Highway Range Ignorance

[Tesla 940]

I find all these stories of actual mpg below EPA ratings to be very surprising. I have a 2006 Toyota Tundra 4x4. It is rated 13 city, 16 highway, 15 combined. In 5 years and 135k miles my lifetime mpg is over 17. This includes approx 50k of cross-country driving at 80+ mph, 5k of cross-country driving towing a trailer with my Tesla on it (13mpg), numerous 4x4 trips going up steep fire roads with 6 people and loaded with gear, and the rest of the miles in true city driving. And oh ya - I finally just replaced my original spark plugs.

 

[brianman]

In any case, for the 535i, I get 28mpg x 18.5 gal = 518 miles. So you can claim 500+ miles at highway speeds (what speed exactly is unknown).

Sorry to be picky but the original question was 550+ miles, hence my answer of "No."

 

[stopcrazypp]

I find all these stories of actual mpg below EPA ratings to be very surprising.

Your results will be different depending on your specific car (for highway, hugely dependent on gearing and efficiency at different rpms). There is no general rule that says everyone will get better than EPA ratings or worse.

 

[Dave EV]

Random web search...
- 28mpg not 31mpg: Fuel Economy of the 2011 BMW 535i

Fuel Economy of the 2012 BMW 535i

highway test doesn't go above 60mph: Detailed Test Information

Which is why they don't use the raw numbers from the test but adjust them. (Of course never mind that the EPA doesn't actually test every single car but relies on the manufacturers to tell the truth with random checks here and there).

If any vehicle I drive gets 2/3rd of the EPA rating on mileage I consider that par for the course.

This used to be the case before the EPA adjusted all the numbers to compensate for "typical" driving patterns.

 

[brianman]

This used to be the case before the EPA adjusted all the numbers to compensate for "typical" driving patterns.

Well they didn't compensate effectively. Or perhaps my 2010 model year vehicle was exempted from the 2008 change.

 

[stopcrazypp]

Just to add another data point about the accuracy of the EPA test as applicable to 70-75mph highway driving:
http://www.popularmechanics.com/car...th-we-put-40-mpg-claims-to-the-test-6651300-2

It's the Elantra vs the Focus. PM measured the gasoline by the weight of the car using a scale and used GPS tracking to determine distance traveled and speed. They didn't use any AC or heating. It's not entirely scientific given it was just one trip (they didn't try to redo the dyno test), so repeatability may be a question.

But anyways both cars exceeded the city rating (although the city test done by PM seemed it like didn't have much stop and go), and was able to easily exceed the highway rating by traveling at 55mph. However, at 70mph, both cars were below the highway rating (Elantra only slightly below with 39.3 vs 40mpg, while the Focus was significantly below with 33.5 vs 40mpg, even lower than the city test).

The difference may have to do with gearing and aerodynamics (Elantra has Cd of 0.28, Focus is 0.295).

 

[neroden]

Ah. Of course you have only 70% of the energy efficiency if you go at 70 mph instead of 55 mph... I remember something about that from back when I was a kid.... "55. It saves gas. It saves lives. And remember, it's not just a good idea: it's the law." Some things aren't different between gas and electric cars.

 

[brianman]

Ah. Of course you have only 70% of the energy efficiency if you go at 70 mph instead of 55 mph... I remember something about that from back when I was a kid.... "55. It saves gas. It saves lives. And remember, it's not just a good idea: it's the law." Some things aren't different between gas and electric cars.

That was the sales pitch, yes. IIRC, only the saves gas part remains of that theory. And that's arguably because vehicles were tuned accordingly.

 

[neroden]

That was the sales pitch, yes.

It's a little odd that I remember it verbatim.

IIRC, only the saves gas part remains of that theory. And that's arguably because vehicles were tuned accordingly.

It actually did reduce death rates. Not much, though -- and as far as I can tell from later studies this was mostly due to reducing the number of people driving at 80 mph and up (which can make for quite extraordinary crashes). And, as you note, it's not the law any more.

It still seems to save gas, and I suspect the reason is that 55 is approximately the point after which increasing aerodynamic drag due to speed becomes the overwhelming factor in energy use.

 

[brianman]

It actually did reduce death rates.

It did, and it didn't. Depends which study you prefer.

Once again, Wikipedia offers an interesting read.
National Maximum Speed Law - Wikipedia, the free encyclopedia

Insurance Institute for Highway Safety workers wrote three papers that argue that increase from 55 to 65 mph (89 to 105 km/h) on rural roads led to a 25% to 30% increase in deaths (1/3 from increased travel, 2/3 from increased speed) while the full repeal in 1995 led to a further 15% increase to fatalities. In contrasting work, researchers at University of California Transportation Science Center argue that the interstates in question are only part of the equation, one also must account for traffic moving off the relatively more dangerous country roads and onto the relatively safer interstates. Accounting for this they find that raising rural speed limits to 65 mph (105 km/h) caused a 3.4% to 5.1% decrease in fatalities.

 

[ckessel]

In reading some comments elsewhere on the Model X, I frequently see people say things like "Yea, that X/Y/Z mile range is ok until you get stuck in traffic!" They're stuck in the mindset that not moving is still burning fuel. EVs typically get better range at slow speeds and even in stop-n-go traffic the range isn't going to drop much. There's some burn for HVAC, but that's not terribly significant.

 

[AnOutsider]

Speaking of this topic, Tesla had a great interactive (touchscreen) display in the reservation tent. It allowed you to select your speed, battery pack, windows up, down etc and see a realistic range (including city vs highway driving). They also had a road trip calculator that you could tell how many miles you wanted to travel and it would show you how far you'd go at X speed before needing to stop and recharge for Y hours (even broke it out by charger type).

I really hope they put it on the TM site at some point.

 

[WhiteKnight]

Speaking of this topic, Tesla had a great interactive (touchscreen) display in the reservation tent. It allowed you to select your speed, battery pack, windows up, down etc and see a realistic range (including city vs highway driving). They also had a road trip calculator that you could tell how many miles you wanted to travel and it would show you how far you'd go at X speed before needing to stop and recharge for Y hours (even broke it out by charger type).

I really hope they put it on the TM site at some point.

Yes! It really was a great interactive display. I spoke with Emily from Tesla who was the person in charge of creating the display and she said it will be in all the stores and eventually make it to the website.

It basically took the Roadster Spreadsheet and made it interactive and easy to calculate your range under multiple scenarios.

I encouraged her to allow it to go up to 75 mph, instead of stopping at 65 mph, because most people are traveling above the speed limit (including parts of Montana where there is no limit).

She seemed to think that at 75 mph the penalty would be less than 30% like it is for the Roadster so that was some good news for Model S owners looking to take road trips.

 

[dsm363]

There are highways in the US where the speed limit is technically 75 mph, right? They should do that then.

 

[ElSupreme]

Yes! It really was a great interactive display. I spoke with Emily from Tesla who was the person in charge of creating the display and she said it will be in all the stores and eventually make it to the website.

It basically took the Roadster Spreadsheet and made it interactive and easy to calculate your range under multiple scenarios.

I encouraged her to allow it to go up to 75 mph, instead of stopping at 65 mph, because most people are traveling above the speed limit (including parts of Montana where there is no limit).

She seemed to think that at 75 mph the penalty would be less than 30% like it is for the Roadster so that was some good news for Model S owners looking to take road trips.

You didn't push for 80mph? You might not be able to stay in the left lane around town. :wink:

 

[Lloyd]

They should make this an Ipad app, and/or availale in the car to help new owners transition.

 

[jimbakker666]

Speaking of this topic, Tesla had a great interactive (touchscreen) display in the reservation tent. It allowed you to select your speed, battery pack, windows up, down etc and see a realistic range (including city vs highway driving). They also had a road trip calculator that you could tell how many miles you wanted to travel and it would show you how far you'd go at X speed before needing to stop and recharge for Y hours (even broke it out by charger type).

I really hope they put it on the TM site at some point.

That would be very helpful, they should definitely put it up there.

 

[drbradfo]

Unfortunately or fortunately, depending on you POV, Montana eliminated the 'no speed limit' years ago. But that doesn't stop people from driving very fast.


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I am here: Google Maps

 

[Lloyd]

Unfortunately or fortunately, depending on you POV, Montana eliminated the 'no speed limit' years ago. But that doesn't stop people from driving very fast.


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l]

Yes but they still don't enforce it like California. I took a drive for the Model X release. Between Santa Maria and Buelleton i counted 7 different CHP officers, and at least 4 were writing tickets. Wow!

 

[Robert.Boston]

California needs to balance its budget somehow, Lloyd!