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Cost of racing: AirTabs Review

Discussion in 'Tech' started by JBall, Mar 6, 2010.

  1. JBall

    JBall REALLY senior member

    One of the big expenses of racing is just getting to the track. The cost for pulling an enclosed trailer can really add up over the length of a season, especially with the cost of gas these days. My setup is typical of many racers. I’m pulling a 6 x 10 enclosed box trailer with a 2007 Ford F150. I bought the trailer with six inches of extra height to have the headroom, and pulling that big tall box down the road really uses the gas with the 5.4 liter engine in the Ford. Over 9 race weekends in the North Central region (including the GNF), I drove about 3800 miles in the 2009 season. I figure the gas cost at a little under a thousand bucks for the year.

    If you could do something to reduce gas costs, maybe you could save a little money to use for something more important (like race tires). I had seen a thread about AirTabs a while ago, which are a way to improve trailer aerodynamics. After trying to do some research, I decided to try them out, and do it in a way where I could accurately see the improvements being made.

    http://forums.13x.com/showthread.php?t=174257&highlight=airtabs

    The physics of items moving through air depends upon both ends of the object. (sides, top and bottom too, but to a lesser extent). The front is easy to visualize, you are pulling a flat surface through the air, which creates resistance that has to be overcome by burning more gas in the tow vehicle. Nose cones or v-nose trailers are used to reduce front end drag.

    The back end is a big contributor to drag as well. As the trailer moves through the air, it displaces a large volume of air that sweeps past the end of the trailer and there is a long distance before the airstream completely recloses. A partial vacuum is formed which creates drag, essentially pulling back on the trailer back and slowing it down. Again, you burn more gas to supply the energy needed to fight that vacuum. Mechanical devices for the back of a trailer to smooth out the airflow are problematic because they interfere with the trailer function.

    Airtabs are a device called a vortex generator. A line of them is installed on the sides and top of the trailer as close as possible to the rear. Each tab creates a vortex of spinning air that helps break up the vacuum behind the trailer and the series of vortices should reduce vacuum and drag. Reduced drag should result in better mileage.

    While the Airtab site had lots of testimonials, there wasn’t a lot of quantitative data. Most of the stories were along the lines of “I installed Airtabs on my trailer and I think my mileage is better.” There were also claims that trailers had less tail wag when around trucks or the rear stayed cleaner (indications of smoother air flow over the back of the trailer). I looked at some other web sites which had less encouraging information. Some were stories by “hyper-milers” who are people that obsessively try to get high fuel mileage by using weird driving habits like coasting long distances up to stop lights or putting aerodynamic devices on their cars. They did not report any gains, but most had put them on the back of vehicles which were fast back designs. If the Airtab can’t get out in the air stream to create a good vortex, it really won’t do anything.

    Installation:
    The Airtabs are installed three to a foot. My trailer took 15 across the top and 16 on each side. They have a sticky back and you pull off a protective piece of paper and stick them on. Instructions call for careful cleaning of the surface and a template is supplied to line them up. The surface should be above 40 degrees to insure they will stay on so I took the trailer to work where I have a garage tall enough to put the trailer inside to clean it and do the install. The sides went well but the top was not quite as good because it was not real flat. A couple did not stick completely down, but they should work if the leading edge is firmly attached. I didn’t lose any on the test drive, which was done when it was pretty cold out.

    Disclaimer: I’m not paid for this in any way and I’d be glad to show anyone my bill for the parts. The tabs are $2.75 each. Total for my trailer was $129.25 plus about 10 bucks shipping.

    Testing for Mileage:

    I make a living testing stuff (pressure relief devices), and know that obtaining accurate results is difficult under the most controlled of conditions. Mileage testing on public highways was not going to be well controlled but I tried to get my comparison done with as few differences between tests as possible.

    First I got a measurement of the mileage of the truck and trailer without the Airtabs installed. It seemed like it was about 12 mpg from last summer but I did a mileage run on the day of the install to get a baseline. I topped off at a gas station about a block from the freeway, reset the trip odometer, noted the time and then started on my test loop. The test loop started by jumping onto 71 South, and then heading on 270 west for a loop all the way around the Columbus beltway. I tried to maintain a pace between 65 and 70 mph, using cruise control where possible. I got back onto 71 North after the lap around Columbus, got off at my starting exit, and went back to the same gas station to refill the tank, noting the miles traveled, total time, and gas used.

    This run took 60 minutes to go 59.5 miles, and used 5.247 gallons of gas. This is 11.34 mpg at an average speed of 59.5 miles per hour. For an idea of the effect of the trailer, the truck recently got 17.3 mpg during a trip to Cleveland and back (traveling about 75 miles per hour).

    I then did the install, drove back to the same starting point, topped off the tank, and went back out for another lap of Columbus. I tried to run the same speed and recorded total time, miles traveled and gas used.

    Results for the second run were 59.5 miles traveled in 56 minutes with 5.127 gallons used. This gave a mileage of 11.61 mpg at an average speed of 63.75 miles per hour.

    Improvement in mileage was therefore 2.38%.

    Conclusions:

    An improvement of 2.38% is probably close to the accuracy of the mileage measurement, so it’s hard to know if you are really getting a benefit, although I was glad to see better milage at a higher average speed. Some of the time difference for the trip was probably the block or so between the gas station and the highway where there was lighter traffic during the second run. More accurate test results would be obtained by driving more miles during the test, to reduce the effects of traffic, but I had only so much time (and gas) to devote to the project.

    If the mileage measurement is good, payback will be about 2300 miles which will be less than one racing season. I was unable to feel any difference in how the trailer performed.

    My guess is that gains should be a bit better at the higher speeds (I normally run about 70 to 75 miles per hour.) Gains might also be better for a wider trailer that hangs outside of the wake of the truck.

    Like all things in this type of a project, YMMV (your mileage may vary)!

    http://www.airtab.com/en/ for more info.
     
  2. JBall

    JBall REALLY senior member

    Step 1: Find the trailer!
     

    Attached Files:

    Last edited: Mar 6, 2010
  3. Bad Dog

    Bad Dog Well-Known Member

    I was going to get these but of course, other stuff came up. I'd like to see you report back in a few weeks and see if your mileage is better or the same. Thanks for doing this.
     
  4. JBall

    JBall REALLY senior member

    My story was the before and after test. I never really tracked the mileage in detail before.
     
  5. Bad Dog

    Bad Dog Well-Known Member

    I want to see if it gets better, :up:
     
  6. JBall

    JBall REALLY senior member

    Installed:
     

    Attached Files:

  7. Bad Dog

    Bad Dog Well-Known Member

    Have you thought about doing the truck too?
     
  8. JBall

    JBall REALLY senior member

    I thought about it but I don't really want to screw up the paint. I don't think they would have too much affect attached to the roof of the cab. Might work better if you had them on the back of a cap, but I have an open bed.
     
  9. Bad Dog

    Bad Dog Well-Known Member

    I just emailed them about that, I asked if they recommend doing the van as well as the trailer.
     
  10. R1Racer99

    R1Racer99 Well-Known Member

    Have you ever tried driving slower? I don't know how your set-up compares to a big truck but the difference of 60 and 70 mph can be huge with a big trailer. I used to drive 75 and barely got 5 mpg, there are guys doing low 60's and getting 7-8. This is with semi's so maybe the effect wouldn't be as large but it's worth trying out. Driving slow sucks but it's free money if you can deal with it.
     
  11. GixxerBlade

    GixxerBlade Oh geez

    Nice write-up and thanks for taking the time to do it. 2.38% savings, to me, isn't enough of a savings to buy them.
     
  12. Europa

    Europa Open The Throttle

    There is only one word regarding true saving when towing anything over 3000 lbs. And that is Diesel...I towed a 7500 lbs trailer from NY to California and back for 980 bucks.The total trip distance was 6200 miles. I was getting 19 mpg on average. I was doing 7 to 75 miles an hour depending on the states speed limit. I had tried many of these gizmo's back in the day and came up with smoke and mirrors. Just my 02.
     
    Last edited: Mar 6, 2010
  13. JBall

    JBall REALLY senior member

    Its amazing how well the diesels do for mileage. Maybe not perfect for a daily driver although I work with a guy who commutes with a big Dodge diesel and gets good milage there too.

    Mostly a question of the inital investment.
     
  14. TurboBlew

    TurboBlew Registers Abusers

    Those foil things arent going to help you unless they catch stray money floating in the air. Frontal area is the biggest concern with mileage. Then weight... Then engine efficiency... then tire width.
     
  15. duggram

    duggram Sunrise Bahia de LA

    My toyhauler is 8' 6" wide, 13' 4" high, 39' 9" long and weighs ~16,000 loaded. Do you think I would see any benefit from these foils? I'm really happy if I can get a solid 9 mpg from my Cummins. Any improvement would be nice.
     
  16. TurboBlew

    TurboBlew Registers Abusers

    youll definitely see more performance improvement from a handheld tuner like SCT or similar.
     
  17. stickboy274

    stickboy274 Stick-a-licious Tire Dude

    If they do work, I do 24 weekends this year alone. It wouldn't take long to recoupe the cash. I have a programmer/intake/exhuast/+ other mods for my ford 7.3 dually, but at 46' with extra height my trailer is a beast. It does have a v nose, but it leaves a hole the size of some small states in the air behind it. Then we also have the weekends with the other camper behind the wifes sub-urban.
     
  18. SPL170db

    SPL170db Trackday winner

    Rather than posting up a new thread I figured I'd just bump this one up. I ordered these up a while back for my 6x10 enclosed trailer that I pull w/ a 2011 grand cherokee V6, it's a ~6ft tall interior so its a pretty high sail in the wind on the highway.

    [​IMG]


    I installed them up each side and along the top of the trailing edge of the trailer as per the recommendations (3 per lineal foot).

    Of course YMMV but the results that I got appear to be decently significant.

    I ran a baseline test by loading up the trailer with my typical equipment for a trackday and headed down to NJMP from my house in northern NJ. It's about a 140mi each way, and I tried to keep it around 65-70 mph most of the way on the highway. Each trip I zero'd the trucks computer and took the value after the drive. Going down it averaged 14mpg, coming back 13.9mpg.

    Installed the Airtabs and it now it gave 15.5 mpg going, and 15.1mpg on the return. If these numbers are accurate (I understand the computer isn't a 100% accurate number, but I would think the %age change would be somewhat accurate), these little plastic thingy's should pay for themselves eventually.
     

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