When driving behind a semi to save gas, how far behind should you drive?

[iamtrout]

I've heard that driving behind a semi can save gas because the semi blocks a lot of the wind that would otherwise put drag on your car. But how far behind should you drive?

Too far and it's pointless.
A little too far and your car gets buffetted around by the semi's wake.
Too close and it gets dangerous, plus pissed off the semi driver.

 

[MikeyIs4Dcats]

for you....six inches...don't forget to roll up your windows and turn off the AC

 

[Ramma2]

If you can't see his mirrors, then he can't see you. Any closer and you run the risk of a blown out tire smashing through your windscreen and crushing your face. Not worth an extra .25 mpg.

 

[vegetation]

You have to pretty darn close, far too close for safety reasons, otherwise the turbulence kicks in and you end up wasting more gas.

 

[mb]

The amount of gas you might save would not be worth the risk.

 

[iamme]

close enough to attach the chain, so you can put your car in neutral

 

[imported_Scourge]

I imagine that most of the improvement comes from the fact that semis generally go at 65-70mph, and so it saves you gas just by driving slower than normal.

 

[iamtrout]

Ok, I was just wondering because I've heard of people doing this, but have always wondered, "uhhh... isn't this really really unsafe?"

 

[Kalvin00]

Originally posted by: Ramma2
If you can't see his mirrors, then he can't see you. Any closer and you run the risk of a blown out tire smashing through your windscreen and crushing your face. Not worth an extra .25 mpg.

Yep. And if not a tire, then rocks cracking your windshield.

Not really worth it.

 

[WiseOldDude]

your IQ in inches, which would put you what less than a yard away from the truck

 

[cubby1223]

Originally posted by: supafly
The amount of gas you might save would not be worth the risk.

When I would do that for the 3.5 hour trip between home & college, I was getting 20% better gas mileage, from 15 to 18mpg. That's a significant enough savings, especially considering today's gas prices.

 

[Sluggo]

I have always heard that the air behind a semi at highway speed is so turbulent that it will actully worsen your gas mileage to try and drive behind one.

 

[Cattlegod]

I heard about 6ft to see any gains. there was a study done on this subject too, and the conclusion is you use more gas trying to keep at a constant 6 feet than you save.

 

[saahmed]

Originally posted by: iamtrout
I've heard that driving behind a semi can save gas because the semi blocks a lot of the wind that would otherwise put drag on your car. But how far behind should you drive?

Too far and it's pointless.
A little too far and your car gets buffetted around by the semi's wake.
Too close and it gets dangerous, plus pissed off the semi driver.

Drive at the point where you can see their side mirrors. They cant see you if you cant see their mirrors.

 

[Zenmervolt]

"Drafting" is a phenomenon that only begins to have an effect at speeds over about 75 mph and even at that speed is requires that you be within 2-3 feet of the vehicle in front of you. This should NOT be done on public roads. Period.

ZV

 

[Zenmervolt]

Originally posted by: cubby1223

Originally posted by: supafly
The amount of gas you might save would not be worth the risk.

When I would do that for the 3.5 hour trip between home & college, I was getting 20% better gas mileage, from 15 to 18mpg. That's a significant enough savings, especially considering today's gas prices.

That difference is consistant with simply driving at 60-65 versus 75.

ZV