Surfing in heavies slipstream

[tenohfive]

I heard about a guy I work with who has a long motorway commute sitting right up the backside of heavies on the motorway in his diesel VW and getting MPG around the 90 mark. I can't say if thats indicated or not, but given the distance he goes and how much fuel he gets through I've no doubt that he gets massively improved economy from doing this.

I have a bit of a commute to do, and I've tried this half a dozen times - picking a slow heavy that isn't interested in overtaking, when theres no more than moderate traffic and when I'm wide awake, and sitting very close up behind him. From doing this I've learned a couple of tricks to make it a bit safer (because there are definately risks involved) and I'm aware of them. That said, I'm sure there are plenty of heavy drivers who have had cars wedged up their backsides, so I'm trying to work out the risk/benefit factor.

So putting the safety element to one side, has anyone else done this and what sort of differences were you noticing with your economy? And how much of it comes from simply driving at the slower speed (60 rather than 70) and how much from being in the heavies slipstream?

[Deva Link]

tenohfive said:

So putting the safety element to one side,

I think you're misunderstanding this sub-forum's title.

[Strangely Brown]

tenohfive said:

... because there are definately risks involved ...

No st, Sherlock!

[Deva Link]

If you're right up the arse (let's exaggerate and say 1mm away) of a big truck and it stops then you will barely bump it.

Then another 42 tonner comes up behind and your whole car is suddenly 1mm long.

[jhfozzy]

Mythbusters confirmed this one in season 5, episode 11 (I looked it up ).

They measured drag in a wind tunnel, then did a full scale test on a track and proved that it does make a fair bit of difference to your MPG.

I still wouldn't try it though.

[scoobydude]

Driving in the hole in the air created by a truck will make your MPG increase significantly on a long haul. However as mentioned before there is the safety problem to consider and also the fact that engine cooling is reduced somewhat as well. Over all I personaly wouldn't deliberately do it.

[tenohfive]

jhfozzy said:

Mythbusters confirmed this one in season 5, episode 11 (I looked it up ).

They measured drag in a wind tunnel, then did a full scale test on a track and proved that it does make a fair bit of difference to your MPG.

Cheers for that. I appreciate the need for safety and there are things that can be done to minimise the risk - but I'm not going to discuss that on a public forum as I don't want to encourage others to do it. Whilst I've tried it a few times I'm not yet decided on whether or not I will do it again - to be able to make that decision I'm after as much information about the benefits, as I'm already aware of the risks.

We all take a risk getting in our car rather than walking 10 minutes away. We take risks going out in the rain (gambling on the ability of other) or ice and snow, and make our own assessments of the benefit versus risk. I'm just trying to do the same thing.

And I'm pleasantly surprised, whilst I know the majority of posters don't approved its not descended into a slanging match. Might be spending a bit more time on this part of PH

[mp3manager]

As a truck-driver, any car who tries slipstreaming me ends up with all the rubbish and debris from the hard shoulder all over their bonnet, as I give the trailer a wiggle.

They're in my blindspot and I don't like it and I don't want them there. Most drivers eventually get the message and overtake.

[Freddie von Rost]

Deva Link said:

tenohfive said:

So putting the safety element to one side,

I think you're misunderstanding this sub-forum's title.

tenohfive I think you are barking mad playing with lorries on the motorway. But hey, what is a few extra mpg compared to your life anyway.

I take that you must be the new Stephen Hawking, as you appear to be able to reduce your breaking distance at will! Any chance of letting me in on your secret, as I am unable to do this on my vented four pots.

Best wishes,

FvR.

[Strangely Brown]

Freddie von Rost said:

you appear to be able to reduce your breaking distance at will!

Oh, I think the distance in which he will break is pretty much established.

Maybe that's the first properly appropriate use of the misspelling.

[tenohfive]

Freddie von Rost said:

Deva Link said:

tenohfive said:

So putting the safety element to one side,

I think you're misunderstanding this sub-forum's title.

tenohfive I think you are barking mad playing with lorries on the motorway. But hey, what is a few extra mpg compared to your life anyway.

I take that you must be the new Stephen Hawking, as you appear to be able to reduce your breaking distance at will! Any chance of letting me in on your secret, as I am unable to do this on my vented four pots.

Best wishes,

FvR.

I'm not going to go into the ins and outs of why I feel its safe enough - frankly, I don't see the need to justify myself. I'm satisfied it is. I acknowledge theres an increased risk - just as when driving over the speed limit - so I'm trying to work out if its worth the added risk and the added stress from concentrating completely on the driving - which is very stressful.

What I'm asking for is an idea of how much more economical this technique would be on a modern turbo diesel. The risks I'm more than capable of assessing myself, and isn't what I'm here to discuss.

Edited by tenohfive on Monday 27th July 21:03

[Strangely Brown]

tenohfive said:

I'm not going to go into the ins and outs of why I feel its safe enough - frankly, I don't see the need to justify myself. I'm satisfied it is.

OK then, if your mind is that closed then there is no point in discussing it with you and you're in the wrong forum. I only hope that when you run into the back of the truck, you are the only one injured.

[BertBert]

The thing is that we can't really answer your question. But we are genuinely interested in the safety aspect. Can you not tell us about how you mitigate the risk?

Bert

[GreenV8S]

I know somebody who does long motorway trips in a woefully under-powered camper van who says he can follow heavies up hill at 56 mph if he stays in the wake, but if he drops back out of the wake he struggles to stay above 40 mph. If you wanted, you could estimate the amount of drag reduction that implies. Judging by his description, to be close enough for this to work you would have to be imo dangerously close.

[Graham E]

At the risk of sounding like a keyboard warrior, are you fking stupid?

If you're tailgating something big, you can't see, or anticipate whats ahppening ahead. Lack of forward observation and general tailgate muppetness is what causes 75% of the pointless little accidents that cause delays on our motorways, and probably about 30% of fatalities.

I hope when it's your turn, you don't cause anyone else to be injured.

[Loque]

Not smart in anyway. I really hope you don't do it with other people in the car.

But yes I believe it does improve your MPG by some margin, not exactly fun driving though is it? And by christ you are at a disadvantage if anything goes wrong.

[deviant]

GreenV8S said:

I know somebody who does long motorway trips in a woefully under-powered camper van who says he can follow heavies up hill at 56 mph if he stays in the wake, but if he drops back out of the wake he struggles to stay above 40 mph. If you wanted, you could estimate the amount of drag reduction that implies. Judging by his description, to be close enough for this to work you would have to be imo dangerously close.

You have to be within a couple of feet for it to work...Close enough that your entire view forward is blocked by the truck, just a sudden lift by the truck or a dab of the brakes would see you in a smash. I don't see at all how the risks that come with this can be reduced.

[tenohfive]

deviant said:

GreenV8S said:

I know somebody who does long motorway trips in a woefully under-powered camper van who says he can follow heavies up hill at 56 mph if he stays in the wake, but if he drops back out of the wake he struggles to stay above 40 mph. If you wanted, you could estimate the amount of drag reduction that implies. Judging by his description, to be close enough for this to work you would have to be imo dangerously close.

You have to be within a couple of feet for it to work...Close enough that your entire view forward is blocked by the truck, just a sudden lift by the truck or a dab of the brakes would see you in a smash. I don't see at all how the risks that come with this can be reduced.

Where'd you come across the figure of 2 feet? Thats far too close without question, and I've certainly never followed that closely before.

[tenohfive]

GreenV8S said:

I know somebody who does long motorway trips in a woefully under-powered camper van who says he can follow heavies up hill at 56 mph if he stays in the wake, but if he drops back out of the wake he struggles to stay above 40 mph. If you wanted, you could estimate the amount of drag reduction that implies. Judging by his description, to be close enough for this to work you would have to be imo dangerously close.

How closely does he follow? Any chance of asking him?

[BertBert]

Will you not tell us then how you mitigate the risks. I'm open-minded enough to listen!

Bert