Questions from a Tesla Owner

[WasserGKuehlt]

I figured the CT's extra aero drag accounted for most of the difference...not the weight.

I didn't think the CT looked like a brick compared to the sedan, but lo and behold the 4CT has a Cd of .26, whereas the 4S is at .22. Still, that is not (all of) it, since the 4SCT is more efficient than the 4CT according to Porsche themselves:

Taycan 4 Cross Turismo: electricity consumption combined 28.1 kWh/100 km
Taycan 4S Cross Turismo: electricity consumption combined 24.8 – 21.3 kWh/100 km (WLTP)

So what do I know.. ?‍

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[f1eng]

FORTRAN on punch cards?

Yes, and stand in a queue to run my deck at one of the two computers at Imperial College, London.

 

[Tooney]

And, after waiting, and finally running the deck of cards, the feeling when the program fails to compile, and you get to repeat.

 

[f1eng]

I remember it well.
I was a pioneer of the use of CAD in Formula 1 and each time I rendered a surface it took about 30 mins and crashed 50% of the time - I learned to backup my model before every attempt.
Laughably easy now.

 

[Zcd1]

I didn't think the CT looked like a brick compared to the sedan, but lo and behold the 4CT has a Cd of .26, whereas the 4S is at .22. Still, that is not (all of) it, since the 4SCT is more efficient than the 4CT according to Porsche themselves:

Taycan 4 Cross Turismo: electricity consumption combined 28.1 kWh/100 km
Taycan 4S Cross Turismo: electricity consumption combined 24.8 – 21.3 kWh/100 km (WLTP)

So what do I know.. ?‍

Cross Turismo’s drag coefficient is 18.182% greater than the Taycan 4S’s.

4S’s overall efficiency is ~19% better and better aero is one factor.

 

[mikezhang31]

Lol between the wagon shape, my bike rack, the cost per mile (fuel wise) is about the same as my parents’ base GTI ?

 

[WasserGKuehlt]

Cross Turismo’s drag coefficient is 18.182% greater than the Taycan 4S’s.

4S’s overall efficiency is ~19% better and better aero is one factor.

Re-pasting from earlier:
Taycan 4 Cross Turismo: electricity consumption combined 28.1 kWh/100 km
Taycan 4S Cross Turismo: electricity consumption combined 24.8 – 21.3 kWh/100 km (WLTP)

 

[Zcd1]

Re-pasting from earlier:
Taycan 4 Cross Turismo: electricity consumption combined 28.1 kWh/100 km
Taycan 4S Cross Turismo: electricity consumption combined 24.8 – 21.3 kWh/100 km (WLTP)

Right, but actual real-world test results show:

The "Taycan" and "Taycan Plus" test results are apparently from single tests (based on the total km driven in testing), so I'd ignore those as outliers whose results would normalize over more tests.

What we're left with is the Cross Turismo ("tourismo" on this sheet) showing real-world results over multiple tests of about 20% (239 wh/KM vs. 189-199 wh/KM) worse than the Taycan...

 

[WasserGKuehlt]

Right, but actual real-world test results show:

The "Taycan" and "Taycan Plus" test results are apparently from single tests (based on the total km driven in testing), so I'd ignore those as outliers whose results would normalize over more tests.

What we're left with is the Cross Turismo ("tourismo" on this sheet) showing real-world results over multiple tests of about 20% (239 wh/KM vs. 189-199 wh/KM) worse than the Taycan...

First I have to apologize for being curt earlier. Your initial assertion was that the difference in efficiency was attributed to aero, which I doubted. It does turn out that the Cd difference is significant (~20% in favor of the sedan) so your assertion was correct - or at least partially so. However, while reading the Porsche literature on aero, the very same doc mentions a roughly 20% difference in efficiency between the 4 and 4S in the same body style (wagon) - so there must be something else at play here. (I suspect the doc is old/pre-update-with-a-P.)

Regarding the table above, something still doesn't make sense: the WLTP efficiency is the same (215 Wh/km) but the WLTP range is different (389 vs 462). That alone would seem to imply the "tank" size (battery capacity) is different, before we even get to the real world tests.

Lastly, on the topic of the real world tests - the data on the 4CT above shows ~3x test distance covered vs the 4S, and so I'd expect the former to be closer to reality (both are short in terms of distance I'd think sufficient to cover a range of weather conditions, but 1k miles of test could basically be one longer trip). Incidentally, as I mentioned before, the 4CT consumption matches exactly my lifetime average at 2.6mi/kWh, but all of my driving was in cold weather with a roofbox on top. (That alone seems to impose a 6-9% penalty on consumption.)

I think this horse is no longer twitching.

 

[bluedonkey]

both vehicles in my experience suffer range loss associated with speed - neither vehicle can "cheat" physics and the Taycan will go further if driven slower - it's a matter of physics - it has to be true and is true. Now it may have sufficient range to go far enough when driven faster, but it's an undeniable fact/consequence that it can go further at 60 mph than it can at 70 mph. There is no "magic" where Taycan avoids the geometric cost increase of V^2 (velocity squared) increase in drag for aero-dynamic loads.

On the one hand I agree, but there is something odd at work in the Taycan because the efficiency number we get seems to be a little better when we have the chance to drive a little faster. Maybe there are other factors at work, but what feels like a steady 60-65 mph run will get 2.9 mi/kWh, maybe 3.0 mi/kWh. At 75-80mph, I will often see 3.1 mi/kWh.

I have a feeling the sweet spot of the Taycan's aerodynamics might be a little higher. The range mode always amuses me when it says it will limit me to 90 mph - well above the freeway limits here in California - but maybe that's a clue as to where the Taycan's sweet spot is.

 

[daveo4EV]

On the one hand I agree, but there is something odd at work in the Taycan because the efficiency number we get seems to be a little better when we have the chance to drive a little faster. Maybe there are other factors at work, but what feels like a steady 60-65 mph run will get 2.9 mi/kWh, maybe 3.0 mi/kWh. At 75-80mph, I will often see 3.1 mi/kWh.

I have a feeling the sweet spot of the Taycan's aerodynamics might be a little higher. The range mode always amuses me when it says it will limit me to 90 mph - well above the freeway limits here in California - but maybe that's a clue as to where the Taycan's sweet spot is.

yeah I just don' know - aero drag which is more than 50% of total energy/or power to move the vehicle after ~40 mph - has a velocity^squared component…

so there is no "magic" where porsche can have "less drag" at 70 mph than Tesla at 70 mph…and since drag _IS_ the major element/cost once you're moving…

I understand what you're saying, but the math says it simple can not be true - V^2'rd is a factor and it can not be "worked around". And at the speeds we're talking about the power to overcome drag is the majority "costs" in terms of consumption.

 

[TDinDC]

yeah I just don' know - aero drag which is more than 50% of total energy/or power to move the vehicle after ~40 mph - has a velocity^squared component…

so there is no "magic" where porsche can have "less drag" at 70 mph than Tesla at 70 mph…and since drag _IS_ the major element/cost once you're moving…

I understand what you're saying, but the math says it simple can not be true - V^2'rd is a factor and it can not be "worked around". And at the speeds we're talking about the power to overcome drag is the majority "costs" in terms of consumption.

It’s not magical, but the hit on range will be exponentially worse with speed for moving a cube than moving a wedge. So, the more aerodynamically efficient a vehicle is, the less of an impact speed would have on range (absent some quirk in the shape). That’s not magic or surprising. Given that I’m comparing a Model X to a Taycan, it really shouldn’t surprise anyone. And I’ve taken enough trips with both cars on the same roads to be able to verify that my observation is accurate with respect to the two vehicles I am comparing.

Nice site to visualize what I experience between Model X and Taycan CT in terms of greater impact on consumption with speed of Model X can be seen here: https://x-engineer.org/aerodynamic-drag/

BUT, here is what I don’t understand. Supposedly the Cd of TMX is 0.24 and its frontal area is 2.59 m2, while the Cd of the CT is 0.26 and its frontal area is 2.37 m2

if true, that means that Fad[N] is 738 for TMX and 732 for CT, and Pad[kW] is 32.8 for TMX and 32.51 for CT at 160 kph . This isn’t orders of magnitude different, but the difference seems big on range while driving.

 

[tchavei]

Naive question... Since we have a gearbox with 2 gears (contrary to other EV) shouldn't there be a moment/speed where the car up shifts so the motors are running at lower rpm despite higher speed (at least briefly). What's the impact on consumption at that point?

For example 65mph in 1st gear vs 70mph in 2nd gear

 

[Zcd1]

The Taycan's 2-speed gearbox likely improves its high-speed efficiency.

 

[Kimbo996]

The car only uses low gear under hard acceleration. Otherwise it stays in top the whole time, and feels more Tesla like. Both kick down and upshift are unnecessarily harsh and uncomfortable and ruin the car imho. Hopefully next gen Porsche will either sort it out or delete it altogether.

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