Tailgating a lorry/semi (modelled in CFD)

[redpoint5]

Drafting a lorry seems relatively safe to me. While you cannot come to a stop within 100ft of distance, neither can the truck unless he hit a concrete wall. All of my vehicles can stop much, much quicker than a semi. Besides that, they only travel 60mph tops where I'm at. This isn't nearly as dangerous as those that tailgate doing 85 in the fast lane.

If avoiding danger is paramount, sitting in a padded room in Switzerland is probably the safest option.

Seriously, do we have tailgating semi truck crash statistics anyone?

[Piwoslaw]

Originally Posted by theycallmeebryan

There have been times when a trucker has slowed down considerably and then just floors it and accelerates away from me. For me to have any chance of staying in the wake, I also have to floor it and try to keep up. Then they'll get up past 60mph and i'll have to play catch-up to try to get back in the wake.

A lot of truckers don't like being tailgated. Maybe they are trying to tell you that?

[UFO]

Originally Posted by redpoint5

Drafting a lorry seems relatively safe to me. While you cannot come to a stop within 100ft of distance, neither can the truck unless he hit a concrete wall. All of my vehicles can stop much, much quicker than a semi. Besides that, they only travel 60mph tops where I'm at. This isn't nearly as dangerous as those that tailgate doing 85 in the fast lane.

If avoiding danger is paramount, sitting in a padded room in Switzerland is probably the safest option.

Seriously, do we have tailgating semi truck crash statistics anyone?

Your perception is just that. What if the truck loses a wheel or runs over a piece of lumber? You will not be able to stop or avoid. I've seen it happen, and I have seen the consequences to the follower.

The padded room comment leads me to think you would not change your view even if you did somehow stumble on some crash statistics. It couldn't happen to you because you are such a good driver, just like everyone else.

[sendler]

Originally Posted by UFO

Following closer than 2 seconds is dangerous, and is often cited the root cause of pileups. Joke all you want, drafting is far less safe than not.

2 seconds is a rule of thumb. Where did it come from? Is it based on some study? 2 seconds is much closer than you think and not that much different from what I recommend. At 65mph, a 2 second following distance is only 59 meters. There will still be some beneficial draft from a truck at that distance. Behind a car that is just dirty air. Better to drop back. I recommend 40 meters from the back of a truck as the best blend between adequate safety vs fuel economy gain. That is 1.35 seconds of space. Now you are 60 meters behind the next DRIVER in front of you so there is your 2 seconds. But, these are advanced driving skills and may not be for everyone. Anyone that doesn't feel safe following at 40 meters, please do not do it.

[UFO]

59 meters is pretty much out of the wake. Mythbusters showed 10% improvement at 100 feet; 100 feet is slightly greater than 1 second and is too close. 10% is not worth following too closely. It is amazing to me people on this thread (and other sites) still argue the safety issue given all this evidence to the contrary.

[sendler]

Originally Posted by UFO

59 It is amazing to me people on this thread (and other sites) still argue the safety issue given all this evidence to the contrary.

Evidence to the contrary of what? The safety or the increase in fuel economy? Anyone with an economy meter can instantly see for themselves where the benefits end. I have a pre gen Insight and can tell you that even as clean as that car is, the draft from a big truck goes way back.

[UFO]

Originally Posted by sendler

Evidence to the contrary of what? The safety or the increase in fuel economy? Anyone with an economy meter can instantly see for themselves where the benefits end. I have a pre gen Insight and can tell you that even as clean as that car is, the draft from a big truck goes way back.

You quoted me. SAFETY.

[redpoint5]

UFO- My opinion about things is readily influenced by statistics. The points you raise are worth serious consideration. I have avoided debris in the road such as a ladder that seemingly appeared from nowhere in traffic. No doubt, had I been following closer the ladder would have been unavoidable.

That said, I have not seen the statistics, so I am left to make my safety and fuel efficiency decisions based on anecdotal evidence. I have never come close to colliding with a truck, nor have I ever seen the doors fly open and the load fall out. I don't even know someone that has had that happen.

Life is an endless series of compromises. If you want greater efficiency, it will come at a cost to safety. Each individual must balance their comfort level with their desire for efficiency. I respect the position of both the driver that follows closely, and the one that is more concerned for their safety.

The honest reason I do not draft semi trucks; I don't like pebbles hitting my car and I want to get to my destination faster than a truck pace allows.

[viio]

I'm afraid I can't model crashing :\

[Arctic Fox]

I have to agree with Sendler and Redpoint5 (Alpha Golf Hotel India Delta?).

And I'd like to mention a few thoughts;

1) Large trucks have a lot of mass. Should something happen instantly in front of them, I feel safer letting that mass plow its way through, clearing the road for me.

2) Ladders, exploding tires, lumber, animals... are all road hazards that could become real problems if one is not quick on the draw. Drafting not only requires paying attention to the rig in front, but as usual one should pay attention to everything -around- your vehicle, should there be a need for a hard-bank-left to dodge something the rig could not get out of the way. *Defensive Driving - do you know how much you can turn the wheels going 60mph without flipping your vehicle? I do.

3) When I drive interstate, I usually install my Uniden Grant CB radio to chat with truckers on the long drive. With that I can ask them if it's okay to draft them so I can save gas. Most say it's fine with them, some ask me not to and I move on.

4) The images here of the aerodynamics and wind resistance are a big help visually, but keep in mind that we're living in a 3-D world filled with randomness. For anyone who drives a light weight vehicle and tries to draft a big rig should know there is a point where all the lines in the images do come together quite violently. The turbulence just before you get to that smooth 'sweet spot' is like a whale's tail; trying to fish-slap your car off the road. There's a similar area near the driver's and passenger's doors as you try to pass one - the deflected wind from the front of the rig is pushed off to the sides. You will notice your car getting a bump away from the rig when you get to these areas.

5) I will NOT draft other cars and trucks on the road - mainly because these regular drivers know nothing about aerodynamics and proper drafting, most flat-out don't know how to drive (defensively), and as I mentioned above, there's just not enough mass for me to feel safe driving that close to them.

The End.
lol