Featured Tesla has been cheating EPA on mpge and range numbers

None of the aerodynamic "C" coefficients were negative so no tailwinds. But 3 out of the 4 Tesla Model3's had a negative driveline "B" coefficient which, to me, suggests Tesla's "neutral" may be providing a little bit of power. If I were an EPA tester I'd either unplug the traction battery or compare the change in the neutral coast state of charge against the change in an idle state of charge for an equivalent amount of time.

You might plausibly use a little more processing power with stability control & antilock braking systems when coasting vs when parked, but to legitimately achieve those coefficients suggest some extra power going to the wheels...

 

from the numbers the Tesla has a slightly bigger frontal area while having a lower cd than the prime giving it a slight 5% advantage in cdA or drag, but this is only important at highway speeds or more. The Tesla also likely is more electrically efficient at high speed. Car and driver has confirmed that both rolling resistance and aerodynamic drag for tesla's are within margin for error of their test so no cheating but there could be rounding. yes wider stickier tires on the Tesla will cause higher rolling resistance, but as speed increases this is less of a factor as it is constant for distance while drag is proportional to the square of velocity. MPGe is based on power from the plug, and I trust Tesla is likely more efficient on the highway and the prime more efficient in the city. That is a good thing as Tesla is tuned toward highway milage for range while city mpge is also great. The Prius prime is going to primarily use gasoline on long highway trips while the batter will be used mainly in the city and just for short highway trips.

That goes to the epa's mpge. The guessometer in the Prius prime tellying you what mpge is, is likely not accurate. I really like my Tesla. My girlfriend in spite of her hatred of Elon muak (and we ended up in a bar with him after he moved here) loves my Tesla. she was mad at me for talking to him nicely.

 

I did this experiment myself. LRR tires reduced rolling friction on the same car at the same temperature and tire pressure by about 40%.

 

40% seems plausible but on the high end. Tests have shown that a 10% decrease in friction gives about 1 or 1.5% improvement in mpg.
Multiple other tests have shown that mpg improvements can vary by about 1.5 to 4.5%

https://en.wikipedia.org/wiki/Low_rolling_resistance_tire

Mike

 

Those tests must be either wrong or all high-speed.

Over the average US car's lifetime, about 2/3rds of the propultion energy is lost to rolling friction and 1/3rd to aero losses. That's because we spend a lot of time and miles in city traffic. My average speed over the last 5 and a half years is 28mph.

 

You should edit the wikipedia page with links to better studies

Mike

 

The article is wrong because of a misinterpretation of the reference it uses.

The article says, "...as approximately 5–15% of the fuel consumed by a typical gas car may be used to overcome rolling resistance.[1]"

This is a screenshot from that reference:



The problem is whoever wrote the article got confused between fuel consumed and energy consumed by motion.

 

I'm not surprised at that figure. Went in for my fifth Covid shot today and on the way back I enabled the info eco screen and it showed 23 MPH and much of the trip was at 55. But then there was the slow stuff in the neighborhood and the stop lights at the end and the slow in the parking lot to lower the average.

 

Those numbers are likely correct for gasoline cars without regen braking, but in EVs the drive train is much more efficient and braking, making aerodynamics and rolling resistance more important.

https://www.nhtsa.gov/DOT/NHTSA/NVS/Vehicle%20Research%20&%20Test%20Center%20%28VRTC%29/ca/Tires/811154.pdf

Here the example has 4.2% of fuel going to rolling resistance, 2.6% to drag, 5.8% to braking.

https://www.fueleconomy.gov/feg/atv-ev.shtml
because there is less loss in charging and the motor, and regen recoups much of the braking energy, the example gives 25% of energy in rolling resistance and 39% as drag, 25% is dissipated as braking, but 22% of that is regen and reused. YMMV!

 

If the relation is 4.2% to rolling resistance and only 2.6% to drag and 5.8% to braking, where'd the other 87.4% go to?

 

Its in that paper, and this was conducted on a non hybrid gasoline car. The bulk goes to engine inefficiency including idling (that part is much better in a hybrid) then their are driveline losses - that is 85% of the gasoline. In a Prius this may be around 70% instead. Then they gave 2.4% to accessories like AC, power steering, etc.

 

You know… the primary purpose of an ICE car… heat!

 

If only mine would heat up. It's been freezing cold these past few mornings! Today I went and bought a 1,500W block heater. That ought to do it!

 

Interesting point, which hadn’t occurred to me before.
ICE vehicles put out >50% of their fuel’s energy as heat. Why isn’t all that heat available more quickly?

I’m guessing all that heat initially goes into heating the engine block?

 

Complete thread derailment here, but on the one hand the problem with ICE's is the heat is mostly available after a person reaches their destination. The problem with using the heater is the engine then takes longer to warm up, and is even more likely to not reach ideal temperatures by the time one gets to their place of work (or wherever).

On the other hand, I've had the crazy idea to add some sort of heat tank to the car to store some of the hot coolant before the radiator even gets used. Then, getting home, have some way of transferring that heat to heat storage at the house for making hot water or home heating or something else that's useful instead of just dissipating it into the atmosphere.

The inverse idea is to have a stationary natural gas generator (natural gas is cheaper per thermal unit than electricity) and use that electricity for charging an EV and the exhaust and engine cooling for heating the home or hot water.

The reality, though, is my place of work is too close. It's just not far enough for the car to warm up properly on the road, even in summer. But when it's already 0°C when I go to work at 4:00AM, it's not very comfortable to walk or ride a bike that far. I do miss our Leaf for driving nice and toasty to work when it's -40°F/-40°C outside.

 

A couple gallons of hot coolant isn't going to do much for heat use at home, and water is heavy to be adding more to the car.

The gen2 Prius had thermos it pumped hot coolant into after shut down to help with the next warm up cycle. The temperature gauge was noticeably lower on Monday mornings after sitting for a week end.

There are 'tiny', home sized cogen generators for supplying power, and using the waste heat. For a larger building, Honda has a natural gas one available in Japan that is a true Atkinson cycle engine.