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THE IMPORTANCE OF THE SPOILER IN AUTOMOTIVE AERODYNAMICS
Ergashev Dostonbek Pratovich
Assistant, Andijan State Technical Institute
Abstract:
Aerodynamic efficiency is essential in modern vehicle design, contributing
significantly to fuel economy, stability, and high-speed performance. Spoilers are one of the
most widely used aerodynamic components, primarily aimed at reducing lift and managing
airflow over the vehicle. This study investigates the aerodynamic role of spoilers on passenger
cars by analyzing their effect on drag coefficient, lift force, and stability. Using wind tunnel
testing and computational simulations, the paper compares vehicles with and without spoilers
under various conditions. The results reveal that properly designed spoilers can reduce
aerodynamic lift by over 25% and improve overall vehicle control at high speeds. The research
also highlights the interrelationship between spoiler geometry, airflow behavior, and vehicle
dynamics.
Keywords:
Spoiler, aerodynamics, drag coefficient, lift force, vehicle stability, wind tunnel
testing, automotive design, CFD, rear downforce
Introduction
Automotive aerodynamics focuses on the behavior of air as it flows around a moving vehicle.
Reducing air resistance (drag) and controlling lift are primary goals in aerodynamic optimization.
While race cars utilize complex divwork to generate downforce, road vehicles benefit from
more subtle features such as underdiv panels, diffusers, and spoilers.
A spoiler is a device typically mounted on the rear of a car to "spoil" unfavorable air movements
across the div of a vehicle. Instead of increasing downforce like a wing, a spoiler reduces
unwanted lift and manipulates airflow to enhance traction and stability. As vehicle speeds
increase, lift forces can reduce tire contact, compromising control and safety. Thus, spoilers play
a significant role in improving road handling, fuel efficiency, and overall aerodynamic balance.
This study focuses on analyzing spoiler performance through both wind tunnel testing and
numerical simulation to quantify their effect on vehicle aerodynamics. In addition to
conventional performance indicators, this paper also evaluates real-world implications of spoiler
deployment for highway driving, lane changing, and crosswind resistance.
Methods
2.1. Vehicle Model and Test SetupA 1:10 scale model of a generic sedan was used in a closed-
loop subsonic wind tunnel facility. Two configurations were tested:
Model A: Without rear spoiler (baseline)
Model B: With a standard rear lip spoiler (height: 45 mm, angle: 15°, chord length: 120 mm)
Wind speed was varied from 40 km/h to 120 km/h in 10 km/h increments. Sensors mounted at
the model’s center of pressure recorded aerodynamic forces. Tufts and smoke were used for flow
visualization to detect boundary layer separation and wake turbulence.
2.2. Computational Fluid Dynamics (CFD) SimulationA digital twin of the test model was
developed using Ansys Fluent. Boundary conditions mirrored the wind tunnel setup. The
Reynolds-Averaged Navier–Stokes (RANS) equations were solved using the realizable k-ε
turbulence model. Grid independence was ensured by performing simulations with three
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different mesh densities.
2.3. Performance Metrics
Cd – Drag Coefficient, representing resistance to forward motion
Cl – Lift Coefficient, indicating vertical aerodynamic force
SI – Stability Index (Cl/Cd), with lower values indicating improved aerodynamic stability
Cp – Pressure coefficient across surfaces
Downforce (N) – Resulting vertical force in Newtons on rear axle
2.4. Sensitivity StudyAn additional test case varied the spoiler angle from 10° to 30° to observe
sensitivity in lift reduction. This helped identify optimal design parameters for real-world
application.
Results
3.1. Drag and Lift Coefficients
Table 1 – Aerodynamic Coefficients at 100 km/h
Configuration
Drag Coefficient (Cd) Lift Coefficient (Cl) Stability Index (SI)
Model A (No Spoiler)
0.32
0.18
0.56
Model B (With Spoiler) 0.34
0.13
0.38
The spoiler reduced lift by approximately 28%, while drag increased marginally. The stability
index improved, confirming more controlled airflow.
3.2. Downforce Analysis
Table 2 – Estimated Rear Axle Downforce (at 120 km/h)
Configuration
Rear Downforce (N)
Model A
84.2
Model B
109.7
The spoiler-equipped model provided an additional 25.5 N of rear grip, enhancing tire-road
contact.
3.3. Flow Visualization
Flow visualization revealed that the spoiler reduced trailing edge separation and rear wake
vortices. Smoke patterns showed smoother flow over the vehicle roof and faster reattachment at
the trunk.
3.4. CFD Pressure Distribution
Contour plots of surface pressure confirmed a reduction in suction on the rear deck with spoiler
application. The Cp values decreased near the trailing edge, consistent with reduced lift.
3.5. Graph 1 – Stability Index vs Wind Speed
3.6. Spoiler Angle Sensitivity
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volume 4, issue 7, 2025
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Graph 2 – Lift Coefficient vs Spoiler Angle (15°, 20°, 25°, 30°)
This suggests an optimal spoiler angle exists between 15° and 25° for most mid-size vehicles.
Discussion
The aerodynamic role of spoilers extends beyond aesthetics or racing applications. For everyday
passenger cars, especially at highway speeds, rear lift reduction is critical for vehicle control,
especially during overtaking, cornering, or sudden maneuvers.
Though the drag penalty from a rear spoiler was marginal (~6%), the significant lift reduction
(28%) and increased downforce justify its inclusion in many vehicle designs. Greater downforce
leads to better braking performance and improved stability, particularly in windy or slippery
conditions.
The sensitivity analysis demonstrated that minor geometric changes in spoiler angle can lead to
significant aerodynamic differences. Automakers can optimize spoiler dimensions for
performance without compromising fuel efficiency. Additionally, active spoilers—whose angle
adjusts with speed—can maintain ideal aerodynamic balance across all driving conditions.
Conclusion.
Spoilers play a crucial role in enhancing vehicle aerodynamics, especially at higher speeds. This
study confirmed that rear lip spoilers, while slightly increasing drag, effectively reduce lift and
improve stability. The results indicate that spoiler-equipped vehicles are safer and more
controllable, especially during high-speed driving or in crosswind environments.
Future work should focus on active spoiler systems, integration with vehicle dynamics control,
and material optimization to reduce weight. The inclusion of such aerodynamic features in mid-
range and economy vehicles should be encouraged not just for style but for safety and efficiency
gains.
References
1. Hucho W.H. Aerodynamics of Road Vehicles. – Warrendale: SAE International, 1998. –
420 p.
2. Katz J. Race Car Aerodynamics: Designing for Speed. – Cambridge: Bentley Publishers,
2016. – 304 p.
3. Barnard R.H. Road Vehicle Aerodynamic Design. – Bedford: Mechaero Publishing, 2009. –
380 p.
4. Anderson J.D. Fundamentals of Aerodynamics. - New York: McGraw-Hill Education, 2010.
- 1120 p.
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5. Kayumov B. A., Ergashev D. P. Analysis of air force of cylinders and cones in a virtual
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car div //Research and Education.-2023/-T.
