If you tailgate another car, do they get better fuel consumption?

[Deleted User] · 02/10/11 - 04:25

Any aerodynamicists on DS? My guess is that maybe they do if you're really close.

SpoonfedVomit · 02/10/11 - 04:26

no you burn more fuel if your going at a slower speed which you would usually do if you were tailing from 4-5 cars behind....

pocatello · 02/10/11 - 04:27

I doubt it, else the lead car in a car race would want the second place to tail gate him...

Nilrem · 02/10/11 - 04:39

IIRC Mythbusters did a test on tailgating a truck with a car, and they found that it did save fuel - but you had to be sitting a couple of inches from it's bumper.

So I'd say no

Carlos_dfc · 02/10/11 - 04:56

Nilrem wrote: »

IIRC Mythbusters did a test on tailgating a truck with a car, and they found that it did save fuel - but you had to be sitting a couple of inches from it's bumper.

Yeah, I saw that episode.
The car behind does get a slipstream effect, but unless you get stupidly close, the effect is negligible.
They did get a significant saving from being dangerously close behind a truck - but only an idiot would take such a risk to save a few quid.

alsmama · 02/10/11 - 06:16

Guess there's a lot of idiots around then from what I see on the road!

Baboo Yagu · 02/10/11 - 06:58

MrHoppy wrote: »

Any aerodynamicists on DS?

Yes there are.

MrHoppy wrote: »

If you tailgate another car, do they get better fuel consumption?

No they don't!

Although I would like you to explain how you think that the car in front of you, the one that has to actually push through the air, gets a better a fuel consumption than a car that's trying to achieve a drag effect by slipstreaming it?

[Deleted User] · 02/10/11 - 07:05

MrHoppy wrote: »

Any aerodynamicists on DS? My guess is that maybe they do if you're really close.

No. You get better fuel consumption in the trailing car because the lead car is pulling you along. The lead car gets worse fuel consumption.
As others have pointed out, you have to be stupidly close to the car in front to get any benefit, so don't do it.

juliancarswell · 02/10/11 - 08:39

No you don't because cars don't run on rails. Things happen in front of the lead car and they brake slightly, the asshole behind ( cos that's what they normally are) over compensates and and brakes hard loosing forward momentum which then has to be regained via their fuel. They then repeat the whole process time and again. Every time they brake hard they are pouring fuel down the drain. It amazes me that they don't learn from it.

Andrue · 02/10/11 - 08:42

It's a crazy idea for one car to try and get a tow from another another on the public road. The effect is negligible and you'd have to be dangerously close. It's more feasible for a car following a tall vehicle like an HGV. You still have to get dangerously close to see more than 10% gain but a safe distance could probably get the following car 5% reduced consumption. I think I read somewhere that if you're between two tall vehicles you can get a further effect by being part of a general movement of air.

The vehicle in front doesn't see any benefit and since you can't get something for nothing it probably loses out.

It's basically not something you should try to do. However if you find yourself following an HGV you can console yourself with the knowledge that you are probably saving a small amount of fuel.

[Deleted User] · 02/10/11 - 14:25

Baboo Yagu wrote: »

Yes there are.

No they don't!

Although I would like you to explain how you think that the car in front of you, the one that has to actually push through the air, gets a better a fuel consumption than a car that's trying to achieve a drag effect by slipstreaming it?

What about train carriages? Consider 3 carriages. The rear carriage is slipstreaming the middle one. All the middle one has is skin drag - nothing dragging on the front or back. The middle carriage i imagine gets less drag than the back one, because of the effect of being in front of another carriage.

I googled this after I posted the question here, and it seems lorries being tailgated by cars to get a very slight drag reduction.

[Deleted User] · 02/10/11 - 14:27

juliancarswell wrote: »

No you don't because cars don't run on rails. Things happen in front of the lead car and they brake slightly, the asshole behind ( cos that's what they normally are) over compensates and and brakes hard loosing forward momentum which then has to be regained via their fuel. They then repeat the whole process time and again. Every time they brake hard they are pouring fuel down the drain. It amazes me that they don't learn from it.

Although I wasn't asking about the fuel consumption of the following car, this is a good point.

[Deleted User] · 02/10/11 - 14:29

Andrue wrote: »

I think I read somewhere that if you're between two tall vehicles you can get a further effect by being part of a general movement of air.

This is the kind of thing i'm talking about.

Andrue wrote: »

The vehicle in front doesn't see any benefit and since you can't get something for nothing it probably loses out.

I don't see that this is logical though.

jackthom · 02/10/11 - 14:36

Andrue wrote: »

It's a crazy idea for one car to try and get a tow from another another on the public road. The effect is negligible and you'd have to be dangerously close. It's more feasible for a car following a tall vehicle like an HGV. You still have to get dangerously close to see more than 10% gain but a safe distance could probably get the following car 5% reduced consumption. I think I read somewhere that if you're between two tall vehicles you can get a further effect by being part of a general movement of air.

The vehicle in front doesn't see any benefit and since you can't get something for nothing it probably loses out.

It's basically not something you should try to do. However if you find yourself following an HGV you can console yourself with the knowledge that you are probably saving a small amount of fuel.

I don't think it gains or loses. If a trailing vehicle isn't present to make some use of the airstream set in motion by the car in front, that moving air will lose it's energy anyway to the surroundings.

Supratad · 02/10/11 - 14:37

MrHoppy wrote: »

What about train carriages? Consider 3 carriages. The rear carriage is slipstreaming the middle one. All the middle one has is skin drag - nothing dragging on the front or back. The middle carriage i imagine gets less drag than the back one, because of the effect of being in front of another carriage.

I googled this after I posted the question here, and it seems lorries being tailgated by cars to get a very slight drag reduction.

Trains are irrelevant, as they are all connected and propelled by the same power source.
The ony way I could possibly see the lead vehicle getting a reduction in drag due to a tailgater is that the lead vehicle's turbulent wake might get smoothed out by having a second vehicle right behind them.
If I understand it correctly, the turbulent air behind creates lower pressure which has the effect of "sucking" the car backwards, thus creating "drag", so high flat backed vehicles suffer more drag than smooth coupe style cars.

Having another car in that turbulent air might then stabilze it
a bit....maybe,

Si_Crewe · 02/10/11 - 15:43

Kinda related, apparently it has long been established that geese fly in a V-formation because it offers lift to all the following birds.
Originally it was thought that the lead bird got a kinda raw deal out of this and they'd eventually fall back into the "V" when it got knackered and allow another bird to take over the lead.

Recent studies have shown, however, that the lead bird does also benefit from the effects of having a bunch of birds following.
I honestly can't remember how the benefit was created. Probably something to do with the following birds flapping their wings in such a way as to waft a small percentage of air forwards and generate some lift forthe bird in front.

Alas, given that vehicles don't have wings that flap, I don't think there's any way for a following vehicle to do much for the performance of a leading vehicle.

I suppose, in extreme situations, a small car being followed by a massive truck might benefit slightly from the "bow wave" of air the truck is pushing in front of it.
If you could actually find a truck able (or allowed) to go fast enough to be beneficial.

Si_Crewe · 02/10/11 - 15:50

Supratad wrote: »

If I understand it correctly, the turbulent air behind creates lower pressure which has the effect of "sucking" the car backwards, thus creating "drag", so high flat backed vehicles suffer more drag than smooth coupe style cars.

Having another car in that turbulent air might then stabilze it
a bit....maybe,

The ideal shape for aerodynamic drag is a "raindrop" shape and a truck isn't exactly "raindrop" shaped so a car following a truck might be beneficial to the truck simply because its presence helps smooth the flow of air at its rear.

As a rule of thumb, aerodynamics really only becomes an issue at speeds in excess of about 70mph.
When Porsche, for example, first started mucking about with active-aero spoilers they found that it made NO difference at all until the car hits around 75mph.

Trouble is that'd mean that any time you saw a Porsche with the spoiler raised it'd mean that the car was breaking the UK speed limit so they twiddled the software so that the spoiler pops up at around 60mph.

Anyway, point being that trucks wouldn't really reap the benefit of a following car smoothing air flow over them because they wouldn't be travelling fast enough for it to be a big deal unless they happened to be facing a 50mph head-wind.

Baboo Yagu · 02/10/11 - 16:38

MrHoppy wrote: »

What about train carriages?

What about them? They're all connected to the same locomotive so your point is moot.

DJPT · 02/10/11 - 22:58

Sadly not OP!

Try some fuel saving tips instead :-)

Came across these while booking my car hire in Tenerife for next month

:cool:

Hey there!

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If you tailgate another car, do they get better fuel consumption?

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