The rim is 45mm deep and 26.5mm wide, with a profile broadly
similar, but not identical, to the 303, a seriously good wheel for
all-round use, and the one that conquered Paris-Roubaix, as you can
read about here.
But there the similarities end. The biggest change is the smooth
rim surface. There are no dimples on Zipp's new 302 wheelset.
Dimples have been a key design feature, and selling point, of
Zipp wheels since they were first introduced on the 404 in 2004.
According to Zipp, the dimples are essential to controlling how the
airflow attaches, flow across and detaches from the rim profile,
ultimately contributing to lower drag.
Does this mean Zipp's new 302 wheels means they must be slower
than the 303 wheels?
"Depending on the conditions, yaw angle and rider style, a 303
wheel will be on average 2 - 3 watts faster than 302. It is the rim
shape more than the dimples that makes 303 Firecrest faster than
302," said Zipp in answer to our question.
"Our goal with the 302 is to offer the performance of Zipp
Carbon Clincher wheels at a great value. We had to give up on some
features. We made the decision to prioritise the features that
cyclists value from Zipp: aero performance, ride quality and
reliability. Zipp Carbon Clinchers are known for impeccable heat
management, which 302 will offer; whereas this is typically the
weakness of other wheels at this price point," Zipp added.
Dimples on golf balls are designed to increase lift and reduce
drag, helping golfers to hit balls further since the 1930s. After
some motor racing manufacturers dabbled with dimpled surfaces, Zipp
embraced the concept and spent time and money developing its now
iconic rim surface, putting them through constant wind-tunnel
The dimples are patented to Zipp and it has developed a special
moulding process in the US to manufacture the rims. The shape,
depth and orientation of the dimples are design to keep the airflow
attached to the rim for longer by forming a turbulent boundary
layer near the surface of the rim.
But to keep manufacturing costs down, Zipp has developed new
moulding tools that dispense with the dimples to make production
more cost-effective. " It is a lot easier and more efficient to
create a smooth tool than a dimpled one and this affects the cost
of the rim," says Zipp.