Slowing down-saving fuel: The numbers...

[dsprik]

This is an interesting article - especially for "numbers" MOCers...

http://money.cnn.com/2008/03/26/auto..._gas/index.htm

[fulltimedreamer]

Dave,

Thanks for the link. We're doing everyting we can to cut costs. We intend to be in the coach all summer. We'll travel less, but still enjoy the camping lifestyle.

[dsprik]

I was especially surprised by the EXPONENTIAL loss of fuel mileage as speed increases. Also they talked about that turbulence suction in the back of vehicles - our Montanas included. I remember a while ago someone having a link to little plastic "fins" that go on the sides of rigs and other large vehicles to reduce this turbulence.

I am typically skeptical of such novelty items - but maybe...

[H. John Kohl]

I found this "MPG station WEB page" by Cummins for big trucks. Coming home from Florida this year I ran 55 as much as I could and found about 1.5 to 2 mpg difference. Of course we did not feel we were getting down the road yet it seamed a little easier driving for me. The mpg is with actual fuel calculations using excel. The truck computer said 2.2 mpg. 1600 miles at 10 mpg and $4.00 per gallon would cost $640 while at 12 mpg $533 a savings of 26.6 gallons or $106.
With the day to day run it does not mean much but added up over the year. If you drive 10000 miles and add 2 mpg it is a savings of 166.6 gallons or $666.67 at $4.00 per gallon.
I guess the biggest point I learned from the Cummins report (in pdf from the above WEB) is that rolling resistance changed over to air resistance at 55 miles per hour. So our tall 5th wheels have that big wind resistance.
Good luck and safe towing.
Thanks Dave for starting this topic.

[richfaa]

Here they are http://www.products4truckers.com/htm...ssories_0.html and they do work.

http://en.wikipedia.org/wiki/Laminar_flow


This is a bit better http://www.airtab.com/

[dsprik]

John, you're welcome. We as RVers can't afford to ignore these numbers at these fuel prices.

Rich, those are the fins I was thinking about.

*On Edit~ Rich I read the details on the bottom of that Air Tab sheet. These would be some things that we as TV/5ver combos would need to consider. Looks like it might not be appropriate for our TVs, but it would work on the back of our trailers


For Tractor-Trailer Application:
When using Airtabs, maintain a tractor-trailer gap of 40" or less
The Airtab will have an adverse effect if the tractor-trailer Gap is larger than 40 inches because it will direct airflow onto the front face of the trailer. The distance is measured from the closest point of the tractor or extenders (fairings) to the leading edge of the trailer. If you have questions Please call (800) 475-2155 for consultation before ordering.

For tractors without a top fairing: If you look at the tractor/trailer from the front (head on) and you are able to see more than 24 inches of the trailer, then Airtabs is not appropriate for the tractor roof. By adding a fairing that matches the trailer height and then adding Airtabs you will see a significant benefit. If you have questions, please call (800) 475-2155.

[tom41]

Dave, thanks for a very interesting link. I can remember very well in the 70's and even the 80's the 55 mph speed limit. Guess I got used to it, for I still maintained 55 to 60 mph to this day. It does make a difference in mpg, plus I dont feel so worn out from one destination to the next. Slower driving makes for a more enjoyable drive.

[TLightning]

When towing, I keep my speed just fast enough so the Allison will get to, and stay, in 6th gear...about 62/63.

[richfaa]

There is another link that I am looking for that talks about use on the TV. These guys are not all that expensive and we are going to get a set. I think The 3400 will need about 25...all around the back, top and sides.

[exav8tr]

Rich, In my flying days we had, and they still do, something called "vortex generators". They wer devices that stuck up on the wings and tail surfaces, Their job is to smoothe the air flow over the surfaces, thus helping to increase stall speed and making for a smoother and more efficient ride.

I am one that travels no more than 62 mph while pulling, I will admit, it is very difficult to do this with all the Indy driver's out there, but HEY, I pay the same for fuel as they do. I also agree that travelling slower makes for a less stressful drive and a more pleasant ride, not to mention less wear and tear on TT and TV.

[rogue]

John, very interesting article from Cummings, especially the 1300 rpm. Wonder if that applies to any of our TV?
"Shifting Techniques
Proper operating techniques result in the lowest number of engine revolutions per mile to maximize MPG. Constant operation below 1300 rpm significantly reduces fuel consumption. Follow two general rules:
-Maximize the percentage of time in top gear.
-Use the full operating range of the engine before gearing down."

Dave, Thanks for starting this very informative topic.

[dsprik]

My 5 spd Allison (2002) runs 1800 rpms at 60 mph. It sounds like after 55 mph aerodynamics are more critical than rolling resistance (proper tires/inflation).

[billhoover]

quote:Originally posted by dsprik

My 5 spd Allison (2002) runs 1800 rpms at 60 mph. It sounds like after 55 mph aerodynamics are more critical than rolling resistance (proper tires/inflation).

Interesting.

My 6 speed turns about 1700/1750 rpm at 65. What makes no sense is that sometime I get better mileage at 55 and 5th gear than a bit faster in 6th.

[H. John Kohl]

quote:Originally posted by billhoover
My 6 speed turns about 1700/1750 rpm at 65. What makes no sense is that sometime I get better mileage at 55 and 5th gear than a bit faster in 6th.

Bill, that Cummins article states that you can loose .1 mpg for every mile over 55. With that thought I bet your close to 1750 or 1800 in 5th gear at 55. What you did not state is what rpm is your best torque.
Cheers,

[c214dick]

I purchase and installed the air tabs on both my truck and Monty. I was not able to install them on the 5ver until after our trip to Branson so the jury is still out on that part of it. However I have noticed an increase on mpg for the truck. I have only filled up a couple of times since installing them but have experienced an increase of almost 1 mpg.

It may be a combination of factors such as the air tabs and keeping the rpms at or below 1500 but it's working. The air tabs cost $2.50 each plus shipping. I could not install them on the roof of the Monty because of the way it is configured and I don't want to take a chance of voiding the warranty by attaching any type of adhesive to the roof. I was also not able to properly secure them to the top 12" of each side of the 5ver because of the taper so I don't know if they will blow off. They are very easy to install and the white matches the Monty's color.

I don't subscribe to "gimmicks" but I think this was worth the investment even if I did over order. "nothing ventured, nothing gained"

If anyone wants additional info, let me know and I will try to post photos or e-mail them to you.

[dsprik]

Dick, I'd like to see a pic of how you installed on your truck and Monty.

[c214dick]

Here they are.

[richfaa]

We are going to purchase those when we get home.. I do think for full effectiveness they should be installed across the top of the roof. I still have questions about where they need to be installed for the best effectiveness. Will talk to some of our NASA friends at home.

[c214dick]

You are absolutely right about the full effectiveness. They do offer an air tab with a different adhesive for certain roofs but I didn't think ours qualified. Please post what you find out because this is still new to me as well. I probably will contact Airtab's tech department and ask about the roof installation.

I installed them where I did as to not corrupt the graphics and because the trim piece did not seem to interfere with the air flow. There are two plastic "tools" that you use to aid in the proper spacing and alignment of the tabs that are sent with the order. If you use it, there will be a space between the air tab and the Monty trim. Just pull the tab off of the surface and place it against the trim.

When you order, you can either order a trailer package which contains 80 or the exact number you need. There are 3/foot installed. I ordered the 80 plus 24 for my truck but as you can see there are areas that are just not flat enough for the air tabs. Also allow for extras to be mounted on your A/C or other areas that could pose a resistance to the wind. The cost still works out to $2.50@ plus shipping and are shipped out of Colorado. If you order on line double check with them any way to insure that they received all of your info. The contacted me two days after I placed my order to tell me that their system only picked up part of my credit card info.

[Rondo]

Dick-- Did you order the ones for your truck in that color or did you have them painted to match?