Drafting 18-wheelers....revisited

[landspeed]

I would also disagree with the parasitic draft theory - and I also note that lorries (semis) in the UK draft each other a lot - often less than 1 car length between the truck behind and the one in front!.

In this case, the truck behind is 'pushing' the vacuum of the truck in front, meaning that the truck in front gets a lot less drag at the back!. The truck behind gets less frontal drag, but identical rear drag. With a car behind, it is just less extreme but the same idea.

It is true that staying back does still improve MPG - an easy test is just to put your hand out of your window a bit. You can feel the point where the wind blowing your hands slows down - that is the start of the drafting zone - and it starts several car lengths behind the truck!

[Bill in Houston]

Drafting them improves their drag coefficient. They just don't like you sitting behind them, just like most people driving any old car would not want you sitting behing them... If you stay a decent distance back they won't care too much and you can still get a mileage boost.

[VetteOwner]

Originally Posted by Bill in Houston

Drafting them improves their drag coefficient. They just don't like you sitting behind them, just like most people driving any old car would not want you sitting behing them... If you stay a decent distance back they won't care too much and you can still get a mileage boost.

yes as an owner of an old car it pisses me the hell off that people will pass me by getting 4 feet from my bumper then whipping around me.or when they stop at red lights their so close i cant see thier headlights anymore.(which is within 2feet)

but yea truckers like to know where everyone is thats around them. since they have HUGE blind zones they have to relaly pay attention to whos near them and if thier drivign along at 65 and can just barely see your side mirror in thier mirror thier prolly getting a bit paranoid.but if your a tiny car ridign thier butt they probably figured out that your just tryign to draft them. i was doing this once and a semi swerved a few times either trying to see me or trying to get me away from him.

[JanGeo]

Apparently the blind spot ends about 300 feet behind the box but the roads around here are curvy enough that you can't get directly behind them unless really close. If I draft I alway stick out to their side so they can see me and keep pretty far back anyway - plus I watch the road ahead and behind me so I know when they need to change lanes and keep in sight when that happens. If they pass me and need to pull back in I also flash my brights when it is clear for them to pull back in - they really appreciate that and usually flash their running lights in reply. Gonna have to bring my 2-way radio on my next trip to have ears on to see if they actually talk on the radio while they drive.

[bzipitidoo]

On one trip on I35, my engine developed troubles. One of the cylinders went bad. Only a 4 cyl engine, too. Drafting was the only way I could stay with the traffic. Otherwise, I didn't have the power to do the safe thing which is go about the same speed as everyone else. Whenever I lost one truck, was a short wait for another truck to pass me, and then pull in behind. Only time I've really noticed how much drafting helps. Without the assist, best the car could do was about 10 to 15 mph slower than the traffic.

Well, I suppose the really safe thing to have done was get off the road and get the car fixed or buy a new one. What price safety? But I made it. When I got home, went to work on the car and found one of the cylinders had a hole in the top!

[slurp812]

Originally Posted by bzipitidoo

When I got home, went to work on the car and found one of the cylinders had a hole in the top!

Thats running a bit too lean!

[psyshack]

Truckers dont like it when you do a close in draft. And it can be quite scary. When you pull the car thru there wake and your only a few feet from the rear of the trailer,,, its mpg heaven.

So if I want to draft say on a day with a headwind. I will stay behind there wake in a distance draft. A small low pressure area develops in this area. I find this area by easing up to the wake. The car start buffeting. At that point I ease out of the wake about half a car length. Really helps with these okie winds that alway seem to be a headwind,, dag nabit.

[Hockey4mnhs]

i just get close sheesh

[BumblingB]

I think VetteOwner summed it up perfect as they have a blindspot. They do still know you're back there, but also consider what they kick up onto your car. What if they have a blowout? Something that is a commonplace for a truck driver. I've got a CDL but maybe 10,000 mile at most of wheel time as it isn't what I do everyday and I've still had 2 blowouts - I'm fanatical about tire care on a 18 wheeler. The people that worked for me back when I drove more regular had MANY more blowouts simply because they didn't take the same precautions. One day you might be behind one of those people.

I did once have a trucker happy to allow me to draft. I was on my motorcycle in TX driving from Tyler to Abilene. I drafted a truck from Ft.Worth all the way into Abilene due to a serious head/cross wind (45+knots). He let me draft and was doing a cool 55mph anyway. When I took my exit he even waved with all five finger - no fist or single finger.

As far as them being jealous - Bullhockey!! I don't believe that one for a moment.

[VetteOwner]

i flashed my lgihts once but he had his signal on and it was raining. i guess from all the spray from his wheels he couldnt judge distances so i flashed my lgihts and he moved over. gave me a nice wave when i passed him a few miles later.

yea ive been near a truck that had a blow out. it was the scaryest thing ever. just driving along half in a daze then all of a sudden a shotgun blast noise came from in front of me and chunks of tire started flying everywhere.