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Looking at the fueleconomy.gov link and only considering the useful output power which is what I was really imagining above; probably less than 55hp for the typical car at cruise and ~22kW for the Tesla. Then while maintaining a cruise the useful power is only split between:
- Rolling Resistance = 7-11%
- Air resistance = 11-16%
Depending on speed either drag or rolling resistance are going to dominate the power required. I really had never considered rolling resistance to be of great importance to a car despite my experiences on a bicycle.
I've got an EcoBoost Fiesta and during the winter here (Canada) the pressure gauges on most of the air pumps at the gas stations seize in the cold and so are practically useless. When it was finally warm enough to accurately check the pressure in my tires they were all around 30-32psi. After inflating them back to the recommended 38psi I noticed my economy improved from 6.5 l/100km to 5.5 l/100km although admittedly the average temperatures had also warmed up from around -15 to -5C. Even so it was enough of an improvement that I was surprised and will be checking tire pressures more frequently in future.
At 60mph the air resistance will be about 85N or about 2.3kW. This is far less than I would have thought and appears much less significant than the typical rolling resistance.
441N x 26.8 m/s = 11.8 kW
Using wikipedia figures the Tesla seems to require approximately 22kW at 60mph but it is extremely low drag and probably has lower rolling resistance than the typical value above. However I'd bet most cars are using 40kW (~55hp) or less to cruise at 60 resulting in the rolling resistance being responsible for 25-50% of the power requirements. I'm not convinced it would be worth it in many cases but recovering 10% of the energy could provide 1kW, the same as a 70A alternator.
I can't think of a cheaper and easier solution than a RAM disk for this particular application.
I'm trying to do a similar thing on the RPi to build a CCTV system. Live streams straight from RAM but to then use the hardware calculated motion vectors to trigger recording onto an SD card. Unfortunately I'm currently stuck trying to find a tool that can perform the HLS packaging of the segmented elementary streams the RPi camera can produce.
I've been utterly shocked at the state of many cars on the road here with no sills left and nothing but rust in other structurally essential parts of the car. I think the OPP can stop cars that they deem unsafe but there certainly is no annual safety inspection and the only required test is a bi-annual emissions check.