Pizza pan wheel cover testing

[bwilson4web]

I'm going to call it a modest success:

• thin green line - suggests the pizza pan wheel covers provide up to ~4% at 70 mph.
  • temperature adjustment - field benchmarks are subject to weather effects, notably temperature. With the covers on, the temperature was ~3F cooler. So I displaced the trend graph, mid-point to match the mid-point of the higher temperature benchmark.
• ~$600 savings - a 4% improvement on a $15,000 Model 3 battery pack.
• unexpected impact of cold - comparing the 63F to 48F, the curves are similar but significantly offset. The colder air should have been about 3.5% denser which was my expected drag offset. Also, it was not uniform across the speed range suggesting at least one other, non-linear, temperature based, mechanism is in effect.
  • The shape of the energy loss curve showed as much as a 25% loss at slowest speeds and ~10% loss at highest speeds. This suggests a loss of energy relative to the drive energy of something like heating that would show an outsized effect at lower speeds where less drive energy is needed. I did get the cabin setting to 71F, windshield and feet, and lowest fan setting. I consider interior windshield heating a hard requirement to avoid condensation from our breathing. This bears future investigation.

Significant cross country drives Monday through Wednesday with the covers on will give the battery management system more samples. This will hopefully update the projected ranges as a function of SOC.

My end goal is to compensate for the ~10% battery degradation and recover my original 240 mi range. A potential 4% reduction in drag energy is a step forward.

Bob Wilson

[bwilson4web]

POST TEST ANALYSIS

The best estimate, a 4% drag energy reduction, is ~40% of my end goal, reversing the ~10% battery capacity degradation. But I need to:

• Review the SAE paper for further drag energy reductions.
• Improve benchmark methodology

SAE PAPER REVIEW

Citation: Brandtm A.m Bergm H., Boizon, M., and Josefsson, L., "The Effects of Wheel Design on the Aerodynamic Drag of Passenger Vehicles," SAE Int. J. Advances & Curr. Prac. in Mobility 1(3):1279-1299, doi: 10.4271/2019-01-0662.

Starting with:


Coverage area dominates the wheel drag. The pizza pan covers fully the wheel area except for five lug nut access holes.

The lug nut holes are the remaining hub depth and have an effect:


The five holes around the center are needed to access the wheel mounting lug nuts. They are open but a smaller, cover could close them and make it flush. But there is one design issue not addressed.

The vehicle side of the wheel spokes are exposed and have a 'squirrel cage' drag effect. The inside of the spokes move air, another drag force. There are design approaches that could also eliminate hub depth.

BENCHMARK IMPROVEMENTS

I used a quadratic equation derived from three data points to generate the trend lines for the 48F, 60F, and 63F benchmarks. A second order quadratic equation is perfect for drag calculations but the EV reports energy units, kWh/mi. Energy typically is a 3d degree equation that requires one more data point.

An ideal, triple point benchmark would include the energy loss at 0 mph. This can be measured by blocking the wheels; putting it in "D" mode, and; measuring the energy loss over time. Do this at different temperatures and we can combine the other two points. This might also give insights to the cold weather effects.

FOLLOW UP

1. Long distance drives to give the Battery Management System (BMS) a chance to recalibrate the EV range with the new covers. This primary metric relates directly to the goal.
2. Cold weather, static in "D" metrics of vehicle energy overhead. Three or more temperature points can provide a basis of estimate for a 3d degree, energy polynomial.
3. Design a fully enclosed, spoke wheel cover system. This could eliminate the lug nut holes associated with a minor hub depth effect.
4. Aerodynamic cleanup of front bumper cover.

Bob Wilson

[Cd]

Great to see some testing on Ecomodder.
Thanks for posting results.
Did you post photos of the 'pans ?
( Not showing up on my phone. )

Sort of off topic :
Do you have a small GoPro style camera ?
I ask, because I'd love to see your car's underbody tuft tested.
It is perfectly flat with great airflow, and I'm wondering how tufts behave on a flat surface with, but with gravity also acting on the tufts.
( Do they stick to the underbody surface, or hang down and flap around ? )
- Thanks

[bwilson4web]

No one seemed interested. Here are the unpainted ones:


I've painted them with flat-black to match the tires. But this led to another challenge at night:



A 1/16" shallow cup drilled in the stud ends filled with clear epoxy and phosphorescent powder. This makes changing a black tire and cover at night possible.

The modified pizza pans are held to the wheels with black, plastic, zip ties.

As for aerodynamics and videos, my next interest is cleaning up the front bumper:

• Confirmal surface to left and right of cooling air inlet.
• Conformal cover for left and right cheek inlets.

In the future, I may investigate:

• Inside wheel covers
• Fully reclining passenger seat (aka., hotel Tesla)
• Thermal insulating bottom of battery pack
• Vortex generators vs rear spoiler
• Underbody 'air dams', front and side
• Removable, exterior mirrors and/or aero tricks
• Rear wheel well covers

Bob Wilson

[Cd]

Clever idea !
So, I see what looks like zip ties at the edges.
So this is what is holding the cover on ?

You have probably seen this video, but if not, it may be if interest : https://youtu.be/x1X0x3SGxP4?si=vWloa3J0siGIFm9Y

This mod looks extremely easy to duplicate, and I'd love to see if it really works as they claim.
A few pieces of black Coroplast would produce the same effect, yet save a ton of money.
Here is the link : https://unpluggedperformance.com/aer...tesla-model-3/

[bwilson4web]

Originally Posted by Cd

Clever idea !
So, I see what looks like zip ties at the edges.
So this is what is holding the cover on ?

Correct. The zip ties are cheap, light weight, and uniform so no problem with balance. Strong as heck, four of them held the prototype cover on at 100 mph and went through a car wash without a hitch.

When I fabricate the inner and outer wheel covers, a tongue and grove configuration will allow the outer cover to easily be removed which eliminates the lug nut access holes. Of course this means I'll have to buy a 2' bed, CNC machine, ~$2,800, to precisely fit the parts.

Hummm, my birthday is Dec 11 and Christmas soon follows. What shall I give myself?

Originally Posted by Cd

You have probably seen this video, but if not, it may be if interest : https://youtu.be/x1X0x3SGxP4?si=vWloa3J0siGIFm9Y

I had not seen that one but we see the same problem areas. I bought a foam 'water noodle' to fabricate inserts on the left and right to cover all but the center, open air inlet. I will experiment with the side, air cheeks. A conformal cover, initially painter's tape but later automotive grade duct tape, will minimize turbulence.

If my benchmarks show success, I'll probably fabricate a pair of light weight covers to precisely match the gaps. Matching paint and they will be all but invisible.

Originally Posted by Cd

This mod looks extremely easy to duplicate, and I'd love to see if it really works as they claim.
A few pieces of black Coroplast would produce the same effect, yet save a ton of money.
Here is the link : https://unpluggedperformance.com/aer...tesla-model-3/

I had seen their web page back in 2019 but got the impression they wanted me to buy something. Their method is first class but D*MN expensive and some parts like exterior mirrors, incomplete.

I replaced two of three underbody panels due to road debris. This was the middle one in front of the battery pack:

The original original one on the left, a plastized fiberboard, is after a road debris strike. The replacement part on the right is injection molded plastic.

My interest is to thermally insulate the bottom of the battery pack. So I will fabricate 1/4-1/2" thick, water noodle like foam, tiles with beveled edges. These will be 'glued' to the bottom of the traction battery in equally spaced, front to back strips. Road debris may take out a column but the damaged ones can easily be replaced. Think Shuttle heat tiles.

I'm after heat management by letting the existing battery thermal system handle the exact temperature. The upper and sides of the battery pack are exposed to the under body slip stream.

Bob Wilson

[aerohead]

Bob, I believe that you're the first to do un-ventilated wheel covers on the Model 3 ( I like it! ).
Back in 2018, Robert Palin, who'd been Tesla's aerodynamicist for all Tesla cars, except the Lotus Elise-based 1st-gen Roadster, reported on the Model 3 aero covers, @ electrek.co.
Palin attributed 10% efficiency increase, and 3% range improvement at 'high' speed, perhaps 141-mph ( it wasn't specified ).
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Then, I think it was Bjorn Nyland, who rented a Tesla Model 3 in Germany, and road tested it, with and without the aero covers.
He drove a 94-km circuit, at up to 150-km/h, and he's one to pre-condition a car to achieve thermal equilibrium before actual testing begins :
1) @ 150 the covers were good for 8-km additional range ( 2.564% ), 320 km vs 312 km.
2) @ 136.7, 1.944%.
3) @ 120.7, 1.335%.
4) @ 104.6, 0.869%
5) @ 88.5, 0.526%
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Bjorn Nyland also tested a Tesla Model 3 from Tesla's Hawthorne, California headquarters, on the San Diego Freeway, at 75-mph ( 120.7-km/h ), in late evening when traffic was minimized.
After thermal equilibrium was achieved, the Model 3 returned 179 Wh/ mi with the aero covers, vs 186 Wh/mi without the covers, a 3.9% energy delta.
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Some messengers report that production tires will have a constant coefficient of power absorption up to 'standing wave' velocity, of which the manufacturer will electronically limit the car's top speed below that threshold. I can't say, one way or another.
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Thanks for the top-shelf testing, data reduction, and reporting!

[Phase]

Are you comparing pizza pans to the aero covers or pizza pans to no covers at all? I’m curious to how much extra range full covers give versus the aero covers

I’ve been experimenting with taking over the cooling slots in my ioniqs aero covers to elimate all ventilation drag. I haven’t been to concerned about the lug nut holes and just use the excuse that they act as mini vortex generators to energize the air flow to help it reattach to the car body after the wheel ( don’t know how true that is)

[Vekke]

Optimal tire size I would try in model 3 is 195/60R17 from new toyota prius.

In that size you can also get wheelcovers easily and use just steel wheels.



Inside wheel covers surely works. Bigger wheels you have more benefits you will get:



My estimation is 2% savings with these 155/70R19 wheels in audi a8 project car. One of the reasons to avoid huge wheels as the inside gap also increases.

[Cd]

Vekke : That inner wheel cover is brilliant !
I'm going to attempt it on my car as well.
Thanks for posting that photo.