The Driver and Accuracy (Part 2)

We all want to hit the ball straight and far of the tee don't we? In more technical terms our goals with the driver are to achieve the highest ball speed possible (distance), along with the desired flight pattern (accuracy). We want cake and we want to eat it too!  Here's a run down on what club manufacturers have been working on to help us keep the ball in the fairway...

The primary factors directed towards accuracy are bulge and gear effect, center of gravity placement, adjustable heads or weights, a preset face angle and the clubhead design.

  • The most interesting element built into each driver that serves to increase accuracy is the one two punch of bulge and horizontal gear effect.  The face of every driver (all clubs requiring a headcover for that matter) has roll and bulge while irons do not.  Bulge is the curvature of the face from its heel to its toe, while roll is the curvature of the face from the crown to the sole.  Bulge starts the ball farther to the right on toe shots and farther to the left on heel shots and is a correction for the clubhead’s center of gravity (CoG) that causes hooking or slicing (gear effect) on off center shots. In other words, manufacturers have built bulge into the face to counter the negative results of gear effect.  Here is an explanation (BTW Irons do display gear effect just far less than drivers):

Here's a definition of gear effect from Dave Tutelman (who has an excellent site for the scientist golfers out there):

Gear effect causes a ball to  have sidespin which is the result of an off-center hit with a club whose center of gravity is well back from the clubface.

Without an off center hit and a CoG that is well behind the face gear effect cannot happen.  In the picture above, we have a toe impact with an iron and a driver.  The center of gravity (CoG) is indicated by the black and white circle.  The collision between the clubface and the ball on the toe creates a torque that causes the club to twist - the club twists around the clubs' CoG which is indicated by the red arrow.

The CoG on the iron is virtually on the face and this type of strike causes the face to rotate open.  This invariably causes the ball to fly weakly to the right as there is no gear effect on the spin imparted on the ball.

The driver is very different.  With the CoG being further back from the face a toe impact causes the entire face to rotate around the CoG.  As the ball compresses and grips on the face the red arrow causes the ball to actually rotate to the left (blue arrow) - the ball and the face actually work like two gears!  Thus the term gear effect.  And the reason why a toe hit with a driver tends to hook and a a heel hit tends to fade.  Bulge helps out by launching a toe hit to the right of the target - a good thing if the ball has draw spin.

  • The design and shape of the clubhead is something that we have seen much tinkering with in recent years.  From the triangular Titleist 907 D1 (how could you forget that!) to the onslaught of ugly square heads - these designs all strive to do one thing - re-position the CoG to stabilize the head during off center hits.  The longer (from face to back) the clubhead is, the further back the center of gravity is from the face which also increases gear effect.  If you can deal with the aesthetics of these scientifically upgraded clubs by all means have at it.
  • Another modern trend that has been proven to straighten wayward tee balls is the advent of adjustable weights or screws on the clubhead.  Originally introduced by TaylorMade in their R7 line, tests have shown that the higher the swing speed the more a golfer is able to curve a ball by changing the weights in the clubhead.  A golfer with a swing speed of 115mph (PGATour average is 112mph) will experience 35 yards of curve while a golfer with an average type speed of 85 mph will only experience 6 yards of corrective curve.
  • Along similar lines are the adjustable heads where the shaft rotates in order to adjust the loft or lie. While changing the loft will not do much to improve your accuracy, altering the lie angle can help you make subtle changes.  Moving the shaft to a more upright position will promote a draw, while flattening will promote a fade.
  • There is also the preset face angle. For those golfers out there who struggle with slicing this has been a tremendous help.  If you feel like you could benefit from this just look for on offset driver or one that says draw somewhere on the head.

There are also rumors that there are certain shafts (Nunchuk) that make the ball go straighter, but I have not read anything or seen any convincing evidence to support this.

Thanks for reading and I hope that now you have a better understanding of what your driver can do for you....

The Driver and Distance (Part 1)

We all want to hit the ball straight and far of the tee don't we?  In more technical terms our goals with the driver are to achieve the highest ball speed possible (distance), along with the desired flight pattern (accuracy).  We want cake and we want to eat it too!  There are numerous elements built into most drivers that often assist us in achieving these goals, yet so many of these small factors almost go unnoticed.  Almost...

Factors in driver technology that influence distance are: length of club; shaft weight; head weight; loft; face material and thickness (CoR) and roll (vertical gear effect).  Distance comes from our ability to convert clubhead speed into ball speed - often referred to as smash factor.  Smash factor is an indicator of our efficiency at impact - are we getting out what we (our driver included!) are putting in?

  • It seems to be fashionable these days for club companies to stretch the length of their drivers to 46 inches and claim that they are "superfast".  The laws of physics indicate they are faster, but in my hands any speed gains are sacrificed with a loss of control.  Ben Hogan used a driver that was 42.5 inches long and nowhere have I ever read that he was a short hitter.  Personally I am not a fan of anything over 45 inches as this seems to be my threshold where distance decreases and control and centerdness of hit diminishes. I believe beginning golfers could use a 43 inch driver with far better results.
  • Over the last decade shaft technology has come a long way and the most notable upgrade has been shaft weight.  Miyazaki makes an incredible 39 Series driver shaft that can be as light as 44 grams - if you you cannot swing that faster then we have a problem.  Barring feel and control issues I am a big fan of lightweight shaft technology and know it is something we should all take advantage of - even Keegan Bradley did.
  • In pursuit of the "lighter is faster" formula a few companies have sought to reduce the weight of the clubhead.  Cleveland Golf has their Ultralight line of drivers that are the lightest on the market today.  A little known fact is that we could actually hit the ball further with a heavier clubhead (with speed being equal).  By increasing the mass ratio of clubhead to ball you can increase ball speed, however the problem here is that as you increase weight you decrease speed, so once again there is a threshold to consider.  The good news is the club companies have done all the research for us and most driver heads fall somewhere between 197 and 212 grams - something we can all manage.
  • The loft of your driver is something that should be determined by an expert (someone who does this for a living!) fitter.  A nice option with the new adjustable heads is that you can now alter the loft of your club without buying a whole new club. The more loft you introduce to the ball at impact the more spin and less ball speed you will create.  The lower the loft, the more ball speed. One problem however - we would like to get the ball in the air and so, once again, there is a trade off.  When it comes to loft, where possible, I encourage a golfer to go with less loft and show them how to overcome the reduction in launch angle by learning how to hit up on the ball.  The golfer does most of the work here, but a reduction in loft can help with distance.
  • The coefficient of restitution (CoR) is the spring like effect the face has when it collides with the golf ball.  As you  might expect the highest CoR on the face is in the center with lower numbers working out from the there.  Golf's governing bodies have made it a rule that this spring like effect cannot be higher than 0.83 and as a result all club companies have made sure that their equipment is right up against the limit.
  • The final, and perhaps most interesting, factor that increases the distance your driver makes the ball go is due to roll - no not roll on the ground, but roll on the face.  Roll is the curvature of the face from top to bottom or crown to sole. Manufacturers include roll into the face design in order to create vertical gear effect on hits that are below or above center.  A ball that is struck above center will actually spin less due to gear effect and as a result launch high with low spin - a winning formula for the long ball.  Of course balls hit low on the face will spin more, but they more than likely need a little more air time. Please see Part 2 of this article for a full explanation of gear effect.
  • I know of no face design or treatment that increases distance - unless you're working the Chapstick for more than just your lips!

The most efficient a golfer could be with the big stick would be to have a clubhead and shaft that fits them in every way, hit the ball from the inside with an ascending blow and strike the ball slightly above the center of the face and a touch towards the toe.  The reason to favor the toe -  the toe of a driver travels about 14% faster than the heel of the club!

I love this PGATour stat that measures how efficient each player on tour is with the driver.  It quantifies  a player's average distance divided by their average swing speed. It also shows each players average swing speed - an interesting read.

Check back soon to learn about what the driver can do for your accuracy....