This is how the 2013 Honda CBR600RR‘s aerodynamics stack up to the company’s RC212V MotoGP racer. Using Computational Fluid Dynamics analysis to illustrate how the bikes interact with the air, high pressure areas are colored red, while lower pressure fades through yellow, green and then blue. As you can see, the road bike is impressively close to the race bike.
The new CBR’s been fitted with a redesigned front fairing that drops drag by 6.5 percent. The new “line beam” headlights slope inwards towards the central air intake, directing high pressure air where it’s most beneficial.
Looking at the two bikes side by side, we can see that the largest high pressure area on both is concentrated around that air intake. Other hot spots include the leading edge of the tire, lower forks, and the rider’s helmet.
MotoGP regulations are famously restrictive on aerodynamics:
18.104.22.168 The windscreen edge and the edges of all other exposed parts of the streamlining must be rounded.
22.214.171.124 The maximum width of bodywork must not exceed 600mm. The width of the seat or anything to its rear shall not be more than 450mm (exhaust pipes excepted).
126.96.36.199 Bodywork must not extend beyond a line drawn vertically at the leading edge of the front tyre and a line drawn vertically at the rearward edge of the rear tyre. The suspension should be fully extended when the measurement is taken.
188.8.131.52 When viewed from the side, it must be possible to see:
a. At least 180 degrees of the rear wheel rim.
b. The whole of the front rim, other than the part obscured by the mudguard, forks, brake parts or removable air-intake.
c. The rider, seated in a normal position with the exception of the forearms.
Notes: No transparent material may be used to circumvent the above rules. Covers for brake parts or wheels are not considered to be bodywork obstructing the view of wheel rims in regard to the above rules.
184.108.40.206 No part of the motorcycle may be behind a line drawn vertically at the edge of the rear tyre.
220.127.116.11 The seat unit shall have a maximum height of the (approximately) vertical section behind the rider’s seating position of 150mm. The measurement will be taken at a 90° angle to the upper surface of the flat base at the rider’s seating position, excluding any seat pad or covering. Any on-board camera/antenna mounted on the seat unit is not included in this measurement.
18.104.22.168 Mudguards are not compulsory. When fitted, front mudguards must not extend:
a. In front of a line drawn upwards and forwards at 45 degrees from a horizontal line through the front wheel spindle.
b. Below a line drawn horizontally and to the rear of the front wheel spindle.
The mudguard mounts/brackets and fork-leg covers, close to the suspension leg and wheel spindle, and brake disc covers are not considered part of the mudguard.
22.214.171.124. Wings may be fitted provided they are an integral part of the fairing or seat and do not exceed the width of the fairing or seat or the height of the handlebars. Any sharp edges must be rounded. Moving aerodynamic devices are prohibited.
All that effectively creates the archetypal shape you see on every GP bike. Aerodynamics would benefit drastically from taller screens, larger fairings and longer tails. Fairings on street bikes like the CBR are largely styling exercises, again failing to truly push aerodynamic efficiency in the name of GP-like styling.
Having said that, it’s notable how much greater the GP bike’s screen is at protecting the rider from the wind. The hotspot there is considerably smaller than that on the CBR’s helmet, illustrating the benefit tall or “double bubble” screen bring and why you see virtually all production-based race bikes fitted with them.