Featured Tesla has been cheating EPA on mpge and range numbers

It may be an imperfect assumption, but it is not "very wrong."

...at very low speeds. They make a small difference at high speeds.

A 4000 lb car with a 0.23 Cd, 25 sqft frontal area, and an average 0.008 Crr needs 322 W to go 5mph and 20,000 W to go 80mph. Slap on some otherworldly super LRR tires that bring the Crr to 0.006 and you'll need 242 W at 5mph and 18,800 W at 80 mph.

So a massive 25% reduction in rolling resistance results in just under a 25% reduction in energy needed at 5mph, but only a 6% reduction at 80mph.

No, it isn't. And contrary to your statements, the 235 tire is going to roll better than an equivalent 195. Wider tires have less rolling resistance than narrower tires. They weigh more and have more frontal area, but we've already accounted for weight & CdA elsewhere.

This is probably the only significant difference you've mentioned so far. The difference in rolling resistance between the best & worst tires Consumer reports tested was 34%. The Michelin Mx4m tires on the standard Model 3 are far from the worst rolling tire out there...

False. Low profile tires have less rolling resistance than equivalent high profile tires. Stiffer sidewalls flex less, wasting less energy.

Lower profile wheels/tires are heavier so you essentially have larger flywheels, but flywheels are very efficient means of storing energy as long as you aren't wasting that energy into brake pads.

No, but that's why he used CdA

Weight really does become a factor when you introduce rapid changes in speed. The EPA tests do not use rapid changes of speed, the acceleration on the highway test is roughly equivalent to an 18 second 0-60 if I recall correctly.

The US06 "aggressive cycle" reaches 80 mph:

 

Not mentioned is the set of roll down coefficients all cars must provide. Available from the EPA Test Car Database, multiplied by velocity gives the drag force at each velocity. So plotted as a graph, you can compare the drag of two or more cars.



Bob Wilson

 

I beg to differ that 1) size isn't going to make that much of a difference. Bigger tires have more surface area, but if the car weighs the same they have less pressure per square inch of that surface area. As a result, as the car increases in size and needs bigger tires the rolling resistance coefficient will stay about the same. If tire size were a major factor in the CRR, then why are there some bike tires with CRR's of as much as 0.040 (5 times higher than a good car tire)? And 2) as pointed out in this and any similar analysis, rolling resistance is a smaller drag.

That can make a slight difference. Put some regular tires on a Prius Prime and tell me how far the efficiency drops. LRR tires make very little difference.

I doubt that's true.

Yes, I took into account the larger width of the Model 3. According to the numbers I could find, the Model 3 actually has a slightly smaller cross sectional area than the Prius Prime. If you find a better source I'll redo the numbers.

I was calculating a real world use case of the two cars, that is, cruising along a highway. I wasn't saying I know how EPA tests work. I also didn't factor how hard braking would affect things or test the regenerative braking of the vehicles. The point being the two cars are close in their energy usage. The type of tires and a person's own driving style may make one use a bit more energy than the other. But we're splitting hairs here, and claiming that the Telsa is going to use huge amounts of energy and so therefore must be cheating and lying is a false claim not based on any trustworthy analysis.

 

He included the cross section area. It is different from what I calculate from the car's list width and height. Model 3 = 2.67sq.m, PP = 2.59sq.m

The bigger battery of the Tesla means it can capture more energy over the same braking profile.

You bring up hard braking and acceleration, and the core EPA test cycles don't even have those at moderate levels.

In 2015, Toyota had a 44% efficient diesel engine in the Hilux and Prado, and it did use SCR for emissions. Others of that time were in the same area. Heavy duty diesels can reach 50% today.
Toyota unveils new diesels with advanced thermal insulation combustion; 15% more fuel efficient, 25% more torque; 44% thermal efficiency - Green Car Congress

 

Ya, I can't find anything that's official, so my numbers could be way off. On the other hand, and as I'm sure you well know, multiplying the height and width gives a rough estimate, which is good, but can still be a bit far off from the actual number, for an example depending on which is boxier or not (square vs circle).

Some other places put the bigger Model S as having the same cross section area as a Prius, so assuming the Model 3 is actually smaller than a Prius doesn't seem far off from reality.

Aerodynamic Tesla Model S Electric Car Wins The Wind-Tunnel Wars (greencarreports.com)

 

Everything. The SAE standard is a little expensive but I found a college paper that had most of it.

Bob Wilson

 

Adding some omitted facts to the data:

@bwilson4web's plot for the drag force is apparently the total drag force including the internal, tire-rolling, and aerodynamic forces.​

• My graphs were for specific model years: 2014 BMW i3-REx; 2017 Prius Prime, and; 2019 Model 3 Std Rng Plus. More modern vehicles need more recent data.
  
• My graph supports replacing the tires and wheels with lighter, smaller cross section ones which I did.

Having owned a 2017 Prius Prime, it is way down my list of candidates: EV range 25 mi; EV mode is not trustworthy when temperatures are 55 F or colder, slow 3.5 kW L2 charging, and; no Fast DC charging.

My 2019 Tesla Model 3 Standard Range Plus with 80,000 miles is not for sale.

Bob Wilson

 

What are the coefficients? I'm wondering how the Tesla closes the gap at 60mph but then the gap starts to grow again at 75mph. I would have expected the lines to cross...

 

The plot shows close to what I calculated, that the Tesla has a higher rolling resistance but lower air drag, reason why the line gets closer to the Prime's the faster they go. If it had the same air drag it would stay about the same amout above the Prime's.

So yes, it looks like the Tesla uses a bit more. But if Toyota went the extra mile they could increase the Prime's mileage over that of the Tesla. Everyone's experience will be different.

 

The 2017 Prime problem was after 25 mi or sooner in cold weather, 55F, it turned on the gas gas engine. In contrast, the Tesla doesn’t have a gas engine to turn on. But why did we keep the 2014 BMW?

The BMW i3-REx has a hard disable of the ICE engine. So we can go 72 miles in EV which is cheaper than the Prime running the ICE. I have to pay for our miles and the Prime too short EV range and poor cold weather control laws was more expensive than the BMW.

Bob Wilson

 

Typical error means they are about the same in the 50 to 75 mph section.

With all the scrutiny Tesla is under, if thy had actually been cheating, they would have been caught.

It is a literal coast down test. The car is taken to 70mph on a track, and foot removed from the accelerator. How long it takes to reach 10mph is timed. The results are used for a coefficient entered into the test dynameter. Parsing out how much is tires, drive train, and aero drag isn't possible, or least not done.

The curve past 70mph is likely just a projection, and not the true value.

 

Just sharing the OpenOffice spreadsheet and sources:

• Data on Cars used for Testing Fuel Economy | US EPA - location of downloadable EPA vehicle data including roll down coefficients.
  
• roll_down.zip contains the OpenOffice spreadsheet

Bob Wilson

 

Can you please give some evidence to that statement. Everything I see says the Prime has a .24 Cd and a bigger cross sectional area. The Model 3 is 2.22m^2 and the Prius Prime 2.399m^2. Show me proof that it isn't please, and I'll accept my error. I put down a few references.

Again, if the M3 had a bigger cross sectional area and the same coefficient of drag in the chart above the M3's drag in lbs would separate even further than the Prime's at higher speeds. You cannot have a less steep curve with worse aerodynamics. Worse aerodynamics will make a steeper curve like the BMW's line.

 

Are those individual contributions already rolled into existing EPA scores? Or is this part of ongoing assessment work in support of future EPA ratings and programs?

Given the 2020 publication date of this paper, it is difficult to believe that its findings would already be rolled into current EPA MPG scores.