Massive efficiency gain when following someone

[jpfive]

If you can’t see the tractor’s mirrors, they can’t see you back there, either.


Back off till at least both mirrors are in sight.

The situational awareness of truckers is probably quite good. I think they generally know if somebody has come up behind them and then not passed. Also, modern trucks probably have rear camera assist - much like many RV's. And if you are in their mirrors, of course they know you are hanging back there, and might prefer you didn't. At any rate the issue of road debris is enough reason, IMHO. During the years that I was riding motorcycles that was the primary reason I avoided the temptation to draft.

 

[ItsNotAboutTheMoney]

Why would @ItsNotAboutTheMoney disagree with science?

Drafting has been proven time and time again.

Just because science says something can be done, doesn't mean you should do it.

Deliberate close drafting is something that should be left to the race track.

 

[dmurphy]

The situational awareness of truckers is probably quite good. I think they generally know if somebody has come up behind them and then not passed. Also, modern trucks probably have rear camera assist - much like many RV's. And if you are in their mirrors, of course they know you are hanging back there, and might prefer you didn't. At any rate the issue of road debris is enough reason, IMHO. During the years that I was riding motorcycles that was the primary reason I avoided the temptation to draft.

Oh, one thousand percent agreed on all counts. But being up so close where you’re invisible to the mirrors? That’s just asking for death. Really.

 

[KenC]

So, 82mph. Just doing some envelope math, that's 120feet/sec. A vehicle is about 16feet, so 2 to 3 lengths is 32 to 48 feet. Either way, at 120ft/sec, we're talking less than ½ a second behind.

I've always just assumed that the setting of "1" on follow distance is 0.5 secs. So, you'd be following at a distance closer than "1". Where I got that, I'm not sure, I think I just calculated it myself. Set the follow distance to 7, follow a vehicle on a flat country road, let the vehicle ahead pass a shadow, and then start counting, you'll pass the shadow between 3 and 4 secs. So, I just figured the increments are 0.5secs.

Whenever I'm behind someone, I look at their vehicle and their mudflaps and their driving. If they look like they're going to throw pebbles, with no flaps, or driving close to the shoulders where dirt accumulates, (semis on windy days can weave), I don't stay behind them. I'm more likely to set my follow distance to 7 on long journeys, and 3, if on fast/short trips like a daily commute. 1 second follow is easy, when alert and in heavy rush-hour traffic, but I prefer 1.5secs. Around Boston, that'll get people cutting into the gap, but so be it, I don't care if people think I leave too much space.

 

[SlimJim]

I have a long range model 3 with the 19 inch wheels, temperature plays a factor but I’ve noticed nothing plays as big of a factor as following kinda close behind someone to get great efficiency, I ran 82 mph for over 20 miles at 2-3 car lengths behind a SUV and averaged 240 wh/mi. Obviously that would increase efficiency just because your car doesn’t have to work as hard to push through the air but since you always see people complaining about how there high efficiency kills their range ,just follow someone running around the same speed as you . The 20 mile trip the opposite direction I ran closer to 65 without following and was closer to 285 wh/mi. There was not really any elevation gain/ loss or winds . Temp was 75f

It would be an awesome experiment to do with 5 identical Model 3 cars vs 1 Model 3 and do 1000 mile freeway travel.
1 control car will run by itself at fixed speed while 5 cars form a line and keep rotating the leading role at the front of the line like a peloton of cyclists. And compare energy consumption.

 

[Xenoilphobe]

I've done it to make it to a long stretch supercharger.. but you shouldn't

Future Darwin Awardees

 

[Uncle Paul]

When you took your drivers license exam, the booklet says to stay at least one car length behind for every 10 mph speed.

Police know this as well, and can ticket for following too close.

In many areas, following only 2 car lengths behind would get your car impounded for reckless driving.

On a more positive note, you will notice on your display that you use less juice not only following behind a semi, but also driving alongside until you get about 2/3 of the way towards the front of the truck. As you finish your pass you can see the wh/mi jump up significantly.

Experienced drivers also know not to follow closely behind a truck because an object the truck can easily pass over can do a lot of damage to your low slung Tesla. Truck will not swerve to miss a tire in the middle of the road as they know it will easily pass underneath it's chassis, but the Tesla following closely behind will notice it for sure.

 

[GoSharks]

My experience is that efficiency gains are very possible while following at a completely safe distance - a distance that exceeds what most drivers allow - with vehicles of sufficient height. At highway speeds, I would never follow a vehicle at less than 4 seconds time, with 5 seconds being ideal (how many car lengths that is depends on the speed of traffic). Yet on these threads, I see many raise safety concerns about this behavior. I tend to drive pretty close to the speed limit - also to improve safety and maximize efficiency. I'd rather find a vehicle that's traveling about my speed and stick behind it, rather than being isolated in the right lane with drivers passing me on the left and then cutting back in front of me.

As long as everyone is maintaining a safe following distance for the speed they are traveling, I fail to see the issue. Rock and debris damage is a legitimate concern, though.

4 second spacing? I guess you never travel in a populated area. That is just impossible in most populated areas unless you’re traveling in the middle of the night.

60mph is 88ft/s. 4*88ft=352 ft, greater than a football field in distance!

 

[MrMassTransit]

4 second spacing? I guess you never travel in a populated area. That is just impossible in most populated areas unless you’re traveling in the middle of the night.

60mph is 88ft/s. 4*88ft=352 ft, greater than a football field in distance!

I definitely live in a populated area, but I'm talking about taking road trips in less populated areas, yes. No reason to worry about following a large vehicle when you're only going a handful of miles and the following distance will be closer by necessity. I'm talking about having the car on autopilot on an open road outside of a metro area.

 

[KenC]

I've done it to make it to a long stretch supercharger.. but you shouldn't

Future Darwin Awardees

First vid, those were just random debris. Some of those people were clouted after 5 secs, not much to do with tailgating. The 2nd vid, is a truck safety video. It says 200ft is the safe distance, so at least 1.5 sec gap at 82mph, or a setting of "3" on adaptive cruise.

The last vid of the cyclist is probably sprint training. The vehicle's trunk is open, or if a van, the doors are open, to create as big a draft as possible.

Interestingly, for cyclists, while you never want to crash, a bike can stop faster than the truck or bus, and even if you did hit the truck, being so close, the relative speed between the two is not that great, the bigger danger is the road rash from sliding on the road, post-crash, and potentially getting run over by a following vehicle. But, most following vehicles know not to follow insane cyclists.

 

[Rottenapplr]

I’d rather use more energy then screwing up my paint drafting behind a semi or suv with big tires.

 

[EVNation]

The situational awareness of truckers is probably quite good. I think they generally know if somebody has come up behind them and then not passed. Also, modern trucks probably have rear camera assist - much like many RV's. And if you are in their mirrors, of course they know you are hanging back there, and might prefer you didn't. At any rate the issue of road debris is enough reason, IMHO. During the years that I was riding motorcycles that was the primary reason I avoided the temptation to draft.

No rear camera on the trailer unless some owner operator that only pulls their own trailer installed one. The majority of truckers are regularly hooking up to different trailers because time spent waiting at a dock for their trailer to unload/ load is unpaid. Also if you’re following a truck too closely, you won’t have time to react when they blow a tire or run over a piece of blown tire and spit it out from under the trailer at you. Many trailers run retreads and even some tractors do.

 

[Atari2600]

Normally I am driving in the left lane because I am going faster than the people in the right lane. On dozens of occasions I've had truckers turn into my lane less than 5 car lengths in right in front of me. This is a situation where they are following each other really close in the right lane. So either they often do not use their mirrors or they are assholes. Often they do not even signal.

 

[EVNation]

Normally I am driving in the left lane because I am going faster than the people in the right lane. On dozens of occasions I've had truckers turn into my lane less than 5 car lengths in right in front of me. This is a situation where they are following each other really close in the right lane. So either they often do not use their mirrors or they are assholes. Often they do not even signal.

Or the traffic spacing makes it difficult to get over and no one wants to let a truck merge in front of them, so they’ve learned that signaling means you’ll probably speed up to prevent them from getting in front of you. If a truck is signaling and you want to let them over, dip your headlights (better than flashing your high beams, but hard to do in a Tesla) to let them know their trailer is clear and you’re letting them in. Don’t be offended if they hesitate because truckers don’t trust 4 wheelers. And yes some truckers are a-holes.

 

[Atari2600]

Or the traffic spacing makes it difficult to get over and no one wants to let a truck merge in front of them, so they’ve learned that signaling means you’ll probably speed up to prevent them from getting in front of you. If a truck is signaling and you want to let them over, dip your headlights (better than flashing your high beams, but hard to do in a Tesla) to let them know their trailer is clear and you’re letting them in. Don’t be offended if they hesitate because truckers don’t trust 4 wheelers. And yes some truckers are a-holes.

99% of the time there is nobody behind me so that's not a valid situation (and that's what really makes me angry). If it were packed traffic yes.. but this is interstate driving through cow pasture land Ohio.

 

[S4WRXTTCS]

I always chuckle at people from CA commenting about how bad it is to draft. It's not that I disagree with them, but what they're saying is completely against how people in CA drive. They're all on top of each other one mistake away from a 20 car fender bender.

How they can comment, and then drive in the very reality that they're arguing against is beyond me. Unless they live in the more rural areas.

Personally I've seen pretty good efficiency improvements even from normal following distances. So if I need to increase efficiency I get a safe distance behind some large vehicle roughly doing the speed limit.

 

[EVNation]

99% of the time there is nobody behind me so that's not a valid situation (and that's what really makes me angry). If it were packed traffic yes.. but this is interstate driving through cow pasture land Ohio.

Could be just an a-hole, but a truck in the right lane in the middle of nowhere doesn’t usually move to the left lane for no reason. Consider this scenario, you’re catching up to a semi in the lane to your right, so your view of the shoulder and the lane ahead of the semi is obstructed by the truck. Up ahead the trucker sees debris in their lane or a stopped car on the shoulder, and wants to move over. You may never see whatever it is because the truck is blocking your view. A lot of midwestern states, including Ohio, have a “move over” law requiring one to change lanes if possible for a stopped vehicle on the shoulder, as well as emergency vehicles and road crews. Maybe there’s a deer. Or maybe the trucker is just an a-hole.

 

[Xenoilphobe]

First vid, those were just random debris. Some of those people were clouted after 5 secs, not much to do with tailgating. The 2nd vid, is a truck safety video. It says 200ft is the safe distance, so at least 1.5 sec gap at 82mph, or a setting of "3" on adaptive cruise.

The last vid of the cyclist is probably sprint training. The vehicle's trunk is open, or if a van, the doors are open, to create as big a draft as possible.

Interestingly, for cyclists, while you never want to crash, a bike can stop faster than the truck or bus, and even if you did hit the truck, being so close, the relative speed between the two is not that great, the bigger danger is the road rash from sliding on the road, post-crash, and potentially getting run over by a following vehicle. But, most following vehicles know not to follow insane cyclists.

Here's a tire gator for you..

 

[rdskill]

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 heard that only the cars with HW 3+ will get it

 

[MassPlay]

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