Do I really need the Max Pack?

[ajdelange]

Are you running the defroster while suffering that 28% loss?

Don't remember but it wouldn't matter much. I averaged 60 mph on that leg. If the defroster took a kW It would consume 1 kWh in the time it took to go 60 miles so the defroster load would be 17 Wh/mi. That's 7% of 300 leaving 21% to be explained elswhere.

Also, what tires are you running to achieve that level of resistance in the rain?

The stock tires.

What are some of your numbers?

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[Autolycus]

I'm willing to bet some percentage of the 'rain loss' is actually just humidity loss. Humid air is denser than dry air, so it offers more resistance. I really don't think the water on the pavement has a whole lot to do with it, but I'm not an expert. Just trying to apply some reasonable logic.

You're reading the chart wrong. The higher the humidity, the less dense the air. Also, the higher the temperature, the lower the density, fwiw.

"Rain loss" is mostly caused by higher rolling resistance from a wet road surface and a small contribution from running wipers and headlights. I honestly don't know what a typical effect will be, but I'm guessing it varies based on tire tread and design.

 

[Inkedsphynx]

You're reading the chart wrong. The higher the humidity, the less dense the air. Also, the higher the temperature, the lower the density, fwiw.

"Rain loss" is mostly caused by higher rolling resistance from a wet road surface and a small contribution from running wipers and headlights. I honestly don't know what a typical effect will be, but I'm guessing it varies based on tire tread and design.

Yep, caught me having stepped away without finishing my second edit update to note that I'd discovered that via some googling. Appreciate the correction.

 

[Autolycus]

There was an accident on takeoff at SFO many years back involving a 747 I think. It clipped the landing lights at the departure end of the runway because it couldn't develop enough lift. The NTSB concluded that when the copilot did the calculations he neglected to include the correction for humidity. Lift is proportional to density. Humid air = less drag and less lift.

As I noted in my other response to this thread, air temp also has a big effect on density. Pilots often dread "hot and high" takeoffs because of the loss of lift from high temps at high altitude. Denver summers often mean they can't load up wide bodies for long-haul flights as much as they want.

 

[ajdelange]

Somebody once pointed out that when you smash a raindrop to smithereens you are heating the water so that energy transfer implies some extra drag but I think that's like the heater/defroster load - small in comparison to the work done pushing the water out of the way.

 

[ajdelange]

As I noted in my other response to this thread, air temp also has a big effect on density. Pilots often dread "hot and high" takeoffs because of the loss of lift from high temps at high altitude. Denver summers often mean they can't load up wide bodies for long-haul flights as much as they want.

I well remember wondering why i got cleared to a very long runway for takeoff even though I was a little bitty single engine job and had landed on a much shorter runway an hour or so earlier. I found out soon enough.

 

[Ray R]

Don't remember but it wouldn't matter much. I averaged 60 mph on that leg. If the defroster took a kW It would consume 1 kWh in the time it took to go 60 miles so the defroster load would be 17 Wh/mi. That's 7% of 300 leaving 21% to be explained elswhere.

The stock tires.

What are some of your numbers?

I don’t track my energy usage anywhere near as diligently as you. But I noticed on my e-Golf and Bolt that if I’m running any sort of HVAC, my range drops @10%. I also know I’ve had tires on the various vehicles I’ve owned over the years that cut through standing water much better than others.

 

[Wanderer]

No, 'fraid not. As I said in my last post I usually do 300 or so on the freeway. Checking my last freeway run in the rain I logged 383. That's a 28% increase. One data point but typical in my experience. Do you have some numbers we could compare with what I've observed?

There's a very good reason. The 300 and 400 mile ranges are based on the EPA protocol which blends in town and highway driving and the highway part is not at the 70-75 mph level that most of us use on the freeways. As speed increases above 60 drag begins to emerge as the dominant energy sink and the drag component of total wh/mi is quadratic with speed above that point.

Everyone has their own experience, and mine is that rain doesn’t make a 20% plus impact on range, it’s much smaller.

Rivian’s estimate actually has nothing to do with EPA that we know of actually. And even if it does, my experience is that I get close to EPA range on the highway in my e tron

https://insideevs.com/reviews/443791/ev-range-test-results/

The overall average EV achieved only 1.3% lower range at constant 70mph than the EPA stated range. For Tesla’s, the average is negative 11.6% and the average non Tesla was actually positive 1.1%. That is influenced by the Taycan which is 30% better, but removing those and the non Tesla average is only negative 4.8%.

A little known fact, but EPA range is actually submitted by the car maker, not the EPA. They are allowed to make adjustments within reason, and Tesla takes full advantage of that. I also suspect that their heavy regen helps with blended numbers but hurts on highway numbers. My Audi coasts like a manual in neutral when foot is off the accelerator, which is more efficient.

 

[Wanderer]

I don’t track my energy usage anywhere near as diligently as you. But I noticed on my e-Golf and Bolt that if I’m running any sort of HVAC, my range drops @10%. I also know I’ve had tires on the various vehicles I’ve owned over the years that cut through standing water much better than others.

That’s just the very inefficient systems in those cars. those with a proper heat pump system is much less. Running AC only drops my range a few miles, or like 1%.

 

[Ray R]

That’s just the very inefficient systems in those cars. those with a proper heat pump system is much less. Running AC only drops my range a few miles, or like 1%.

Agreed. Do we know for sure what type of system the Rivian will have?

 

[Wanderer]

Agreed. Do we know for sure what type of system the Rivian will have?

Don’t know that I’ve seen for sure, but I’d sure expect heat pump at that price level.

 

[smiesguy]

Living with a Tesla the past few years, I would pay up for range whenever possible. Living in the MidWest, cold weather is such a range zap making even small road trips a real challenge. I did a 250 mile round trip and with cold temps and wind had to charge twice to make the trip. That's with a fairly reliable Tesla Supercharger network.

 

[CommodoreAmiga]

Agreed. Do we know for sure what type of system the Rivian will have?

Not a heat pump, unfortunately.

 

[ajdelange]

Rivian’s estimate actually has nothing to do with EPA that we know of actually.

Given that we do not know exactly how Rivian calculated 300 and 400 we can only assume they did what a prudent man would do and that is evolve the best estimate of what the EPA rating will be and publish that. If the number that ultimately appears on the Monroney sticker is appreciably less than 400 (in the case of the Max) RJ Scaringe will wind up next to Trevor Milton in the automotive rogues gallery. If it is appreciably better he will be accused of sandbagging and that won't look so good for him either. Maybe I'm naive but it seems this company is high on integrity and so I have to believe those numbers are their honest assessment of where the EPA numbers will come in.

And even if it does, my experience is that I get close to EPA range on the highway in my e tron.

What you get depends on how, where and when you drive. I get better than EPA when I drive under EPA - like conditions and worse when I drive in conditions more demanding than the EPA protocols.

The overall average EV achieved only 1.3% lower range at constant 70mph than the EPA stated range. For Tesla’s, the average is negative 11.6% and the average non Tesla was actually positive 1.1%. That is influenced by the Taycan which is 30% better, but removing those and the non Tesla average is only negative 4.8%.

I have no idea where those numbers come from nor anything about the test procedure, sample size etc. so I can't comment. I do have some data collected from the Tesla fleet - all models. The average Tesla driver at this time of year attains 88% efficiency with respect to EPA rated consumption. Only 17% realize better than 100% and less than 1% realize rhe efficiency I do (118%). Note that this is mixed over all Teslas and all driving conditions. It is historical data collected from the cars as they are drive.

A little known fact, but EPA range is actually submitted by the car maker, not the EPA.

It is widely known that OEMs sometimes do the tests and sometimes the EPA does them and sometimes they are contracted out. It is widely known that the tests are done on a brake dynamometer following standardized test procedures. As the vehicle is not in motion it is not subject to drag force or the forces required to move a vehicle up a hill. These forces must be simulated by the brake portion. Drag is modeled as a cubic polynomial with cofficients fitted to rolling data. Every step is supervised and must be approved by EPA. The OEM can supply any coefficients he wants but the EPA must approve them. The same is true of the coefficeints that blend in-town and highway,

They are allowed to make adjustments within reason, and Tesla takes full advantage of that.

And everyone else sandbags?

I also suspect that their heavy regen helps with blended numbers but hurts on highway numbers. My Audi coasts like a manual in neutral when foot is off the accelerator, which is more efficient.

No it's not. The SAE profiles require that the vehicle decellerate more than it would were drag and rolling resistance the only retarding forces. The requisite retarding force must be supplied by either regen or friction brake. Clearly regen is more efficient. It helps in town and it helps on the highway especially in hilly terrain.

 

[ajdelange]

All these cars have heat pumps. It's just that only some cars have the heat pump arranged to pump heat from the ambient air into the vehicle. They all pump heat in the opposite direction. Heat pumps can be helpful where the destination and source are close in temperature as COP (the rotio of the heat pumped plus energy expended to pump it to energy expended can be 3 or more. As the temperature delta gets high (it gets cold outside) COP approaches unity and the heat pump has no advantage over straight electric heat.

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