Benefits of drafting.
 

Today I had a trip over to the south side of Edinburgh. Being a Sunday morning, the roads were reasonably quiet. I managed to get in behind a couple of HGVs at parts of my return journey (careful to keep a safe distance back), which helped push the air aside.
Here is the information for today's trip, as computed by my ScanGauge E:
65.1 mpg (UK)
54.2 mpg (US)
4.34 Litres/100km
Max coolant temp: 84°C
Distance travelled: 86.7 miles
Maximum revs: 2957 rpm
Max speed: 56 mph
Average speed: 35 mph

A nice Average mpg. Pretty pleased about that.

IN the US roads have 13 stripes per 528 feet (.1 mile). I find that 3 stripes separation (close to stopping distance) at 70 MPH gives me about the same MPG as 55 MPH with no drafting opportunity. I prefer to drive the 55 MPH routes but sometimes there is a necessity to get there quickly. The Interstate here is 70 MPH going west, but the traffic is heavy almost always. There are spots where the average lane sees a car a second pass over the same spot (86,400 every 24 hours) on occasion. That's traffic density where it is very difficult to maintain even the speed limit.

A big truck, travelling at 56 mph makes a much bigger hole in the air than one travelling at 40 mph. I found that today, through the mandatory 40 zone on the new bridge.
We are advised to leave 2 seconds between vehicles (Only a fool breaks the two second rule).
Goods vehicles, in Scotland, are restricted to 40 mph on single carriageways (two lane), 50 mph on dual carriageways and 60 mph on motorways. Trucks are fitted with speed limiters set to 56 mph. So if you sit in the lane the trucks are using there is no need to speed.
Most trucks seem to sit on the limiter, when road and traffic allows, irrespective of the actual legal limit.

At 70mph, including reaction time to a surprise event, I'd think 4 stripes would be more likely the minimum stopping distance. Three might work for 60mph. I usually follow at least 7 or 8 stripes back at 60mph or above. The little bit of fuel savings isn't worth the potential little bit of dead being close enough to benefit might entail. EEMMV

Drafting behind a truck to gain a few miles per gallon is throwing the dice for very little gain.

Not if you leave a safe distance between you and the truck. Sitting right on his rear bumper is stupid but sitting 50 - 60 yards behind him still gives an aero advantage with plenty of time to stop if he does. Biggest issue I have is other motorists pulling into the gap I have left.

Drive my roads here for 50 years. 3 stripes is a luxury when traffic is heavy. At times you won't see 3 stripes between a single vehicle out of 100 cars chosen at random. Add another stripe and some other drive pulls over 20 feet in front of you, which is half of ONE stripes distance.

I have never had an accident where my distance behind the car in front of me was an issue. Try the DC beltway, or Atlanta, LA, Jacksonville Florida, New York City, Detroit or any other major metropolitan area. I pick the spot and lane so I have an escape route to the right, only on Interstates. The only through roads here are east to west or reverse. Stand next to the entrance of the Hampton Roads Bridge tunnel and count the car per second for one 86,400 second day. then preach to me how to drive in that traffic for 50 years without a single incident.

I don't allow any outside distractions when I am in that driving scenario. Sure I prefer the less traveled routes, but at times it is not an option. Want more separation, go ahead, then look in your mirror and there is an 18 wheeler 20 feet from your rear bumper. It's called the corridor effect.

I'm with Airstreamer67. Regardless of how much fuel you might save, "following too closely" is an offense where I live. Aside from that, it's dangerous on public roads (i.e., off a race track, amongst other trained racers). To put it in simple terms, when sh*t happens and the vehicle you're tailgating stops suddenly, you end up with your face in his ***. Very undignified. There are lots of Car Crash Videos on YouTube with dash-cams that have caught exactly this scenario.

Another scenario -- also caught abundantly by dash-cams -- is the driver in front of you suddenly swerves to avoid an obstacle (like a stopped vehicle), and you (tailgater) have insufficient time to react, so you end up driving right into the obstacle. Again, it's highly undignified to participate in such easily avoidable, driver-induced collisions, whose risks are amply covered in Driver's Ed 101: See far enough ahead for your speed to be able to easily (1) Identify and assess risks, (2) plan an avoidance or mitigation strategy, (3) have the time to react when risk becomes hazard, (4) get your wits about you, and (5) execute your plan flawlessly.

When you're tailgating a rig, you're flying blind and hoping for the best. I strongly recommend against that, regardless of you fuel economy benefits. I'm pretty sure the police would agree.

It's drafting if you are a NASCAR or other racing driver. It's tailgating if you are on a public road. And it may work great for who knows how long but it's like the kid who eventually says "Yeah, but I didn't break my leg the first 834 times I jumped off the roof.".

Where have I ever said I follow closely? I always leave a good safe gap between myself and the vehicle in front. The same for a truck as a car. I also position myself so that the trucker can see me in his mirrors, switching sides to give myself the best view ahead. I sit well over two seconds behind the vehicle I am following (recommended minimum safe distance as per UK Highways Authority). 50 - 60 yards behind a large HGV, travelling at 50 mph, gives me perfectly adequate room to stop as well as an aero advantage. Sure, I could get better mpg sitting right on his tail, but I want to live a lot longer. I have 50 years driving experience and I would like survive for at least another 20.

No point trying to get R.I.D.E to understand, he's too old and stubborn. Most of us are kind of bored of his rude, arrogant, niave, know it all "I've been driving like this for 10,000 years so I know better than anyone and I'm always right and you're always wrong" attitude, but he's entitled to be a douchebag if he so wishes.

You don't have to be tailgating to gain the benefits of drafting. Following someone at the safe and legal distance takes less effort to push the air out of the way than being in front of them.

I guess some people are to stupid to understand traffic. Check the HRBT entrance where a car passes the same point every SECOND during summer. Just check it at 5 PM then come back and preach to me about drafting.

YOU HAVE NO CHOICE and if your are to ignorant or stupid to understand that then it's on you.

JockoT, as a comparison, what numbers do you post when NOT drafting?

At 50 mph, on my own, on a flat section of dual carriageway, my ScanGauge will show an Instantaneous mpg of 43 - 46 mpg.
At the same speed, 50 - 60 yards behind a large HGV (semi-trailer), and I can see 55 - 65 mpg, depending on prevailing wind direction (best improvement into a head wind).

That's about the same number I observe Jocko T. I would be much happier if the roads here were deserted and actively pursue roads that are "less traveled". If you watched the video and are even capable of understanding that some people have to live in that environment then you might understand that it is possible to get great mileage even in the worst of scenarios, maybe not driving a cab in New York City.

Just coasting in neutral in crawling traffic, say 15 mph, it's possible to get 50+ mpg. My ultragauge shows 3-400 coasting at 50 mph, just push the clutch in and you're there.
I can double that mileage if I want to average 20 mph on a deserted road.

Want to argue 4 seconds versus 3, that's YOUR prerogative, my techniques have been honed to perfection, right lane always allows escape rout right. Big rigs here mean people pass them before climbing up there arse. That gives you an advantage just staying in the right lane behind one and keeping alert for whatever may come, prepared to instantly swerve right.

Of course there are those here who can barely navigate a two lane road with oncoming traffic. Now that is dangerous, when the nitwit, on the hand held device, drifts over into your lane at 100 mph combined.

I have stopped, blown my horn and flashed my lights to keep that nitwit from slamming into me at 50 mph, or run into the ditch 18 inches from the edge of the road, wreck you car and the nitwit just drives past you, oblivious to their surroundings.

I always follow HGVs in the LH lane (same reason you use the RH lane). I only draft on a dual carriageway or motorway. Never on a two lane. Too much to go wrong on a two lane. Plus it gives fast drivers the chance to pass me, then pass the HGV when an opportunity arises.
I was drafting a HGV today when two cars pushed straight in from an on ramp and squeezed in between me and the HGV. Nutters.

The truck drivers here are professionals as I am sure they are there. Even the total Morons in their jacked up crap crabbing down the road and tires that would make you deaf in 5 years or less, have enough sense to not mess with 18 wheelers. Seen one Chevy Citation that cut off a big rig. The truck rolled him sideways, under the front bumper, and pulled over into the median continuing on tow hundred yards, like a pavement roller truck, except the Citation was the roller. The driver died that day, call it culling the herd.

The amount of ignorance I see in the average motorist while driving my rig would probably make some of you give up on humanity. I say ignorance because there's no shame in that; motorists really aren't taught at all how to deal with trucks. Until I started piloting one, I never knew just how much I wasn't taught.

I can second that sentiment. I was a bus and coach driver for a spell, fairly recently, and the average motorist does not give a thought for the difficulties experienced by drivers of large and relatively heavy vehicles, in today's busy traffic.

If you observed the traffic cameras linked earlier, the single exception to the lack of 3 stripes separation is behind an 18 wheeler. It's why I like to tuck in behind them and it's the only place you have the luxury of decent separation. If a car every second passes over the same spot at 55 mph the math (never lies) is 1.47 X 55 feet AVERAGE SEPARATION. Lets say about 82 feet, but that INCLUDES THE VEHICLE.

Now were talking about 50-70 feet. Each stripe in the US is right at 43 feet. Maybe with that math facing you even the most ignorant (no name) should realize that 3 stripes, about 129 feet, is a luxury and in many places where I have driven, the average separation is even worse. If you think not then check out the many areas on the eastern US coast with traffic cameras. VDOT has them all around DC and I have lived and worked there. Used to do route 123, Chain Bridge road, from Tysons Corner to Glebe road in Arlington avoiding the Interstate altogether. 35 mph perfectly timed traffic lights, in my 84 CRX it was good for 50 mpg (averaged 44 for 50k miles) 35 years ago. watching the bumper to bumper crawling traffic on the Interstates going in and out of Washington DC. The Mercedes dealership (still remember the address and phone number) had the customers park on the ROOF of the building. Property values were way to high for ground level parking lots, even for Mercedes Benz customers.

I have always loved driving, still do, but rules and regulations are subservient to survival. A cop once told me that I had to legally sit at an intersection and wait for the idiot to plow into my rear end, at a red light, when i saw it coming. I replied, "That's assault with a deadly weapon, and I have every right to do ANYTHING to defend myself." I do fine explaining that to the judge and have pulled into an intersection when the light was red to keep from getting rear ended on numerous occasions. Once in a 59 Corvette I pulled over into the median and the driver thanked me for my action that prevented HIM from slamming into my rear end. I had enough distance from the car in front of me to pull over, situational awareness and preparation saved me from potential incineration as had happened to an identical Corvette a couple of weeks earlier to a woman, who was fried alive. In another instance I was being tailgated and pulled over into the right lane when the 68 GTO slammed on brakes in front of me (fresh brake job, mechanic road testing the car). The right lane was clear. The Chevelle behind me slammed into the GTO. They found the Chevelle drivers baby under the dash of the car, no child safety seats or 911 back then. I called the police from the nearest business location and waited for the police and ambulance to arrive.

Drafting behind trucks while riding 450cc motorcycles is..... interesting. As you move closer at a certain point, you pick up the buffeting. At you move closer yet, you feel the airflow shedding from either side of the truck in alternating time. The rhythm of the alternating waves of air, rock you left or right. At the same time, your hand has to reduce throttle because low air pressure is beginning to suck you towards the truck. If you get even closer, you are now in front of the alternating shedding airflows & are in a zone of steady air. You really have to reduce cycle throttle, or it would suck you right into the back end of the truck. If you do this for long hours of driving, you're asking to be killed if the truck brakes, or runs over any debris on the road or a truck tire blows out, or lots of other things!
Anyhow, the only following truck, you can reduce your chances of dying in hard braking situations, is behind single axle trucks with smaller front wheels. Their 60mph to 0mph braking distances are longer than tractor trailer trucks.

I remember an internet image of a bike rider with his head implanted in the rear door of the trailer, hanging there dead. Seldom do I bike on the freeways here but never close behind a truck, but you sure get a good feel for the effects of distance behind a truck and the aero drag reduction. I think a good bicyclist has reached speeds of over 80 MPH in a controlled experiment where he pedaled just behind a vehicle with a purpose build wind deflector.

I've had a truck toss a 2 pound rock into the windshield of a car I was test driving, GOING IN THE OPPOSITE DIRECTION on a two lane road. I always stay to the right side, of the right lane on freeways, but close enough to avoid having another car pull over between us although some still do that since in many cases it's the largest gap between vehicles in a mile of roadway.

167 mph at Bonneville Salt Flats, behind a dragster!

Was dat w/brakes on so he wouldn't be sucked into the rear of the dragster? ha ha ha :whistling:

Oh, on my motorcycle, drafting was the last thing I wanted to do....