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Aero Wheels & Range - I'm confused

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...

Mycroft | 11 novembre 2011

Because the Model S has such a low Cd (.22) and with the air suspension, it can get VERY close to the ground on the freeway, the type of wheels may in fact make that much of a difference.

mcornwell | 11 novembre 2011

So that would mean that this car shouldn't suffer from the (significant) decreased range at freeway speeds?

Mycroft | 11 novembre 2011

We be hoping!

EdG | 11 novembre 2011

Looking at the curves posted elsewhere, there's no question but that higher speeds incur reduced range. The peak efficiency in the last curve I saw was near 20 mph, but that point will move a bit when real numbers are put in.

When Tesla says "300 miles range" or "320 miles range" we don't know whether they're claiming this at highway speeds or at peak efficiency at, for example, 23 mph. I assume the latter.

cerjor | 11 novembre 2011

Will the aero wheels be standard or an option?

mcornwell | 11 novembre 2011

Optional

William13 | 11 novembre 2011

Tesla's range for the Roadster was very close to the eventual EPA mixed use range. This includes both city and highway driving.

The way I see it would be a 10% increase on highway speeds and 4% on city driving resulting in a 6.7% overall range increase.

jackhub | 12 novembre 2011

I believe I read that the 320 range figure came from EPA tests. When Elon mentioned the 320 mile range, he implied Tesla was not expecting it. Did anyone else pick this up somewhere?

Thumper | 12 novembre 2011

I know they are not in fashion, but how about fender skirts for the rear for long trips? They should help more than aero wheels.

Volker.Berlin | 12 novembre 2011

Tesla's figures are definitely EPA(-like) figures. The Roadster was the first EV that actually achieved its claimed range in reality. Tesla gained a lot of reputation from that. They won't start publishing fantastic, irrelevant numbers for the Model S. Of course there is no EPA rating yet for the Model S, but that's the kind of mixed use range their claims apply to.

It's true that the peak range for the Roadster is at 17 mph, but that's 410 miles! The specified range for the Roadster is a more relevant 245 miles, which on the chart can be found at 55 mph. That's the kind of speed at which I expect to have the Model S' specified ranges of 160/230/300 miles available (at otherwise ideal conditions -- no wind, no inclines).

Volker.Berlin | 12 novembre 2011

Forgot the link to the Roadster range chart. Recommended read, anyway:
http://www.teslamotors.com/blog/roadster-efficiency-and-range

brianman | 12 novembre 2011

"It's true that the peak range for the Roadster is at 17 mph"
I'm not sure that's true.

At 17mph, you might have some bikers towing you out of sympathy... bringing it up to 18 or 19mph.

That's assuming you don't get pulled over for obstructing traffic.

Brian H | 12 novembre 2011

brianman;
That's the actual graph point at which max range is achieved, and it's over 400 miles for the Roadster. It's a physics thing; it costs less energy to accelerate to a lower speed (about proportional to the square of the speed).

Reminds me of old joke: Cop in the early days of autos pulls over a spinster doing a break-neck 30mph down the main street. Asked why she's driving so uncharacteristically fast, she says she's almost out of gas and was hurrying to get to the pump before she ran dry.
I doubt he was successful at explaining to her she was using more gas per mile by hurrying!

Larry Chanin | 12 novembre 2011

I believe that the Roadster EPA ratings were based on EPA test procedures in place in 2008. The EPA test rating for 2012 are likely to be more stringent. Since the Model S may be subject to more stringent EPA testing it is possible, even likely, that the 2012 EPA range for the Model S will actually be less than the Roadster's 2008 EPA range.

Stated another way, even if the Model S actually achieves a range of 300 miles when traveling at a constant 55 MPH, that is probably not how EPA is going to measure range in 2012.

Larry

brianman | 12 novembre 2011

@BrianH
I realize...

Reread my post, mentally inserting a smilie after the 2nd sentence. Maybe that will clarify it for you. Heh.

Larry Chanin | 12 novembre 2011

In an early 10-K financial statement Tesla management anticipated the potential impact of a revised EPA standard that could lower the advertised range.

http://www.sec.gov/Archives/edgar/data/1318605/000119312510188792/d10q.htm

"Any changes to the Federal Trade Commission’s electric vehicle range testing procedure or the United States Environmental Protection Agency’s energy consumption regulations for electric vehicles could result in a reduction to the advertised range of our vehicles which could negatively impact our sales and harm our business.

The Federal Trade Commission, or FTC, requires us to calculate and display the range of our electric vehicles on a label we affix to the vehicle’s window. The FTC specifies that we follow testing requirements set forth by the Society of Automotive Engineers, or SAE, which further requires that we test using the United States Environmental Protection Agency’s, or EPA’s, combined city and highway testing cycles. The EPA recently announced that it would develop and establish new energy efficiency testing methodologies for electric vehicles. Based on initial indications from the EPA, we believe it is likely that the EPA will modify its testing cycles in a manner that, when applied to our vehicles, could reduce the advertised range of our vehicles by up to 30% as compared to the combined two-cycle test currently applicable to our vehicles. However, there can be no assurance that the modified EPA testing cycles will not result in a greater reduction. To the extent that the FTC adopts these procedures in place of the current procedures from the SAE, this could impair our ability to advertise the Tesla Roadster as a vehicle that is capable of going in excess of 200 miles. Moreover, such changes could impair our ability to deliver the Model S with the initially advertised range, which could result in the cancellation of a number of the approximately 2,600 reservations that have been placed for the Model S as of June 30, 2010. Any reduction in the advertised range of our vehicles could negatively impact our vehicle sales and harm our business."

It appears that the Roadster range numbers were grandfathered back to the two-cycle test used in 2008. There is a new 5-cycle test being proposed for 2012 EPA testing. Indications are that the Model S may be subjected to this new test, or the results of the the old 2-cycle test (as performed for the Roadster) would be reduced by 30%. If that were the case the EPA range of Model S would be closer to 200 miles rather than 300 miles.

Larry

Leofingal | 13 novembre 2011

If this is the case, I would guess that the implication is that Elon will pull another "under-promise/over-deliver" and we will be pleasantly surprised by the fact that the S meets advertised goals with the new tighter standards.

Larry Chanin | 13 novembre 2011

Hi Leo,

We can always hope.

Larry

Larry Chanin | 13 novembre 2011

Hi Leo,

From the 10-K statement:

"Moreover, such changes could impair our ability to deliver the Model S with the initially advertised range,..."

It certainly sounds like the initial advertised range for the Model S used a different testing procedure than the new proposed EPA testing standard. Regaining the loss of 30% of the initially advertised range in just a year's time might be rather difficult to do, even for Tesla.

Although the stricter EPA range might have an effect on the rate of new orders placed, I still feel somewhat optimistic knowing that it is likely that the Model S will still be able to achieve around 300 miles when travel at a constant speed of about 55 MPH.

Larry

Volker.Berlin | 13 novembre 2011

I still feel somewhat optimistic knowing that it is likely that the Model S will still be able to achieve around 300 miles when travel at a constant speed of about 55 MPH. (Larry Chanin)

Or about 500 miles at 17 mph! ;-)

Timo | 13 novembre 2011

Brian H; That's the actual graph point at which max range is achieved, and it's over 400 miles for the Roadster. It's a physics thing; it costs less energy to accelerate to a lower speed (about proportional to the square of the speed).

That's not the reason why range is higher there, its maintaining the speed at that point that takes less energy because of way lesser aerodynamic drag, less drivetrain losses and somewhat lesser rolling resistance.

Accelerating to certain speeds fast or slow takes approximately same amount of energy, because faster acceleration just requires less time to get to the desired speed. In reality faster acceleration rarely is quite as efficient because of higher losses, but it still gets close. Ultimately you just transform electric energy to kinetic energy and accumulated kinetic energy with slow and fast accelerations are same. If there is no difference in efficiencies difference in range comes from faster acceleration getting you sooner to desired speed which usually is not the optimal speed (~17mph) and then there is time difference between energy requirement in maintained speed.

With electric engines that difference is small. With ICE that loses huge amount of energy in accelerations that makes much bigger difference.

Compared to Roadster because of higher rolling resistance of Model S and approximately same air drag and probably a bit better efficiency engine (liquid-cooled) you probably get the range sweet spot a bit higher with Model S than with Roadster, I approx it to be somewhere close to 25-30mph (which means it would have really great range in city traffic).

Ramon123 | 13 novembre 2011

Lots of guessing but the facts will only be known when Tesla (or some auto mag) produces some numbers based on various factors.

Brian H | 13 novembre 2011

@Timo;
I said nothing about rate of acceleration, only terminal speed: "it costs less energy to accelerate to a lower speed". E=mv^2. It's called "physics". You have to put in that kinetic energy, quickly or slowly.

@Larry;
I don't have the link, but the scuttlebutt from the 'S' beta testers was that the rated ranges were conservative in daily use; they were getting more.

Larry Chanin | 13 novembre 2011

@Brian,
I don't have the link, but the scuttlebutt from the 'S' beta testers was that the rated ranges were conservative in daily use; they were getting more.

Thanks for the information.

If by daily use they are referring to typical daily speeds with a heavy mix of less than 55 MPH, then its not surprising if the Model S range versus speed curve is similiar to the Roadster. However, when I think of range considerations it is in the context of a long trip with highway driving. As we know realistic highway driving speeds result in a significantly reduced range even when compared to the range derived from less rigorous 2-cycle EPA testing method that was used to measure the Roadster.

I guess we'll just have to wait to see what the official 2012 EPA range tests reveal, but with a more stringent EPA test likely to be implemented, it may be prudent if we moderated our expectations regarding the ultimate advertised range.

Larry

sarge7359 | 13 novembre 2011

If the ranges go down for both Roadster and Model S, wouldn't they go down for all EV competitors as well? And what does this do to Hybrid range calcs?

Wait and see appears to apply to all electrical vehicles, including those with electrical assist. Could see a bunch of ratings fall.

Timo | 13 novembre 2011

Brian H; 1/2 mv^2. You are remembering Einstein: E=mc^2, but we are moving quite a bit under relativistic speeds (unless Elon "surprise" to us is an optional warp drive).

nhurst | 14 novembre 2011

Careful Timo. Methinks your slip is showing.

Larry Chanin | 14 novembre 2011

@sarge7359
"If the ranges go down for both Roadster and Model S, wouldn't they go down for all EV competitors as well? And what does this do to Hybrid range calcs?

Wait and see appears to apply to all electrical vehicles, including those with electrical assist. Could see a bunch of ratings fall."

The Volt and Leaf have already been effected by new EPA standards, so we've been making comparisons to the Model S's expected range which may be be optimistic. (For instance, prior to becoming aware of this issue, I remarked that the Model S has up to 4 times the range of the Leaf.)

So far the Roadster's EPA range has been grandfathered to the less strict standard. This may be due to the fact that the Roadster is considered a 2008 model year vehicle.

Below is an excerpt from Tesla's 10-K filed today that describes the current status of the subject.

http://files.shareholder.com/downloads/ABEA-4CW8X0/1359152139x6414652xS1...

Any changes to the Federal Trade Commission’s electric vehicle range testing procedure and recent changes made by the United States Environmental Protection Agency’s energy consumption regulations for electric vehicles could result in a reduction to the advertised range of our vehicles which could negatively impact our sales and harm our business.

The Federal Trade Commission (FTC) requires us to calculate and display the range of our electric vehicles on a label we affix to the vehicle’s window. The FTC specifies that we follow testing requirements set forth by the Society of Automotive Engineers (SAE) which further requires that we test using the EPA’s combined city and highway testing cycles. The EPA recently established new requirements for the fuel economy stickers that appear on new cars offered for sale (i.e., the Monroney label). In addition to the new labels and as part of that final rule published on July 6, 2011, EPA has also modified its testing cycles in a manner that, when applied to our vehicles, could reduce the advertised
range of our vehicles by up to 30% as compared to the combined two-cycle test currently applicable to our vehicles. While we intend to
demonstrate to the EPA that a more appropriate derating factor applies to our vehicles, there is no guarantee that the EPA would approve such a factor. These new requirements apply to all model year 2013 and later vehicles. Following EPA’s announcement, the FTC also issued an Advanced Notice of Proposed Rulemaking seeking comment from interested stakeholders as to whether that Federal Agency should adopt procedures similar to EPA’s under its labeling requirements. In the meantime, the FTC has also published an Enforcement Policy noticing that the FTC would forebear enforcement against any vehicle manufacturer that utilized labels meeting the new EPA requirements versus the existing FTC requirements. This indicates FTC’s inclination to move towards harmonization of their labeling requirements with EPA’s new
requirements. If the FTC continues in this direction, this could impair our ability to deliver the Model S with the initially advertised range, which could result in the cancellation of reservations that have been placed for the Model S. Any reduction in the advertised range of our vehicles could negatively impact our vehicle sales and harm our business.

Larry

Straight Shooter | 14 novembre 2011

Stage 5 test results vs Stage 2.......

Lets not forget that if Telsa experiences a 30% drop (or more) in their range estimates, that these Stage 5 test cases apply to all EVs. Tesla already has a solid reputation at exaggerating the least out of all of the EV manufactures.

Any guesses as to what the 100mile range on the Leaf will be? Realistic EPA ranges already peg it at about 65miles. We could easily see that hit 40-50miles when the Leaf is subjected to Stage 5 tests.

Tesla will still be double, triple and quadruple the range of other cars.

Hopefully we'll se a drop in battery price or at the very least an expidited R&D by battery makers to double the existing storage capacity of their products.

The end result will be a level playing field and no more big auto maker Marketing Departments spreading outrageous lies, just little "white lies" like they currently do for ICEs.

brianman | 14 novembre 2011

Part that stuck out for me...
"These new requirements apply to all model year 2013 and later vehicles."

jbunn | 14 novembre 2011

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.

Nicu | 14 novembre 2011

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).

Brian H | 14 novembre 2011

@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.

Robert.Boston | 14 novembre 2011

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.

Larry Chanin | 14 novembre 2011

@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

Larry Chanin | 14 novembre 2011

"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

stephen.kamichik | 14 novembre 2011

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.

Denis Vincent | 14 novembre 2011

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!

Denis Vincent | 14 novembre 2011

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

Volker.Berlin | 15 novembre 2011

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.

EdG | 15 novembre 2011

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.

Volker.Berlin | 15 novembre 2011

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.)

EdG | 15 novembre 2011

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.

Robert.Boston | 15 novembre 2011

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!

Thumper | 15 novembre 2011

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

Brian H | 15 novembre 2011

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

Thumper | 15 novembre 2011

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

Larry Chanin | 15 novembre 2011

"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

Sudre | 15 novembre 2011

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.

Denis Vincent | 15 novembre 2011

@ 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!

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