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Topic: MPG and weight

Posted By: ticki2 on 03/15/12 06:41pm

With all the threads about MPG and how varied the reports are for different rigs I thought I would try to look at it from another angle. From my old school days I remember that the definition of work is weight ( pounds ) X ( distance ) = work ( inch pounds , foot pounds , mile pounds ). So the question is how much work do we get from our fuel . For this first example I compared two diesel trucks with campers .

Rig 1 , mid size 4 cyl diesel with small TC
25 mpg , gross weight 6600#

Rig 2 , full size 8 cyl. diesel with med TC
15 mpg , gross weight 11000#

The formula--- weight x miles / gal = work ( pm/g )


Rig 1 , 6600# x 25 miles / 1 gal = 165000 pm/g

Rig 2 , 11000# x 15 miles / 1 gal = 165000 pm/g


Now before someone jumps all over me , I fully realize there are many factors that affect fuel millage such as speed , wind , terrain , etc . This is only a quick guide to see how you are doing with your rig , in your terrain and your driving habits .


So , how much work are you getting from your fuel.


'68 Avion C-11
'02 GMC DRW D/A


Posted By: JaredWPhillips on 03/15/12 07:07pm

I'm curious about fuel mileage as well.
I have a 2001 Silverado 1500 5.3 V8 4x4.
Last year I had a Jayco T24Z ToyHauler. It weighed around 6800 pounds. When pulling it I got a whopping 9-11MPG MAX. I thought to myself, "this is way too much weight to pull and get decent mileage."
Empty my truck can get as much as 18-19MPG if I drive VERY carefully. (I miss my diesel)
So, I thought a light-weight camper should give good mileage. I purchased a 2011 KZ Sportsmen 14FTH Toyhauler. It was only 15' long and weighed 2200 pounds. I thought I should get at least 14-15 MPG, since it weighs 4500 pounds or so LESS. Guess what I got? 9-11MPG. Then I realized it has to do with wind resistance. Both trailers were about the same height; both acted as a giant parachute going down the road. Didn't matter which was longer or which weight more. The truck didn't care about pulling the weight.
So now, I am shopping for a pop-up truck camper. I'm looking at a Palomino 1251, weight around 1500 pounds. I'm inclined to think that being a pop-up, the wind resistance factor will be very low and yield decent fuel mileage. I don't expect anywhere near my empty MPG but I would hope to see 14-15mpg? Maybe not, but it has to be better than dragging a trailer.


MY RVing BLOG
  • 1999 Ram 3500 12V Cummins, DRW, NV4500, 4x4, Flatbed

  • 2001 Chevy Silverado 1500 ext cab 4x4 5.3 V8. GoodYear Wrangler Authority E-Rated tires, FireStone AirBags.

  • 5th Wheel: 2012 Jayco Eagle 31.5FBHS



Posted By: GMCPU53 on 03/15/12 07:11pm

I'm not real good at numbers , but if I understand your formula correctly, you are ending up with the same value for each rig, so you are equal on work you are getting per gallon, but if you want to haul a heavier rig with a larger engine, you're trading off on the distance you are going for that one gallon. Now I think I just confused myself.
Going to go rest my brain


Joe


2011 Silverado 3500HD LT4x4 Ext.Cab L/B SRW
2008 S&S Montana Ponderosa 8.5 FBSC


Posted By: toad and the toadett on 03/15/12 07:23pm

I drive a Chevy 2500HD (2005) with a 6.0 gas engine and 4.10 gears. I carry a Palomino 1251 sb pop up truck camper. When i to our 24 foot travel trailer I get about 10mph no matter what the speed or terrain. With the slide in I can get as high as 14 mph at about 800 feet above sea level at 55 mph on level ground. Faster means less mph and so does driving in hilly or mountainous terrain. Went to Alaaka last summer and averaged about 11-11.5. Tom


Posted By: SkipJ on 03/15/12 07:29pm

I believe drag caused by pulling an object through the air increased by the cube of the speed. My old boss , who was an rver,said at speed, pulling the trailer through the air took most of energy.
SkipJ


1992 Airstream B-190 van
1989 Airstream 25' Excella Trailer
Outfitter Apex 9.5 Truck Camper Ford F-350 Diesel 4x4



Posted By: christopherglenn on 03/15/12 07:41pm

Drag is far more important then weight - unless you are on a steep hill / mountain. A motorcycle will get 30-50mpg with a single rider wearing a (packed) parachute on the freeway. Deploy the chute - no change in weight, only drag, and same bike will get 1/4 or less the prior mpg's.


2007 Chevrolet 3500 CC/LB Duramax/Dually 4X4 Mine r4tech, Reese Signature Series 18k +slider, duratrac, Titan 62 gallon, diamond eye, Cheetah 64
2011 Keystone Fusion 405 TrailAir & Triglide, Centerpoint, gen-turi, 3 PVX-840T, XANTREX FREEDOM SW3012, G614



Posted By: JaredWPhillips on 03/15/12 07:51pm

I was surprised that I got the same MPG towing 2200 pounds as I did towing 7000 pounds. Both campers were the same height. I'm guessing that if the 7000 pound camper was only 4 ft tall and aerodynamic, I would get much better mileage than towing the taller 2200 pound rig.


Posted By: ticki2 on 03/15/12 07:43pm

GMCPU53
It just so happened that the examples given , two very different rigs , had the same results . Others will yield different result . Have you tried yours ?


Posted By: GMCPU53 on 03/15/12 07:59pm

ticki2 wrote:

GMCPU53
It just so happened that the examples given , two very different rigs , had the same results . Others will yield different result . Have you tried yours ?



Yes , my results are not as good, 132000 (pm/g) on a good day with few hills and no headwinds

Joe


Posted By: CloudDriver on 03/15/12 08:17pm

ticki2 wrote:

With all the threads about MPG and how varied the reports are for different rigs I thought I would try to look at it from another angle. From my old school days I remember that the definition of work is weight ( pounds ) X ( distance ) = work ( inch pounds , foot pounds , mile pounds ).

Actually, the definition of Work is a Force applied over a Distance.

Weight is factor because a heavier vehicle will require more force to accelerate from a stop to cruising speed and will require more fuel during acceleration than a lighter vehicle. However, the acceleration portion of driving is very short compared with total trip time, so weight is not a large factor in overall fuel consumption. Once at speed, the aerodynamic drag of a vehicle is by far the largest force that the engine (aka fuel) must overcome. RVs are very high drag vehicles.


2003 Winnebago Minnie 24F - Ford E-450



Posted By: Dragonfly on 03/15/12 08:36pm

JaredWPhillips wrote:

I'm curious about fuel mileage as well.
I have a 2001 Silverado 1500 5.3 V8 4x4.
Last year I had a Jayco T24Z ToyHauler. It weighed around 6800 pounds. When pulling it I got a whopping 9-11MPG MAX. I thought to myself, "this is way too much weight to pull and get decent mileage."
Empty my truck can get as much as 18-19MPG if I drive VERY carefully. (I miss my diesel)
So, I thought a light-weight camper should give good mileage. I purchased a 2011 KZ Sportsmen 14FTH Toyhauler. It was only 15' long and weighed 2200 pounds. I thought I should get at least 14-15 MPG, since it weighs 4500 pounds or so LESS. Guess what I got? 9-11MPG. Then I realized it has to do with wind resistance. Both trailers were about the same height; both acted as a giant parachute going down the road. Didn't matter which was longer or which weight more. The truck didn't care about pulling the weight.
So now, I am shopping for a pop-up truck camper. I'm looking at a Palomino 1251, weight around 1500 pounds. I'm inclined to think that being a pop-up, the wind resistance factor will be very low and yield decent fuel mileage. I don't expect anywhere near my empty MPG but I would hope to see 14-15mpg? Maybe not, but it has to be better than dragging a trailer.


PLEASE REPORT BACK ON THAT. I AM IN THE PROCESS OF MATCHING A TRUCK CAMPER TO A HEAVY DUTY HALF TON FORD (SEE SIGNATURE) AND WOULD BE VERY INTERESTED IN YOUR RESULTS WITH THE CHEVY AND A POP UP.


DRAGONFLY - 2014, 19' Airstream Flying Cloud, towed by a Ford F-150, 4WD, extended cab, long bed, with Ecoboost engine, max payload & tow pkg, and 8200 lbs GVWR



Posted By: Jackthewonderdog on 03/15/12 09:05pm

ticki2 wrote:

With all the threads about MPG and how varied the reports are for different rigs I thought I would try to look at it from another angle. From my old school days I remember that the definition of work is weight ( pounds ) X ( distance ) = work ( inch pounds , foot pounds , mile pounds ). So the question is how much work do we get from our fuel . For this first example I compared two diesel trucks with campers .

Rig 1 , mid size 4 cyl diesel with small TC
25 mpg , gross weight 6600#

Rig 2 , full size 8 cyl. diesel with med TC
15 mpg , gross weight 11000#

The formula--- weight x miles / gal = work ( pm/g )


Rig 1 , 6600# x 25 miles / 1 gal = 165000 pm/g

Rig 2 , 11000# x 15 miles / 1 gal = 165000 pm/g


Now before someone jumps all over me , I fully realize there are many factors that affect fuel millage such as speed , wind , terrain , etc . This is only a quick guide to see how you are doing with your rig , in your terrain and your driving habits .


So , how much work are you getting from your fuel.


Here is how I figure MPG. Desire * Cost/gal = destination (solve for desire)


Posted By: av8rds on 03/15/12 09:20pm

christopherglenn wrote:

Drag is far more important then weight


IME thats on the money. My truck with camper on gets 10mpg give or take a few tenths. When I flat towed my DD Jeep behind it(3500lbs total) or my Off-road truck(6500lbs total) it only drops an average of .5 mpg on my normal trips. The big drag chute upfront makes more of a difference than the weight of my set up.


'08 Lance 992
'06 X-cab Powerstroke Dually 4x4
'75 Ford Bronco Rockcrawler



Posted By: Kemahsabe on 03/15/12 09:34pm

SkipJ wrote:

I believe drag caused by pulling an object through the air increased by the cube of the speed. My old boss , who was an rver,said at speed, pulling the trailer through the air took most of energy. SkipJ

At highway speeds, wind drag claims most of your gas. Drag increases with the square of the speed, so if you increase your speed from 60 to 70 (16.7%) your wind drag increases by 36.2% (1.167 x 1.167).

A couple years ago I had a LOOONG drive on a flat road with very little wind so I started experimenting with speed and mpg. I drove at 55, 60 and 65 and recorded the computer mpg several times at each speed. Turns out the change in mpg could have been predicted with the above formula. Almost all the change was due to wind drag.

I also learned that people don't like it when you drive 55 on the interstate!


Posted By: WyoTraveler on 03/15/12 09:39pm

I towed my 6000 pound TT at 65 MPH and got 9 mpg. Today I just towed my stock trailer at 50 mph with a 10,000 pound load and got 11 mpg. I think the biggest factor is speed and wind resistance.


2013 Monaco Monarch
2012 Jeep Wrangler
AC6CV, ex-WN8RUR, ex-W8RUR, ex-K7RIO, ex-WB6GBR since 1954
Commercial 1st class Radio Telephone, & Telegraph certificate
ARRL 35 WPM Certificate.



Posted By: rexlion on 03/15/12 09:44pm

The example makes suppositions about what fuel economy will be achieved with the rigs. The smaller rig IMO is unlikely to get close to 25 unless (and maybe not even if) its wind resistance is substantially lower than the large rig's.


Posted By: sirdrakejr on 03/15/12 10:21pm

I got an actual average of 12MPG when I was towing my 5th wheel and the combo weighed 19,460#.
I now get about 13MPG average carrying my TC and we weight 10,450# total. So I gained 1MPG dropping about 9,000#.
Same truck, same way of driving. Not bad I guess but I wish I got better.
Frank


2011 Palomino Maverick 1000SLLB on a 2004 Dodge Quadcab CTD Ram3500 SRW long bed equipped with Timbren springs, Stable Load bump stops, Rickson 19.5" wheels/"G" range tires and a Helwig "Big Wig" rear anti sway bar.



Posted By: wnjj on 03/15/12 11:17pm

CloudDriver wrote:

ticki2 wrote:

With all the threads about MPG and how varied the reports are for different rigs I thought I would try to look at it from another angle. From my old school days I remember that the definition of work is weight ( pounds ) X ( distance ) = work ( inch pounds , foot pounds , mile pounds ).

Actually, the definition of Work is a Force applied over a Distance.

Weight is factor because a heavier vehicle will require more force to accelerate from a stop to cruising speed and will require more fuel during acceleration than a lighter vehicle. However, the acceleration portion of driving is very short compared with total trip time, so weight is not a large factor in overall fuel consumption. Once at speed, the aerodynamic drag of a vehicle is by far the largest force that the engine (aka fuel) must overcome. RVs are very high drag vehicles.


Correct. Plus there are a couple more factors to consdier with heavier vehicles:

1) A heavier vehicle will have a higher rolling resistance due to heavier loaded bearings, more tires/axles or both.

2) A heavier vehicle takes more work to move uphill (force working against gravity). While some of this will be returned in the form of coasting on downhills, any time you use engine compression or brakes you're losing some that stored kinetic energy in the form of heat.

I agree that wind resistance plays the biggest part but when comparing vehicles with a similar shape but different weights the above comes into play, particularly in stop and go or hilly driving.


Posted By: sabconsulting on 03/16/12 01:44am

Of course as the camper gets bigger (and hence heavier) so does the cross sectional area and therefore the wind resistance.

Rig 1 in Ticki2's example is taken from my camper. Below is a picture I stole from one of Sleepy's trip reports showing his and Reddog1's campers parked next to a small truck carrying the same model of camper as I have (as you can see from my signature picture).



Apologies to Sleepy for reproducing his picture.

Steve.


'07 Ford Ranger XLT Supercab diesel + '91 Shadow Cruiser - Sky Cruiser 1
'92 Suzuki Samurai 4x4 1.6
'09 Fiat Panda 1.2
'10 Citroen DS3 1.6 turbo



Posted By: SugarHillCTD on 03/16/12 02:35am

Couple weeks ago we took a trip to Florida with our latest truck/TC combo to visit Cathy's parents. (The truck allowed us to carry our bicycles behind the front seat)

Had a time limit for the trip, so leisurely travel was not an option- 1300 miles each way- 2 days going down, 2 days for the return trip. On the highway I kept the cruise control between 65 and 67 mph. 6.0L gas 4x4 x-cab.

Fully loaded we are just under 9000#. Once we were out of the big hills of NH, Vt and northern Mass we were getting almost exactly 10 mpg. We would stop for a quick gas/potty/very short leg stretch between 160 and 180 miles.

So our pm/g was easy to calculate 90,000+/-

Just paid the credit card bill for fuel- just under $1100. Sister-in-law flew there and met us in Florida. Her airfare was $550.
Wanna' guess who had a better time traveling? We had a great time!

When is the next vacation?


John & Cathy
'12 Chevy 2500HD CC 4x4 sb
'12 Lance 855S
B4 that a few other TCs and a TT


Posted By: snowdance on 03/16/12 05:37am

For years we had an Airstream. It was a 25 foot Trade winds. It was very light as every thing inside was built like the inside of an aircraft so only wood was the floor. We lived in Fla. Flat so no hills. A friend had a 32 foot Airstream with a lot of wood and far heavier. He got sick so I pulled his far heavier 32 footer from the Fla Keys where we spent lots of time to St Augustine. Got the same fuel mileage as mine. Both had the same frontal area. We spent a lot of time in the Tennessee with family. Pulled it many times from Fla. Friend got sick pulled his 32 footer back got lower mileage than I ever got with my rig. Mts and hills took more fuel to pull the weight. Never been sure how to figure it other than when you hit the Mts all fuel mileage is out the window..


Snowdance

We spent most of our money traveling... Just wasted the rest..

Chevy 7.4 Vortex
2000 Jamboree 23b Rear Kitchen

http://www.flickr.com/photos/snowdance38



Posted By: superbird69 on 03/16/12 11:37am

Our truck and trailer weighes in at a combo of 28,000. We get 12 to 13 pulling the 5th wheeler and get 15mgp after we drop off the trailer.


FINALLY -FULLTIMING AND LOVEING IT


Posted By: chloe's ranch on 03/16/12 12:08pm

The highway mpg on my Tundra with the 4.6 V8 drops from 19-20 empty to 14-15 when I have the 1251 Bronco on.


Posted By: SugarHillCTD on 03/16/12 02:46pm

Not to throw water on anyone's campfire, but this is the truck camper forum, right?


Posted By: ticki2 on 03/16/12 02:53pm

superbird69 wrote:

Our truck and trailer weighes in at a combo of 28,000. We get 12 to 13 pulling the 5th wheeler and get 15mgp after we drop off the trailer.


Wow , you only loose 2-3 mpg pulling a 20,000# trailer . That has to set the record for PM/G .


Posted By: ticki2 on 03/16/12 02:58pm

SugarHillCTD wrote:

Not to throw water on anyone's campfire, but this is the truck camper forum, right?


That was the intention . I had also hoped folk would post their actual numbers , not just comment .


Posted By: ejfranz on 03/16/12 04:02pm

60 mph (100 km/h) 12.6 mpg (18.6 L/100 Km) average.
55 mph (90 km/h) 13.5 mpg (17.4 L/100 Km) average.

Work = Applied force that is parallel to the distance travelled X distance.

Travelling at a constant velocity on flat ground the applied force would be equal to the frictional forces ( Air, rolling and drive train). The mass of the camper will only change the rolling resistance once you get moving. Accelerating is another story as the more mass you have to accelerate, the more force you will need - so more work and more energy needed F(net)=ma.

* This post was edited 03/16/12 05:39pm by ejfranz *


06 Chevy Silverado 3500 Crewcab SRW 4WD - Allison 6 speed & Duramax LBZ.
Upgrades: BD diesel exhaust manifold, Edge Evolution, Timbrens & KYB Monomax.
Camper: 2005 Adventurer 90FWS - Electric jacks, LEDs, 6V batteries, roof rack, ladder & awning.



Posted By: Photog101 on 03/17/12 02:07pm

Well, I have a weird truck. Normally, I hold it right at the speed limits and get 9.5-9.75 MPG on the highway. City I get 7.5-8 MPG. This is while running empty. When I load my RL1200 on and drive at the speed limits on on the highway, I get 9.0-9.5, in good conditions. In the city, I still get 7.5-8 MPG.

Now, if I am empty and I drive this same truck at 80-90 MPH, I will get 10.5+ MPG. I found this out, when I had driven up north, 255 miles, in Michigan on a business trip. While I was up north, I got an emergency call and drove like a mad-man to get to my mother's bed side. I got 9.5 going up and 10.75 coming back on the same route.

So thinking that it was a fluke, I drove to the west side of Michigan, 190 miles, at the speed limit and still got 9.6 MPG. On the way back I drove at speeds up to 90 MPH back to the originating point and filled up again. I got 10.5 MPG. This was all two years ago.

Last year I had to go out to Vegas, NV, but I had to stop in Denver. As I drove through the states with the lower speed limits, I was getting 9.5 to 9.75 MPG. Once I got to Omaha Nebraska, I started to do my higher speed checks. The mileage started going up. When I got to Utah, I really opened it up and cruised at around 85-90 and the MPG continued to climb. The best that I got was 11.3 MPG in Utah. On the way back, I once again got the same readings.

I took all my findings to a GM Rep, and they told me that I had to have made a mistake. RIGHT!!!!!

Of course I would not even try that with the T/C on the back.

Just thought that I would add some information to what has been posted.


Combat Vietnam Veteran Support our troops for serving our great country.
1997 Veri Lite RL1200 on a '02, K3500, CC, DRW, 8.1L, Allison, 4.1 gears, Bridgestone 225/70R19.5 tires.



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