Independent Aerodynamic Study of Tesla Model 3 by Unplugged Performance

Aftermarket Performance Efficiency Gains Created by CFD Integrated Aerodynamic Design

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by Ben Schaffer  |  CEO

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Abstract


Unplugged Performance develops products and complete car programs for Tesla owners who seek to upgrade their vehicles beyond the factory specifications. Tesla’s mission is to accelerate the world’s transition to sustainable energy. Unplugged Performance seeks to further enhance all categories of performance that come standard on Tesla vehicles. Of specific interest to Unplugged Performance, and the reason for this study, is the focus of reducing energy expenditure and increasing long distance travel capabilities on Tesla’s mass-produced vehicle, the Tesla Model 3.

Unplugged Performance has a history developing motorsports-optimized products. For this study Unplugged Performance tapped their motorsports resources and set out to apply race car-technology and knowhow to the challenge of adding real-world efficiency in a daily driven compliant package. While the aftermarket has a long history of adding value to the mission of car manufacturers, it remains rare for such a data-driven aerodynamics product development program to be attempted in the aftermarket.

Ultimately a simple series of three Unplugged Performance products were validated through a Computational Fluid Dynamics (CFD) study to provide a substantial 21% total reduction in drag while improving high speed stability, balancing everyday functionality and providing an enhanced sporty aesthetic.

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Introduction


In 2018 Unplugged Performance set out to apply the discipline of CFD to the study and development of aftermarket products for the Tesla Model 3. The method of CFD utilized herein is commonly used by engineers in the highest levels of professional motorsports and is also extensively utilized in vehicle development by all vehicle manufacturers, including Tesla. Unplugged Performance utilized their industry motorsports partners and applied existing motorsports development methodology to optimize for reducing kilograms-force (kgf) of drag on the production spec of the 2018 Tesla Model 3. Reducing drag is a key factor in reducing energy consumption (measured in kWh) per mile driven. As such, a reduction in energy consumption increases the total distance a Tesla can travel on a single battery charge, while simultaneously reducing the environmental energy impact and relative energy cost per mile travelled. A secondary goal of the CFD study and product development plan was to make alterations to low drag designs that further optimize for both front and rear downforce to further improve vehicle handling and stability. Unplugged Performance has always been a driving satisfaction- orientated company; any gain in sustainable energy efficiency must also come without sacrifice to performance driving, and ideally with a tangible upside of performance and vehicle dynamics whether on the street or the race track.

Motivation


The primary motivation of the CFD study and product development plan was to create an easy–to- install series of parts that can create a sizeable impact on drag reduction for the purposes of improving vehicle range and lowering cost of ownership. Rather than creating extreme products with fringe use cases, every product would need to be able to be installed rapidly and fully removable. Specific to each product design requirement is further consideration that each product can be used every day without detriment to the vast majority of daily uses for which the typical Model 3 is used. Lastly, every part required the equivalent durability and longevity to the vehicle itself.

This target was focused into some specific internal goals:

  • Can Model 3 vehicle drag be decreased by a substantial value (more than 15%)?
  • Can a Model 3 be modified to reach a Cd (drag coefficient) of less than 0.20?
  • Can Model 3 aftermarket parts be developed that ultimately save owners money after install?
  • Can a Model 3 gain tangible efficiency while simultaneously increasing downforce?
  • Can a Model 3 aftermarket trunk spoiler be developed that exceeds the results of the Tesla factory-optional trunk spoiler for both the reduction of drag and increase of downforce?
  • Can a Model 3 add-on front spoiler design increase range without impacting practical daily usability?

Method


Unplugged Performance hired a private engineering firm with expertise in the highest levels of motorsports CFD study and aerodynamic product development. This company travelled to Unplugged Performance’s Hawthorne headquarters with their equipment to review a Tesla Model 3. The Model 3 was physically inspected in standard configuration and then then 3D scanned. The 3D scanning encompassed the complete exterior of the vehicle, including the underbody, and with the wheels removed to scan the wheel wells. The vehicle was scanned with and without optional items such as the Tesla factory optional trunk spoiler (standard on the Tesla Model 3 Performance)

The vehicle was surfaced into CAD and imported into ANSYS CFD software for simulations. The first target was to establish a baseline with the factory car before evaluating any changes to the vehicle. Specific measurement values of focus to optimize product development outcomes were:

  • Drag (kgf)
  • Cd
  • Front Downforce
  • Rear Downforce

The above data points were then studied at different air speed simulations.

It is important to note that CFD does not carry with it external variables which bias results found in real- world testing. Driving tests, for example, have inconsistent yaw angle due to variables which cannot be controlled; wind tunnels have other challenges with calibration variability. The key point is that accuracy remains high when testing variations within a closed system. Therefore, the focus of the study was on measured result change in a closed system with everything else remaining constant other than the specific product variables under study. Comparing, for example, a data point in CFD to a data point on a different wind tunnel would introduce inaccuracy across systems. However, comparing data within a closed CFD study is precise to a level of detail unattainable with many other methods.

The methodology of utilizing CFD to approach solving a real-world increase in efficiency was well stated by Tesla’s Lead Aerodynamicist, Robert Palin, in a 2015 SAE International Journal “Application of Real- World Wind Conditions for Assessing Aerodynamic Drag for On-Road Range Prediction”,

“A general trend towards increasing power with increasing yaw angle was evident, although the level of scatter in the data precluded prediction of drag coefficient to a level of precision available through either wind tunnel testing or CFD simulation. However, further analysis of the data showed a trend between the level of turbulence intensity (calculated through the measured standard deviation values) and drag. Increased turbulence had the effect of decreasing the vehicle's yaw sensitivity to drag, but raised the overall level of drag. In the range of typical yaw angles seen by a vehicle traveling at highway speed, increased turbulence levels serve to increase the power required to maintain a speed. CFD simulation methodology to replicate the real world environment was explored with positive results.” (Palin, Application of Real-World Wind Conditions for Assessing Aerodynamic Drag for On-Road Range Prediction, 2015)1

Of interest for the test was the evaluation of previously discussed theories and existing products to measure the numerical impact they have on vehicle aerodynamic properties. For example, Tesla’s CEO, Elon Musk, was referenced discussing that removing mirrors on a Tesla Roadster could result in a reduction of drag of nearly 5% at highway speed. (Lambert, 2018)2

As such, the study tests mirror removal on the Model 3 as a case study to determine the impact on drag at various speeds ranging from 75mph to 150mph.

The further intent was to determine if additional new products could be made that create a similar or greater benefit of drag reduction without the limitation of safety and legality restrictions that come with removal of mirrors. It should be noted that removal of mirrors typically comes with a replacement of thin stalks which house cameras. For the tests performed, the mirrors were removed completely, and were not replaced with stalks, which theoretically would impact the drag savings benefit (depending on design, camera position and size).

Another example of interest is the frequent public discussion that the Model 3’s top speed is limited on non-Performance version cars due to the absence of the Tesla factory optional Performance rear spoiler. An underlying theory is that the rear spoiler increases rear downforce, therefor helping high speed stability and enabling a safer maximum velocity. The study tested rear spoilers at 150mph to explore this subject.

CFD simulation was used as a method of design exploration and optimization for a new Unplugged Performance clean-sheet rear trunk spoiler design. A series of more than 100 CFD tests were made evaluating micro adjustments to shape and how those changes impacted drag and downforce.

Ultimately, after multiple weeks of computational machine time and 143 CFD simulation runs, two specific targeted outcomes were reached. One outcome was a new trunk spoiler design that outperforms the factory trunk spoiler design in drag reduction for maximized efficiency gain. The second outcome was a trunk spoiler that outperforms the factory spoiler, with greater rear downforce for maximized high-speed stability. During the 143 simulations, it was a likely outcome that two very different rear spoiler designs would be required to reach these two specific goals. During the CFD process, over 100 different rear spoilers were created, the designs of which varied greatly. However, the outcome was a design which achieved both targets at once, marrying a larger reduction in drag and a larger increase in downforce within a single trunk spoiler design that utilizes an optional attachable element. The attachable and removable element is a gurney flap that adds modularity to the trunk spoiler. With the gurney flap’s easy attachment, it converts the trunk spoiler from a high efficiency spoiler to a high downforce spoiler.

CFD also enabled the study of existing Unplugged Performance suspension offerings. Many users of Unplugged Performance Dual Rate Linear Lowering Springs have independently reported significant increase in range1 (Discussion, 2018)3.

This prompted the further study of how ride height impacts drag and Cd of the Model 3. Specific focus was made to measure the change in drag specific to vehicle height and to evaluate how that directly correlates to Unplugged Performance’s most popular dual linear rate spring set, “Moderate”, which averages a 1.5” height reduction.

A note about Drag Coefficient (Cd)

The topic of Cd (drag coefficient) is one of frequent controversy and misunderstanding. It would be convenient for this study to make an absolute statement about the Cd of the Tesla Model 3, however, there are many ways for a vehicle manufacturer to calculate Cd. For the same reason that measurements between a wind tunnel and CFD are not accurately cross-compatible (yet remain entirely relevant within tests of their specifically calibrated closed system), all Cd data is only accurate as a change from baseline as parts are substituted in testing. The report of Cd change calculated within the tests performed is highly accurate from within the closed CFD system, and therefore are used for reference.

Conversely, applying a total Cd result to the test performed would require taking Tesla’s Model 3 official Cd of 0.23 and then making quite a few assumptions for which variables they utilized such as wheel selection, calculation of frontal area, rotation method of wheel load measurement in the wind tunnel, and Reynolds number used for testing. For example, a referenced or “official” Cd figure likely would include the wheels in rotation which will have an impact on total Cd, whereas the current study performed had the wheels stationary to remove the three Model 3 wheel options as a variable.

Tesla’s Lead Aerodynamicist Robert Palin explains the significant effect a Tesla aero wheel design (utilizing an attachable aero cap) has when in motion to further reduce the car’s total Cd, below, as stated in a 2012 SAE International Journal “The Aerodynamic Development of the Tesla Model S - Part 2: Wheel Design Optimization”,

“Many studies have been conducted on the aerodynamics of an isolated rotating wheel and tire in ground effect, both empirically and in CFD. The flow field and pressure distribution around such geometry is relatively well studied. One of the key results is that a rotating wheel has a lower drag coefficient than that of the same wheel not rotating. Several papers looking into the behavior of a wheel on passenger vehicles have also been published. While the general trends are useful to note, the specifics of any wheel on-vehicle is going to be dependent on geometry that surrounds it, which can induce turbulence downstream and affect the local flow's yaw and pitch angles.

Waschle shows that there are worthwhile gains in vehicle performance to be gained by optimizing wheel geometry for aerodynamics as well as the normal parameters of weight, strength, and styling. Generally speaking, wheels produce around 25% of the drag on a modern production car. It is interesting to note that in most examples overall drag again decreases by rotating the wheels in an on-vehicle case.” (Palin, The Aerodynamic Development of the Tesla Model S - Part 2: Wheel Design Optimization, 2012)4

As a result, and to summarize the subject of drag coefficient as a data point, the focus of this test was to ensure a high level of accuracy in measuring the specific change in Cd observed when interchanging parts within the closed CFD system.

Results


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Product Tested:
Removing Factory Mirrors

Overview: Due to the popularity of this topic within Tesla’s marketing on concept cars, as well as the general public’s interest in this data, it can serve as a reference point for comparison.

Result: From a factory baseline Tesla Model 3, it was determined that removing the mirrors entirely resulted in a 2.8% total decrease in vehicle drag and a reduction of Cd by 0.006.

 
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Product:
Unplugged Performance Front Lip Spoiler

Overview: This product is an add-on front lip spoiler that attaches in under 30 minutes to a standard front bumper and requires no alterations to the car in order to be fitted. The product was developed out of a durable impact-resistant polymer and is designed for everyday use. The ground clearance after installation is within one eighth of an inch of the factory spec.

Result: This product provides a 6.6% total decrease in vehicle drag; a 236% better relative outcome than removing the vehicle mirrors. This result further reduces the total drag coefficient by 0.015. Of additional interest, the front lip spoiler provided a 35.4% improvement in front downforce.

PRODUCT PAGE
OEM Front End

UP Front Lip Spoiler

 
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Product: 
Unplugged Performance Moderate Dual Rate Linear Lowering Spring Set

Overview: The Dual Rate Linear Lowering Spring Set was developed to provide a slightly softer primary spring rate for city driving, while simultaneously offering a secondary linear spring rate that is more firm. The secondary spring rate is activated upon compression, typically during spirited driving as g forces are loaded onto the car. While the product has been well tested on race tracks to reduce lap times, there also remains a correlation between vehicle height and drag.

Result: As the testing has illustrated, the 1.5” lower ride height provided by installation of the springs yields a reduction in overall vehicle drag. The vehicle’s total drag after lowering factory ride height of 28.5 inches to 27.0 inches (measured at center of the front fender) was reduced by 8.1%. This further lessened the vehicle’s total drag coefficient (Cd) by 0.019.

PRODUCT PAGE

OEM Ride Height

UP Moderate
Dual Rate Lowering Springs

 
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Product:
Tesla Factory Rear Spoiler (available on Performance variant Model 3)

Overview: The optional factory Tesla rear spoiler provides sleek looks with optimized airflow characteristics to enhance efficiency as well as high speed stability.

Result: As expected, this product is not just for looks, it indeed performs improvements in high-speed stability and drag reduction. The vehicle’s total drag was reduced by 2.3% and the rear downforce was increased over baseline by 34.7%. This reduced the total drag coefficient (Cd) by 0.005.

 
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Product:
Unplugged Performance High Efficiency Rear Spoiler

Overview: This rear spoiler was developed within a similar design criterion to Tesla’s factory optional rear spoiler. The underlying premise was to make a product which can adhere to the trunk of the car without drilling, can be utilized without loss of rear visibility, and that looks both sporty and appropriate to the vehicle’s design. Of highest priority, however, is the focus on drag reduction to help increase vehicle efficiency.

Result: The total vehicle drag was reduced by 6.3% relative to the factory car baseline, representing a 273% relative improvement over the optional factory rear spoiler. Rear downforce was increased over baseline by 83.7%, representing a 241% relative improvement. This reduction of drag reduced the total drag coefficient (Cd) by 0.015.

PRODUCT PAGE
 
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Product:
Unplugged Performance High Downforce Rear Spoiler (Modular Configuration)

Overview: The optional gurney flap is added to the High Efficiency Rear Trunk Spoiler to create the Unplugged Performance High Downforce Rear Trunk Spoiler optimized for racing use. The design allows rapid attachment as well as rapid removal based on the desired driving behavior and goals of the owner. Intended use is to drive a long distance in high efficiency without the gurney flap to a race track, to fit the gurney flap for high downforce when racing, and then to remove the gurney flap for a long distance high efficiency return trip.

Result: The specific shape of the gurney flap in combination with the rear spoiler allows a significant performance outcome. Rear downforce was increased over baseline by 160.9%, representing a 464% relative improvement over the Tesla rear spoiler and a further 192% improvement over the Unplugged Performance High Efficiency Rear Trunk Spoiler. The total drag was reduced by 0.1% relative to the factory car baseline in this configuration, making this configuration nearly drag neutral despite the specific downforce focus.

PRODUCT PAGE

Relationship between Drag Reduction and Range Increase

Electric vehicle owners share the desire of wanting to travel further on a single battery charge, lowering energy cost, reducing energy impact while driving, and enabling longer trips with less time spent charging. There is a clear relationship between reducing Cd and improving range, however that relationship is variable depending on numerous factors.

A challenge of the study was reinterpreting the CFD-validated drag coefficient reduction of 0.049 into relatable efficiency improvements that can be felt, understood, and appreciated by the owner of a Tesla Model 3. An easy visualization technique is to look at before and after data of the same vehicle traveling at different speeds and to measure the percentage increase in range over speed. Converting drag reduction data for the purposes of this visualization requires the following calculation of Force on Vehicle at Steady State Velocity:

FD = cR mg + ½ pcD AV2

cR = Coefficient of rolling resistance [0.010]

cD = Drag coefficient [baseline and - 0.049 reduction]

m = Mass of Vehicle [1864kg]

A = Frontal Surface Area [m2]

g = Gravity 9.8 m/s

ρ = Density of air, 1.2 kg/m3 @STP

V = Velocity

At low speeds, drag is less important than mechanical losses with regards to kWh efficiency. However, as speeds increase above 30mph and approach typical “highway speeds,” the relationship between percentage drag reduction and percentage kWh efficiency gain approaches a 1:1 ratio.

Based on this model, we estimate that utilizing the front lip, rear wing, and lowering springs will produce 43 miles of additional range (13.33%) at a steady speed of 70 miles per hour, on top of the Model 3’s expected efficiency. When utilized on a Model 3 Long Range Rear Wheel Drive (EPA-5 system rated 325 miles of range) this added 43 miles of range at 70 miles per hour can have significant real-world impact for long-distance driving. In much higher speeds, such as in Germany on the Autobahn, the efficiency gain is estimated to exceed 19% improvement at a top speed of 163mph.

Aftermarket Products as a Means of Energy Savings and Cost-Benefit Analysis

The study’s result that the tested products can significantly reduce energy consumption for the Model 3 introduces new questions about the relationship between purchase cost and long-term financial value of studied aerodynamic upgrades. Using the data, a cost-benefit analysis can be performed.

Traditionally, aftermarket products are considered a sunk cost by the owner, however with energy consumption savings comes a reduction of energy expense. At the time of publishing, March, 2019 the cost offered to Tesla vehicle owners at Tesla Superchargers in California is approximately $0.34 per kWh. Tesla does not consider Superchargers as profit centers, therefore the $0.34 per kWh cost could be considered reasonable as a baseline figure.

For the purposes of this study we will apply some data to a theoretical Model 3 vehicle usage of 100,000 miles. The generally accepted factory energy usage for the Model 3 Long Range RWD is 24 kWh per 100 miles. Utilizing these data points with the $0.34 cost per kWh the total energy expense in such a scenario is $8,160 over 100,000 miles.

In the above section, Relationship between Drag Reduction and Range Increase, the correlation between drag and range increase is explored. The study’s model predicts that, at high speeds the correlation approaches 1:1, while at very low speeds (eg: 5 miles per hour), the two subjects are disassociated due to negligible drag at very low speed.

In evaluating 100,000 miles of Tesla Model 3 use, if we assume the vehicle travels daily on the freeway at freeway speeds of 75mph, it is not unreasonable to assume that this study’s outcome of a combined 21% of drag reduction would result in approximately 12.5% of energy reduction. If the driver goes above the speed limit, the 12.5% would increase; if the driver sits in bumper to bumper traffic the 12.5% would decrease. In the 12.5% example, the $8,160 in energy expense would be reduced to $7,140, and results in a cost savings of $1,020 over 100,000 miles of use.

Every driver with a Model 3 will undoubtedly have different energy costs, different driving speeds, and different driving behaviors, depending on their use case. While the energy savings calculation is not exact in any specific scenario, the underlying data can be applied to specific examples and cost savings can be estimated.

The aforementioned products have the theoretical return on investment potential to cover a bulk of their acquisition costs from energy cost savings, while reducing environmental impact and increasing long range utility of the car.

UP Front Lip Spoiler

UP High-Efficiency Rear Spoiler

Conclusion


Unplugged Performance’s CFD testing, study, and integration into product development has yielded substantial improvements. By installing three simple upgrades, the Model 3’s drag coefficient was reduced from baseline by 0.049, total aerodynamic drag was reduced by 21%, and, simultaneously, both front and rear downforce were increased.

It is important to note that Unplugged Performance’s aftermarket product development enjoys some freedoms for which original car manufacturers, Tesla in this case, operate within different constraints. This document does not suggest that Tesla’s world- class aerodynamics team fell short of optimizing for the original vehicle. Tesla factory vehicles must adhere to a long set of complicated global homologation regulations, which can create restrictions on design. Furthermore, Tesla has mass market audience targets and perhaps cannot take the same degree of liberties to design parts in a pure performance-oriented way. Due to the Model 3 serving as snow-driven cars, taxi cabs, and a wide additional variety of use cases, it should be stated that the specialized nature of Unplugged Performance’s parts and opt-in client base is a partial reason that enables the significant improvements shown. Nonetheless, Unplugged Performance and Tesla share the same mission of reducing energy costs (both environmentally and financially), increasing maximum distance travelled per charge, and increasing ownership satisfaction. Unplugged Performance will continue to utilize CFD studies to refine and develop new aerodynamic parts for the purposes of further increasing efficiency, as well as for motorsports use.

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REFERENCES


1 Palin, R. (2015, April 14). Application of Real-World Wind Conditions for Assessing Aerodynamic Drag for On-Road Range Prediction. Retrieved from SAE International Journal: https://www.sae.org/publications/technical-papers/content/2015-01-1551/

2 Lambert, F. (2018, August 17). Elon Musk talks next-gen Tesla Roadster, hints at potentially having no mirrors, and more. Retrieved from Elektrek: https://electrek.co/2018/08/17/tesla-roadster-elon-musk-no-mirrors/

3 Reddit Discussion. (2018, July). 12% Range Improvement with Lowering Springs over 3,700 miles. Retrieved from r/TeslaModel3 Sub-Reddit : https://www.reddit.com/r/TeslaModel3/comments/92pecs/12_range_improvement_with_lowering_springs_over/

4 Palin, R. (2012, April 16). The Aerodynamic Development of the Tesla Model S - Part 2: Wheel Design Optimization. Retrieved from SAE International Journal: https://www.sae.org/publications/technical-papers/content/2012-01-0177/