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Massive efficiency gain when following someone

JayNJ

Member
Jul 13, 2018
253
151
New Jersey
Mythbusters (episode 80) did a good test on this years ago Mythbusters: drafting 10 feet behind a big rig will improve mileage 39 percent on a controlled strip so they could get repeatable results.

The short results were (@ 55 mph)
  • 11% improvement @ 100 feet behind
  • 20% improvement @ 50 feet behind
  • 27% improvement @ 20 feet behind
  • 10% improvement @ 10 feet behind
Two other numbers make this scary to capitalize on:
  • 5280 feet in a mile, 3600 seconds in an hour. So 55 mph is 80.7 ft/sec, 80 mph is 117 ft/sec
  • Human reaction time is right around 3/4 of a second. At 55 mph you've consumed 60 feet in that time, at 80 mph you've consumed 88 ft
"Safe" following distance is considered to be 3 seconds, or 242 ft @ 55 mph, 351 ft @ 80 mph.

So this falls into the "yes you can" and "yes your nuts" if you're getting close enough to get significant savings as if the truck runs over something in the road, swerves to avoid a stopped object, or brakes suddenly, you're toast. Best to wait for Tesla to get the "convoy" functionality deployed for the Semi and provides a way for 3/Y to join a Semi "convoy" on FSD

I would say the sweet spot is @75 feet. Plenty of distance and good improvement. 242 feet follow distance seems is crazy, I would say75 - 100 ft is normal. When you calculate reaction time, you have to consider the braking time of the truck in front of you. If he slams on his brakes he will not come to an instant stop.
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
5,956
11,287
Springfield, VA
I would say the sweet spot is @75 feet. Plenty of distance and good improvement. 242 feet follow distance seems is crazy, I would say75 - 100 ft is normal. When you calculate reaction time, you have to consider the braking time of the truck in front of you. If he slams on his brakes he will not come to an instant stop.
What if the truck hits a stopped object in front of it, like a multi-car accident. There goes your buffer.
 
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dmurphy

Supporting Member
Supporting Member
Dec 7, 2018
3,831
5,416
New Jersey - Morris County
I would say the sweet spot is @75 feet. Plenty of distance and good improvement. 242 feet follow distance seems is crazy, I would say75 - 100 ft is normal. When you calculate reaction time, you have to consider the braking time of the truck in front of you. If he slams on his brakes he will not come to an instant stop.

75 feet is WAY too close. That's less than a second of closing distance at highway speed. Truck hits something hard, you're done for.

Stole this chart from Safelite, but it's pretty accurate.

safe-driving-distance-infobyte.jpg
 

S4WRXTTCS

Well-Known Member
May 3, 2015
5,739
6,897
Snohomish, WA
75 feet is WAY too close. That's less than a second of closing distance at highway speed. Truck hits something hard, you're done for.

Stole this chart from Safelite, but it's pretty accurate.

View attachment 536553

What would be interesting to see is the average following distance, and not best practices ones. Like lets for a second ignore rules like the 2 second rule or the rule to follow trucks at a larger distance.

I ask this because I firmly believe that most drivers in congested areas follow way too closely, and this is why I think TACC is actually a safety feature. It forces people to have a bit more distance.

I tend to use a setting of 3 under normal situations, and 5 if I have some reason why I want to be farther back (like behind trucks). With a setting of 3 it's pretty common for people to change lanes into the lane in front of me either because they need to get into my lane or they were behind me, and felt like I was giving too much distance.

Now I don't know the distance a setting of 3 translates into. My understanding is that it's time based, and 3 would be 3 seconds. But, other people claim that each step is a half second so a setting of 3 would be 1.5second.

To my eyes it appears to be roughly about 6 car lengths (at 60mph). To those that say it's too close I'd say that I'm pretty average or above average in how much distance I give. I'd really have to use a setting of 1 to come close to what I see on average.
 
Last edited:

Jccope64

Member
Feb 24, 2020
36
20
North carolina
What would be interesting to see is the average following distance, and not best practices ones. Like lets for a second ignore rules like the 2 second rule or the rule to follow trucks at a larger distance.

I ask this because I firmly believe that most drivers in congested areas follow way too closely, and this is why I think TACC is actually a safety feature. It forces people to have a bit more distance.

I tend to use a setting of 3 under normal situations, and 5 if I have some reason why I want to be farther back (like behind trucks). With a setting of 3 it's pretty common for people to change lanes into the lane in front of me either because they need to get into my lane or they were behind me, and felt like I was giving too much distance.

Now I don't know the distance a setting of 3 translates into. My understanding is that it's time based, and 3 would be 3 seconds. But, other people claim that each step is a half second so a setting of 3 would be 1.5second.

To my eyes it appears to be roughly about 6 car lengths (at 60mph). To those that say it's too close I'd say that I'm pretty average or above average in how much distance I give. I'd really have to use a setting of 1 to come close to what I see on average.
People saying Teslas 3 is too close are all full of crap . If your in minimal traffic running at 3 it is perfectly safe . After all it’s a computer that can make instant decisions, these people act like the vehicle they are following stop instantly . No one follows at 300 feet even in minor traffic .
 

dmurphy

Supporting Member
Supporting Member
Dec 7, 2018
3,831
5,416
New Jersey - Morris County
People saying Teslas 3 is too close are all full of crap . If your in minimal traffic running at 3 it is perfectly safe . After all it’s a computer that can make instant decisions, these people act like the vehicle they are following stop instantly . No one follows at 300 feet even in minor traffic .

The processor in my Tesla has much, much better reaction time than I ever will. Within milliseconds. I'm orders of magnitude slower than that.. as are you, and every other meatbag behind the wheel.

I'm not going to just what is/isn't safe for Autopilot, but measuring it against a meatspace metric isn't the most logical thing to do, either.
 

SageBrush

REJECT Fascism
May 7, 2015
12,588
16,769
New Mexico
We are a software delivery away from being able to join a "train" where a group of cars coordinate to run in a high speed lane as a single unit. Lead car would be compensated for breaking wind and all in group would benefit from gang drafting.
Software would maintain bumper to bumper spacing and manage "join and exit" maneuvering.
I expect this too, although not as soon as you. It really is the obvious way to enable 80+ mph long distance travel without needing a 120 kWh battery
 

SageBrush

REJECT Fascism
May 7, 2015
12,588
16,769
New Mexico
People saying Teslas 3 is too close are all full of crap . If your in minimal traffic running at 3 it is perfectly safe . After all it’s a computer that can make instant decisions, these people act like the vehicle they are following stop instantly . No one follows at 300 feet even in minor traffic .
I would like to see data to back up that assertion, since the actual AP implementation is a trade-off with phantom braking.
 

KenC

Active Member
Sep 4, 2018
3,761
3,496
Maine
There's a vendor that sells protective film, ClearPlex, for the wing window of the Model 3, Targe Indus. Presumably they also install the front windshield ClearPlex. I got the ClearPlex for my Model 3 wing window, and installed it over the weekend when it finally warmed up above 50F. Impossible to say how well it'll work for preventing break-ins, since it just looks like PPF, but I assume it must work. Easy to install, if you've done PPF. Here's the link to the ClearPlex thread:
Vendor - Window protection for your Tesla
 

MassPlay

Member
Feb 9, 2020
54
67
Boston
I would say the sweet spot is @75 feet. Plenty of distance and good improvement. 242 feet follow distance seems is crazy, I would say75 - 100 ft is normal. When you calculate reaction time, you have to consider the braking time of the truck in front of you. If he slams on his brakes he will not come to an instant stop.

The truck hits something, runs over something in the road, drives through a large pothole, swerves to avoid a stopped vehicle, all cases where you're in an accident @ 75 feet as you have less than 1 second to react and avoid. Even if you could process and decide on a course in that second (brake, swerve (is the left lane open? the right one?)), you still have muscle time to move the wheel/step on the brake and reaction time for the car to do what you asked. You're wrecked before you move a muscle @ 75 ft and 55 mph+
 

MassPlay

Member
Feb 9, 2020
54
67
Boston
People saying Teslas 3 is too close are all full of crap . If your in minimal traffic running at 3 it is perfectly safe . After all it’s a computer that can make instant decisions, these people act like the vehicle they are following stop instantly . No one follows at 300 feet even in minor traffic .

Right now all AP can do is brake without a human input. So if its something that requires swerving (fixed object in the lane, chain reaction rear-ender, pothole, etc.) then it can't help. Nor can it help if the object in front has a shorter stopping distance (the 3's 60-0 distance is good, however it trails a fair swath of ICE sports/premium cars which are 400-500lbs lighter).
 
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Adopado

Active Member
Aug 19, 2019
4,302
3,252
Scotland
Finally I pull into the left lane so they pass. Then I’m stuck behind them because now they are driving slower than I was. Pass them again and you see them with a flip phone plastered to their ear.

Ah yes, I understand what's happening. The warping of space-time put you behind someone from the year 2000. They are not even aware of your presence. (The flip phone was the clue ;))
 

Watts_Up

Active Member
Mar 4, 2019
3,721
2,703
In a galaxy far, far away

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