Car Tuning Aerodynamics and Body Styling 4 — Questions and Answers
Question 1: What is 'drag coefficient' (Cd) and why do tuners care about it?
- A measure of tire rolling resistance on different surfaces
- A dimensionless number quantifying how efficiently a shape moves through air (Correct answer)
- The ratio of downforce to vehicle weight
- The horsepower lost to wind resistance per mph
Correct answer: A dimensionless number quantifying how efficiently a shape moves through air
Cd quantifies aerodynamic drag relative to frontal area and air density; a lower Cd means less power wasted pushing air aside at speed.
Question 2: Which type of hood modification helps both cool the engine and reduce hood lift at high speed?
- Hood louvers venting near the windshield
- A functional hood scoop with a forward-facing opening (Correct answer)
- Flush-mounted hood pins only
- A carbon fiber hood without any venting
Correct answer: A functional hood scoop with a forward-facing opening
A forward-facing hood scoop uses ram pressure to force cool air into the engine bay, while the venting reduces positive pressure that would lift the hood.
Question 3: What does 'rake' refer to when setting up the aerodynamics of a race-inspired build?
- The angle at which the car sits lower at the front than the rear (Correct answer)
- The angle of the rear wing relative to horizontal
- The sweep angle of the front splitter
- The tilt of the diffuser fins
Correct answer: The angle at which the car sits lower at the front than the rear
Rake means the car is pitched with the nose lower than the tail, which accelerates underbody airflow and enhances diffuser efficiency.
Question 4: Why might a tuner choose polyurethane (PU) bumpers over fiberglass for a street-driven car?
- Polyurethane weighs significantly less than fiberglass
- Polyurethane flexes on minor impact rather than cracking or shattering (Correct answer)
- Polyurethane has a higher melting point for heat resistance
- Polyurethane is easier to bond to carbon fiber panels
Correct answer: Polyurethane flexes on minor impact rather than cracking or shattering
PU is flexible and absorbs low-speed impacts without cracking, making it practical for street use where minor bumps are common.
Question 5: What is the aerodynamic role of side skirts on a modified car?
- Increase ground effect by blocking high-pressure air from rushing under the car (Correct answer)
- Reduce side-wind lift by acting as lateral fins
- Add structural rigidity to the door sills
- Deflect exhaust gases away from the body sides
Correct answer: Increase ground effect by blocking high-pressure air from rushing under the car
Side skirts seal the gap between the lower body and ground, maintaining a low-pressure zone under the car for improved ground effect downforce.
Question 6: When a rear wing is described as having a high angle of attack, what trade-off does this create?
- More downforce but also significantly more drag (Correct answer)
- Less downforce with greatly reduced drag
- Equal downforce and drag at all speeds
- More downforce with no meaningful drag increase
Correct answer: More downforce but also significantly more drag
Steepening a wing's angle increases its effective camber and downforce, but also dramatically raises induced drag, costing top speed.
Question 7: What is the purpose of a 'wicker bill' modification applied to an existing trunk lid?
- Provide a mounting bracket for a tow hitch
- Add a small upturned lip to generate rear downforce without a full wing (Correct answer)
- Seal the trunk lid gap to reduce wind noise
- Reflect brake light illumination rearward
Correct answer: Add a small upturned lip to generate rear downforce without a full wing
A wicker bill is a small upturned strip at the trailing edge of a trunk lid that creates a low-pressure region to generate modest rear downforce.
Car Tuning Aerodynamics and Body Styling 4
What is 'drag coefficient' (Cd) and why do tuners care about it?