Project FR-S: Aero Fender Concept

Project FR-S: Aero Fender Concept

by Cheston Chiu

Following up on fantastic fabrication of the Project FR-S’s initial aero modifications from the splitter, rear diffuser and rear wing installation there was a desire to enhance the aerodynamic efficiency of the front splitter and rear diffuser by attempting to reduce underbody drag, which most noticeably will be felt on high-speed tracks. 

There are a few ways of achieving this: raking the vehicle such that the nose is lower than the rear to physically limit the amount of air allowed underneath the car, adding side skirt extensions to reduce side airflow interruptions prior to diffuser inlet, and reducing turbulent air flow off the front wheels that interrupts the air channeling underneath.

The blue arrows represent the direction of airflow we like, front to rear. The tires interfere with this flow (red and yellow arrows). Let’s try to make the blue flow smoothly.

We like free mods and raking the vehicle is one such modification; so it’s pretty much a no-brainer to add the rake by tilting the nose of the vehicle downward. Side skirt/running board extensions are also relatively easy to do, and we’ll save that for a future update article. So, really the hard problem (and justification for this article) is reducing wheel drag.  After we added the square wheel and tire setup for the track (265-35-18 Achilles race compounds mounted on Advan Racing RG-D wheels 18×9.5+40) there was considerably more tire width up front than a typical stock FR-S setup— and this is where we’d like improve the current state of the vehicle.  Wheel drag is a significant percentage of the overall drag on a given vehicle, and if we increased wheel drag in exchange for more front cornering grip, it would be nice to do something to counteract the negative aspect of the trade. One potential solution would mean front fender and fender liner modifications. 

An additional desire to pursue a fender modification to the Project FRS was to find a solution to inner firewall / outer fender liner rubbing from hard cornering due to the aggressiveness of the tire/wheel offset combination.  We are constantly trying different suspension geometries for the Project FRS and having the option of spacing the wheel further out or trying different tire sizes in the future would be an ideal side benefit.

More width = more drag. Let's do something about it.

Concept Rationale

A good place to start before investing any time and effort are asking the smart questions: “is there anything commercially available?” and “Are we crazy?” It didn’t take long to answer both: No and Yes. There are some fender offerings currently available for purchase on the market, but for proper installation, it called for irreversible modifications to the OEM fender or Frame (i.e., cutting) and even then, there are clearance issues with tire travel.  And since this is a MotoIQ Project car, you already knew we were bat shit crazy nutsos.     

Like all (smart) design projects, there needs to be something written down for us to build to. Discussing amongst MotoIQ staff, and the fellow nerds at Victory Function USA, we came up with a handful of basic minimum design requirements that the new aero fender needed to have.  

1. Fenders shall be vented and/or have openings for proper air pressure extraction.
2. Fenders shall be wider than stock to allow for unobstructed square tire fitment.
   1. Threshold Requirement: 265-35-18 on 18×9.5+40.
   2. Objective Requirement:  275-35-18 on 18×9.5+35.
3. Fenders shall require NO modifications to the OEM front bumper.
4. Fenders shall require NO modifications to the existing vehicle frame.
5. Fenders shall use existing OEM fender mounting holes. 

They sound simple enough, until you get into the details.  Also a sixth, “non-listed” requirement was that the aesthetics needed to retain the natural body/door lines already present in the FR-S—it wasn’t a hard requirement since it’s a little subjective, but I think while during the design phase we tried our best to achieve all six.