I'll plead again:
When you make assertions be clear about your assumptions and other conditions. Otherwise we just have a cacophony of garbage content in our threads.
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When you make assertions be clear about your assumptions and other conditions. Otherwise we just have a cacophony of garbage content in our threads.
I used to have an original Honda Insight. Drafting made about a 12mpg difference (60 vs 72 approx.) A benefit could be had a clearly safe distance.
I suspect most of us drive closer to the car in front of us than is needed for a benefit in congested conditions or just by habit. You really can be quite far back and see a gain. As an earlier poster said, if you are going to be behind a vehicle, might as well be behind the one that helps you.
1 to 2 car lengths is crazy.
I could crack my window and as I approached the semi, I would hear the air flow diminish/smooth. That is when I knew I was in the sweet spot, as far away as I could be and still see a benefit. Try it for yourself and see if you feel the distance is safe. I did.
I suspect most of us drive closer to the car in front of us than is needed for a benefit in congested conditions or just by habit. You really can be quite far back and see a gain. As an earlier poster said, if you are going to be behind a vehicle, might as well be behind the one that helps you.
1 to 2 car lengths is crazy.
I could crack my window and as I approached the semi, I would hear the air flow diminish/smooth. That is when I knew I was in the sweet spot, as far away as I could be and still see a benefit. Try it for yourself and see if you feel the distance is safe. I did.
Although I thought the Model S's braking distance is much shorter. From 60-0 it takes 85 125 ft and P85 113 ft. Source here: Performance Data for 85KWh and P85 KWh | Forums | Tesla Motors
I don't have data for the later models, but I remember seeing a youtube video on P85D that says it stops in less than 110 ft. Would love to see data for the current models, though.
green1
Active Member
A few things to keep in mind with your risk tolerance...
Braking distances are quoted from the time you hit the brakes until the vehicle stops, they do NOT include reaction time, which at highway speeds is substantial.
A semi truck may not be able to stop as fast as your MS, but it stopping normally isn't your problem, if the truck changes lanes or turns off suddenly, will you follow? if not you could find yourself staring at a stationary object that you couldn't see until it got out of the way (very common occurrence, and cause of MANY collisions). Also, if the truck drives over debris on the road, will you have room to swerve? (or worse, if something falls off the truck!)
All that said, I would probably be inclined to try "drafting" with TACC set to 1 behind a big rig on open highway, but no closer than that, and never in traffic or an area with many turn offs. You'd gain some advantage, with only limited risk.
Braking distances are quoted from the time you hit the brakes until the vehicle stops, they do NOT include reaction time, which at highway speeds is substantial.
A semi truck may not be able to stop as fast as your MS, but it stopping normally isn't your problem, if the truck changes lanes or turns off suddenly, will you follow? if not you could find yourself staring at a stationary object that you couldn't see until it got out of the way (very common occurrence, and cause of MANY collisions). Also, if the truck drives over debris on the road, will you have room to swerve? (or worse, if something falls off the truck!)
All that said, I would probably be inclined to try "drafting" with TACC set to 1 behind a big rig on open highway, but no closer than that, and never in traffic or an area with many turn offs. You'd gain some advantage, with only limited risk.
Motor Trend tested the P85D and reported a 60-0 stopping distance of 113 feet, the same as the P85 number you listed above.
Carspotter Daily
Tesla > ICE
I don't think that that info is correct.... My AEB kicked in at highway speeds, not stopping in time and hitting the car ahead. I was about 3 car lengths away from the person in front... Even the AEB didn't stop me in time. Keep in mind, if you do draft, the curb weight of your car is 5000 lbs! I don't think it's safe to draft at any speed. Matter of opinion I guess.
green1
Active Member
Not opinion, scientific fact...
As for AEB, nowhere does anyone related to tesla claim that AEB will avoid any collision, only that it will reduce the impact. don't count on it to stop you.
Carspotter Daily
Tesla > ICE
Sorry, i put that the wrong way... At first the AEB kicked in, slowing the car earlier than I could press the pedal, the rest of the way I was braking. And it still didn't stop in 113 or 125 ft. I'd say it took at least 150ft to completely stop and that was with the help of the car in front of me.
green1
Active Member
Sounds like AEB worked exactly as advertised, it reduced the impact of a collision that was already unavoidable.
I'm not sure what your objection to the 113 feet measurement is. 3 car lengths is about 45 feet. For AEB to stop without hitting a stationary object, it would need to start braking at about 8 car lengths.
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Ah, you provided more information before I finished my reply. 113 feet is presumably the result of testing on dry, even and smooth asphalt. On uneven roads, with deposited oil from other vehicles or any other surface imperfections, you might well experience somewhat worse braking performance. 150 feet is a bit more of a drop-off than I'd expect with the brakes in full anti-lock mode, but perhaps the road surface was poor or your tires were not in perfect shape or there were some other factors at play. Its still a pretty good bet that a semi travelling at the same speed would have required much more distance to stop.
green1
Active Member
Only if you make the assumption that it's upright, travelling in a straight line, and trying to stop.
As mentioned previously, the biggest risk isn't that the truck stops, it's that it moves out of your path to reveal a stationary obstacle ahead, by that point you will never be able to avoid that collision.
1. Bear in mind that the actual difference will depend on the aerodynamics of the car. I suspect Mythbusters used a car with "average" aerodynamics.
2. You could also slow down two or three mph. This would give the same benefit as drafting at a safe distance, and be far less likely to get a rock through the windshield.
FlatSix911
Porsche 918 Hybrid
At a following distance of 2 feet you might as well use a tow strap and put the car in neutral ... Infinite mileage!
I think the percentages would still scale roughly. And a 15% improvement is huge in the Tesla. What I found interesting was that if you close to less than five feet, the feathering of the accelerator actually causes you to start heading down the other side of the efficiency bell curve.
At a following distance of 2 feet you might as well use a tow strap and put the car in neutral ... Infinite mileage!
No neutral. Let the car think it is going down a hill and regen. Get a free charge !
No, then the truck driver might feel he was pulling extra weight. Believe it or not, I've actually thought about this. By rigging up a bumper/boom type system that extends off the front, you could use those magnets at the top of security doors. They work on a 24v electromagnet system that could attach your apparatus to the rear bumper of the semi at the flip of a switch. And those units are rated for around 500-600lbs of pull force so in the case of you slamming on the brakes, you could easily detach, but if you had it in neutral, you could coast along just fine.
green1
Active Member
Having witnessed a truck blowout in front of me a week or so ago, I'll say please don't do this. Truck tire blowouts are incredibly dangerous. Search youtube for "tire explosion" or "tire blowout" if you want to see.
I was in the on the interstate, light traffic, with a tractor-trailer about 0.2 mi ahead. His tire let go, without warning, with a big cloud of smoke and a bang I could hear down the road. I was slowing down to avoid the random debris, when a couple feet of tire tread dropped from the sky about 100 feet in front of me. When the tread unwound from the tire, it flung almost straight up in the air.
I remember a story years back about a truck's dock plate (the 1/4" thick steel plate they use to bridge the gap between the truck and the loading dock) coming loose and going through the windshield of the car behind, killing the driver instantly.
Just say no. Is achieving a personal best Wh/mi really worth it?
I was in the on the interstate, light traffic, with a tractor-trailer about 0.2 mi ahead. His tire let go, without warning, with a big cloud of smoke and a bang I could hear down the road. I was slowing down to avoid the random debris, when a couple feet of tire tread dropped from the sky about 100 feet in front of me. When the tread unwound from the tire, it flung almost straight up in the air.
I remember a story years back about a truck's dock plate (the 1/4" thick steel plate they use to bridge the gap between the truck and the loading dock) coming loose and going through the windshield of the car behind, killing the driver instantly.
Just say no. Is achieving a personal best Wh/mi really worth it?
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