Everything
you ever wanted to know about dimples
By Frank Thomas
Consider the dimple. What are those cute little indentations all over the surface of a golf ball there for? Are they just decoration? Wouldn’t putting be more precise if the ball’s surface was completely smooth?
The fact is that a perfectly smooth golf ball with no dimples would travel about 130 yards when hit with a driver by a good player. On the other hand, a ball with well-designed dimples, struck the same way, will travel about 290 yards. Why the difference? Aerodynamics.
The smooth ball flies like a bullet, and has no "lift." The dimpled ball, because it is spinning, climbs up into the sky, taking off like an airplane. Also, the dimples create a turbulent layer around the surface of the ball, which actually makes it slide through the air more easily -- the dimples reduce the drag. The ball must, however, spin for the lift force to be created, and unfortunately a spinning ball has more drag than a nonspinning ball. But this is the trade off.
It is the combination of the lift and drag properties of the ball, as well as its speed, launch angle and spin rate, which will dictate the flight path or trajectory of the ball, and thus the distance it will go.
What are the USGA’s rules on dimple design? There aren’t any. There are restrictions on the weight, size and initial velocity of a ball, but when it comes to dimples, anything goes.
Are there good dimples and bad dimples? Yes there are. The size, shape, depth, number, distribution pattern and overall surface coverage of the dimples all influence the ball’s aerodynamic lift and drag properties. Unfortunately, analysis of air flow over a golf ball’s dimples is not a huge priority for NASA, and dimples are not a threat to national security, so most of what’s known about effective dimple design has been arrived at through experimentation, trial and error and some science on the part of manufacturers. Dimple design has changed significantly over time, from random patterns, to formal rows, to interstitial designs. The depth, shape and number have all been varied and tested.
With regard to the number of dimples, manufacturers have done it all. Obviously, as you increase the number of dimples, the smaller they must be to fit on the ball. Eventually, as the number increases, the dimples get smaller and the ball becomes almost smooth--and will perform likewise. So a compromise is the answer.
It has generally been found that less than about 300 dimples is too few, and more than about 500 is too many. Most balls on the market today have thus converged to the middle ground with between 350 and 450 dimples (although one company produced a ball with 812, which didn’t set the world on fire).
So next time there’s a wait on the tee, check out the dimples (the ones on the golf ball.) If it’s a really long wait, you could even count ’em.
This column appeared on golfdigest.com where Frank contributes on a weekly basis. Check it out every Saturday.