I Don't Play Golf so Why am I Covered In Dimples?

It has recently been postulated that cycling is the new golf. This idea is in fact very plausible and explains certain things. Think of our friend Mr. Dentist who feels the need to get fit and decides on cycling because, similar to golf, it is a sport that you can spend exorbitant amounts of money on equipment in order to become marginally better. However the world of cycling may seem treacherous to one whose previous domains were quiet green fields and plush clubhouses. Just like the Italians brought spaghetti and Mafia Movies with them to America the new cyclists has brought with him certain aspects of his culture he left in order to make his new environment seem more hospitable. Case in point:Note how this particular group of ex-golfers are absolutely covered in dimples and argyle, both staples of the golfing culture.

What other benefits may dimples have other than helping with cultural transition? AERODYNAMICS!!!!! But, if you think that the dimples on Zipp's famous deep section wheels function like those of a golf ball, you are absolutely wrong. If you think about it, it is easily observed that the golf ball and the wheel have very little in common. First of all, unless you're riding close to 70 miles per hour, your bike wheel speed does not come close to matching the speed at which a golf ball travels through the air. This is important because a primary factor in aerodynamic similarity is the speed and size of the body traveling through the air. In fact at slower speeds dimples will actually create more drag, I even did this experiment as part of a lab last year and at 35 mph wind speed a smooth golf ball had less drag than a dimpled golf ball. The second difference is in orientation of the body, a golf ball can spin in any direction and has to be nearly aerodynamically similar in every orientation in order it obtain stable flight. The wheel however, while still spinning, is for the most part fixed in it's orientation.

Instead the section of a bicycle rim is much more closely related to an aircraft wing. And the purpose of dimples on the rim section is to prevent what is called 'stall'. Stall occurs when the angle at which the airflow hits the wing is at such a great angle that the flow separates and circulates on the downwind side of the aircraft. This creates massive amounts of drag and reduces lift, but lift isn't really a concern for bicycles. So dimples also have an aircraft equivalent. These equivalents are called vortex generators. These vortex generators are small pieces of metal attached to the top side of wings, they disrupt the flow over the top of an airfoil, which allows the flow over the airfoil to remain attached to the surface longer, which in turns allows for a greater angle of attack before stall results. Zipp claims that most of the time a rider is riding into at least a slight crosswind. This is important because in an ideal situation where there is no lateral component of wind, the dimples on the wheels may actually create more drag than a smooth surface.
So the dimples prevent stall in crosswinds which is the main culprit of form drag, but the dimples also increase the skin friction drag over the wheel which may have a adverse affect on the net drag of the rider not riding into a crosswind. Bicycle races are won by the smallest margins, so every little bit helps, even if the benefit are really really tiny and serves a mostly marketing purpose.