Semi-drafting

[Bill in Houston]

They might believe that it costs them mileage, but it doesn't. I'm not saying that they don't believe it... :-)

[Wyldesoul]

I was prone to believe it, though. Because when you draft behind a truck on a bike, you can actually let off the "gas" completely, and just be pulled forward by the wind at your back, and none in front. Even in minor acceleration. I've read a lot about that being done

Now, something HAS to provide the power to keep your bike moving, and since obviously you aren't, it stands to reason the semi is. And if the semi is exerting that little bit of power to pull you forward, it isn't free, right?

[psyshack]

OOOO God

Drafting 101.

Close in draft. Dangerous as hell. Dont do it. Massive mpg help. Why because you are in the trailers lowest air pressure area. Your not helping the truck or hurting it. Your in the zone hes waisted energy to make.

If you back out of the zone to the point the back of the car, bike, pogo stick,, what ever starts buffeting. Thats the first wake. Stay on the front side of this wake and it starts hurting the trucks mpg a tiny amount. This is the point to where your surfing the wake from the inside.

Back out some more you pogo stick starts getting beat pretty bad. This is where the wake starts collapsing on your car. Not good for you or the semi.

Back out farther and feel clean air again. This is the distant draft. The wake has come around the truck crashed back together. But leaving a small calm area. Good for about 40% of what a close in will give you. Depending on speed. Is there a head wind to start with or a tail wind,,, or cross wind. It could fall into the 2 sec rule or the 10 sec rule. Or no rule.

Rule of thumb. If you want to draft. You come in slowly wait until you get the buffeting on the front of the car. Then ease up just outside of this wake. That will be the distant draft. If winds and speeds put you in to close then dont do it. Other time it may well put you back to a point folks will pass you and get in the wake. All the better for you.

There is also the side draft. This is at the point where a semi pass you and just after they blow you side ways the calm comes. Riding here is great. But not safe.

I like to surf. If on a multi lane hwy. Let them push you along. You can do this off either corner of the cab. This and the side draft are the most common and happen to everybody on the hwy daily if there near semi's. A semi will let you surf and not think a thing about it.

psy

[Bill in Houston]

The truck is sucking all that air along no matter what. If you get into it, you take advantage of it. You might even decrease the amount of air that he is moving, and help him. But it would not be safe to follow close enough to help him. So, you hang back at a safe distance and get something for free, and it doesn't hurt him. Might make him mad, but it doesn't hurt him.

Do you watch NASCAR? Which is faster, a single car, or a "train" of five? The train is faster because the front car is benefitted by having the other cars behind him. Having the cars behind him reduces the power required to maintain a certain speed. Now, he could let off the gas and get better mileage, or he could keep it hammered and go faster. Since it's racing, he chooses to go faster. The draft is even better for the guys behind him, but it does benefit the front driver some too. If you do the math, being able to go from 180 while not in the train up to 184 while leading the train, that front guy is seeing about a 7% reduction in his aero drag. When a guy is leading the train, does he say "forget this!" and jump out? No, he knows he is getting a boost, so he stays there.

Can you convince a trucker of any of this? Doubtful. He has been taught his whole trucker life that having someone behind him costs him money, and eloquent arguments, even when NASCAR is invoked, are unlikely to persuade him.

[brucepick]

Originally Posted by psyshack

OOOO God
Drafting 101...
...I like to surf. If on a multi lane hwy. Let them push you along. You can do this off either corner of the cab. This and the side draft are the most common and happen to everybody on the hwy daily if there near semi's. A semi will let you surf and not think a thing about it.

psy

psy -
Can you clarify surf? Are you close to the semi's cab, maybe with car's nose even with trailer's front? Another case where you have to feel the buffeting and then back off just a bit to be in clear air?

[psyshack]

Originally Posted by brucepick

psy -
Can you clarify surf? Are you close to the semi's cab, maybe with car's nose even with trailer's front? Another case where you have to feel the buffeting and then back off just a bit to be in clear air?

The surf is when you are riding the cushion of air that is built up in front of the truck. The best surf is when you are to either front corner of the truck on a multi lane hwy. You are still having to bust your own hole in the air. But you have the trucks huge cushion of air behind you. In a surf you slow down to find the turbulence. Soon as you feel it pull up a bit. Just to where you barely feel it. Then you are surfing. Truckers over all dont mind you surfing as long as there are other lanes for traffic to move thru. You can surf them from straight in front of them. BUT this can put them in a tail gating mode. Of which they wont like. Nor do I. So thats why I surf off the front corners at times.

psy

[brucepick]

Thanks, psy