I read about drafting behind trucks and other large vehicles to improve mpg. How close to the truck is the appropriate zone for max mpg. When I ride the motorcyle behind trucks I get a lot of side to side turbulence at about one truck length back: that can't be good for mpg.

So, is there an optimum distance behind a truck to draft?

Mike

 

Surely you jest.

Yes, close drafting can get as much as a 50% increase in fuel economy. That close behind an 18-wheeler and you are likely to miss exits if you either don't know the route by heart or have a Nav, not to mention the safety risks.

www.cleanmpg.com has gone on the record to discourge this practice.

 

Max Fe would be bumper to bumper and that would be insane. BUT there are effects as far back as 10 car lengths.

 

I've heard 2-3 seconds and I never get closer than the distance between power poles. I'm not drafting as much as using the truck as a 'pace car' so I'm not seen as 'holding up traffic.'

I look for trucks that hold to 65 mph by corporate policy, state law or heavy load, and follow them at a safe distance. Traffic behind me will see the truck and pass without a thought. Meanwhile, I'm in my speed sweet-spot for mileage.

The only risk, and it is a real risk, is a truck tire can toss up a pebble that could crack your windshield or chip paint. But at a safe following distance, you can steer around any road debre.

Bob Wilson

 

I drafted a truck for about 30 miles this summer. I had just filled up and had less than 2 miles on the new tank when I pulled onto the highway and fell in behind an 18 wheeler doing between 70-75mph. I sat about 1 car length (12-16ft) behind him. I was close enough that he had no idea that I was back there.

When he finally pulled off at an exit I was showing 62.2 mpg. I normally get about 51 at 60-65 mph.

Certainly wasn't safe, and I wouldn't recommend it, but I was bored and it gave me something to do. You really have to pay attention while drafting. Your reaction time is decreased dramatically.

 

I was at 101 miles per hour last weekend getting about 22 MPG. But that doesn't mean I recommend it. In this case, a better answer is to look at:

1) radar assisted cruise control - this ensures the following distance is maintained using radar or other sensor, computer controlled operation.

2) work for 'smart car transponder systems' - to establish laws and regulations so properly equipped and maintained cars can form their own 'trains' on public roads. But this means addressing some interesting engineering issues.

My excursion to 101 miles per hour was long enough to verify it was 'stable' and then I backed off. I needed the data to understand that end of the performance scale and I have no need to repeat the experiment, ever.

If someone else needs a copy of the data, send me a PM and we'll work out the logistics.

Bob Wilson

 

This is your lucky day! I watched this test on the TV program, Mythbusters. Here are the results:

Mike Ryan, Hollywood stunt driver, was there to educate Grant on the ins and outs of drafting. Also on-hand was Andrew Smith, test engineer, who helped them hook up a computer to the fuel injection system to accurately measure the fuel consumption.

55mph control: 32mpg
100ft: 35.5mpg, 11% improvement
50ft: 38.5mpg, 20%
20ft: 40.5mpg, 27%
10ft: 44.5mpg, 39%
2ft: 41mpg, 29%


The fall off at 2 ft was thought to result from the difficulty of trying keep so close without running into the truck.

Check it out: kwc.org/mythbusters/2007/06/episode_80_big_rig_myths.html

Oh, by the way, this episode also found that an exploding truck tire can decapitate a, person.

 

I think that standard highway lane line 'dashes' are on 40 foot intervals, but an official document on this does not readily spring to hand. This might help the daring, as an alternative to counting seconds, etc.

My only safety suggestion is NOT AT NIGHT! Seeing (only at the last moment) truck-tire fragments fly up and over my car is an experience I'd rather not repeat.

DAS

 

Drafting can have strange results. I've only drafted for a long trip once with good results, from Hartford - Danbury. 79 miles trip, kept about 70-80 feet behind a SWIFT rig. He didn't seem to mind, he could see me I'm sure because I could see his mirrors while going throgh turns. I had a trip of 62 mpg after that. I was pretty amazed considering I had to break 3k RPM's to keep up on hills and even downhills since he broke 85 on the downhill.

Although I would advice to not draft at night. Trucks seem to get annoyed, and either speed up, slow down, or put on flashers and pull over. I assume their worried about a drunk driver following a big target.

 

A Car & Driver editor in early 2000 was challenged to get a Honda Insight over 100mpg...he was allowed to do anything, so he did it. Over 100 miles he cruised at 58mph inches behind a Ford Explorer with plywood to effectively make it like drafting behind an 18-wheeler....probably better as the plywood went lower. They were communicating by cell phone as they were inches apart - not for the faint-hearted. Undrafted, I would get about 75mpg at 58mph - he got 121mpg.

A more legit way of breaking 100mpg, would have been driving the Insight on an isolated two lane road at 40-45mph, undrafted...still not typical driving, but more legitimate than close drafting.