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Old 06-29-2010, 09:55 PM   #1
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2500 6.0 Suburban 4x4 3.73 gears towing at elevations

Need some real user input. I have a 2003 Suburban 2500 4x4 with 3.73 gears and 6.0 engine.

Published specs state a tow rating of 7600 lbs for the 3.73 and 6.0 (and 9600 lbs for the 6.0 and 4.10's). If I apply the 10% and 20% rule of thumb I should not be towing more than 6800 and 6000 lbs respectively.

1. The vehicle with the 8.1 and 3.73's is rated to tow 10100 lbs. Therefore the chassis should "handle" the weight (ie stopping, drive ability) and the rating is really about power/torque to the rear wheels.

2. I have towed 8000 lbs of equipment from southern Ill. to PA and barely knew that I had a load behind me. I did slow down on the WV hill climbs but still maintained 55 mph.

3. I also tow about 9300 lbs of equipment locally (within 2 hours). That I know is behind me but I can keep it going 55-60 on the highway no problem. I have never towed it through the mountains.

4. All of my towing has been with over sized tires which effectively make my gear ratio go from 3.73 to 3.42 (estimating that 10% oversize in tires equal about a 10% reduction in perceived gear ratio)

Lots of forum comments on the mfg rating, unloaded trailer weight,, passenger weight and then the rules of thumb for 10% for wear and tear on TV and 20% for loses in higher elevations.

Soooo, I have towed much heavier loads than the "experts" recommend but have not had any white knuckle experiences or power issues. My concern however is as follows:

1. Airstreams will have more wind resistance than towing equipment.
2. Looking at taking a trip out to Denver area while towing about 8500 lbs behind me. Denver has a much higher elevation than western PA. Also may get adventurous and have to drive a 10K foot mountain pass.

I can't justify buying a new TV or modifying my current vehicle for a few trips out west. I also have a hard time with the 10% reduction considering that the manufacturers are building safety factors into their tow ratings. The 20% makes sense to me due to decrease in O2 levels at altitude.

Anyone have any personal experience with a similar setup? Should I be concerned with more than my speed dropping and watching my temp gauges?
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Old 06-29-2010, 10:48 PM   #2
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Welcome to the forum.

Hi, with a tow vehicle rated to tow 7,600 lbs and you planning to tow a trailer weighing 8,500 lbs, I would not be concerned about tire size, final adjusted ratio, power and torque, or high altitudes. I would be more concerned that if anything went wrong and someone was injured or killed, that it would ultimately be your fault for towing beyond the tow vehicles documented capacity. Still can't justify buying a proper tow vehicle?

"You may not like what I have to tell you, but it's the truth". You asked!
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Old 06-29-2010, 11:33 PM   #3
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Yep...read that in other forums. Are you an attorney?

The gross weight rating according to the manufacturer is 12000 lbs based on the chassis. IE that's why I can simply install 4.10 gears and not modify anything else in the vehicle and be within the manufacturer rating of 9600 lbs with the same engine and chassis and below the 12K rating. (FYI the 12K rating is with the 8.1 engine and 4.10 gears and all things mechanical remaining equivalent)

As for liability, if the 12000 lb limit was exceeded then there would be an issue with liability.

Any SAE engineers out there or farm boys got input on this topic?

FYI....just because the mfg rating is 12K doesn't mean I would tow 12K with it, but the reason for that is based on tow vehicle weight versus trailer weight. The TV would be lighter than the TT and you get pushed around. But that is based on experience....Been there, done that.
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Old 06-29-2010, 11:46 PM   #4
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My personal rule is to add 10% to the TV manufacturer's ratings in the mountains and 20% in the flatlands, but I don't necessarily recommend that for others.

You do have to decide for yourself how much of the manufacturer's ratings are based on things like science, engineering, and testing and how much are based on things like product line differentiation, market positioning, and controlling warranty costs.
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Old 06-29-2010, 11:49 PM   #5
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DaKarch,

It sounds like you have read the forums on this topic and they appear to indicate that the majority of Airstream owners in your situation would not exceed the tow rating on the vehicle.
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Old 06-29-2010, 11:53 PM   #6
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Quote:
Originally Posted by ROBERTSUNRUS View Post
I would be more concerned that if anything went wrong and someone was injured or killed, that it would ultimately be your fault for towing beyond the tow vehicles documented capacity.
I think it's important to carry sufficient insurance.

I also would welcome citations of any cases where fault was ascribed in an accident involving non-commercial towing where a major factor in the outcome of the case was that the GCWR or rated towing capacity of the tow vehicle was exceeded.

Most travel trailer accidents involve sway or separation of the trailer and the tow vehicle yet we have people who won't buy a 4 bar hitch or spend the extra $20 for the right kind of safety chain extensions. In some cases these same people will spend $10,000 super-sizing their tow vehicle. Go figure.
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Old 06-30-2010, 12:00 AM   #7
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i sense a trolln postnthread but...

ok, welcome.

Quote:
Originally Posted by DaKarch View Post
...the rating is really about power/torque to the rear wheels...
so u know this HOW?

many debate how ratings are developed and applied,

the many mysteries of ratings and ...

p/t to the rear wheels is seldom suggested as...

the key issue.

Quote:
Originally Posted by DaKarch View Post
...I did slow down on the WV hill climbs but still maintained 55 mph....
without data or rpms, tranny temp, brake performance and so on...

hills at 55 means zip2me.

Quote:
Originally Posted by DaKarch View Post
... All of my towing has been with over sized tires which effectively make my gear ratio go from 3.73 to 3.42...
ok so this is pretty close to correct BUT only 1 of the issues with "oversized rubber"

this note is starting to remind me of an older thread on burbons and fat tires and speed...

http://www.airforums.com/forums/f463...way-31760.html

hopefully YOU are brighter than dimmer...

Quote:
Originally Posted by DaKarch View Post
...Denver has a much higher elevation than western PA.

The 20% makes sense to me due to decrease in O2 levels at altitude...
while it's true denver is higher than western pa, there is NO DECREASE in O2 levels at altitude...

the partial pressure (Pa) goes down with elevation not the 02 level (concentration)...

as the partial pressure drops and the absolute volume of O2 burned goes down, the fuel mix gets RICH

forced induction reduces this effect significantly, not completely.

something similar happens in yer blood stream and this is not helped by turbo chargers.

Quote:
Originally Posted by DaKarch View Post
...Should I be concerned with more than my speed dropping and watching my temp gauges?
yeah, stopping, lane stability control in the twisties and so on....

((REread the linked thread above))

lots of issues to be concerned with besides speed.

and there are very few modifications that would be meaningful for a NA gasser burb towing in the rockies.

except appropriately sized tires, tranny cooler, fresh brakes, fluids, gear oil and so on...

your note basically suggests...
1. you've done it all
2. the expert views are irrelevant
3. no plans to buy or tweak the burb...

so what exactly IS the point?

go west have fun and hold on...

if towing a sizeable stream expect to go UP hill slowly with an over heating tranny...

and down hill too rapidly with hot brakes all around.

cheers
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Old 06-30-2010, 12:15 AM   #8
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2air his point is that the rocket scientists in Detroit sold exactly the same 'burb with exactly the same parts EXCEPT for the 8.1 gasser in place of the 6.0 gasser and in the 8.1 configuration uprate the GCWR by 2500 pounds. The 8.1 gasser is not going to improve control in the twisties or give a cooler running trans. All it's going to do is have lower RPMs because the PCM shift points are reprogrammed, and go a little faster off the line.

Highly relevant for those who are taking their traylah to track day, but otherwise, what difference does it really make?
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Old 06-30-2010, 12:22 AM   #9
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Quote:
Originally Posted by Jammer View Post
I also would welcome citations of any cases where fault was ascribed in an accident involving non-commercial towing where a major factor in the outcome of the case was that the GCWR or rated towing capacity of the tow vehicle was exceeded.
Hi, call it hear-say, or whatever. I have read, and heard, that this comes into play if there is a fatality involved. Other than that I have no documentation and I don't want to find out first hand.
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Old 06-30-2010, 12:29 AM   #10
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Quote:
Originally Posted by Jammer View Post
...his point is that the rocket scientists in Detroit sold exactly the same 'burb with exactly the same parts EXCEPT for the 8.1 gasser in place of the 6.0 gasser...
o i get dat point...

but simple conclusions (how the ratings were created)

based on PARTIAL simple observations lead to ...

simple minds.

like mine.

cheers
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and my gas money is still on trolln.
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Old 06-30-2010, 12:54 AM   #11
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Look....basically if the forum is an AS forum or a diesel forum or a towing forum I see the same debates, same points and the same personal opinions being pushed as the Gospel.

What I was looking for was personal experiences. Did you go and buy a TV based what you read on the internet, do calculations, or have some experience that made you purchases. More specifically, has anyone out there towed with this or a similar vehicle and a similar load?

That is the point of the post. I think that why I typed in my first post, "Anyone have any personal experience with a similar setup? "

Per 2airishuman....

In its simplest form the 03 Towing guide (Nothing more nothing less. I didn't make it up. I just repeated how they published it.) list vehicle configurations and "p/t to being the issue" is based on the mfg tow rating only being changed due to 2 things engine size and gear ratio.

FYI engine HP and torque can be related to rear wheel HP and torque. The gear head rule of thumb is an assumption of about 15% loss through the drive train.

As for handling and stopping then you need to look at wheel base vs trailer length, TV weight vs TT weight, proper hitch equipment etc.

Don't remember rpms (certainly wasn't in overdrive and I vaguely remember it kicking from 3rd to 2nd on one of the pulls going into WV), brakes never faded or got hot enough for me to smell them, tranny temps were well under the red (can't remember the exact number but it never alarmed me).

The over sized tires are no longer installed, but they were on during some of my towing experiences and they were mentioned because they do have an impact on the net drive train. My personal experience is that around PA a realized 3.42 ratio did not seem to cause me problems. I expect the Rockies to be a totally different story and therefore have installed stock size tires.

Altitude, can we agree that the air is less dense and therefore will impact engine performance?

Items such as general maintenance, brake fluid replacement, trans cooler are all done. I don't think I have missed anything, but I bet someone will tell me if I did .

So no I am not going to buy a new TV and I may change the gears out. I agree, there is little to do to that is cost effective to a gas'r engine that will have any large magnitude effect at altitude.
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Old 06-30-2010, 01:18 AM   #12
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Jammer you got it!

There will be personal opinions that maybe a 3/4 ton burb should not be pulling 8500 lbs

But the published data states 2 variables to determine the tow rating one being engine displacement and the other being gear ratio. Nothing else.

I have talked to AS support and even tried the local GM dealer. Their responses are canned. Which brings me to the post looking for real world experience with something similar TV and load.
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Old 06-30-2010, 01:44 AM   #13
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well go read,

there are 100s if not 1000s of posts here with personal experience based on that combo...

what combo? the stream isn't specified.

and the personal experience is ALL OVER THE BOARD.

i've yet to read from ne1 posting they SWAPPED engines big way up...

but there are lots of posts with personal reports.

i loathe posting personal experience, in many cases it is worse than NO info...

and the specifics matter ENTIRELY while the personal reports seldom include important details...

so it becomes LIKE mpg reports (which are all fish stories) while towing.
__________

i do have 75,000-100, 000 miles of 454/airstream driving experience...

that figure is JUST in the rockies, crossing the c/d, wyoming, the cascades, bc rockies and so on...

i've also used that combo in the keystone state (about 2-3k miles)

they is NO COMPARISON.

above 5,000 feet the towing changes significantly

from 8000 ft and climbin to 10 or 11,000 is many times different than the 5,000 ft issues.

SLOW UP HILL really really slow, with brakes and gearing and steering and tires tested on the downslopes...

often miles and miles of downslopes producing stresses that are different but JUST AS TOUGH...

as the UPslopes.

climbing at 15-30 miles per hour on the interstates WITHOUT truck lanes or in tunnels OR when problems happen is no fun.

blocking traffic is no fun.

parking and waiting for a cool down is no fun.

smoking the brakes or tranny DOWNHILL is no fun.

and so on.

of course THAT personal experience is not with the 6 l or 8 liter, but rather a 70s 454...

that was TWEAKED TO THE MAX and moved at 80+ mph easily on the flats (even at altitude)

eat it with a shake of salt.
_________

1 time doing the rockies, and the report is..."i've done this and survived, so i must be cool..."

but take these routes many times and the wimpy performance matters, and the ratings become IRRELEVANT.

blocking traffic, getting crap tossed at your slow moving rig, having the fuzz suggest MOVING to the shoulder is no fun...
_________

altitude tests gear. pa has NO altitude and simply doesn't compare to the high plains or big rocks in da west.
_________

again since NO UPGRADES are planned what's the point of reports good or bad, just go and try it yourself.

Quote:
Originally Posted by DaKarch View Post
the published data states 2 variables to determine the tow rating one being engine displacement and the other being gear ratio. Nothing else...
this statement is patently incorrect and it's so incorrect that explaining WHY would require starting so far back...

and it's been done already.
________

IF you've solved the rating puzzle, and

IF all the forums have ALL the same arguments...

then it seems likely,

they must also have ALL the same personal experience reports too...



next!

cheers
2air'
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Old 06-30-2010, 01:46 AM   #14
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I can't give you personal experience. But I can give you some useful information.

Normally aspirated engines typically lose 3% of their horsepower per 1000 ft. of altitude. To complicate matters you have to take into account air temperature at altitude to get "density altitude." This web page gives a clear explanation and a chart:
Private Pilot Resources - Aviation Blog: Density Altitude Chart

On a hot summer day a location like Denver can have density altitude of 7000+ ft. or more. A location like the summit of a 10,000 ft. pass can have density altitude of 12,000+ ft in 60 degree temps. So at the crankshaft Denver summer daytime power and torque could be down to the 75% power range and at the summits 55% range. The engine would make roughly 160 horsepower at 10,000 ft. and 220 ft pounds of torque. Drivetrain losses being constant reduce the percentage a bit more.

As one that has driven in these conditions but not towed your expected load, I'd say the biggest problem is getting the load moving and getting the engine RPM into the meat of the powerband. Certainly getting shorter gearing in the axles would be of benefit. But I honestly have no idea how well this would work.
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