Tailgating a lorry/semi (modelled in CFD)

[Vekke]

Yes I agree with daox. It does not matter how the truck driver drives unless you are not able to predict his behaviour. Faster he goes more you will save in time. You just need to start learning how to use push and glide effectively behind a semi while still maintaining the safety distances. I have made some videos how I do it if I am trying to get best fuel consumtion figures.

Last simulation is not looking so nice than the first ones. I tried to find similar simulations that would so the wake as long but had no luck.

[sendler]

Mythbusters proved drafting saves gas empirically. There are big gains to be had as far back as 100 feet which is starting to get pretty safe as you can then also see all the way up and under the front bumper of the truck. Too bad they didn't do a couple more runs at greater distances to find the edge of the effect.

[Vekke]

Best I could find.

[Ardent]

Originally Posted by UFO

. . . On a drag strip, you are looking for that light to drop and the best anyone can do is 0.4 seconds to start. . . .

That 0.400 seconds does include human reaction time, the vehicle's mechanical reaction time, and also the time to transit the roll-out distance (allowing the beam broken by the front tires while staging to be reconnected ).

Alert (key word alert) human reaction times are common in the 0.170 to 0.180 second range. However, going beyond the binary stop/go decision to the processing and decision making of whether one is dealing with a superfluous brake tap, normal to moderate slowing, or heavy emergency braking can add significantly to the total time involved.

While the likelihood of contact increases (exponentially?) with closer following distances, the impact velocity decreases, since the velocity of the leading vehicle has had less time to change.

[UFO]

Originally Posted by sendler

Mythbusters proved drafting saves gas empirically. There are big gains to be had as far back as 100 feet which is starting to get pretty safe as you can then also see all the way up and under the front bumper of the truck. Too bad they didn't do a couple more runs at greater distances to find the edge of the effect.

At 100 feet you only have 1 second to make a decision; that is not even close to "safe".

[sendler]

Originally Posted by UFO

At 100 feet you only have 1 second to make a decision; that is not even close to "safe".

It's been pretty safe for me for the last 300,000 miles.

[UFO]

Originally Posted by sendler

It's been pretty safe for me for the last 300,000 miles.

Right. You have 300k miles logged at 100' off a semi truck. I hope your insurance premiums are paid up. Forgive me if I don't believe you.

[sendler]

Originally Posted by UFO

Right. You have 300k miles logged at 100' off a semi truck. I hope your insurance premiums are paid up. Forgive me if I don't believe you.

22 years. 80 miles per day. 23,000 per year. 80% highway. Same commute. What's not to believe?
Big city freeway traffic considers 30 feet at 75mph to be normal. 30-40 meters behind a tractor trailer is not really as unnatural as it sounds on paper. If traffic volume is packing both lanes, this distance seems quite normal at that point and impatient drivers will be diving into any gap bigger than that so why not continue to do it when the road is clear. Very safe. Much safer than leading out the open road on your own. Anything bad that can happen such as an animal running out into the road, will happen to him. How long is a semi rig? you are actually 80 meters behind the driver. If he sees something and reacts it is as if you are following a car at 80 meters. And, truckers can see much better than cars in bad weather. This another reason to adopt one as blocker/ guardian angle. Your own lights are also amplified in bad weather as they bounce off of the back of the truck to light up the scene in front of you like day. I only half jokingly envision the day when the energy police will give you a ticket for not drafting. "Hey! What's wrong with you. Get up there and fill in that gap before I give you a ticket".

[Georgboy]

I have done the follow super close and you can actually feel the cushion when you get in the sweet spot.... That being said I am a truck driver and I know of the headache of having to stop and a drug test and so on and so on... Do it only late at night and on the interstate is my recommendation. Just put a cb in your car like me and let the guy know what you're doing, if the truck driver is cool with it then go for it ..

[UFO]

Originally Posted by sendler

22 years. 80 miles per day. 23,000 per year. 80% highway. Same commute. What's not to believe?

That you drafted semis with 1 second reaction time for 300k miles and had no incidents. Your claim is rhetorical at best.

Originally Posted by sendler

Big city freeway traffic considers 30 feet at 75mph to be normal. 30-40 meters behind a tractor trailer is not really as unnatural as it sounds on paper. If traffic volume is packing both lanes, this distance seems quite normal at that point and impatient drivers will be diving into any gap bigger than that so why not continue to do it when the road is clear. Very safe. Much safer than leading out the open road on your own. Anything bad that can happen such as an animal running out into the road, will happen to him. How long is a semi rig? you are actually 80 meters behind the driver. If he sees something and reacts it is as if you are following a car at 80 meters. And, truckers can see much better than cars in bad weather. This another reason to adopt one as blocker/ guardian angle. Your own lights are also amplified in bad weather as they bounce off of the back of the truck to light up the scene in front of you like day. I only half jokingly envision the day when the energy police will give you a ticket for not drafting. "Hey! What's wrong with you. Get up there and fill in that gap before I give you a ticket".

Traffic volume is irrelevant and not an excuse to follow at an unsafe distance. Timing your following distance to 2 seconds minimum is a good rule of thumb, and is safe for an alert driver. Then it does not matter whether the semi brakes or drops a load, you have time to stop or avoid. Following closer than 2 seconds is dangerous, and is often cited the root cause of pileups. Joke all you want, drafting is far less safe than not.