Using golfspeak to explain the finer points of the game to a non-golfer will often baffle and bemuse them. But explaining the latest technological advancements in golf equipment can solicit the same puzzled looks from even the most informed golfers.
Here’s a glossary of terms that will hopefully make it easy to understand the difference between lie angles and launch angles and appreciate the intricacies of MOI and Smash Factor.
Lie Angle
The angle between the centre of the club shaft and the back edge of the heel as it makes contact with the ground is known as the lie angle. A perfect lie angle has the sole of the club head sitting level with the ground.
If the toe of the club is higher than the heel at impact, a pull/hook ball flight is produced and if the heel is higher than the toe, a push/slice tends to result.
Clubs typically come with standard lie angles of between 59-64 degrees for long irons through to wedges but most can be customised to match a golfer’s specific lie angle requirements.
Moment Of Inertia (MOI)
Every golfer would’ve experienced the effortless sensation when a shot rockets out of a club’s sweet spot in perfect balance.
But when a strike is off-centre, lateral torque, or twisting, of the clubface occurs at impact. This twisting slightly opens or shuts the clubface, depending on where the strike was, and the ball speed off the clubface is slashed significantly.
Moment Of Inertia is basically a measurement of resistance to this twisting effect. It is used to assess how well a golf club performs when a strike is off-centre.
A high MOI means the clubface is more resistant to twisting (i.e. stays squarer) at impact and helps poor strikes fly straighter and longer, increasing the club’s forgiveness.
Forged/Cast irons
Irons are manufactured using either the forging or casting process.
A single, solid piece of metal is cut, shaped and stamped to produce forged irons, whereas molten metal is poured into moulds and cooled to produce cast irons.
Both methods produce quality clubheads and it often comes down to individual preference and feel when choosing between forged or cast irons.
Smash Factor
Although it may sound like a measurement of 19th hole festivities, Smash Factor is actually a clubhead-to-ball speed ratio.
Calculated by dividing the ball speed by the clubhead speed, it is useful to determine how efficient a golfer’s transfer of energy from club to ball is.
A golfer with a ball speed of 140mph and a clubhead speed of 100mph will record a smash factor of 1.4. Clubhead and ball speeds are measured using a golf simulator.
Smash factors will vary for different clubs, with more lofted clubs having a lower smash factor. While an increased smash factor can translate into longer distances with a driver, a high smash factor can be detrimental for short irons and wedges. Golf balls also have a bearing on smash factor, with their design and energy transfer efficiency another attribute to consider.
Centre Of Gravity (CG)
If you’ve ever balanced an object on the tip of your finger, you’ve discovered the centre of gravity, or balance point.
In golf clubs, the centre of gravity will influence the ball flight of a club according to where it is positioned.
If a driver has a CG located low and towards the back of the clubhead, it will produce a high trajectory and low spin ball flight. If it is further towards the face and higher, a lower trajectory and higher spin rate will be the result.
A CG that is closer to the clubshaft can negate a push/slice by helping to square the club at impact. A CG further away from the shaft will tend to open the clubface to stop pulls/hooks.
Small changes to the CG can dramatically alter the ball flight and that is the idea behind drivers and fairway woods with adjustable weights.
Players can alter the CG and tweak their ball flight simply by sliding small weights around the sole of the club.
Launch Angle
Launch angle is the initial trajectory of the ball after it leaves the clubface, relative to the turf.
The launch angle of a driver is significant for golfers as it has a big impact on distance off the tee.
The loft of a driver isn’t the same as the launch angle but is a major factor in determining a ball’s initial trajectory. Clubhead speed and angle of attack into the ball also play a part.
A club can have a huge variance of launch angles when used by different golfers because of these factors.
A high launch angle is ideal for generating carry and distance for most golfers at an optimum spin rate.
Bounce
The angle between the leading edge of a wedge and the point its sole touches the ground is known as bounce.
Bounce is built into wedges to control how much of the leading edge cuts into the turf at impact.
A high bounce wedge sole will “bounce” off the turf and have more of a “brushing” motion through the turf. A wedge with low bounce will take more of a carving divot as the leading edge is more exposed to the turf.
High bounce wedges are particularly handy in soft sand bunkers and playing from thick rough or soft fairways. If you have a steep angle of attack or hit your wedges a tad flubby, extra bounce will prevent the leading edge digging in.
Low bounce wedges are the better option for golfers who take shallow divots. Low bounce wedges are better off tight lies, firm or wet sand bunkers and hard fairways.
Offset
Offset clubs have the shaft slightly in front of the leading edge of the clubhead.
They are designed to make it easier to square the clubface at impact and diminish the effects of a slice.
With the shaft arriving just a fraction earlier than the clubhead, it allows a player’s hands more time to get the clubface square and also promotes a hands-ahead-of-the-ball strike for more compression at impact.
Offset clubs also have a higher launch angle, with the centre of gravity located further back from the shaft, and can help players struggling to get the ball airborne, particularly with longer irons.
Forgiveness
Golf club engineers worked out that golf is more fun when, despite swinging it like a rusty gate, your ball still flies a decent distance and can be found after most shots.
Forgiveness is good news when talking about golf clubs. Basically, when a bad swing deserves to be punished but isn’t, that is forgiveness.
Off-centre strikes can still fly straight and long thanks to design principles that spread the weight around the edges of the clubhead, also known as perimeter weighting.
Forgiveness is associated with Moment Of Inertia, the two principles making the game a little kinder when talent runs out.
Flight Bias
A flight bias means a club will naturally shape the ball from either left-to-right or right-to-left.
A fade or draw bias is particularly useful to counteract a nasty slice or level out a confidence-sapping duck-hook.
The bias is produced by changing the centre of gravity of the club. A draw bias will have the CG positioned closer to the heel to close the clubface quicker through impact while a fade bias will move it further away to make the clubface close slower.
An offset can also be used to create a fade bias.
Coefficent Of Restitution (COR)
COR is a figure between 0 and 1 that indicates the proportion of energy transferred from the clubhead to ball at impact.
For example, a COR of 0.60 means 60 per cent of energy from the clubhead is transferred to the ball at impact. The other 40 per cent is considered lost, chewed up when the ball compresses against the clubface and the clubface flexes inwards in response.
A driver with a high COR is more efficient at transferring energy from clubhead to ball, which leads to a greater ball speed, higher trajectory and more distance.
Club designers can increase COR by making the faces of clubs thinner so they deform and rebound when striking the ball, creating what's known as a "trampoline" effect.
Although the concept of “trampoline effect” sounds like the ball is caught and slung back off the clubface like a spring, it is actually just the increased clubface flexing that boosts the COR.
A slight loss of energy through greater flexing of the clubhead results in the ball compressing less, meaning more energy is retained and ball speed off the clubface soars.
Gear Effect
When a strike isn’t out of the centre of the club, a phenomenon called “gear effect” is generated.
When the CG (centre of gravity) of the clubhead and CG of the ball aren’t in perfect alignment at impact, nasty things start happening. The clubface twists around the CG, opening if the strike is out of the toe or shutting if the strike is closer to the heel.
A strike off the toe will cause a hooking ball flight but here’s the thing: the clubface will actually open at impact as it rotates clockwise (for a right-hander) around the COG of the clubhead.
But wait, an open clubface should cause a slice shouldn’t it?
It sounds contradictory, but picture a clubhead and ball at impact as two cogs coupled together.
The clockwise opening motion of the clubface through impact produces the opposite motion in the ball: anti-clockwise spin. And voila, there’s your hook. The same is true for strikes off the heel, but in reverse.
No gear effect is produced when the strike is out of the centre, just a straight and pure ball flight like the club manufacturer intended.
Clubs that have a high MOI (moment of inertia) are more resistant to the twisting of the clubhead that initiates gear effect. High MOI clubs are more stable through impact when the strike is off-centre, leading to better strikes and straighter shots.