Posted 2012-06-23 11:58 AM (#145052) Subject: Fuel mileage: 7' v 7'6" tall trailer
Elite Veteran
Posts: 736 Location: Western WA
I was just reminded that diesel was $2 gallon 3 1/2 years ago, and it made me wonder about fuel efficiency of pulling a 7' tall vs 7'6" tall trailer regarding wind resistance, all other factors staying the same (shape of nose, size of trailer, etc). Anyone have any comparisons to share?
Posted 2012-06-23 1:58 PM (#145057 - in reply to #145054) Subject: RE: Fuel mileage: 7' v 7'6" tall trailer
Extreme Veteran
Posts: 316 Location: Illinois
Probably a difference, just as even an empty rack on a station wagon/suv/van/ adds drag on a vehicle and reduces fuel efficiency. I recently read car top carriers can reduce a vehicles fuel efficiency by as much as 5%. Even so, I would base the height of the trailer on the height of the horses that will ride in the trailer more then anything else.
Posted 2012-06-23 5:37 PM (#145061 - in reply to #145052) Subject: RE: Fuel mileage: 7' v 7'6" tall trailer
Member
Posts: 22
Location: 03303
I've towed various different styles of bumper-pull trailers behind my F-250 (single wheel) significant distances (over 700 miles one way). Load my stock trailer with four horses and I'll notice the weight going up and down, but not too much at the fuel pump. Put an eight-foot wide trailer behind the truck that weighs the same as my stock trailer (the stock trailer is heavy steel and about seven-feet wide) and I don't notice the up and down much, but will tank about four miles per gallon (from 12 mpg to 8 mpg). Height is also a bit above my stock trailer. Going higher but not wider (height clearance on the stock trailer is eleven-feet) results in a decrease of about 2 mpg from the twelve I get with my stock trailer.
Duallies, from talking with people in the hauling business, seem to be a bit less width sensitive, because of the truck's greater width.
But driving speed and style can be a big factor. Going west to east compared to east to west can be as big a factor. Engine can make a big difference. (I've got an older 7.3 without a lot of pollution stuff on it.) And my Mazda gets 40 mpg but can't haul crap.
Talk with some of the haulers of trailers and get their opinion, but I'm not sure you're going to find a clear answer.
Posted 2012-06-24 6:34 AM (#145069 - in reply to #145052) Subject: RE: Fuel mileage: 7' v 7'6" tall trailer
Expert
Posts: 5870 Location: western PA
The drag coefficient of a trailer is based on a few details. The size and shape of the trailer's frontal area, will determine how hard the trailer will pull. The larger it is, the more drag it will produce. The shape of the nose will have a direct effect as well. A "V" nose or one that is tapered, will cause less disturbance than a flat area.
A 7' wide trailer, 7' high with a "V" nose, will have much less resistance than an 8' wide trailer, with a flat nose of the same heighth. If any of the proportions are increased, so will the aerodynamic drag.
The speed at which you travel has a direct result on your gas mileage. Aerodynamic resistance is squared with an increase in speed. If your speed doubles, the amount of HP needed to overcome the resistance is quadrupled. This is why slowing from 75 mph to 65 often has beneficial results with the fuel mileage. It also exlplains why driving with the wind direction, yields better fuel mileage results, than when fighting a head wind.
The elevation at which your trailer is being pulled, will also determine the amount of drag resistance it encounters. Air at lower elevations is more dense than at a higher elevation. The more dense the air, the more HP it takes to pull an object through it. That is a catch 22 though, as an engine looses power at higher elevations, and works harder to maintain the same speed.
The outside air temperature also is a factor. Hot air is less dense than cold air, and causes less resistance. Again the catch 22. Less dense air also results in less HP. The same truck on a hot Summer day, will use more fuel than during a cool crisp, Fall encounter.
Parasitic drag quickly adds up. The largest examples of drag will be found in the hay racks and generator attachements added to the roof of a trailer. Loading lights, vents, open windows, air conditioners, side mounted spares and awnings, all contribute to drag and the increased loss of mileage.
The larger and flater the front of a trailer is, the greater the drag and fuel costs will be.
Posted 2012-06-25 12:48 PM (#145089 - in reply to #145052) Subject: RE: Fuel mileage: 7' v 7'6" tall trailer
Expert
Posts: 3853 Location: Vermont
Originally written by headhunter on 2012-06-23 11:58 AM
I was just reminded that diesel was $2 gallon 3 1/2 years ago, and it made me wonder about fuel efficiency of pulling a 7' tall vs 7'6" tall trailer regarding wind resistance, all other factors staying the same (shape of nose, size of trailer, etc). Anyone have any comparisons to share?
You could add a roof air deflector to your tow vehicle...people have experienced up to 10% improvement in mpg with one while towing
Fuel mileage: 7' v 7'6" tall trailer
