Testing pizza plan wheel covers

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bwilson4web

bwilson4web

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My prototype in test:
  • car wash - no problem
  • 100 mph (160 kph) - no problem
  • standing water (not done, yet)
1696581111153-png.50425


Lessons learned:
  • ZIP heads holding pizza pan on the inside of tire
  • buff painted surface to match tire
  • paint and buff "road rash" on wheels
  • (optional) paint and buff wheel inner hub and lug nuts
  • chest mount LED light at night
I'll do two series of three-speed benchmark: 30 mph; 55 mph, and; 75 mph. The first set without the wheel covers and the second with and curve fit to a quadratic equation.

Bob Wilson
 
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Bob, I applaud your ability to get tie-wraps in place to hold your pizza pans onto your wheels! It would have been much tougher if you put them on without removing the wheels first. What is the chest-mount LED about?

I was impressed with the max-aero wheel covers on a Model 3 at the recent Drive Electric Week event in Ann Arbor. In addition to improved aerodynamics, this Tesla also sported extra booster batteries, but they pretty much hogged the entire frunk.

upload_2023-10-7_1-30-37.webp
 
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One of my design issues was how to attach the pizza pans to the wheels. With seven spokes, I would have required the same number of identical weight and form factor 'hooks' or clamps. Then I had the thought to just mount the pan to the wheel semi-permanently with tie-wraps. Strong, light, and located near the rim, a simple, cheap solution. The tire has to come off to install the tie-wraps but this meant I also needed a way to remount the wheel.

Five holes large enough for the lug wrench solved the mount and subsequent removal problem. I was worried that they might 'whistle' but testing up to 100 mph verified it was silent. The lug nuts are near the center of the hub and the gaps between the pan and wheel hub avoids any sort of resonance chamber. Given the small gaps and location close to the hub, any 'bleed' air would be insignificant compared to the previous, open spokes.

The last bit was access to the valve stem via a 1/2" hole. Rather than extend the stem, I took the cap off and have an extension for my 12 V air pump. Insert the extension, screw it on, and inflate the tire.

The chest or shirt neck LED is to illuminate the studs when putting the tire and wheel on the car. I need to use both hands and shoes to raise and align the wheel but off-axis lights do not show the deep studs behind the five lug nut holes. Sure there are LED equipped forehead and eye glass frames but I really don't want my light wandering around. A chest mounted or in the shirt neck line would give the steady light I need. Yes, a smart phone could also work with a 'mount' holder.

Bob Wilson
 
So mounting the pizza pan covers, I inspected the tires closely and found the passenger side, rear had reached "end of life," with flush wear bars on one tread:
1698220569082-png.50711



Not unexpected as I normally swap tires left-and-right but I wanted to find out how good (or bad) my last alignment had been. FYI, I got more than 50,000 miles use on these discontinued Bridgestone ECOPIA. The driver side tires have normal wear. IMHO, the passenger side camber link should be adjusted:
1698220978876-png.50712


I'm pretty sure the camber adjust bolt is nearest the brake disk. I'll download the maintenance page and confirm to also get the torque values. Anyone know for sure?

As is my practice, I will move the front tires to the rear and mount a new pair on the front:

1698222352684-png.50713

My ordinary tire rotations, left-and-right, equalizes the tire wear for maximum life. But this can mask an alignment problem if you are not 'anal retentive.'

The front-to-rear allows adoption of new tires to replace discontinued ones. I will also let the tire installers sell me new tire pressure sensors.

Sure, there are occasional '4 for the price of 3' tire sales. But this usually means three serviceable tires go to 'tire heaven.' My goal is to get the maximum service of every tire ... my savings.

Bob Wilson
 
Normally, I only see 161 mi when charged to 75%. Now:

1698250224472-png.50716

  • +6.8% = ( 172 - 161 ) / 161
  • $1,020 = 6.8% * $15,000 (battery replacement cost)
  • ~229 mi maximum range, 240 mi new
Success!

Bob Wilson
 
bwilson4web said:
So mounting the pizza pan covers, I inspected the tires closely and found the passenger side, rear had reached "end of life," with flush wear bars on one tread:
1698220569082-png.50711



Not unexpected as I normally swap tires left-and-right but I wanted to find out how good (or bad) my last alignment had been. FYI, I got more than 50,000 miles use on these discontinued Bridgestone ECOPIA. The driver side tires have normal wear. IMHO, the passenger side camber link should be adjusted:
1698220978876-png.50712


I'm pretty sure the camber adjust bolt is nearest the brake disk. I'll download the maintenance page and confirm to also get the torque values. Anyone know for sure?

As is my practice, I will move the front tires to the rear and mount a new pair on the front:

1698222352684-png.50713

My ordinary tire rotations, left-and-right, equalizes the tire wear for maximum life. But this can mask an alignment problem if you are not 'anal retentive.'

The front-to-rear allows adoption of new tires to replace discontinued ones. I will also let the tire installers sell me new tire pressure sensors.

Sure, there are occasional '4 for the price of 3' tire sales. But this usually means three serviceable tires go to 'tire heaven.' My goal is to get the maximum service of every tire ... my savings.

Bob Wilson
Click to expand...
My compliments on your great graphics!

According to InsideEVs' article about a Tire Rack video, for the best range, you should keep driving those tires until they fall apart: "worn tires increase range quite substantially."

Oh wait, the next sentence is "However, those same worn tires aren't as safe and don't perform as well."
 
Suspicious of my earlier metrics, I reran my benchmarks::
  • distance: 12.4 mi
  • elevations: 564, 588, 618 ft
    • Elliott Cemetery #1, Hillsboro, AL
    • Chevron Courtland, Courtland, AL
  • speeds: 40, 55, and 70 mph
    • regenerative braking, U-turn at opposite end
    • recorded a single, kWh/mi, for both passes
  • temperature ranges:
    • 48F(1-4 AM)
    • 63F (1-3 PM)
  • trend line quadratic coefficients: (A*v**2) + (B*v) + C
  • cabin temperature: 71 F
    • lowest fan speed venting feet and windshield
  • exposed wheel spokes
    • front: Pirelli P7 AS, ~200 mi, 50 psi
    • rear: Bridgestone ECOPIA, ~50,000 mi, 50 psi
Results:

index.php

The graphs are 1024 pixels wide. Opening them in a separate window gives full size.

Observations:
  • Power curves, kWh/mi, are smooth and as expected.
  • Energy curves showed:
    • @63F local minimum 55-60 mph
    • @48F local minumum 66 mph
The power, kWh/mi, varies by speed as expected. Divide the rate into the battery kWh and you have the 0-100% range. I was surprised that the minimum energy speeds varied by temperature.

As the temperature goes down, the air density increases which increases the aerodynamic drag and energy needed. The "U" shape of the energy curves reflect higher overhead and tire energy at lower speeds and higher aerodynamic energy at faster speeds. The middle is when the overhead energy and aerodynamic energy are equal.

In theory, the static drivetrain and electrical overhead could be calculated by adding a 25 mph benchmark point and solving for a 3d degree trend line plotted to 0 mph. This would also include the cabin heating load. But I would rather measure these directly.

Now I feel comfortable rerunning benchmarks with the wheel covers. The earlier results showed the pizza pan covers reduced high-speed drag but I am interested in more details.

Bob Wilson
 

Attachments

  • kWh:mi vs MPH.webp
    kWh:mi vs MPH.webp
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I'm going to call it a modest success:
cover_graph_01.webp

  • thin green line - suggests having the pizza pan wheel covers provides 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
 
Every oil will have a higher viscosity when cold. I have noticed in my Kia that the dash efficiency number is lower on a round trip when starting out cold, assumed something like this is in play.
I think you need to buck up for science and turn the heat off....

Wondering about effect on brakes. Holes in the wheels are primarily to vent the brakes
 
Well I FSD struck out and drove home on Autopilot which has a different stop light algorithm. I had to do a shuddering stop to avoid running a red light.

Bob Wilson
 
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