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[oldgeeksguide]

I’m changing up the bed configuration of the Lightning. Going from a tonneau cover to a cap. We get more space and more solar panel mounting space, so it’s win-win-win.

To do that, I decided to wash the bed after removing the tonneau cover. But I wanted to use the pressure washer and the hose location is too far from an outlet in the workshop and I didn’t want to run an extension cord. Fortunately the truck has plenty of electric power to run a pressure washer.

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I’m picturing plugging it into an outlet in the bed while washing the bed and wondering what happens when you point it at the outlet

 

[Chavannigans]

I had taken the statement to mean that they thought that the biggest impact was wiper motors, not the biggest impact is rain. While the latter often necessitates the former, the wiper motors can be on without there being any rain—I knew a kid in high school who always drove with the wiper motors on. Very bizarre.

I discount the energy costs of wiper motor, headlights, etc. With modern vehicles, those are minimally impactful. I can even go out to measure it in the truck if needed.

Rain in the air impact on aerodynamics has only a couple percent impact on automobile drag (so overall not a large percent on total range). Though we get soaked during a rainstorm, the relative density of the air doesn’t change a lot, and the mass of the rain only matters a little bit.

However, as you noted: a thin film of water on the road will absolutely increase rolling resistance. It will depend a bit on the tire tread. Here’s one example from a research paper where they did experiments on the roads in Poland and Sweden.

You can see that for an 80 kph test, at about 0.65-0.7 mm of rain on the road surface, the rolling resistance is increased by about 40%. It gets even higher at higher speeds. This is in part due to the vehicle pushing water as you mentioned. It’s also because the tire temperature is decreased and that causes lower pressure and thus increased rolling resistance. This is just rolling resistance. This impact will be more noticeable at low speeds since rolling resistance has a greater relative effect on efficiency at low speeds. At higher speeds, drag takes over.

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Humidity doesn’t have a large impact on aerodynamic drag; this is mostly because high humidity air tends to be warmer air and density is more dependent on temperature than humidity, so highly humid air tends to be less dense.

Overall, for an EV, on a no-HVAC drive, something like >95% of the energy gets to the driveline (as opposed to ICEs, which lose about 79% of the energy to heating up the surroundings without producing useful work). Driveline losses cost about 2% - 5%. So about 90% of the energy is delivered to the wheels.

On the highway, about 45%-50% of the total energy expenditure is spent on pushing the air out of the way. If there’s a 4% increase in aerodynamic drag due to rain, that’s a 2% increase in total energy expenditure. 350 miles * 0.02 = 7 miles reduction in range.

For rolling resistance, at highway speeds, about 15% of the total energy expended is due to rolling resistance. If that increases by 50%, that’s another 7%-8% increase in total energy expense, which is about 28 miles reduction in range assuming 350 miles range.


Reducing speed a bit will overcome most or all of that increase in resistance.

Thank you for being thorough and taking the time to demystify things as you do.

I was pretty skeptical about the claim but the most surprising part of your insight to me was the tire pressure being lowered by the heat transfer with the water.

I’m sure we have all had the pleasure of a tire pressure warning light greeting us on a frigid winter morning, and witnessed it disappear after a few minutes of driving.

Does the study flesh out the temperature delta as well as well as the pressure variance?

Trucks and SUVs tend to run higher pressures so it makes me wonder if they will experience the same impact as a sedan.

Electric vehicles tend to be even heavier so I imagine factory recommended pressures for Scouts will be higher than their ICE counterparts.

So would it cause as much of an impact for the larger and heavier vehicles?

 

[SpaceEVDriver]

I’m picturing plugging it into an outlet in the bed while washing the bed and wondering what happens when you point it at the outlet

Plugged it into the frunk for just that reason.

 

[SpaceEVDriver]

Thank you for being thorough and taking the time to demystify things as you do.

I was pretty skeptical about the claim but the most surprising part of your insight to me was the tire pressure being lowered by the heat transfer with the water.

I’m sure we have all had the pleasure of a tire pressure warning light greeting us on a frigid winter morning, and witnessed it disappear after a few minutes of driving.

Does the study flesh out the temperature delta as well as well as the pressure variance?

Trucks and SUVs tend to run higher pressures so it makes me wonder if they will experience the same impact as a sedan.

Electric vehicles tend to be even heavier so I imagine factory recommended pressures for Scouts will be higher than their ICE counterparts.

So would it cause as much of an impact for the larger and heavier vehicles?

I'll have to dig into the papers when I can see straight. To better understand the specifics of temperature changes, I will need to find several more papers too. I imagine it will depend a lot on tire construction, composition, mass, size, and temperature before encountering the water. A low profile street tire may be affected more than a large AT tire, for example. A hot tire will lose more energy than a cooler tire, and so will lose more pressure. I'll have to read up.

The recommended pressure for the Lightning is 36 PSI for AT and 42 for AS tires. For the ICE trucks, it's 35, 40 for the F-150 HD package, and 38 for the Raptor off-road tires. I run the Lightning at 48-50 on the ATs. It's a harsher ride, but the handling is far superior. I imagine the impact of water-cooling will not be much different between the two power plants.

 

[dreamweaver]

Plugged it into the frunk for just that reason.

I haven't been able to find a definitive answer for this question. Are EV electrical outlets GFCI and/or AFCI protected?