Pizza pan wheel cover testing

My prototype in test:

• car wash - no problem
• 100 mph (160 kph) - no problem
• standing water (not done, yet)

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 benchmarks at: 30 mph; 55 mph, and; 75 mph. The first series without the wheel covers and the second with and curve fit into a quadratic equation.

Bob Wilson

 

Not by me. Regenerative braking means almost no heating.

Bob Wilson

 

Ran benchmarks last night but during a 20 minute charging session, a front passed through. The temperature dropped 6 F and wind direction changed and blew stronger. This would have significantly impacted the last, 75 mph test. I won't speculate on the effect but it very likely impacted the second, 75 mph pass. Regardless, this is what my preliminary data shows:

These preliminary results suggest at least a 5% improvement in high speed performance at 65 mph which also increases the range. Since my battery has a -10% degradation, it looks like half of the lost battery capacity will come back.


I plan to paint the covers flat black to match the tire rubber. This will also mask the 'rough finish' of these prototype covers.


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:



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:


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:


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

 

Ever try to mount a tire with black wheel covers at night?

Bob Wilson

 

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

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

Success!

Bob Wilson

 

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 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:


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

 

I'm going to call it a modest success:

• 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

 

The problem was the 2019 wheels and tires were too heavy for the Std Rng PLUS. Lighter wheels and Bridgestone ECOPIA gave a solid efficiency boost below 45 mph. But the wheel vendor has no wheel covers.

Bob Wilson