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Holy Smokes! If I stay in the truck lane at 55 MPH I can go 413 miles in my RWD LR!?!? Wow!https://i.redd.it/fcd1127n4ut11.jpg
here's a great range chart for the various models. The "true" range of a Model 3 LR RWD using 18" wheels + the aero, going 65 mph on the highway is around 350 miles. A P3D+ on 20" tires is 284. Downrating the Model 3 LR by 17% (260 MR range advertised / 310 LR range advertised) gives you 293 miles at 65 mph.
So yes, very possible for her MR to outrange your P3D+ on 20" tires. But the more important factor by far will be "how fast do you drive"
Yes. I thought she would want white. SHE pushed for white on my car saying it wouldn't burn her legs in the summer. In the end she liked black to match the black aero hubcaps.Did they allow white on the LR?
Hi. Here is a chart I created [...]
Strictly by the numbers, no.is it fair to say in the real world, we should expect the MR3 to be better than P3D+?
Troy - thanks for the detailed response, and I stand by my previous statement: Great chart! I wasn't trying to impugn the overall methodology you used - I just wanted to note one aspect which I thought might have skewed the results as far as the 3LR vs. 3AWD/3P were concerned.Hi, @ulrichw. If you look at the range numbers [...]
I'm unable to come up with any reasonable explanation for the negative coefficients other than measurement error.As for the negative number in coefficients, I'm sure there is an explanation for it. If you look at the tab, "Test Car List Data" column G here, 8 different cars from BMW, Tesla, Volvo, and Hyundai have negative numbers. One possible explanation is that the coast down test doesn't involve the following drivetrain losses that should be considered during the dyno test:
- Inverter
- Motor
- Motor controller and wires
- Gearbox
This is the part I'm not comfortable with. I don't believe that the results are proportionally correct. I think the error margin is significant due to the difference in models.The important thing here is whether or not the dyno scores are comparable to other dyno scores. For example, if the Model 3 LRD's dyno score is lower than LR, that should mean the LRD has less range than LR. As long as that's proportionally correct, that's all I need. [...]
Thanks, I have that file: You'll note that I referenced this site in my original post.@ulrichw, there is a spreadsheet on the EPA website that has the coefficients of thousands of cars.
This paper's actually making my point: Here's how the "negative" force is defined: "the driving force at the wheel Fw that propel the vehicle."1. I found a document here that talks about negative values. If you search for the word "negative" in the document, you can find that section.
First of all, coming up with an entry is not a "blunder" - it is simply measurement inaccuracies or tolerances. Because the linear component and the quadratic components are being derived indirectly, and because a potentially small range of speeds is used for the measurements, the split between the linear and quadratic components may be quite sensitive to small variances in raw measurements.There are two possibilities:
- The B coefficient is negative because there is a reason behind it that makes sense like a road that isn't flat or back wind or some other reason that we don't know because we haven't looked into it in detail.
- 26% of entries are incorrect and BMW blundered 343 times in 2018, Toyota blundered 121 times etc
As for the negative number in coefficients said:I am an Aeronautical Engineer and have studied this question and have experience to understand it with 100% confidence. The short answer to the theoretically impossible negative coefficient is, it's a mathematical anomaly to curve fitting limited data.
The "theoretical" equation for aerodynamic drag implies that Cd is constant, but it is not. Cd is a function of Reynolds, Mach, Prandtl, ... numbers. The underlying physics of why Cd is not constant is a very long complex discussion. But for cars the very low Reynolds number means there is a big laminar separation bubble and garbage flow at low speeds so the Cd is higher at low speeds. At high speeds the Cd becomes constant until very high speeds where some flow approaches supersonic and Cd again increases (Mach effects).
The EPA probably only does coast down from 65 or 75 mph. So using this poor speed range and fitting a polynomial results in the a b c coefficients.
I backed out the M3 CdA based on the C=0.01498 and the aerodynamic drag equation...:
CdA = 0.001498*(45/66)^2/(0.5*0.002377) = 2.71 ft2 which implies a crazy low 0.12 drag coefficient.
(45/66)^2 correction from mph to ft/s
0.002377 = standard day density
Another way to look at this is the drag increases very slowly up to 65 or 75 mph because the aerodynamics improve, i.e. less flow separation, which makes the curve fitting produce an artificially low drag coefficient. Another complicating factor is wheel drag.
At top speed, the Tesla 0.23 (or 0.21 with aero wheels?) Cd is accurate.
I am hoping to buy a M3 very soon to replace a polluting VW Golf TDI and supplement the i-MiEV's (great little city car BTW!) short range so the wife and I both can drive an EV. The M3's very low CdA is 35% to 40% lower than all competing EV's, and since long range really only matters practically at high speeds on long trips, and other EV's weights (wheel friction drag) are very close, the important metric to look at when comparing is kWh/CdA.
*For example comparing the M3 with 50kwh to the Bolt with 60kwh:
kWh/CdA
10.6 M3 50kwh (+41% range vs Bolt)
7.5 Bolt 60kwh
* There are a lot of Cd and CdA numbers for the M3 so the M3 CdA=4.7 might not be correct. I found 4.3, 4.7, and 5. I used 4.7 believing that it might be correct for aero wheels.
Bottom line, I would only consider buying the Bolt Premier for 25K not including rebates. BTW the Bolt has less total volume (cargo + passenger volume), 110.9cuft vs 112.3cuft.
Finally, here's a chart of the model 3 LR and LRD's coefficients converted into drag (lb force) at speed (mph):
View attachment 346661
The grey line is the percentage difference in modeled drag of the LR vs the LRD, the other two lines are the LR and LRD drags expressed in pounds force. The X axis is speed in mph
I charted the percentage difference between the two lines to illustrate the relationship of the efficiency and how it changes vs. speed. Based on a theoretical analysis of the two cars, you would expect this relationship to be smoothly decreasing as the aerodynamic drag takes over (Basically you'd expect the quadratic component for the two cars to be identical, and the linear and constant components to be larger for the LRD vs. the LR).
The other thing to take from this chart is that the quadratic component and the fixed component are by far the most important factors in determining the shape of the chart - the negative coefficient on the linear component affects things, too, but the impact is fairly subtle.
I've ratholed this thread on this discussion, so I'll make this my last detailed response. Again, I appreciate all the work you've put into your data, and on the whole your chart is very valuable.
Hopefully we'll get better empirical data on LR vs. LRD (vs P) efficiency. My feeling is that actual results will be significantly closer than the EPA numbers imply.