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Old 10-15-2017, 08:30 AM   #1
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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: 84C
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.
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Old 10-15-2017, 09:19 AM   #2
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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.
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Old 10-15-2017, 09:44 AM   #3
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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.
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Old 10-15-2017, 10:01 AM   #4
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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
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Old 10-18-2017, 04:41 PM   #5
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Drafting behind a truck to gain a few miles per gallon is throwing the dice for very little gain.
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Old 10-18-2017, 11:03 PM   #6
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Originally Posted by Airstreamer67 View Post
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.
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Old 10-19-2017, 04:54 AM   #7
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Originally Posted by Airstreamer67 View Post
Drafting behind a truck to gain a few miles per gallon is throwing the dice for very little gain.
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.
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Old 10-19-2017, 08:49 AM   #8
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Originally Posted by Airstreamer67 View Post
Drafting behind a truck to gain a few miles per gallon is throwing the dice for very little gain.
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.
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Old 10-19-2017, 08:54 AM   #9
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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.".
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Old 10-19-2017, 11:53 AM   #10
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I'm with Airstreamer67. Regardless of how much fuel you might save, "following too closely" is an offense where I live.
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.
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