Mythbusters : Drafting video

[Old Tele man]

...what are you asking for? a "Smart Highway" from our government...sounds like a "motoring oxymoron" to me!

[msirach]

Originally Posted by Bicycle Bob

There is almost no danger driving 2' behind another vehicle, except for the cosmetics on the bumpers. Even if the lead vehicle slams on their brakes, the relative speed at impact is under 8 MPH. Pilots flying in really close formation know this.

A

You have made a VERY dangerous statement. There is a BIG difference in Nascar drivers and the public drafting. Nascar drivers are trained drivers and all the drivers use the same method.

Drafting a semi as close as 2' in a car is VERY dangerous. Vehicle mass and stopping distances are two factors very different from NASCAR.


Drafting is a dangerous practice that is not recommended. There are many other more safe ways to achieve great mileage.

[tasdrouille]

I'd just like to point out that stopping distances for cars are shorter than semis. So that just leaves reaction time as a factor. The reason I don't do it is flying road gators.

Ratio of Speed to Stopping Distance
Oregon Trucking Associations: Stopping Distances For Cars vs. Trucks

[Old Mechanic]

I think the best compromise is to draft when an opportunity arises.

Example:

On I64 yesterday the traffic was heavy. Many vehicles including big rigs were tailgating at 1 car length at 60 MPH.

I usually stay in the right lane and look for a 3 stripe cushion behind a large vehicle, preferably one with the undercarriage close to the ground.

It also sends a message to aggressive drivers that I am not interested in the left lane antics that are very dangerous. Most sane drivers will not try to pass on the right using my 150 foot cushion of distance, even when it is at least 5 times the average distance between vehicles.

Staying in the right lane with a 125 to 150 foot separation distance gives me the chance to stop completely in that cushion distance or swerve right to the shoulder if a large object is in the road.

It does require a greater level of concentration that driving on a deserted highway, but nothing compared to the level of concentration the aggressive tailgaters need to apply to their stupidity.

I would much prefer no drafting and a relaxed drive, but in some circumstances here it is just not a possibility, unless you want to feel like a doormat as people blast by you with 3 feet of clearance to pass, on the right, someone in the left lane. It's highly illegal but seldom enforced here.

regards
Mech

[jamesqf]

On the other hand, driving on typical Northern California freeways (and I suppose elsewhere), you can't possibly avoid drafting. Maybe not at 2 feet, but if you leave much more than a car length following distance from the vehicle ahead, someone is sure to cut in. So you might as well find a semi to follow...

[blueflame]

Some days everyone was drafting except me, the only hypermiler and ecomodder doing it slowly on my own.

So I decided to learn to draft properly and with more safety. Which was good as I was driving a slow diesel van with the aero's of a brick, and drafting really helps high CDa vehicles.

Side drafting is easy and safe. Sometimes in the middle of three lanes you get cars on both sides helping. Quite a technical skill as cornering on the extreme inside line(to reduce distances traveled), cross winds, leading vehicle shapes, beside road hillsides and windblocks, have to be constantly calculated.

Rear drafting at a good distance is perfectly safe and is better than no drafting at all.

Drafting at the right time begs consideration, especially in underpowered vehicles like Japanese diesel vans. If I was climbing a freeway hill and its going to be a strong headwind near the top, I would look for a lead vehicle prior to the accent which would allow the climb without needing to change down or reduce speed. Was a very courteous thing to do for other motorists who would have been inconvenienced by my slow van.

When boating I would always look for a wake to surf, or an island to get leeward of.

Doing a night drive Wellington to Auckland when gas was expensive, around 3am I saw 15 or so big rigs all drafting each other at around 65mph. Probably saved a stack of money. Really dangerous.

Dolphins draft up front, so the lead does benefit too

[aerohead]

I think that the 1/24-scale windtunnel models were operating below critical Reynolds Number,so those numbers could be a little squirrely.--------- In full-scale,and without the "throttle feathering" they might have seen a full 50% improvement,which would agree with Kelly and Holcombe's research,constituting a 100% drag reduction.--------- And I'm with Bicycle Bob on the safety aspect at 2-foot clearance.Should the 18-wheeler jam the brake pedal,inertial effects would still allow for a soft kiss since they're starting at identical velocity.If they were touching it would be the safest.( test course driving,not the real world ).

[Old Tele man]

...yeah, it's only those pesky "sudden" stops that get you!

[Frank Lee]

Still, I was not interested in "kissing" that trailer on a bike!

[Bicycle Bob]

Good plan. When bike racers are drafting closely, and wheels touch, the back rider goes down. There's no bumper, and they fall over if steered by a tow vehicle, or other contact.

With cars and trucks, as drafting distance decreases, the chance of collision keeps going up. However, when very close, the severity of the collision begins decreasing to zero, if the bumpers match.