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Aero Wheels & Range - I'm confused

With all of this talk about how range goes down at freeway speeds, how is it that they can get 320 miles with them? I'm guessing that the benefits of the aero wheels don't really help until you reach freeway speeds, at which point you wouldn't be getting the 300 mile range in order to add 20 to it...

How I figured out my range...

I have a 70 mile commute each way. I wanted to make sure if the power was out, or I forgot to plug, circut breaker tripped, whatever that I could still make it to work the following day. (for longer outages, severe weather, etc, I'll pull the 4WD truck out of the barn. Good to have a Plan B)

So I need 140 miles. I then multiply by 1.3 to account for 30% pack degradation. That brought me up to 182, just slighty over the base model limit, so I moved up to the next pack.

That keeps me from having to wake up in the middle of the night wondering if I plugged the thing in, accounts for eventual wear on the battery capacity, and leaves me with plenty of reserves if I want to run side errands, or go out after work.

In 7 or 10 years, If I don't move to a newer model, I'll upgrade to the latest cold fusion or dilithium pack or whatever battery makers came up with in the intervening decade.

Anyway, my rule of thumb for what it's worth.

If you want to account for 30% pack degradation, you should multiply by 1.428 instead of 1.3 (so that 70% of that is 1).

@Timo,
Yeah, forgot the 1/2. Point is, kinetic energy increases as the square of the speed; if two (e.g) Roadsters go past your POV on the ground in synch, they have the same kinetic energy regardless of how long each took to get up to speed (acceleration curve).

@jbunn;
As Nicu observes, you should divide by 0.7 rather than multiplying by 1.3.
Early on, someone reported capacity changes after 28,000 miles on a Roadster, that worked out to about 1.2% loss per 10,000 mi., IIRC. It would be interesting to get mileage/capacity numbers now from Roadster owners to make comparisons.

I suspect the 30% loss is a max, worst-case conservative number that Tesla feels safe with.

This degradation issue is really important in selecting a battery. For example, a 160-mile pack with 30% degradation and running at Standard charge (so accessing only 70% of the battery capability) has only 160*0.7*0.7 = 78 ideal miles of range.

@Straight Shooter
"Any guesses as to what the 100mile range on the Leaf will be?"

The Leaf had a 2-cycle EPA range of a little over 100 miles. This value was multiplied by .70 to comply with the new 5-cycle EPA test. The result is a range of 73 miles.

I suspect that the 160, 230 and 300 advertised ranges for the Model S was in accordance with the 2-cycle EPA tests. These ranges could likewise be adjusted downward by 30% to comply with the new testing method, yielding 112, 161 and 210 respectively.

Larry

"This degradation issue is really important in selecting a battery. For example, a 160-mile pack with 30% degradation and running at Standard charge (so accessing only 70% of the battery capability) has only 160*0.7*0.7 = 78 ideal miles of range."

Hi Robert,

And if one is driving with a mix of real world conditions, such as low, medium and high speed driving, with some aggressive acceleration, and with the air conditioning on, that 78 ideal miles may become 55 miles range. The new EPA testing method is supposed to address those real-world aspects.

Here's an interesting read authored by Darryl Siry, the former Chief Marketing Officer for Tesla. He touchs on the end of life issue as well.

The Problem with EV Range Figures

Larry

I have a slightly different take on range. In regular charge mode, the batteries are charged to 80%. EVs are very efficient in city traffic. Therefore city mileage is 80% of ideal range, thus in the city the ranges are 160*0.8=128 miles, 230*0.8=184 miles and 300*0.8=240 miles. At 60 mph the range drops about 30%. Therefore the highway ranges are 128*0.7=89.6 miles, 184*0.7=128.8 miles and 240*0.7=168 miles.

There should be an assterisks placed next to the name of Disgruntled Xemployees of a company that recognizes a mole in their presence and no longer are willing to tolerate their negativities and lack of support. Let's compare apples to apples, orange to oranges and leave bananas out of the mix!

@Larry Chanin To be more specific I was making reference to the article written by Darryl Siry, "The Problem with EV Range Figures".

From a German perspective, the EPA figures seem to be very realistic and fair, for EVs as well as for ICEs. Over here, we are used to much more unrealistic ratings, but honestly, once you get used to it it's fine. The main point is that you can compare ratings -- a car with a better rating will achieve better range or mpg in reality, than another car with a worse rating.

How the rating corresponds with your personal mpg is a totally different story, and everybody here just knows that and accounts for it. If a car is rated 5l/100km you know that you will actually need around 7 liters, but that's ok because you will still need considerably less than another car rated at 7l/100km (probably more like 10l in reality).

The figures that car magazines state are usually on the other end of the spectrum, because they test-drive hard as they can. Now, between the official rating, and the number stated in the motor press, there is somewhere your personal actual mileage.

Not only that, but we all know from experience that even individually "your mileage may vary". If I'm driving around town, I expect worse numbers than steady highway driving, and I've learned to account for it.

This issue for EVs is analogous. As V.B says, at least we can compare cars from different manufacturers.

If I'm driving around town, I expect worse numbers than steady highway driving, and I've learned to account for it. (EdG)

And, fortunately, with EVs, it's just the other way around! :-) Like anybody who has never bothered about cars would sensibly expect. This counter-intuitive behavior of ICEs actually tells me that ICEs are inherently inadequate for moving vehicles around... It's really just the gas tank (gas energy density) that helped them to where they are today. But I digress.

(EdG, my comment is not criticizing your argument in any way.)

Hah! Why would I take a reasoned explanation as criticism? You're adding detail.

"... inherently inadequate.." Every time I drive, I find myself more and more amazed that we see ICEs as normal. When the population of EVs gets to the point that many people have been in one, I think the public mindset will morph to EVs as normal, and ICEs as special purpose - trucks, large construction equipment, etc., occurring over the next 20 years. Maybe even those will go away.

Particular ICE cars will be collectors' items for those who remember how to keep them running. But with youth focusing more on internet connectivity than car repair, it looks to be a small niche hobby or something only seen in 1950s teen movies.

As I drive through Boston rush-hour traffic, with all of its start/stop/slow, I'm increasingly mindful of how much energy I'm wasting as I brake/accelerate/brake. I'm truly looking forward to regen!

Robert, I heard that there is reluctance for people to ride-share through the Big Dig. It's called carpool tunnel syndrome.

Thumper, for that you should change your handle to "Thumped", and consider yourself to have been electronically head-butted.
Good one!
>8-)

Thanks, I have to credit my brother. It is original with him.

"There should be an assterisks placed next to the name of Disgruntled Xemployees of a company that recognizes a mole in their presence and no longer are willing to tolerate their negativities and lack of support. Let's compare apples to apples, orange to oranges and leave bananas out of the mix!

To be more specific I was making reference to the article written by Darryl Siry, "The Problem with EV Range Figures"."

Hi Denis,

What specific aspects of Mr. Siry's remarks do you take exception?

Do you disagree that "your mileage may vary” based on driving conditions?

Do you disagree that batteries are not usually charged to their maximum range?

Do you disagree that the range of batteries decreases at end of life?

Do you disagree that "manufacturers need to communicate honestly and transparently about the realities of range"?

The fact that Mr. Siry is an ex-Tesla employee doesn't prevent us from evaluating his statements on their face value. It doesn't automatically mean that they are incorrect.

Larry

Anyone who has ever owned a car, electric or not, knows whatever number is thrown on the sticker is irrelevant. I really don't care how the EPA or who ever wants to rate the distance the car can travel as long as it's consistent.

They can rate the Roadster at 240 Ducks and the Leaf at 100 Ducks. At least I have something to compare with. I'll find out how many miles a Duck can go when I drive it.... or I can look at what the owners of both cars are averaging to see reality.

The problem I can see is the governments changing the system for electric cars every time a new regime is voted in and has a different belief system..... it needs to stay consistent.

@ Larry Chanin Don't get the wrong impression, I do not disagree with any of the statements Siry's made, however, what I don't agree with their relevance; Would you not agree that the mileage of an ICE V may vary based on driving conditions? ; Would you not agree that when refueling an ICE V, the gas tank is not usually filled to its maximum capacity? ; Would you not agree that the range (performance) of an ICE V decreases at the end of the life cycles of the spark plugs, air filters, oil filters, timing belts, head gaskets, ect., ect, ?; Would you not agree that manufactures of ICE V need to communicate honestly and transparently about the realities of range (performance) in respect to these deteriorations ...... What I really question here is the motivation of such an irrelevant article that makes reference to the obvious and does not take into account a level playing field. The fact that Mr. Siry is an ex-Tesla employee speaks for itself, period!

Thumped;
Yeah, I'm into puns too. And the ideal response is the fading scream of pain as the listener flees.
>:p

Sudre++

Aha, Brian H is a Callahan's fan. Or he picked up the pun reaction from same place Spider Robinson did.

And /agree with Denis -- I don't see why EVs are special in that mileage varies with how it is driven, etc. And that's the substance of the linked blog post. It could be that EVs vary more widely than ICE, but then again so do varies forms of ICE... which brings use right back to the numbers simply being a way of comparing 'ducks per liter per parsec' or whatever.

MAJOR Callahan's fan. Best bar in the galaxy.

Should stage a rush-hour road race; 'S' vs. "30 mpg" ICE car back and forth across town through traffic for 3 or 4 hours. Heh. Can you spell "sucking gas"?

;)

"Don't get the wrong impression, I do not disagree with any of the statements Siry's made, however, what I don't agree with their relevance;...What I really question here is the motivation of such an irrelevant article that makes reference to the obvious and does not take into account a level playing field."

Hi Denis,

The point is that the new 5-cycle testing that EPA is implementing is being applied to both I.C.E. and advanced technology vehicles to establish more reasonable expectations by the driving public. The new tests incorporate many of these common sense issues that Mr. Siry discusses.

Larry

I wonder if the "aero wheels" will be "tall and skinny"...? In any case, the diameter of the Model S' wheels is on the upper bound of typical wheel sizes, so that may be a hint.
http://www.greencarreports.com/news/1066754_tall-skinny-tires-newest-gre...

I don't think that anybody has ever said that Elon Musk's statement regarding ultra aerodynamic wheels/320 miles range explicitly referred to the rims and to the rims only. IMO, there may be special rubber, too.

Special one-way rubber, that grabs hard on the way down but releases easy on the way up ...
>:D
Ain't nanotech wonderful?

I read something a few years ago about how geckos manage this. As I recall, the surface at the end of the toe pads divides finer and finer until it has a huge amount of surface area, clinging with van der Waals force, or perhaps capilary action.

If I have one way rubber, can I rotate my tires to the other side of the car when I'm ready to slow down?

I haven't seen the "Hot Wheels" feature listed yet. The one where you can spin the steering wheel 180 degrees. With that you've got a chance.


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