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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...

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.

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

We be hoping!

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.

Will the aero wheels be standard or an option?

Optional

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.

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?

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.

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).

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

"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.

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!

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

@BrianH
I realize...

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

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

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.

Hi Leo,

We can always hope.

Larry

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

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! ;-)

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).

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

@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.

@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

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.

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).

Careful Timo. Methinks your slip is showing.

@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

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.

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


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