Experiences with drafting?

I saw the same increase as you. The faster the semi the greater the benefit. In drafted semis on a 380mile trip to Iowa, and after had some road rash on my front bumper. Not worth it up close for this reason and safety but otherwise a must on the highway. Also works on fatty SUVs.

 

I learned the hard way against drafting. I slammed into the back of a semi which locked up it's brakes. Now I make sure to leave plenty of car lengths between me and the vehicle in front of me. No amount of better MPG is worth one's life or well being.

 

Have tried it for short periods a couple times with some noticeable effect but I also got a bit nervous about being a target for kicked up road debris.

 

Blu-ray voices an important warning.

Note also that rear-ending a semi trailer carries a higher risk of injury / death / decapitation than a similar impact into another passenger car. That 'Mansfield Bar' or underride guard hanging below the rear of the trailer in North America is not really adequate to properly engage the front crash protection of your car.

Some other regions have more effective trailer underride guards than we have here in the U.S.

 

How far was it from your car to the semi and at what speed?

 

IMO it's not worth the risk to try and squeeze out a couple more mpgs. You are already driving a car that gets better mpgs than 9 out of 10 cars on the road. Would you prefer to arrive at your destination safely or risk your life and other peoples lives for something that is inconsequential and means nothing in the long run?

 

1 to 2 car lengths is 15 to 30 feet. (Edit: Make that 13 to 26 feet for a 'c'.) Where I live, that is hard core tailgating.

At 55 mph, the common 2 second rule (yes, I know this is unrealistic in heavy urban traffic in much of the country) is 161 feet. Minimum legal following distance in my state at 55 mph is 110 feet.

Converted to time, your 1-2 car lengths is 0.16 - 0.33 seconds. Legal minimum here is 1.36 seconds.

 

Way too close. Trucks are usually slow to stop, but there are other things to think about. Things like ladders, blown tires, and crap falling out of pickup trucks that will fly out from under the big truck in front of you that you won't see in time to avoid. No fuel economy in the world is worth dying for.

There are other threads about this on the site. You should read them if you wish to continue tailgating. There are those from both sides of the issue. For me, nothing closer than 30-40 yds.

 

Conditions are obviously different in my part of the world, but I dare say the 2 second rule should pretty much hold if you're behind a semi. The authorities actually try to promote 3 seconds here. I agree with the consensus here though... you don't really want to be spending that much time that close to a heavy vehicle. Not worth it on so many levels.

 

After my accident I started doing the 5 second rule. I'm now down to 3 seconds, any closer and I start to get fidgety and it's been 17 years. I walked away from my accident by some luck. I literally shoved the door open and walked away. Everyone said I should have been dead or seriously injured. The pickup I was driving (Ford F150) was totaled along with my shorts. No air bags, no anti-lock brakes, just a seat belt. The passenger side seat had a piece of the engine wedged in it that had broken off and gone through the dash. Some how, the area around where I was sitting was unscathed. That was the first totaled vehicle accident I was ever in. In 2004 I was driving my roommates Toyota Camry when a lady ran a red light in an old firebird and T-boned me in the passenger side. Again, I walked away without any injuries. Passenger seat was again a nightmare. The top part had wedged itself between my back and the back of the driver's seat.

But yeah, at 55MPH and 2 car lengths, that's not nearly enough room. You don't have enough time to respond to them braking and be able to brake also.

 

I'm all for travelling behind trucks. I'm also for being able to stop on my own. If you can't see the truck's mirrors you are too close.

State Police everywhere are overlooking a gold mine. Whenever there is some huge pile-up on an Interstate they should issue tickets for tailgating to everyone that ran into the first vehicles in the collision.

 

I'm pretty sure that here they do just that.

Droid RAZR HD MAXX

 

You know, I posted a thread similar to yours on a RV forum and got all the same responses, none of which had any bearing on what I was looking for. Similar to what's above, things just like, "OMG yer gonna die!!"... or "You're gonna murder everyone on the road!"

So, back to topic---
I do, and I'll continue to do it. In my case, I have done the occasional drafting, and like you mentioned, at a comfortable distance. I've noticed a pretty big jump. Flat freeway, 65mph, I can get over 60mpg. And just as you stated, the faster the semi, the more the benefit. I do though, try to avoid dirty looking rigs, or especially dump trucks that look like they'll drop dirt/rocks.

 

Sounds like I don't want to be one of your passengers...

Here is some information that the mythbusters did on this very subject... it shows that even at 100ft you see a benefit.

 

On my recent trip, I drafted behind slower moving vehicles (60 mph or less). I don't care what it is, it could be a tractor trailer, an SUV, or a Van. I've even drafted behind a Camry. When going up a steep hill, I tried to get behind a truck because I know it'll be climbing at a slower speed. I wasn't able to draft the entire trip because I'd only draft behind slower moving vehicles.

My 450 miles trip started with an elevation of 550 ft, went as high as 2700 ft and arrived at 750 ft and made the return trip on the same highway. 30 of the 450 miles were city driving. The outside temp was over 90 and I had my A/C set on between 77 and 80 the whole time and I had 4 people including myself. I've never made this trip on a Prius before but under the condition that I just mentioned, I didn't expect to get 57.8 mpg especially when I had to climb 2000 ft with A/C running.

 

Not really. All the big trucks go 71 mph, which means my fuel economy is worse than when I go 55 mph anyway.

 

As many have said: draftiung on the highway, especially interstates is dangerous.
I have a relative who drives semis for a living and I have drafted his semi for a hundred miles and found a 15% gain in mpg from48 to 55 mpg. Since we had cb's and in constant communication so the danger was less. Still, I had to ride just a few feet off his trailer rear and if he stopped quickly there would probsbly have been a wreck. Remember if you can't see the driver he can't see you - and doesn't want you there cause he knows you're gonna have a wreck and mess up his schedule. IOf you know how important that schedule is you won't get anywhere near him even after the police asrrive. He will not be happy with the idiot drafter.
PS based on racing experience the semi needs to have less ground clearance to really make drafting useful. The Prius basically would almost fit under the trailer and though air is deflected its not enough to be useful as an aero aid.
Way toio much buffeting so drafting is not comfortable either.

 

I am a 50 year veteran semi truck driver. Please do not draft. Any truck driver worth his/her salt is aware you are drafting and is more nervous about it than you. If the semi driver doesn't know you're drafting you should be very afraid. Your C gets very good mileage and you really don't need to draft.
I remember back in the good old days there were stories of people in air cooled VW's who drafted trucks and blew their engines as a result. Might be an old urban legend, though. Drafting probably won't hurt your C's engine, but, it will if you slam into the back of the truck. Again, please don't tailgate the truck drivers. Their job is stressful enough.