Nothing technically true about it without using proper model and numbers.
Note that cD is more important than A. Size of windscreen is secondary to its shape since it's still better than pushing piece of plywood flat-side facing wind. Putting rounded nose on house-brick will make it more aero even though it's blocking exact same amount of air.
There's a pocket formed by your arms and chest which directs air torwards torso that traps air into dead-end tunnel, not good. Better to reverse that pocket with nose-cone. You can actually double frontal surface area and still have less drag if shape is smoother. That's why bikes with fairings are significantly faster even though they block more wind. Total air-drag is.
Fd = cd*1/2*ρ*(v^2)*A
use ρ = 1.2 kg/m3 for air at STP
Note that while drag goes up by square-power of velocity, power-required to overcome that drag goes up by cube-power of speed. So to go twice as fast requires 8x more power!
A double-bubble windscreen on '08+ Ninja 250 raises top-speed by 2-3mph down front-straight at Thunderhill Raceway and 1.5-2mph at Laguna Seca. Helps air get over shoulders and back better than stock unit. New-gen '08+ windscreen way better than tiny '88-07 pre-gen screens that leave arms and shoulders in wind. Try skydiving to see how absolutely inefficient human body is at deflecting wind around it. Pretty much any windscreen is better than none because it's more aero than shoulders and arms.
Here's pre-gen Ninja 250 with windscreen about 10x larger than stock and significantly improves airflow. As measured by improved mileage from 55-60mpg stock to 116mpg!!! Top-speed would also be improved significantly as well, but wasn't tested and measured.
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Only time bike without windscreen would be faster, is when there's no human on it.
Note that cD is more important than A. Size of windscreen is secondary to its shape since it's still better than pushing piece of plywood flat-side facing wind. Putting rounded nose on house-brick will make it more aero even though it's blocking exact same amount of air.
There's a pocket formed by your arms and chest which directs air torwards torso that traps air into dead-end tunnel, not good. Better to reverse that pocket with nose-cone. You can actually double frontal surface area and still have less drag if shape is smoother. That's why bikes with fairings are significantly faster even though they block more wind. Total air-drag is.
Fd = cd*1/2*ρ*(v^2)*A
use ρ = 1.2 kg/m3 for air at STP
Note that while drag goes up by square-power of velocity, power-required to overcome that drag goes up by cube-power of speed. So to go twice as fast requires 8x more power!
A double-bubble windscreen on '08+ Ninja 250 raises top-speed by 2-3mph down front-straight at Thunderhill Raceway and 1.5-2mph at Laguna Seca. Helps air get over shoulders and back better than stock unit. New-gen '08+ windscreen way better than tiny '88-07 pre-gen screens that leave arms and shoulders in wind. Try skydiving to see how absolutely inefficient human body is at deflecting wind around it. Pretty much any windscreen is better than none because it's more aero than shoulders and arms.
Here's pre-gen Ninja 250 with windscreen about 10x larger than stock and significantly improves airflow. As measured by improved mileage from 55-60mpg stock to 116mpg!!! Top-speed would also be improved significantly as well, but wasn't tested and measured.
Only time bike without windscreen would be faster, is when there's no human on it.
