Pizza pan wheel cover benchmark results

[bwilson4web]

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 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

ps. I will post additional details about how I made them.

[bwilson4web]

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 set 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