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Old 05-26-2008, 10:48 PM   #1
1 Rivet Member
San Francisco , California
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8 MPG and one other question

Hello there everyone,

I am happy to say that I am the now proud owner of a 2008 AS 25FB International Signature Series CCD. I picked it up at Toscano RV at Los Banos in California and started towing it with a new 2008 3/4 ton Suburban LT. I realize that this is not quite the Toyota Prius (averaging 15 mpg) without towing anything but when I got 8 mpg on the first 100 miles towing the trailer, even I was a bit surprised. Call me naive but I was hoping for something like >= 10mpg.

I have a few new-owner questions (only the first one related to mpg):
  1. What's the typical MPG that you get? Am interested in your car/trailer combo to compare.
  2. I have the Primus Brake Control (and it's set to 2.5, as installed by the RV dealership) - when I hit the brakes, there's a significant jerking going on when the trailer brakes engage. Is that normal? Is there a more appopriate brake control setting?
  3. I have read some threads that went like this: "I got a Suburban 2500 and I don't even notice that I am pulling anything". I have to say that that's not at all my experience. I feel a significant drag on the car (to the point that I called the dealership asking them for the brake release on the trailer) ... not that simple physic knowledge wouldn't tell me that but I am still wondering whether those other threads tell the true story. Is a significant drag expected?
  4. Whenever I make fairly tight turns or get going, there's this aching noise from the hitch and the trailer tires. May be it's not all broken in yet but is this normal?
Thanks for all your help getting my expectations set correctly.


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Old 05-26-2008, 11:56 PM   #2
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You have a 3/4 ton Surburban, but we don't know what axle ratios you have. I am betting either a 3.42 or a 3.73. From what you describe, I would not be surprised if it is 3.42 which is not as good as a 3.73 for towing. I used to have a 350c.i. TBI with 3.42 gears on a Yukon and got 6 mpg @ 60 mph towing a 31 ft trailer....I get 12 mpg @ 65-70 mph towing it with my Duramax/Allison Diesel and 3.73 gears.

Also, we don't know the motor size you have purchased. Sometimes people buy smaller motor for better gas mileage for all those miles they are not towing, and just bite the bullet when they do tow. An 8.1 litre is a towing machine, but the gas mileage when you are not towing will not be very good.

I see you live in California. This means you no doubt have the California Emmissions package on your vehicle which CHOKES the power completely out of it lest you potentially harm the enviroment, and I am not even sure the 8.1 litre is offered in Caleeeefornia. Perhaps you can appeal to the Governator to get the enviromentalists to run into the Pacific and not come back.

I don't know what kind of hitch you have, but it does sound like you have a dual cam weight distribution set up, or a friction anti-sway set up. They make aching noises in the turns at slow speeds....that's just the way it is.

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Old 05-27-2008, 12:37 AM   #3
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I have read some threads that went like this: "I got a Suburban 2500 and I don't even notice that I am pulling anything". I have to say that that's not at all my experience.

Hi, anytime someone says that they can't tell anything is back there, is either bragging about their new-found monster truck, Diesel, lying, or shouldn't be towing on the road with the rest of us. Dangerous. I can feel the difference with more gas in the tank or one more passenger in my vehicles; And people say they can't feel the difference with 1 1/2 to 5 tons of trailer behind them! If you really can't feel that trailer behind you, then you can have major surgery with out having the doctor turning your lights out. [my opinion]

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Old 05-27-2008, 04:03 AM   #4
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2007 28' International CCD
Windermere , Florida
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Is your truck a diesel? Or, gas? Calif emmission equip may be your problem. Diesels improve in performance quite a bit after breaking in.
Not feeling the TT is just an expression. With a heavier TV, a longer wheel base, and a beefier motor, the towing experience can be like night and day.
Compared to some SUV's. Proper hitch set up is critical though.

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Old 05-27-2008, 04:49 AM   #5
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Brake controller?

Just because the RV dealer installed the controller doesn't mean it is done correctly. After you tow awhile stop and check you hub temps, cool is good. When coasting down hill does the rig slow down on it's own? What kind of mileage do you get not towing? Lots of variables!
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Old 05-27-2008, 05:25 AM   #6
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Please follow JayRay's suggestion about the brake controller possibly not being installed or adjusted correctly.

FYI: We have a '08 Safari 27 FB SE and pull with an F-150 4x4 with the 5.4L motor and 3.73 rear. Although we've only had it out twice, I got 10.5 - 11.0 mpg. My trailer is heavier than yours and I probably have a smaller TV since you're is the 2500. I DEFINATELY know I've got a big aluminum rig behind me when towing.

We have an EZ-Lift WD hitch and it moans and groans all the time when doing slow turns. No big deal.
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Old 05-27-2008, 05:58 AM   #7
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David -- 3.43 is actually slightly better for mileage than a 3.7; it just transfers less torque to the drive wheels. 4.1 transfers the most torque and gives less mileage -- members have reported that is hard to tell in real life. I probably wouldn't want a 3.43 rear end for any weighty towing.

'08 Burb? GM discontinued diesel for Burbs maybe almost 2 years now? Twink could tell you for sure but I think that ended for the '07 model year. Likewise the 8.1L gasser -- it has been discontinued for a while now.

Helge, it would be useful to know what your engine displacement and axle ratio are anyway. Driving style probably has the most impact on mileage. The trailer tires are rated at 65mph (depending on inflation). I'd certainly stick to no more than 65 in hot areas! I pulled my 25' FB SE for 150 miles this last weekend. One direction I kept an absolutely soft foot on the accelerator and pegged at 55mph. I'm not a jackrabbit on the gas pedal but I decided to cruise at 65mph on almost 2/3d's of the ride home. I only got 1mpg improvement by going 55mph (may not be a real test for your situation; I have a diesel). Other significant impacts on mileage are whether you pull with water in the tank and whether the tow vehicle air conditioner is in heavy use.

I did have a Nissan Titan at one time -- 5.6L engine, 4.1 equivalent axle. With a 5-speed, it would shift down 2 gears when addressing any hill. I had to work and have very favorable roads to get anything over 9.5mpg.

I don't know that brake controller. If you can manually actuate the trailer brakes, the setting should be strong enough to bring the combined duo to a fairly rapid stop from 20mph (don't do that at higher speeds). Will it do as well if you lighten the setting? Read the instructions about calibration like this. The more well known Tekonsha Prodigy has a problem with jerky stops. I've got one and have lived with it so far.

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Old 05-27-2008, 06:15 AM   #8
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I have pulled for about 75,000 miles and have found that several things that help me with my mileage.
1. Steady speed with cruise where pratical
2. speed at 60 mph or less provides the best mileage for me its 1800 rpm.
3. don't accelerate up hill, gather speed before the grade and get into the right lane when your speed falls off, regain speed as you decend the grade.
4. plan your trip so you don't have to be in a hurry, I get 13+ mpg at 60 but only about 11 at 68-70 so I plan my day accordingly. A 450 mile day is a big day, yes I have done 600 plus but very infrequently and usually only when coming home.
5. Wind speed and direction can have as much influence on mileage as the speed indicated on your speedometer. Tail winds have given me a 2-3 mpg boost head winds have done the some in a negative direction.
6. reduce speed, drive in the right hand lane, enjoy the countryside and the increased fuel mileage. Another plus is you don't have to be concerned about the highway patrol.
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Old 05-27-2008, 06:24 AM   #9
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Yea, GM diesels in Suburbans have not been available for 10 or more years, so unless you got something a lot of us have been drooling for, you most likely have a gasser and if it's 3/4 ton, most likely around a 6.0L since the 8.1L was nixed for the 07 model year.

I have a 2004 6.0L 3/4 ton Burb towing a 25er and I have 4.10 gears and I average 11mpg. Mostly cause I drive about 62 to 65mph. When I towed at 50mph following the suggested GM break-in period of the first 500 miles towing I actually got near 16mpg towing the 25er and that is with 4.10 gears!

Something must be wrong or you are towing in hills or non-flatland. I have the Prodigy brake controller because my burb came with adjustable pedals. I installed it myself in about 15 minutes or less. I have never heard of your brake controller, but I would suggest that you look at either the brake controller and or the brakes on the trailer if the vehicle acts as it should when not towing.

A good way to see if you have any brake drag is when towing, feel the inside of the center of the wheel by touching your finger on the brake drum. With your rims, it should be fairly easy to do, but be careful mind you, if they are hot, you can get burned pretty easy, so slowly see feel before touching if heat is coming off before making contact.

Also don't rely on the DIC in the dashboard for the instant MPG. It's the average MPG that you should be concerned. I have seen my instant go down to 1 or 2 MPG, but that was temp as I was going up a hill.

Depending on your hitch setup, yes the groaning and creeking is fairly normal. I have the Reese Dual Cam and place a very, very, very, very sight amount of Vasilene on the cams and I also lube up the ball generously as I do the hitch side of the trunnion weight bars. I also place a very light coating of WD-40 on the chains, dab them dry and these steps on my particualr setup seems to reduces the creeks and groans significantly.

On an unrelated note:

Remember, GM has a 500 mile suggested break-in of 50 mph for the first 500 miles of towing if the truck is new. Older meaning more than say 6000 miles the break-in is not as important. I got my truck with near 0 miles on it, so the break-in was a good idea, followed by a change of fluids across the driveline (including the front diff, transfer case, trans, rear diff and of course motor oil change) after the first 3000-4000 miles. This will get out any of the metal particles that are worn off during break in. Flushing the fluids helps purge these contaminants from the fluids and can extend operational life of the equipment. I actually went with Amsoil fully synthetic and severe gear rear end diff oil.
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Old 05-27-2008, 06:28 AM   #10
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3.43 is actually slightly better for mileage than a 3.7; it just transfers less torque to the drive wheels. 4.1 transfers the most torque and gives less
About torque and axle ratios:

An engine develops torque and horsepower irrespective of the rear end ratio that the vehicle it is installed in has. Torque (what gets mass in motion) occurs at a lower RPM than horsepower. For the sake of arguement, lets say that an engine develops its maximun torque at 2500 RPM and that the vehicle has a 3.50 axle ratio. Lets also say that this vehicle is traveling at 65 mph at 2500 RPM. Not the ideal situation for getting mass in motion, although could prove beneficial for fast crusing up the mountains! Now, lets put a lower (higher numerically) axle ratio in the same vehicle, now that peak torque arrives at a lower vehicle speed, although still at 2500 RPM. As the vehicle accelerates through the gears, the peak torque is reached at lower speeds which is beneficial for getting the rig moving. So, you see, the axle ratio has nothing to do with the amount of torque being delivered to the wheels, just at what speed the peak is being delivered.

Fuel consumption is affected by axle ratios because the higher the number, the slower the vehicle will be travelling at a given RPM. Generally, the higher the RPM at a given speed, the more fuel is consumed. Now, if we were talking about diesel boats, the story would differ, but that is not suitable here.
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Old 05-27-2008, 06:37 AM   #11
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I did a very unscientific test of two nearly identical 3/4 ton burbs a few years back, both towing Airstream trailers of similar weights and length.

My burb has the 4.10s and the other burb (also a 3/4 ton with same setup) had 3.73s. We filled up and continued on from the midwest rally to Savanna, IL. I expected my truck to eat more gas, but what I found was that the fuel hit between 3.73 and 4.10 is negligible. DICs, fuel gauges were basically identical for the same distances and road conditions traveled. I also had 2 more passengers, two dogs (65lbs and 25lbs) and some additional cargo in the truck for the kids (15 and 8). My engine RPMs were very close to that of the truck with the 3.73. I had expected worse MPG and far higher RPMs, which really in this comparison didn't happen.

Of course this is not scientific, but given some of the conversations on this forum about the disparaging difference in MPG for the higher ratio gears, I found these comments to be not accurate, at least between 3.73 and 4.10s of vehicles of nearly identical build and road condition traveled. Your milage may and most likely will vary comparing 4.10s to 3.42s.
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Old 05-27-2008, 06:45 AM   #12
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Helge, something is wrong. I suspect it may be your brake controller and/or hitch setup. 8 mpg is not realistic for towing a 25’ with that truck. As your truck is new, it must have the 6.0l and either 3:73 or 4:10 final gear (GM would not put lower gear ration in a ľ ton). This setup is fine and should yield better performance than what you are now seeing.
I think either the brakes are dragging (carefully check your hubs; ouch! Hot!) or your spring bars are not set to provide proper weight distribution (this would cause the “awkward” handling).
You have plenty of truck for that camper and should be cruising along and getting maybe 11-12 mpg?!
Relax, review your equipment, and try again,
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Old 05-27-2008, 07:41 AM   #13
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I get 14 to 16MPG with a 1999 1500 4X4 Burb towing our 20 foot Argosy (5.7L, 3.73 rear), and between 15 to 18MPG when not towing. The biggest factor I've found in geting better MPG is keeping my size 13 off the gas and keeping the speed down to 55 to 60MPH. Just speeding up to 65 MPH makes the gas gauge start to move!

Having said that, coming home this weekend in heavy traffic, I got somewhere between 11 to 12 MPG. It took us 5 hours for the 100 mile drive, so it was a lot of stop and go...
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Old 05-27-2008, 08:27 AM   #14
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Proper driving technique is what separates the best from the worst drivers of a given rig (all other things being the same), a difference of 30% from transportation studies on commercial vehicles. In other words, knowing what to do in a given situation counts most.

For most of us, past the point where we have some experience under our belts with a given rig, ALL the increases are incremental, AND one must be able to quantify them in order to KNOW what is working and what is not. Thus, is the tow vehicle achieving its' estimated EPA mileage in solo driving conditions after suitable break-in? If not, what needs to be checked, or what do I need to modify in my driving?

My first step with any rig is a set of weights taken at a certified vehicle weight scale: first the tractor, then the trailer, (with a travel trailer, include the tongue weight), and the combined rig. Preferably, one would be able to weigh the rig wheel-by-wheel, but this type of portable scale set is pretty much the province of very large institutions and not available to the general public.

We want to know not only the gross weights, as above, but preferably any discrepancies of balance. All three, four or five axles have an individual rating, and I NEED to know it.

Second, the suspension alignment of tractor and trailer, is often, (even new) off from spec. And an unbalanced rig -- due to hitch rigging, poor load arrangement in the trailer or tractor -- can cause undue weight on a given axle or axles. This "can" result in the need for increased steering input as either the steering axle is unloaded, or the trailer is tail-heavy, etc. Even the combination thereof. This "wander" results in a fairly significant penalty, ESPECIALLY when aggravated by winds, etc. It is foremost a matter of safety, and fuel economy second.

Having addressed the alignment of all axles -- and having confirmed that tires, shocks, brakes and bearings are in proper working order -- the specifics of the hitch rigging need to be seen to. There are many excellent threads on this subject on this forum. The work necessary is somewhat painstaking the first time through, but, as it is also a matter of safety which no one else will do for you, you'll find that the work is satisfying and confidence-inducing.

Others have mentioned the effects of wind, traffic and terrain. I would start any conversation on trailer-towing with a discussion of how one is, now, NO LONGER just another vehicle on the road. There are many who, sheep-like, feel "obligated" to "keep up with the flow", etc. No.

An RV is the least-capable vehicle on the road (outside of some million-dollar buses), and needs to be driven accordingly: under the speed limit, with exaggerated following distances; the need to be always aware of overtaking traffic, etc. There is a way to smoothly drive in this new environment for best fuel mileage, but it is an issue of safety first followed by best possible fuel mileage for current conditions of road, traffic and weather.

Numbers must also be kept as to fuel mileage overall, solo and towing to gauge the vehicle condition. A drop of 10-12% from established norms means something needs attention.

In short, what does the trailer weigh, travel-ready? Tongue weight?

What does the tow vehicle weigh, same condition? Their combined weights (as expressed by individual axles)?

Are all tires, brakes, shocks operating properly? Are all axles in alignment?

Hitch rigging? An analysis here, per experienced members, will yield safety and fuel economy gains.

Driving an RV, not a car, it IS different. One does not try to keep up with traffic but is always concerned with smooth, safe, economical operation at all times, giving great respect to road speed versus conditions of traffic, weather and surfaces being traveled (the pitch, the composition, the markings, the lighting, the available space fore and aft as well as side-to-side) and always saving energy for the unforeseen. One needs reserves in all areas to operate most efficiently.

These basics addressed, then an average -- of over several thousand miles -- will confirm the range of fuel economy versus speed, terrain, weather and traffic.

These are the basics of analysis for comparing one rig versus another, or changes to ones tow vehicle. Gearing, camshaft selection, engine size or type, tow vehicle weight and aerodynamics. It is simple to say, "I don't have the right TV", but one needs to check all parameters FIRST.

An Airstream, of a given size, will be less affected by road surface or wind than its competition. One must then factor in the weight to compare to other, seemingly similar TV/Airstream rigs.

I have read more than a hundred threads, with a few thousand posts, to find other, comparable rigs against which I can judge mine, and now have a pair of comparable rigs: One, with a near-identical truck and A/S (mine is another brand of aerodynamic aluminum trailer), and the other has a competing brand of truck with the same brand (but different-sized) trailer.

My mileage appears to be at the top of the range for all measured conditions. With a near identical trailer, my father pulled with a 3/4T V8-454/T-400/3.54 TBI Suburban and achieved 7-8 mpg for many years and miles which was part of my impetus to have a diesel truck.

I average 15 mpg at 63 mph on smooth, lightly-trafficked Interstate with a rig grossing 15,570-lbs). The alignments are all corrected, the tires are new and inflated per directions; tire/wheel balance is perfected, brakes do not drag or pull; the hitch rigging -- though not yet ideal -- is good; the TV has no operating issues, etc.

I have to address the unfinished questions of proper TV weight transfer; the 60" gap between the TV camper shell and the trailer (big truck studies show that there is significant fuel mileage loss on gaps over 30"), trailer "tracking" that I am not yet satisfied with, etc. I see it as ongoing. The price of fuel is not as important to me as would be accelerated wear, not to mention safety.

Take care about seemingly simple answers. It may be that increases with your current rig can be found if small things are addressed, and then that the big one (driver skill) is improved. It's a bit of trouble, granted, but dirt cheap compared to another TV.

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