Does a windshield help with a bike's aero?

[JSH]

Originally Posted by cRiPpLe_rOoStEr

Yet some full-size windscreens, as long as they're curved and inclined enough to act as a wind deflector, could improve aerodynamics.

Bingo. To improve aerodynamics you have to either reduce the coefficient of drag (Make the object "smoother") or decrease the frontal area. Windshields do both.

It isn't hard to make a windshield smoother than a human and that is compounded by the fact that windshields lean back with airflow while humans on a motorcycle lean forward - into the wind - and act like a scoop.

If we curve the windshield so it creates a larger bubble of still air behind it than the frontal area of the windshield we reduce the frontal area. For example the parabellum windshield I had came to about chin level but sent airflow just over my helmet. It eliminated the frontal area of my helmet.

Originally Posted by j-c-c

However, I don't yet see consensus here on these two points.

You will never get full consensus on any topic.

[freebeard]

You will never get full consensus on any topic.

Not necessarily.

[j-c-c]

Originally Posted by freebeard

Not necessarily.

[Grant-53]

A curved front fairing and a high tail box such as the Vetter Challenge bike of Vic Valdez and others can double mpg. Time and again ecomodders have found that a good aero shape and driving techniques can double mpg on all types of vehicles. I build fairings for bicycles. I test using yarn tufts and coast down tests. Attaching the fairing to the frame instead of the forks minimizes crosswind inputs.

[freebeard]

It seems the trade-off would be between aerodynamic efficiency and visual distortion. Compound vs simple curvature. Curve vs refractive index.

[j-c-c]

Originally Posted by freebeard

It seems the trade-off would be between aerodynamic efficiency and visual distortion. Compound vs simple curvature. Curve vs refractive index.

i don't see ( pun intended) that minor distortion is much of a factor riding at the speeds that effect mpg greatly, being a rider normally is focusing way in front of the windshield in most cases at speed on the street with anything but a very tall windscreen.

[cRiPpLe_rOoStEr]

Originally Posted by j-c-c

i don't see ( pun intended) that minor distortion is much of a factor riding at the speeds that effect mpg greatly

Having a shorter time to react because it took longer for you to see a hazard ahead may be the difference between life and death.

[j-c-c]

It's IMO rather rare since one is seldom looking and focusing thru a windshield in normal riding conditions. Peaking over the top is the norm if a windscreen is in play, and i suspect the larger taller screens are flatter and less curvature and therefore less prone to distortion anyway. This distortion issue here is besides representative of poor design, manufacturing, and low cost and I submit a non issue in this discussion.

[cRiPpLe_rOoStEr]

Might be different if you're considering a crotch-rocket, instead of those tourers such as a BMW K1600 or a GoldWing.

[j-c-c]

Well I addressed that, so back up your claim in rebuttal.