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Help Me Decide Between Long Range and Performance

freeAgent

Member
Oct 29, 2020
132
107
SoCal
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Mahamilto

Member
Feb 20, 2021
386
307
New York, NY

Let’s end this. Actual published physics paper by an actual physics department.

In the exact same car, with real world data, obtained to determine weight and position of cargo on stopping distance.

Spoiler alert; when you add weight the stopping distance increases. Period. Every time.

Yes, we can yammer about the equations over and over, but classical physics as discussed calls for too many things to be “constant”. The reality is that the force to stop the car is based in the amount of energy to overcome its forward interia; which is 100% related to its mass.

The point of the paper wasn’t to prove this; which was accepted as absolute reality by the authors, but to show how loading cargo near front/rear axles or higher or lower from the COG impacts mass shift as the car decelerates and inevitably nose dives.

Unsurprisingly, if more mass was placed in the same place.... stopping distance is increased.

Now, admittedly the distances didn’t change dramatically when mass added wasn’t a large % of the total empty gross weight, but they changed. Measurably.

Weight is not going to be the predominant factor as the prior discussion went; but it is a measurable variable.
 

sroy

Closed
Mar 13, 2021
542
224
New Jersey
You can't go "let's end this" with the wrong answer.

@freeAgent You quote a study for trucks which I mentioned are operating in different limits than cars. Not only is the figure you show displaying a small difference, it is a small difference for trucks. Like differences in tons. So the differences between the SR+ and an LR are relatively that much smaller. Insignificant even.

@Mahamilto Again, this is for vans and pickups that could have loads of the order of tons, not pounds. The smallest weight they use is 250kg which is like 550 lbs. That's the smallest increment. All other weights are bigger. And the stopping distances measured vary by less than 3 feet across all weights. I mean experimentally speaking, they can't even say the braking distances are different with a straight face. If you cherry pick the longest braking distance from the lightest weight vs the shortest of the 1 ton distances, it would "say" less weight yields longer braking distance. I mean there is no error bars analysis so it's probably all equal within error bars which suggests the exact opposite i.e. that braking distance is the same. The article rather correlates the center of mass with braking distance which is a weird way to say that when the weight is poorly distributed, you brake more with the front wheels and this is almost enough to bring those non-cars with outside the operating limits of "braking distance is only a function of tires quality i.e. mass independent". The main conclusion that they draw is NOT that mass affects braking distance but rather that weight position does and only for the heaviest loads. Loads that are about 1/4 the weight of the LR. Arguably, the weight distribution on an SR+ vs LR is different but I can bet you can't measure braking distance differences between the 2.

There is less than 500lbs weight differences between the SR+ and the LR. Yes higher weight means longer braking distance. But within operating limits of the model 3, the weight differences between the SR+ and the LR will not result in measurably different braking distances.
 

Mahamilto

Member
Feb 20, 2021
386
307
New York, NY
insignificant vs measurable.
I never said it was significantly different as it can or would prevent an accident. Only state that it’s measurable. Mass and momentum matter even if it’s a millimeter. Anyway. Done with this. Wasted too much time already proving something that is generally accepted. No more forum arguments for me.

I agreed from the jump that the tire compound was the most significant factor when contact patch is equal. That’s not a debate.
 

Pyre

Member
Apr 10, 2021
284
123
Syracuse, NY
1620351273252.png
 

MikeyC

Member
Aug 19, 2019
350
507
Florida
Without using any equations, stopping any vehicle will result in the tire tread heating up. Assuming the braking system (brakes + ABS) can always keep up with the amount of friction needed to stop the car optimally within the limits of traction, the more weight you add, the hotter the tire tread will become while braking. I also assume the tire will have a different coefficient of friction based on the tread temperature. Some amount of the tire will get worn off, basically liquefied by friction on each stop and I would hazard a guess that the more weight you put on it, the hotter the tire becomes, and the more of it will get torn away due to heat and shearing force. So one way or another, I'd think you would see a difference in braking distances with a change in weight. Regardless of the type of vehicle used.

Mike
 
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freeAgent

Member
Oct 29, 2020
132
107
SoCal
You can't go "let's end this" with the wrong answer.

@freeAgent You quote a study for trucks which I mentioned are operating in different limits than cars. Not only is the figure you show displaying a small difference, it is a small difference for trucks. Like differences in tons. So the differences between the SR+ and an LR are relatively that much smaller. Insignificant even.

@Mahamilto Again, this is for vans and pickups that could have loads of the order of tons, not pounds. The smallest weight they use is 250kg which is like 550 lbs. That's the smallest increment. All other weights are bigger. And the stopping distances measured vary by less than 3 feet across all weights. I mean experimentally speaking, they can't even say the braking distances are different with a straight face. If you cherry pick the longest braking distance from the lightest weight vs the shortest of the 1 ton distances, it would "say" less weight yields longer braking distance. I mean there is no error bars analysis so it's probably all equal within error bars which suggests the exact opposite i.e. that braking distance is the same. The article rather correlates the center of mass with braking distance which is a weird way to say that when the weight is poorly distributed, you brake more with the front wheels and this is almost enough to bring those non-cars with outside the operating limits of "braking distance is only a function of tires quality i.e. mass independent". The main conclusion that they draw is NOT that mass affects braking distance but rather that weight position does and only for the heaviest loads. Loads that are about 1/4 the weight of the LR. Arguably, the weight distribution on an SR+ vs LR is different but I can bet you can't measure braking distance differences between the 2.

There is less than 500lbs weight differences between the SR+ and the LR. Yes higher weight means longer braking distance. But within operating limits of the model 3, the weight differences between the SR+ and the LR will not result in measurably different braking distances.
Point out where I said that there was a "significant" difference. This all started when I said,

they'd probably brake exactly the same (at least the P and LR would since they weigh the same...SR+ would beat them, and it may already beat them in braking stock)
I never said that I think the difference is significant, only that there should, in theory, be a difference in stopping. And, shockingly, that seems to be the case:
 

sroy

Closed
Mar 13, 2021
542
224
New Jersey
I am confused I don't see any braking tests in the video. Just a drag race. Am I missing something? Besides, that won't mean anything unless they run a test designed to take out reaction time from the equation. I posted a link above. The 3 models are rated at 131ft braking distance. The same 131ft for all 3 cars:

 

freeAgent

Member
Oct 29, 2020
132
107
SoCal
I am confused I don't see any braking tests in the video. Just a drag race. Am I missing something? Besides, that won't mean anything unless they run a test designed to take out reaction time from the equation. I posted a link above. The 3 models are rated at 131ft braking distance. The same 131ft for all 3 cars:

I included a timestamp in the video link. It should start right at where the brake test starts: 8m33s. Ratings and real-world are different. We know that wheels affect range, for example, but Tesla does not indicate that when swapping between the Aeros and 19" wheels.
 

MikeyC

Member
Aug 19, 2019
350
507
Florida
I love carwow. They get straight to the point and just do drag racing and brake tests. My problem with their tests is that it is either raining or the runway is wet from a previous rain for 95% of their tests and the three "lanes" often dry at different rates. So (like in this video), it's not a good test because some cars have a more dry/wet surface than the others.

Mike
 

Knightshade

Well-Known Member
Jul 31, 2017
11,945
16,532
NC
I am confused I don't see any braking tests in the video. Just a drag race. Am I missing something? Besides, that won't mean anything unless they run a test designed to take out reaction time from the equation. I posted a link above. The 3 models are rated at 131ft braking distance. The same 131ft for all 3 cars:



That site appears to just be cutting and pasting from other sources.

And often quite poorly.

Here's the chart where they show EVERY trim of the 3 taking 131 feet 60-0.

It's the same chart where it shows EVERY trim taking 5.1 seconds 0-60, and EVERY trim taking 13.3 in the 1/4 mile- which is obviously not remotely accurate.


Trim Name 0-60 MPH Standing 1/4-mile Braking (60 - 0 MPH)
Mid Range 4dr Sedan (electric DD) w/Prod. End 3/19 5.1 sec 13.3 sec 131 ft.
Performance 4dr Sedan AWD (electric DD) 5.1 sec 13.3 sec 131 ft.
Long Range 4dr Sedan AWD (electric DD) 5.1 sec 13.3 sec 131 ft.
Long Range 4dr Sedan (electric DD) 5.1 sec 13.3 sec 131 ft.
Standard Range Plus 4dr Sedan (electric DD) 5.1 sec 13.3 sec 131 ft.
Standard Range 4dr Sedan (electric DD) 5.1 sec 13.3 sec 131 ft.
 

Knightshade

Well-Known Member
Jul 31, 2017
11,945
16,532
NC
I love carwow. They get straight to the point and just do drag racing and brake tests. My problem with their tests is that it is either raining or the runway is wet from a previous rain for 95% of their tests and the three "lanes" often dry at different rates. So (like in this video), it's not a good test because some cars have a more dry/wet surface than the others.

Mike


Not only that, and they even call this out with the results- the cars have different tires and different reaction times from different drivers on braking- so those results aren't especially useful since there's a number of important variables regardless of weight (as evidenced by the 2 basically identical weight cars ALSO stopping at different distances)
 

sroy

Closed
Mar 13, 2021
542
224
New Jersey
Different wheels would have an impact as well as car height (i.e. perf vs the others or after market etc). All else equal, weight not a measurable factor.
 

Black306

Member
Oct 14, 2019
561
787
Sacramento
Different wheels would have an impact as well as car height (i.e. perf vs the others or after market etc). All else equal, weight not a measurable factor.
Just want to make sure I’m following…

All else being equal (rims, brakes, tires, road grade, weather, etc), a 3500lbs car will stop in the same exact distance as a 4000lbs car?
 

sroy

Closed
Mar 13, 2021
542
224
New Jersey
But what happens when we reach 0 lbs?
Operating limits. Fortunately a mass-less object is literally light so braking is quantum if any. At least electromagnetic. If you go very small weight, tires stop being the limiting factor. Drag is. Would have to look up the weight factor but I suspect that drag factor becomes the main one. Much higher weight like a 53', brakes are becoming a factor in which case mass does play a role. There is probably a crossover between the car and the 53' going through the 18' and/or with a trailer load on a car.
 

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