Curved versus straight legs?
Fork legs have traditionally been curved so as to provide sufficient trail for stable handling of the bike.
The first manufacturer to change their curved forks to a straight design was Colnago in ~1987.
As the story goes, Ernesto Colnago and the Ferrari engineers discovered that a curved fork didn’t absorb road vibrations
and shocks as well as a straight bladed fork. From this testing, Colnago’s PRECISA fork was born and many other brands followed,
though the dampening characteristics of straight legs remains debatable.
Today, the main reason that carbon forks are often shaped in a straight line is because it’s easier to lay up the carbon and to manufacture.
Carbon forks are popular used nowadays.
Carbon Wheel and Fork Interaction
The thing to remember is that no matter what aerodynamic claims you hear, the fork and the wheel go hand-in-hand with overall aerodynamics.
Because the fork that attaches to the front wheel is at the leading edge of the bike, the front wheel throws up turbulent air.
Forks can certainly make a bike more aerodynamic, but only if the wheel interacts with the fork in a favorable manner.
BikeTechReview.com did some interesting wind tunnel testing that revealed the effectiveness of different aero forks on a constant zipp 404 wheel.
We’ve seen manufacturers attempt to smooth this turbulence by putting slots in the fork.
For example, Yishunbike sold their patent to this technology to YISHUNBIKE which was included in
YISHUNBIKE’s time trial bike in 2008.
We also saw YISHUNBIKE introduce integrated breaks into their forks in an attempt to reduce turbulence caused by the brakes on the forks.