GM vs Cybertruck battery size & $

[Diehard]

D,

Regarding turbulence, it is not that simple. As some of us discussed, there are devices called "VGs" or Vortex Generators. They intentionally create little vortexes, or "tornados". That is "turbulence" or energized airflow. But this energy allows the air to flow over a surface that it wouldn't be able to follow without it. Do they cause some level of drag? Yep! But the small amount they cause is offset by the additional lift, or elimination of drag to a much larger area. Again, look at a modern F1 car. They have little curved spikes all over the car. They are there to manage the airflow either away from something, or towards something, or to keep the flow attached to a surface for one reason. Golf balls are the greatest common example of "a little turbulence is a good thing". Take the turbulence from the dimples away, and you can't get the ball to travel anywhere near as far. Or to put it in more grasp-able terms, I still can't hit a dimpled ball as far as John Daly could hit a smooth ball, but a serious golfer could.

As for your cd truck comparison, assuming all else is equal (tires, size, temp, rolling resistance, etc) this is what I get...

Fair=0.5∗Cd∗A∗rho∗V2

Where:
Fair is the air resistance force (the force that opposes the motion of the truck).
Cd is the coefficient of drag (0.46 for one truck and 0.3 for the other).
A is the frontal area of the truck.
rho is the air density.
V is the velocity of the truck. (V2 is "Squared")

Off the top of my head, and only 1/2 way through my coffee after flying through 9 time zones yesterday, this is the equation;
0.5∗0.46∗A∗rho∗(802)=0.5∗0.3∗A∗rho∗(80−x)2
(again, the little 2 means squared)
Since I let the app do my math due to my severe lack of caffeination and extreme laziness, I get;
x≈−24.71

Meaning that the 0.30cd going 80 has roughly the same drag as the .46cd doing 55.29.

I think you solved for the wrong V. This is my calculation:

0.5∗0.46∗A∗rho∗Vsq=0.5∗0.3∗A∗rho∗(80sq)
0.46∗Vsq=0.3∗(80sq)
Vsq=1920/0.46
V= 64.6

I am not saying turbulence can not be helpful. Just saying I doubt that flat surface in the back window area was intentional to help drag coefficient. Lets see if next generation Aptera comes with dimples.

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[PilotPete]

I think you solved for the wrong V. This is my calculation:

0.5∗0.46∗A∗rho∗Vsq=0.5∗0.3∗A∗rho∗(80sq)
0.46∗Vsq=0.3∗(80sq)
Vsq=1920/0.46
V= 64.6

I am not saying turbulence can not be helpful. Just saying I doubt that flat surface in the back window area was intentional to help drag coefficient. Lets see if next generation Aptera comes with dimples.

Dammit D,

You're making me do math! This is how I think it should be solved...
Since both trucks are traveling at the same speed (80 mph), we can set up the equation like this:

0.5∗0.46∗A∗rho∗(802)=0.5∗0.3∗A∗rho∗(80−x)2

Simplify the equation: (remove rho and A constants from both sides)
0.46∗802=0.3∗(80−x)2

Divide both sides by 0.3:
0.46∗802/0.3=(80−x)2

Get the square root of both sides:
sqrt(0.46∗802/0.3)=80−x

Fix the left side of the equation:
0.46∗802/0.3=99.06

Now, solve for x:
80−x=99.06

take 80 from both sides:
−x=99.06−80
−x=19.06

Multiply both sides by -1 to get a positive x
x=−19.06

Which is the speed you have to "add" from 80 to get the same drag value. (adding a negative)
80-19.06=60.94mph

So I was off when I input the numbers into the app, and it's about 5 mph faster than I quoted. But I THINK this is right. I put the steps out to get checked. And yes, I cut off everything more than 2 to the right of the decimal because I'm lazy and at 80mph, who cares about 0.0033293020969ft/sec

And I'm just saying the mirrors might fix that, or the plat part MIGHT create something that helps at the back.

Or it's just a stying thing and screw it, it looks tough.

 

[Diehard]

Dammit D,

You're making me do math! This is how I think it should be solved...
Since both trucks are traveling at the same speed (80 mph), we can set up the equation like this:

0.5∗0.46∗A∗rho∗(802)=0.5∗0.3∗A∗rho∗(80−x)2

Simplify the equation: (remove rho and A constants from both sides)
0.46∗802=0.3∗(80−x)2

Divide both sides by 0.3:
0.46∗802/0.3=(80−x)2

Get the square root of both sides:
sqrt(0.46∗802/0.3)=80−x

Fix the left side of the equation:
0.46∗802/0.3=99.06

Now, solve for x:
80−x=99.06

take 80 from both sides:
−x=99.06−80
−x=19.06

Multiply both sides by -1 to get a positive x
x=−19.06

Which is the speed you have to "add" from 80 to get the same drag value. (adding a negative)
80-19.06=60.94mph

So I was off when I input the numbers into the app, and it's about 5 mph faster than I quoted. But I THINK this is right. I put the steps out to get checked. And yes, I cut off everything more than 2 to the right of the decimal because I'm lazy and at 80mph, who cares about 0.0033293020969ft/sec

And I'm just saying the mirrors might fix that, or the plat part MIGHT create something that helps at the back.

Or it's just a stying thing and screw it, it looks tough.

That is why I put it out to the forum. Last time I did math was more than 3 decades ago.

I think the disconnect is here not your calculation:

0.5∗0.46∗A∗rho∗(80)2=0.5∗0.3∗A∗rho∗(80−x)2

Left side is Lightning. Right side is CT. We want to know by how much Lightning should slow down to have the same consumption as CT. so whether you are solving for the speed reduction (x) or the new speed V, what you are looking for should be on the left where the drag is 0.46. So the reds should be swapped. Am I making sense or making things more confusing.

 

[PilotPete]

That is why I put it out to the forum. Last time I did math was more than 3 decades ago.

I think the disconnect is here not your calculation:

0.5∗0.46∗A∗rho∗(80)2=0.5∗0.3∗A∗rho∗(80−x)2

Left side is Lightning. Right side is CT. We want to know by how much Lightning should slow down to have the same consumption as CT. so whether you are solving for the speed reduction (x) or the new speed V, what you are looking for should be on the left where the drag is 0.46. So the reds should be swapped. Am I making sense or making things more confusing.

Ok.

I'm a bit fuzzy today, but let me try this... I always go through a reasonableness check on my math at work, so let's try it here.

If we do it your way,
0.46*(80-x)2=0.3*802

divide both by0.46
(80-x)2=0.3*802/0.46

Then
80-x=sqrt(03*802/0.46)

Fix the right
80-x=64.61

drop the 80
-x=-15.39
or x=15.39

which would mean the 0.46cd could go 80-15.39 for the same drag. I think it also means that the 0.3cd truck could do 19.06 FASTER than the 0.46 truck at 80. I was solving for the wrong side of the question. I bow to your alertness.

I think you are correct. I got jet lag...

 

[Diehard]

Ok.

I'm a bit fuzzy today, but let me try this... I always go through a reasonableness check on my math at work, so let's try it here.

If we do it your way,
0.46*(80-x)2=0.3*802

divide both by0.46
(80-x)2=0.3*802/0.46

Then
80-x=sqrt(03*802/0.46)

Fix the right
80-x=64.61

drop the 80
-x=-15.39
or x=15.39

which would mean the 0.46cd could go 80-15.39 for the same drag. I think it also means that the 0.3cd truck could do 19.06 FASTER than the 0.46 truck at 80. I was solving for the wrong side of the question. I bow to your alertness.

I think you are correct. I got jet lag...

I can barely remember my name when I am sleep deprived. Hope you either had a lot of fun, made a lot of money or both on at least one end of that plane ride. Get some sleep, it is a cheap way of making the world a better place.

 

[WHIZZARD OF OZ]

I'll add EPA (or equiv) info the chart when CT numbers are aout. Real world the 1000 lb weight is insignificant.
That is people choosing a CT or comparing to other BEV pickups for their hauling they need to know that even if the CT is 1000 lbs lighter that is not what is getting them real world mileage.

Oh heck. I saw that and forgot to correct it. The Rivian numbers are very good overall.

As we wait for 'real world' figures or EPA and so on, are you thinking any particular battery pack size and if so what's your rough in of consumption?
Could the TRI/QUAD run a 175 kWh pack and deliver a hypothetical 3.1 miles/kWh?
It would SMASH the competition if it this was the case.
Edit: On reflection, and reading Elon notes beyond 2019, l might be too heavy handed on that pack size. Something about carrying around batteries and a ~330 mile range. A salute to the environ_mental CT.

 

[Jhodgesatmb]

here’s a scenario for you to ponder.

Musk on spec release:

“Understanding that in 2019 we stated the tri would have 500mi range, we have since then collected millions of miles of data, and expanded the supercharger system by [X]-fold - and we’ve come to think better of it.

CT has a ~330mi range. You may be wondering about towing. We don’t believe the solution to towing is large packs, that on average sit idol for 98% of the year. We believe the solution to towing is charging infrastructure. Fact is, few people tow, even fewer tow regularly, even fewer than that regularly for long distances. We understand there will be still be folks hoping for longer towing range, and for them we say super chargers are coming at an unprecedented rate. And also that in a few years we believe battery advances will contribute significantly.

For everyone else, the CT range plus supercharger system will meet every need.”

I do not know when Elon made this comment but it really isn't his call to make when it gets right down to it. For most of us, regardless of the day-to-day usage, we believe that more range is better, and he promised us a 500+-mile range. The only way a 330-mile range would be acceptable to me would be if the Cybertruck gets 330 miles, fully loaded, at actual highway speed, in the dead of winter, based on how much Tesla wants us to charge the battery (e.g., 20%-80%). Otherwise he is simply demonstrating that he doesn't drive a car in actual conditions. He flies in a private jet to some place and tools around in a Cybertruck for 10 minutes and thinks that he understands the rest of us? Chevy and others seem to get it.

 

[Jhodgesatmb]

Our F-150 doesn't even get started up unless we are going to tow or use the bed.

Of course, my Cybertruck will not follow that rule at all! At least not for the first year or two.

My car is full all the time and the Cybertruck will be as well. Didn't Tesla advertise this thing as replacing the F-150 as a work truck? People can whine all day long about space for the battery, cost, etc. but to replace a work truck you better meet or beat all of its performance specs (cargo, towing, range). Who cares how many charging stations there are if you have to wait in line to use one, or if you have to charge at every single one like we did last winter. Its BS.

 

[Crissa]

If you're towing something, you really don't have any room to complain. It takes loads of energy to tow, and you gotta get it somewhere.

-Crissa

 

[scottf200]

here’s a scenario for you to ponder.

Musk on spec release:

“Understanding that in 2019 we stated the tri would have 500mi range, we have since then collected millions of miles of data, and expanded the supercharger system by [X]-fold - and we’ve come to think better of it.

CT has a ~330mi range. You may be wondering about towing. We don’t believe the solution to towing is large packs, that on average sit idol for 98% of the year. We believe the solution to towing is charging infrastructure. Fact is, few people tow, even fewer tow regularly, even fewer than that regularly for long distances. We understand there will be still be folks hoping for longer towing range, and for them we say super chargers are coming at an unprecedented rate. And also that in a few years we believe battery advances will contribute significantly.

For everyone else, the CT range plus supercharger system will meet every need.”

Where did that quote come from? There is no source. I've never seen it and can't locate it. TIA

 

[cvalue13]

Where did that quote come from? There is no source. I've never seen it and can't locate it. TIA

my bad - I was using quotes not to cite but to caption the hypo

 

[cvalue13]

I do not know when Elon made this comment but it really isn't his call to make when it gets right down to it.

if say it sort of is his call. Whether you like it, is a separate matter

but you might want to prepare yourself for roughly this scenario

 

[Jhodgesatmb]

if say it sort of is his call. Whether you like it, is a separate matter

but you might want to prepare yourself for roughly this scenario

I am prepared to bail if the tri-motor isn’t as promised. But you are taking my comment out of context. Elon can do what he wants with the Cybertruck specs, of course, but it is not his call to say what kind of range we want or need. And god damn him for even trying. And Elon has much bigger problems to deal with than ‘me’ bailing if he welches on his promises.

 

[HaulingAss]

My car is full all the time and the Cybertruck will be as well. Didn't Tesla advertise this thing as replacing the F-150 as a work truck? People can whine all day long about space for the battery, cost, etc. but to replace a work truck you better meet or beat all of its performance specs (cargo, towing, range). Who cares how many charging stations there are if you have to wait in line to use one, or if you have to charge at every single one like we did last winter. Its BS.

With the way you're looking at it, it's a wonder you have any interest in EVs at all. If you need to tow long-distances, and don't want to charge along the way, why don't you get a gas or diesel tow rig? You're bellyaching about something you have complete control over.

Why do you even consider yourself an EV enthusiast? Does anyone make an EV that's good enough for your needs? It doesn't sound like it.

 

[cvalue13]

I am prepared to bail if the tri-motor isn’t as promised. But you are taking my comment out of context. Elon can do what he wants with the Cybertruck specs, of course, but it is not his call to say what kind of range we want or need. And god damn him for even trying. And Elon has much bigger problems to deal with than ‘me’ bailing if he welches on his promises.

you’ve always sort of taken the position that the 2019 unveil specs were each and every ‘promised’

That position by no means do I think is unfair or unreasonable, but it is just one of several available positions

and by now it’s fairly clear that promises or not, they’re not all going to be met

and yes, top spec range I think is amongst them

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