on the 'sweet spot' the club face doesn't twist or rotate and the maximum amount of energy is transferred to the ball.

The CG can be moved around the club head by shifting weight, move weight towards the toe the CG goes towards the toe (a small bit, not a huge amount). Moving the weight around influences the flight of a ball by utilising gear effect to help the golfer. More weight in the heel will promote a draw from centred strikes and straighter shots from heel strikes. The spin rate can also be influenced by moving the CG higher or lower.

Moment of Inertia (MOI)

Moment of inertia (MOI) is the measure of an object's resistance to twisting. The higher the MOI the more the object will resist twisting. For a golf club this means for shots that are mishit a head with higher MOI will twist less offline then a club with lower MOI.

In golf heads weight is moved to the perimeter to increase MOI and make them more forgiving. So a cavity back will be more forgiving then a blade. This is also the process that makes a 'sweet spot' bigger, it's not making the 'sweet spot' bigger but the club head twists less giving more forgiveness and the illusion of a bigger sweet spot.

It also helps with putters a big mallet style putter with weight moved to the extremes will not twist as much as a blade style putter meaning the ball will start more online with mishits.

Roll & Bulge

Roll is the curvature on the face of a wood from crown to sole.

Bulge is the curvature on the face of a wood from heel to toe

Bulge and roll are there to counteract what is known as gear effect. When a driver is struck off-centre, the head wants to twist, roughly about it's centre of gravity. In the period of time between impact and separation, the friction between the club face and ball adds spin to the ball in the opposite direction to the rotation of the club head. this is much the same way that in a 2 gear system, if one gear is rotated, the other rotates in the opposite direction (thus the name gear effect.) 

The purpose of bulge is to modify the initial launch direction to compensate for the shape in ball flight caused by an off centre hit. For example on a heel strike the ball will move more left to right and as a result we would like the ball to start further left to compensate for this.

Roll directly effects loft in the vertical plane on the face. A ball hit higher on the face will spin less due to gear effect but will launch higher due to the roll, a ball hit lower on the face will spin more due to gear effect but will launch lower due to roll. These compensations lead to better results from mishits.


Any questions or comments are appreciated.

Effect of Temperature on Golf Balls

As we are well in the Winter season a good question would be how much does the temperature of a golf ball effect performance?

Is it ok to leave your balls in your bag in the car or garage or should you take them indoors? To test this I put 20 Titleist Pro V1s in the car and left them there overnight on a frosty night, air temperatures dropped to -3 degrees C. Also I kept 20 Pro V1s indoors at room temperature.

As soon as the frost cleared the following day I hit 20 balls that were kept in the car and 20 balls that were kept at room temperature. The golf balls that were kept in the car were noticeably cold to touch, the room temperature balls felt normal.

The balls were hit with a Callaway Big Bertha Alpha, 9.5 degrees of loft and a Fujikura Speeder 757 S Flex shaft. The results were recorded on a Trackman 111 launch monitor. 5 cold balls were hit, then 5 room temperature balls were hit until a total of 20 of each ball were hit. The temperature was around 6 degrees when the balls were hit with little or no wind and sun shining.

Results

Ball	Club Speed (mph)	Ball Speed	Launch Angle	Spin Rate	Carry (yards)	Total	Side (feet)
Cold	101.7	152.5	11.3	2722	228.0	246.8	47.04
Room Temp.	102.1	152.4	11.5	2613	229.8	250.4	44.04

Ball speed is the big factor we are interested in and as we see from the results, ball speeds are practically identical, 152.5 mph with the cold ball and 152.4 mph with the room temperature ball. The room temperature ball has a slightly longer carry (229.8 yards against 228) and overall distance (250.4 against 246.8) which is a result of a slightly higher launch angle and lower spin rate.

Can this be attributed to the lower ball temperature? Probably not, it's more then likely down to the vagaries of strike point on the club face. The intention with hitting 20 balls with each was to eliminate this as much as possible but as the test subject wasn't Iron Byron there's always little differences in the strike.

Conclusion

As there was no difference in ball speeds between the cold balls and room temperature balls we can conclude that ball temperature has little effect on the performance of the ball. No need to be storing golf balls indoors!

The biggest factor in loss of distance in the Winter is colder air and unfortunately we cannot control that.

Next experiment will be to see if warming the balls on a heater will have an effect. Any questions or comments are appreciated.

3 Golf Equipment Terms Explained and How They Can Help Your Game

Loft

Loft is defined as the angle between the shaft axis when it's perpendicular to the ground and the plane of the face and is measured in degrees

Loft is a big determining factor in how far the ball will go. One thing to note is the lofts on irons have been decreasing over the years, for example the Taylor Made RSi 1 7 iron has a loft of 30.5 degrees, 7 iron lofts used to be 36-38 degrees. This is one of the reasons why long irons are disappearing and gap wedges are appearing, what used to be a 3 iron is now a 5 iron!

What this means for the player is that they should ignore what's on the bottom of the club and have a set make up that delivers a consistent gap of 10-15 yards between each club. For some that maybe a 4 degree gap in loft and for slower swing speeds that could be a 6 degree gap. This could also mean that you might need less clubs in the bag.  

Flex & Kick Point

Flex is simply how much the shaft bends. Most are labelled Ladies L-Flex, Senior or A-Flex, Regular R-Flex, Stiff S-Flex and Extra Stiff or X-Flex. There is no industry standard as to what each of the flexes means so one company's stiff flex could be anothers regular flex.

Also the shaft doesn't necessarily have the same flex the whole length of the shaft. This is particularly true for graphite shafts and this is another reason why two shafts of similar flex can perform very differently. It's never a great idea to assume just because a shaft flex suits you then every shaft of that flex will suit you even if they are the same weight.

Kick point is the point on a shaft that flexes the greatest. You will hear about high, low and mid kick points but all these points are within 3-4 inches on a shaft and not up near the butt or down by the tip. Also generally a high kick point will hit the ball low and a low kick point will hit it high.

It is better to talk about high launching shafts, mid launching shafts and low launching shafts rather then kick point. 

Bounce

Bounce is the angle between the leading edge (front) of the club's sole, the trailing (back) edge and the ground. It is most apparent in wedges. It prevents the club from digging into the ground. When used correctly its possible to hit the ground before the ball and still get a reasonable golf shot.

'Bounce' is your friend! Using the bounce correctly means having the sole of the club hit the ground first as opposed to the leading edge. A shallower angle of attack helps this.

Higher bounce helps in soft turf conditions, golfers with steeper angles of attack (think golfers with big divots!) and in bunkers, sand is generally softer then turf. Low bounce is good for harder turf conditions, very firm sand (particularly wet compacted sand) and some golfers who take little or no divot.



Any questions or comments are greatly appreciated.

The Effect of Friction on Loft and Spin

Friction has a big roll in spin generation particularly with irons. If there is less friction then there is less spin. This is the infamous 'flyer' that occurs with irons where the ball goes much further then expected. Also the tee shot that dips when the driver face is wet is also caused by less friction.

Grass, dirt and moisture between the ball and club face are the main culprits that lower friction and cause the flyer.

Lately I've been noticing that flyers occur mainly in short irons and that the opposite is occurring in longer irons i.e. more spin is being produced then expected from lies that cause flyers e.g. grassy or wet. This also means instead of the ball travelling further then expected, it's actually travelling less.

Recently I hit some shots from wet grassy lies to test what I've been noticing. I hit 10 shots with each iron from pitching wedge to 4 iron and recorded the results on a Trackman 111 launch monitor. It was a really nice December day around 10 degree Celsius and little wind. The Miura MB 001 was the iron used and the ball used was the Titleist Pro V1.

An example of a wet grassy lie that leads to flyers.

Data

Below are the results from the test.

Club	Club Speed (mph)	Ball Speed	Launch Angle	Spin Rate	Carry (yards)	Total
PW	80.1	93.4	28.6	5218	118.8	125.1
9i	81.5	100.4	26.0	4633	135.3	143.7
8i	84.7	107.5	19.6	6736	139.1	144.8
7i	87.3	114.1	17.7	5686	150.5	158.3
6i	89.6	119.6	13.8	6402	158.4	166.1
5i	90.4	123.1	13.1	6332	164.4	172.4
4i	92.6	126.4	11.3	5207	172.9	184.1

 

What spin rate would we expect from each club? Spin is calculated by club speed x spin loft x 2.6 for irons. For the 9 iron above we would expect 81.5 x 34.6 x 2.6 = 7,332 and the 4 iron would be 92.6 x 17.3 x 2.6 = 4,165. A reasonable rule of thumb to calculate spin for an iron is to multiply the iron number by 1,000 e.g. 4 iron 4,000, 5 iron 5,000 etc.

Looking at the data, the spin for the 9 iron was 4633 on average, much lower then expected, this is what a flyer would be, ball travelling further through the air and running more on landing. The spin for the 4 iron was 5207, higher then expected which means ball doesn't fly as far and runs less on landing. 

The 7, 8, 9 and PW have spins less then expected. The spin for the 6 iron is slightly higher then expected and much higher then expected for the 4 and 5 irons.

Below is data taken from shots taken by two more golfers during the Summer.

Club	Club Speed (mph)	Ball Speed	Launch Angle	Spin Rate	Carry (yards)	Total
8i	87.8	111.5	28.3	4080	160.6	169.7
4i	96.3	123.4	15.7	5633	175.3	187.3

Club	Club Speed (mph)	Ball Speed	Launch Angle	Spin Rate	Carry (yards)	Total
9i	89.6	114.6	23.1	5694	159.9	167.7
5i	101.5	136.9	10.7	6490	190.5	199.3

Both these golfers were hitting from slightly longer then fairway grass and we can see in the shorter irons spin rates are less then expected and in the longer irons spin rates are higher then expected.

Why does this happen?

I'm not sure at all, more investigation is needed. It also seems to happen only in irons as spin rates decrease on woods and hybrids due to decreased friction (think of the dipping tee shot due to a wet wood face). It also seems that it is around the loft of a six iron (30-32 degrees) that the change in spin rates in irons seems to happen.

What this means for your golf? 

In 'flyer' lies e.g. wet and grassy, long irons travel less then expected and shorter irons travel more then expected. This needs to be taken into consideration in club selection, e.g. trying to carry water with a long iron from a slightly damp semi rough lie might be a bad idea. Playing a 7 iron from 'flyer' lies might lead to much better results then long irons.


Questions and comments are appreciated.