[hatchy]

So I am not an aero expert, much as I wish I were. Anybody out there got any advice on drafting cars that are in the next lane over? Specifically on ideal positioning- If you have professional aero advice, please share your thoughts. In my personal experience in urban heavy traffic there are times when it may be both possible and safe to do this. Depending on positioning, it could be just as safe as not doing it at all. Under dense traffic conditions anyway.

I should probably go watch some nascar as research. Or maybe ecomodder has got something. Birds and cylists seem to do well with diagonal drafting. It seems a lot safety-er (and legaller) than drafting guys in front of you. For the guys itching to post about how dangerous and stupid this post is.. Even in normal driving sometimes just by chance my car is in (what I think is) a good position to get a diagonal draft benefit.

 

[California]

I think the problem with diagonal drafting is the different lanes need to be allowed to move at different speeds, no matter how slight the difference, to reduce traffic congestion. Your lane change to let traffic go by may not be possible if there's much traffic.

 

[redpoint5]

The only way drafting next to someone would be beneficial is if there were a cross-wind. Pressure on the sides of vehicles pushing outwards isn't a benefit. When you pass a truck, you can feel that pressure pushing you away, and then you get "sucked" back in once in front of that high pressure bubble.

There is a benefit if you're extremely close to something. Nascar drivers do this by getting close to the wall.

 

[martinknutson]

The only way drafting next to someone would be beneficial is if there were a cross-wind. Pressure on the sides of vehicles pushing outwards isn't a benefit. When you pass a truck, you can feel that pressure pushing you away, and then you get "sucked" back in once in front of that high pressure bubble.

There is a benefit if you're extremely close to something. Nascar drivers do this by getting close to the wall.

This. Cyclists ride an echelon if there is a crosswind. If there is not a crosswind, they ride in a paceline, and getting even a few inches out of the draft slows you down considerably.

 

[GetOffYourGas]

When I have played around with drafting on a bicycle (with a friend, not in a race), we found that the best spot was with the front edge of the front tire about even with the lead bicycle's rear axle. To get that overlap, you have to go "diagonally" somewhat, of course. But you really want the two tires as close to touching as possible, to get more "behind" than "diagonal".

When geese fly, the flapping of their wings creates an invisible horizontal vortex. It to is this vortex that the following goose aligns its own wing for a boost.

 

[martinknutson]

When I have played around with drafting on a bicycle (with a friend, not in a race), we found that the best spot was with the front edge of the front tire about even with the lead bicycle's rear axle. To get that overlap, you have to go "diagonally" somewhat, of course. But you really want the two tires as close to touching as possible, to get more "behind" than "diagonal".

When geese fly, the flapping of their wings creates an invisible horizontal vortex. It to is this vortex that the following goose aligns its own wing for a boost.

Have a look at any team time trial event, and unless there is a crosswind, you'll see this. The only time someone comes off the line is when they are done with their pull, and drops back to the end of the group.

 

[hatchy]

Nobody told these guys..

 

[redpoint5]

Flight is different than ground travel. You don't want to be in the vacuum bubble of the guy in front of you when flying because you require air density to maintain lift. On the ground, it's perfectly fine to be in a vacuum because you don't need to keep from falling from the sky.

 

[Curt]

I figure I'm now old enough to rant once in a while...

Staying in a specific drafting position distracts from one's attention and increases the surprise factor and the risk of hitting something in the road. And all drafting boils down to theft of someone else's range.

Drafting diagonally would likely keep one in someone's blind spot for extended periods, making it even more dangerous and annoying to victims than regular drafting, as well as roadblocking others in traffic.

Ok I'm done now.

 

[redpoint5]

Ranting is fine, but make sure it's factual. Your first part about not being able to react seems right. Everything else after that isn't. Drafting benefits both the front vehicle and the one following. By filling in the low pressure area behind the lead vehicle, it benefits by having a reduced volume of low pressure dragging it backwards. The following vehicle is pulled forward by the low pressure.

Autonomous driving can allow "platooning" where a line of vehicles (especially trucks) follow closely, all benefiting from vastly improved fuel economy.

We've established already that diagonal "drafting" is not beneficial unless there's a side wind.

I'm of 2 minds about drafting a semi. It's true that being close behind doesn't give much time to react. On the other hand, the semi is going to clear any major obstacles such as deer or even other vehicles if you're following close behind, and you can always stop faster than a semi unless it hits a stone mountain or something similarly immovable. I'd mostly be concerned about rock chips due to following too closely. Then there's the freak accidents where the dully tires fling a heavy object rearward.

 

[martinknutson]

Flight is different than ground travel. You don't want to be in the vacuum bubble of the guy in front of you when flying because you require air density to maintain lift. On the ground, it's perfectly fine to be in a vacuum because you don't need to keep from falling from the sky.

For a little more detail, see https://www.nationalgeographic.com/...at-fly-in-a-v-formation-use-an-amazing-trick/. Not only is it important that birds have wings, but they need to flap their wings at the right rate to get the lift benefits of the vee formation.

 

[Bolted On]

My frequency of drafting on road trips has declined as my range anxiety has lessened. One experience I had drafting a few months ago, soon after I bought my Bolt was an angry truck driver. He started running on the shoulder of the interstate trying to throw rocks up on my car, swerved, etc. Finally, I go the message and pulled around him. He was really mad that I was drafting on his truck.

 

[redpoint5]

I've never understood why truck drivers care. A car can stop way faster than they ever could. The only time a car couldn't stop faster is if they hit a brick wall, in which case they have bigger problems and the scratched paint on their rear bumper won't be one of them. Probably just some primitive emotion that wells up from not liking "tailgaters".

I always figured I'm doing them a favor following close enough that my headlights aren't in their rearview mirrors.

 

[hatchy]

drafting diagonally would likely keep one in someone's blind spot for extended periods,

Not if you're back far enough. I'm not sure if it would be of a benefit that far back, but like I said, I'm not an aerodynamically schooled person. I won't rule out the possibility until I see some data..

If there is a low pressure bubble behind tractor trailers, I'm assuming the air to the right and left of said bubble will tend to be drawn into that bubble.

There are folks who put pie plates on their wheels to get a percent or three.. and good for them. I'm curious if those kinds of gains are possible. I'm not talking about expectations of 25%.

 

[redpoint5]

If there is a low pressure bubble behind tractor trailers, I'm assuming the air to the right and left of said bubble will tend to be drawn into that bubble.

There are folks who put pie plates on their wheels to get a percent or three.. and good for them. I'm curious if those kinds of gains are possible. I'm not talking about expectations of 25%.

To the right and left of the bubble is a higher pressure area, as all the air in front had to be diverted around. You can feel the high pressure push you away when you pass close to a truck. Much of that air is getting sucked back into the vacuum, which is the cause of all the turbulence as air tumbles around trying to reach equilibrium again.

Pie plates on the wheels are among the least beneficial mods to make, but every bit adds up. Removing side mirrors helps a surprising amount, but is not legal in most (all?) states.

 

[hatchy]

I get the generalities of how the air behaves in a diagonal drafting situation, but I'd like to see some data. I have a suspicion if you hang back a certain distance from a big truck you can see a few percent benefit. If you know the right spot and hit it correctly. Love to be proven wrong by some data. I can't afford wind tunnel time..

 

[redpoint5]

I get the generalities of how the air behaves in a diagonal drafting situation, but I'd like to see some data. I have a suspicion if you hang back a certain distance from a big truck you can see a few percent benefit. If you know the right spot and hit it correctly. Love to be proven wrong by some data. I can't afford wind tunnel time..

The ideal location is directly behind the truck, as close as possible. If there is a crosswind, that ideal location shifts depending on the crosswind direction and speed, and the speed of travel.