Weight Distribution, Trailer Weight and MPG

[RobWNY]

I'm trying to figure something out. This past weekend, we went camping. A 400 mile round trip. I averaged 7.8 mpg going to the campground and 6.7 mpg coming home. The difference in mpg is easily explained by a head/tail wind, terrain etc. The trip was mostly East/West traveling. Today, I took my camper to the dealer for some repairs to the slide out and I knew it was going to be at the dealer for a while, so I pretty much emptied the trailer and front pass through storage before leaving. I'm guessing a 1000 pounds of stuff or more. I also didn't crank down on the weight distribution like I normally do because it doesn't raise the back of my 2500HD anyway no matter how hard I crank on the spring bars so I thought I would see how it towed this way. So to my astonishment, the trailer towed much better and I averaged 11.4 mpg. The trip to the dealer was all done driving North. So does 1000-1200 pounds cause that much difference in mpg or does weight distribution play a role in mpg or both?

[2001400ex]

Going from 65mph to 55 mph is the biggest factor. Wind drag increases exponentially over a certain speed.

[RobWNY]

Yes, my engine is a 6.0 gas. Chevy Silverado 2500HD and a constant 65 MPH was the speed going camping (mostly expressway driving) while going North to the dealer, a lot more stop and go 2 way roads and top speed was 55 MPH. There wasn't nearly the number of long hills to climb on the short trip North but from 6.7 mpg to 11.4 mpg seems like a big jump to me regardless of the conditions.

[DougE]

Aerodynamics is the main drag. Best condition typically is with the front slightly lower than the rear. Then rolling resistance. More weight and/or lower tire pressure increase rolling resistance. Then it's weight associated with elevation changes. Going up - bad, going down - good.

[jerem0621]

I think this is by far to small of a sample to say definitively. Aerodynamics is the #1 factor for MPG with weight behind that. I read somewhere that once rolling it takes about 100 hp to maintain 60 MPH with approx a 7,000 lb TT.

IMHO...you may have been more careful about your driving and slowing down is typicically what causes the most positive impact on MPG. Of course conditions matter as well...if you have to run the motor hard it will drink more gas. Run it easy and there is better MPG.

Also, diesel does provide better MPG condition for condition. I'm a huge gas fan so I am not flaming diesel, this is a fact...diesel, driving condition for driving condition, will out perform gas on MPG nearly every time. It is typically about 30% better MPG.

Your truck is a 6.0 gasser based on your MPG. Please correct me if I am wrong.

Weight does have an impact but the only way you would know for sure is to take the lightly loaded camper on the same 400 mile run, same time of day, same road conditions, similar temp outside, drive the same way, and then compare MPG.


There are two campgrounds that my family loves. One of them is in the flatlands close to my house...one I have to climb a mountain to get to. I can't compare the MPG between the two because the driving conditions are totally different.

Thanks!

Jeremiah

[icanon]

Me Again wrote:
It was result of the position of the Sun, Moon and Stars in relationship to the Magnet North Pole and your direct of travel divided by 2 plus an unknown variable.

Unknown variable = cosmic rays :B

[Me_Again]

It was result of the position of the Sun, Moon and Stars in relationship to the Magnet North Pole and your direct of travel divided by 2 plus an unknown variable.

[2001400ex]

I am on my third toy hauler since 2008, 2 bumper pulls and my current fifth wheel. My current 08 Duramax has hauled all 3. I have only ever seen that big of a swing in mileage based on wind, elevation or speed. I track every tank by hand with an app and have since I bought this pickup. When towing completely empty or weigh a full load of over 2,000 pounds, my mileage isn't drastically different. Now there is differences in handling, my last small toy hauler would bounce around more when full of water, for example. But I can't really see a mileage difference with the weight, especially not 4 mpg. Same with WD hitch, my pickup was noticeably more stable with the hitch setup, but no change in mileage on my experience. If anything I would think it would get better mileage with it.

The biggest factor in my mileage is speed, and that can cause a 2-3 mpg difference. At 55 I get over 12, at 70 I get under 10.

[ktmrfs]

RobWNY wrote:
I'm trying to figure something out. This past weekend, we went camping. A 400 mile round trip. I averaged 7.8 mpg going to the campground and 6.7 mpg coming home. The difference in mpg is easily explained by a head/tail wind, terrain etc. The trip was mostly East/West traveling. Today, I took my camper to the dealer for some repairs to the slide out and I knew it was going to be at the dealer for a while, so I pretty much emptied the trailer and front pass through storage before leaving. I'm guessing a 1000 pounds of stuff or more. I also didn't crank down on the weight distribution like I normally do because it doesn't raise the back of my 2500HD anyway no matter how hard I crank on the spring bars so I thought I would see how it towed this way. So to my astonishment, the trailer towed much better and I averaged 11.4 mpg. The trip to the dealer was all done driving North. So does 1000-1200 pounds cause that much difference in mpg or does weight distribution play a role in mpg or both?

short answer: Not really, it is on average a very minor effect when your towing a trailer with lots of wind drag and frontal area.

biggest impact is wind drag. On level ground and constant speed weight has almost no impact on fuel economy. you aren't doing any work moving the weight itself if the velocity doesn't change or altitude doesn't change. The work done is overcoming rolling resistance and wind resistance.

And when weight effects mileage, it is a linear effect.

Wind resistance is a square law effect. so even a 10 mph headwind can have a noticeable effect. same goes for bearing friction losses, engine rpm changes, they are all square law effects.

Now, during stop and go driving or going over mountains or in rolling terrain, then weight does have an effect, it's effect is related linearly to the change in speed, or the change in altitude or both.

now if your talking a car with low drag going through an EPA cycle or around town, then yes weight does have a noticeable effect. First wind drag is very low compared to a trailer. Second the work done is a lot of varying speeds. Then weight has a very noticeable effect.

My guess is that if you loaded that 1000 lbs back into the trailer and repeated the trip, it wouldn't make much difference. Even 1000 lbs when your talking 12K + lbs total is small compared to wind drag unless you never went over 30 or 40 mph.

As a real world example I have two trailers. the first is a cargo trailer, 7x14 with little frontal area and weight of about 5000lbs loaded. the second is a 35ft TT 10K lbs with about double the frontal area of the cargo trailer. Both dual axle. I travel quite a bit with one or the other. I've towed each of them over 25K miles, often on the same route. I keep track of the mileage towing each of them. the differnce between them over that mileage is less than 2 mpg. The big trailer averages in the mid 11 range with my diesel towing at between 60 and 65. The cargo trailer averages in the upper 12mpg range, same truck, same speeds. figure 1.5mpg difference at most. And a big chunk of the difference is the frontal area difference.