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-   -   Stiffer suspension? (https://www.airforums.com/forums/f463/stiffer-suspension-122264.html)

pjtaia 07-08-2014 09:06 AM

Stiffer suspension?
 
I tow with a 2005 Yukon XL, with the 8.1 ltr engine. Tow rating is 12,000 lbs, plenty for my "new" 34' Airstream with slide out. But the 1,250 lbs hitch weight seems to be a challenge. The rear end of the Yukon sags or squats visibly. The Hensley hitch can't seem to throw enough weight onto the front of the Yukon. The rig handles fine, although the steering seems a bit "light".

I'm considering somehow beefing up the rear suspension, or adding air bags. I have NO experience with this type of thing.

Any advice would be appreciated.

Thanks
L.A. Phil (In Irvine)

BoldAdventure 07-14-2014 02:03 PM

Airlift 1000 bags are fairly inexpensive and easy to install. GMC Yukon 2000-2014 Air Helper Springs - Air Lift 1000 #60769 - 2011 2010 2009 | SuspensionConnection.com

They will help with sag.

Also, Rancho RS5000 or the Bilstein 5100 rear shocks. You'll want a heavy duty shock, not the factory stuff, which is usually a little softer for ride comfort. If you're running factory shocks, there is part of your problem.

Hope this helps.

Tim A. 07-14-2014 02:43 PM

Check with Hensley. Sounds like you need heavier spring bars for your hitch.

Tim

pjtaia 07-14-2014 02:47 PM

Tim: Thanks. I already did that, after I discovered that they had sent the 800 lb. bars. When I told him what my hitch weight was, he quickly sent out the replacement bars (1,400 lb.)

Still won't handle it...

Phil

87MH 07-14-2014 04:14 PM

Quote:

Originally Posted by pjtaia (Post 1479631)
I tow with a 2005 Yukon XL, with the 8.1 ltr engine. Tow rating is 12,000 lbs, plenty for my "new" 34' Airstream with slide out. But the 1,250 lbs hitch weight seems to be a challenge. The rear end of the Yukon sags or squats visibly. ...
I'm considering somehow beefing up the rear suspension, or adding air bags. I have NO experience with this type of thing.

Adding Airbags does NOTHING for the axle rating. Best to take your rig as it is now and get a full set of scale readings. Get the unloaded axle weights of the Yukon, the weights of the three axles on the AS, and the actual tongue weight (don't forget to throw in the weight of the Hensley somewhere).

Usually the first thing to bust specs is the rear axle. With the extra weight of the slide on the AS, I'm betting that you are overweight with just the AS and Hensley on the tongue. I would not take a chance on overloading the Yukon.

BoldAdventure 07-14-2014 06:17 PM

Quote:

Originally Posted by 87MH (Post 1482299)
Adding Airbags does NOTHING for the axle rating. Best to take your rig as it is now and get a full set of scale readings.

No one said anything about axle ratings or airbags increasing them. He said he has sag/squat. Airbags can help with that. Especially on rear coil spring vehicles, GM uses a progressive and linear rate spring. The Linear rate springs will collapse or sag more under load than the progressive rate springs they use on the Z71's for example. Both have similar ratings, but both compress differently, and both ride differently.

Axle ratings is a whole other subject. If your sagging and NOT overweight on your axle, then Airbags are viable.

Gregsch 07-14-2014 07:46 PM

I am certainly not an expert on tow vehicle suspensions but, I know from experience when I put air in the rear air bags in my MH I can raise the rear of the vehicle at least 3" measured at the wheel well. I would venture to say that adding air bags would fix your problem. The beauty of the air bags is when you are not carrying the load you can reduce the air pressure in the air bags and enjoy the smooth ride you had before. I purchased mine through SD Truck Springs and they were very reasonably priced.

BoldAdventure 07-15-2014 08:08 PM

You can still have sag and not be overloaded. It's a problem in Dodge Ram 1500's for example.

To be 100% clear, all springs will sag, the difference is if they are a linear spring rate - put on x weight, get k*x sag.

The Z71 springs are non-linear (Progressive rate), so they get stiffer as you add more weight.

So for example purposes, put on 100lbs of weight and it might sag 1", put on 200 lbs of weight and it might sag 1.5" - whereas a linear spring would sag 2" with 200 lbs of weight.

So while a weight distributing hitch might help, it is not the end all be all of this sag discussion.

What your spring rates are, and whether they are progressive or linear is a factor in how they compress.

But hey, engineering and math, what do I know.

norsea 07-15-2014 09:29 PM

12,000 LBS tow rating????
 
Quote:

Originally Posted by pjtaia (Post 1479631)
I tow with a 2005 Yukon XL, with the 8.1 ltr engine. Tow rating is 12,000 lbs, plenty for my "new" 34' Airstream with slide out. But the 1,250 lbs hitch weight seems to be a challenge. The rear end of the Yukon sags or squats visibly. The Hensley hitch can't seem to throw enough weight onto the front of the Yukon. The rig handles fine, although the steering seems a bit "light".

I'm considering somehow beefing up the rear suspension, or adding air bags. I have NO experience with this type of thing.

Any advice would be appreciated.

Thanks
L.A. Phil (In Irvine)

L.A. Phil,

This enqueuing mind wants to know:

Where does your 12,000 LBS tow rating come from?

Everything I have looked at lists the following for your vehicle:

MAXIMUM TOWING CAPACITY** 8400 LBS

** When adequately equipped, which may require engine and/or other drivetrain upgrades.

And what is worse, the Maximum Gross Combined Vehicle Weight Rating (GCWR) for your vehicle is 14,000 lbs.

The Gross Vehicle Weight Rating(GVWR) for your vehicle is 8,600 lbs.

8,600 + 12,000 = 20,600 LBS which means you are 6,600 LBS overweight for your GCVWR, to say nothing of how overloaded your rear axle is; not surprising that it sags.

This tells me that your vehicle is beyond being inadequate for towing your Airstream.

Jim

dkottum 07-15-2014 09:47 PM

I think he's got the 2500, not the 1500?

dkottum 07-15-2014 09:54 PM

Maybe the first thing is to actually weigh the trailer at the coupler to see what the truck receiver is carrying, if that has not been done. Verify the Hensley has been installed with the correct angle on the head so the bars can get enough lift.

norsea 07-15-2014 10:10 PM

No difference in the numbers....
 
Quote:

Originally Posted by dkottum (Post 1482812)
I think he's got the 2500, not the 1500?

OK

I'll take the bait.

I looked up a 2500 and the specifications are identical to that of the 1500.

I'll now wait for the OP to respond...

Thanks,

Jim

dkottum 07-15-2014 10:29 PM

I found this chart showing his 12,000 lb tow rating statement.

GMC Yukon XL Compare - Engines and Performance - MSN Autos

pjtaia 07-16-2014 03:23 PM

The 12,000 lb. rating is from the factory specs with the towing package, the 8.1 ltr engine, etc. Also verified in trailer Life's Tow Rating Guides.

https://www.trailerlife.com/wp-conten...Guide-2005.pdf

GCWR is 19,000 lb.

I will be weighing the rig on Friday. I would love to have an expert check out the Hensley to verify that it is installed correctly - anyone know of a Hensley Expert in So Cal?

Thanks, everyone for all your help!

Phil

Air-Texas 07-18-2014 12:28 PM

Hi Phil,
I am dealing with the same questions. Let me know if you get any good answers!.
Mike

dkottum 07-18-2014 12:53 PM

When weighing get the towing hitch weight by pulling the truck onto the scale with the Airstream attached and weight distribution set, but behind the scale. Then disconnect the hitch and weigh the truck alone. The difference is the amount of payload the Airstream adds to the truck so you can see if the truck is rated high enough to carry your Airstream's weight, as well as the weight on each truck axle.

The pull the while rig onto the scale and see what you have as a combination and the trailer itself.

The expert on Airstream towing combinations is Andrew Thomson at Can Am Airstream in London, Ontario. Call them for good advice.

pjtaia 07-19-2014 01:49 PM

Thanks for all your advice. Today we weighed the whole rig: Tell me what this means to you:

Disconnected:
Yukon front 3720, rear 3600, total 7320
Airstream wheels 8820, tongue 1720, total 10540 (Includes Hensley hitch)

Connected without weight distribution:
Yukon front 2840, rear 5440, total 8280
Airstream wheels 9180

Connected with weight distribution:
Yukon front 3160, rear 5160, total 8320
Yukon front is lighter by 560 lb than solo; rear is 1560 lb heavier than solo
Yukon front is heavier by 320 lb than without WD; rear is 280 lb lighter than w/o WD
Airstream wheels 9140

My conclusions: Tongue weight is WAY above what Airstream advertises, weight distribution is working, but inadequate - we still need 800 lb or more thrown forward from the rear.

Your thoughts?

Thanks
Phil

dkottum 07-19-2014 02:01 PM

It appears the airstream hitch weight is too heavy for the weight distribution system and the truck and it's receiver. Again call Andrew Thomson at Can Am, he's most probably seen this many times.

rostam 07-19-2014 08:10 PM

With 1720# on the jack, you are probably exceeding the hitch rating as well.


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JFScheck 07-22-2014 06:41 PM

But on the bright side, better to be informed than in the dark... :D

slowmover 11-05-2014 10:26 AM

As this thread has to do with OP's later thread on best WD hitch:

Connected with weight distribution:
Yukon front 3160,
rear 5160
TT 9140

Connected without weight distribution:
Yukon front 2840
rear 5440
TT 9180

Disconnected:
Yukon front 3720,
rear 3600



[Ron Gratz Chart]

Weighing #1 -- TT attached and Weight Distribution Activated
Let Front Axle Load be "FA1" 3160
Let Rear Axle Load be "RA1" 5160
Let TT Axles Load be "TT1" 9140

Then, while in same position on scales, take
Weighing #2 -- TT attached and Weight Distribution Not Activated (WD bars unloaded, but hanging in place)
Let Front Axle Load be "FA2" 2840
Let Rear Axle Load be "RA2" 5440
Let TT Axles Load be "TT2" 9180

Then, drive off scales and drop TT. Return to scales and take
Weighing #3 -- TV only -- TT Not Attached
Let Front Axle Load be "FA3" 3720
Let Rear Axle Load be "RA3" 3600

From the above values, you can calculate:

TV weight = FA3 + RA3 7320

Gross Combined Weight = (FA1 + RA1 + TT1)
{should also be equal to (FA2 + RA2 + TT2) if scale weights are correct}

17,460 & 17,460

TT Weight = Gross Combined Weight - TV Weight

10,140

Tongue Weight = (FA2 + RA2) - (FA3 + RA3)

8280 - 7320 = 960

Load Transferred to TT Axles
when WD System is Activated = TT1 - TT2 40



Something is off somewhere (TW, mainly. 12% of 10,140 is 1215-lbs as example). Were the readings all done at the same time?

.

pjtaia 11-05-2014 07:08 PM

Slowmover: I don't get your calculation of Tongue Weight equaling TV without Weight Distribution minus TV alone. I get 9,180-7,320=1,860; When I weighed just the trailer sitting on the tongue jack I got 1,720; either one is way different than the 960 you calculated...

I did make all these weights at the same time. I went back again at a later date to verify and several of the first few measurements were the same, so I didn't continue to do them all.

I have since determined that my OEM hitch receiver from GMC is rated at only 1,500 lbs, so I am in the process of purchasing and installing a Curt hitch receiver with 2,400 lb rating. We'll see if it makes any difference...

slowmover 11-05-2014 07:11 PM

Stiffer suspension?
 
Read through the way the chart is arranged. Cross checks. Did I accidentally change the scale numbers? If not then the TW is as shown.

Is your TW really 19%? 9% doesn't seem right either.


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