Air bags and cat scale shock

[TN_Sportsman]

Hi all, it's been awhile since I have posted. We recently took our first spring trip this year to do some fishing. This was the first time I had hooked up the bass boat with my TC, and I noticed that it has a little more squat than I would like, even though my boat trailer tongue weight is only 220 lbs. My truck sits fairly level when unloaded to begin with, so the resulting squat is no real surprise even with the Stabiloads. I also noticed some porpoise when going across bumpy roads as well, which has got me thinking I need to install air bags to get me back to level, and increase handling. I can get a set of Air Lift bags for my truck for about $340. Any thoughts?

I knew that I was pushing my trucks limits, so I wanted to get weighed with a full load. My previous calculations had me right at GVWR (8600 lbs.), and 1000 lbs. under my rear axle rating (6000 lbs.). After being weighed with this setup I was 480 lbs. over GVWR, and 520 lbs. under my rear axle rating. The GVWR doesn't really bother me, but dang I didn't want to get that close to my rear axle rating! I know air bags don't increase your carrying capacities or ratings, but I am thinking they would help the handling and the ride.

I know I am going to get an array of opinion on here for my setup, but I was just wondering if any of you are operating within similar limits and your experiences doing so. This is our first TC and we really like it, but this pop-up is HEAVY!! I really don't want to get rid of it, but maybe we should have gotten the model without the toilet? 😞

[TN_Sportsman]

Thanks for the replies folks. All good info, especially for a TC newbie like myself. I'm actually on a weekend fishing trip currently with the camper. I noticed while driving on the way, that I didn't really experience a lot of porpoising, and the truck seemed to recover pretty well after some significant bumps. However, I did notice more of a floating sensation on my front end. Made the steering feel a little loose. I was driving through some big winds though, so I'm sure that didn't help things.

[Otterman]

HMS Beagle wrote:
Porpoising is often caused by a difference in suspension frequency, front to rear. Classically, you want the rear suspension frequency to be higher than the front so that it can 'catch up' after a bump. If the rear is the same as, or slower than the front it will contribute to porpoising. With a heavy load in the back, and a trailer beyond, you may have reduced the rear frequency too much. The only way to change it is to reduce the weight or increase the spring rate. All of the various suspension band-aids increase the spring rate. The only one that is easily tunable is air bags.

Shocks can dampen the oscillations and reduce the problem, but don't really address the cause.

There is a pretty good explanation of it here if you are interested in the theory.

That's great information, thank you!

[Vinsil]

jimh425 wrote:

HMS Beagle wrote:
Shocks can dampen the oscillations and reduce the problem, but don't really address the cause.

Neither do springs by themselves.

TN Sportsman, your springs are holding some of the weight unless you really add a lot of air to the air bags. The airbags can hold part without holding all. Many of us intentionally spread the load across the springs and airbags. That's why we add extended bump stops to engage the overloads even though we have air bags.

It's all about balancing the system. You can't there with a unique configuration without trying different things.

This. I put 25-40 psi in bags, and the combo of stableloads, bags and my spring pack carries the load fine. Gotta remember, it's a system of things you need to work in harmony. I'd personally go for bags for adjustability but the timbrens would work too.

Your going to just have jump in and know it's not how you like it at this point. Since a new truck is not in the works just keep going until this one feels right. Full PSI in the rear tires and I'd play with the fronts as well. They could be contributing to your bounce as well.

[jimh406]

HMS Beagle wrote:
Shocks can dampen the oscillations and reduce the problem, but don't really address the cause.

Neither do springs by themselves.

TN Sportsman, your springs are holding some of the weight unless you really add a lot of air to the air bags. The airbags can hold part without holding all. Many of us intentionally spread the load across the springs and airbags. That's why we add extended bump stops to engage the overloads even though we have air bags.

It's all about balancing the system. You can't there with a unique configuration without trying different things.

[TN_Sportsman]

So besides the issue of porpoising, would HD jounces (Timbren, SumoSprings, etc., actually reduce my squat getting me back to level? Especially since putting 30 lbs. in a set of bags would only lift 1500 lbs., and my camper weighs 2000 lbs., not counting the tongue weight. I guess it would be a hard question to answer, because it would vary from truck to truck. I guess I could just measured the gap between the axle and frame where they would mount before and after loading. Then if you knew the height of the jounce and how much it would compress, you could figure out how much the truck would travel/squat right? Or I could just say screw it, go get 'em and try it:@

[HMS_Beagle]

Porpoising is often caused by a difference in suspension frequency, front to rear. Classically, you want the rear suspension frequency to be higher than the front so that it can 'catch up' after a bump. If the rear is the same as, or slower than the front it will contribute to porpoising. With a heavy load in the back, and a trailer beyond, you may have reduced the rear frequency too much. The only way to change it is to reduce the weight or increase the spring rate. All of the various suspension band-aids increase the spring rate. The only one that is easily tunable is air bags.

Shocks can dampen the oscillations and reduce the problem, but don't really address the cause.

There is a pretty good explanation of it here if you are interested in the theory.

[jimh406]

Yes, that's what the shock valving does. It can balance the rocking movement from front to rear. The wrong type of valving doesn't slow the movement enough.

[TN_Sportsman]

Kayteg1 wrote:
Airbags are rated for 5000 lb @ about 100 psi, meaning 30 psi should give you 1500lb lift. Is that about the weight of your camper?

Actually I'm right at 2000 lbs. loaded.:o I know, crazy for a pop-up.

Jim, what do you mean by "valving to slow rebound"? Do you mean the shocks are what stops, or softens the porposing effect?

[Kayteg1]

TN Sportsman wrote:


On a side note regarding air bags, I just found out that Torklift recommends running NO MORE than 30 lbs. in air bags if you have Stabilloads installed. Since I do, would 30 lbs. even be worth having in my situation, even if I could custom build a set? I'm thinking not. Timbrens may be my best option.

Airbags are rated for 5000 lb @ about 100 psi, meaning 30 psi should give you 1500lb lift.
Is that about the weight of your camper?

[jimh406]

Timbrens and air bags don't have valving to slow rebound. That's only going to happen with shocks.

Yes, max the tire pressure in the rear.

[TN_Sportsman]

Vinsil wrote:
Well in that case I'd be inclined to blame your shocks possibly not able to control your suspension. On top of that, I'd still be leary of spring rates. Yes, the truck could be everything the 89-98 3/4 ton trucks were but it's also a design that is nearing close to 30 years old. Those older trucks did carry weight and campers and you are heavier with the crew cab....you might just be close to taxing the thing. Tires can also contribute to the issues as well. Are you running full/correct pressure and are your tires rated for the weight?

I don't think your trying to do too much with your truck. I think you just need some work/parts to make it comfortable to YOU. Have you had a TC before? What you are experiencing might very well be what it is. Some need a F550 to carry what you are, others do it with a ford ranger. LOL...

Comfort is key, shocks, tires and then maybe some supersprings/timbrens. Should fix you right up.

I am running Michelin M/S Load range E, over 3000 lb. rating @ 80 psi. I am running my rear tires 75 psi., and my front 65 psi. Should I just go ahead and max 'em out? I am ignorant to spring rates, so the only thing I can tell you about mine is that I have one less leaf than a 2500 HD.

This is actually my first TC, so you could be right in that what I am experiencing is just normal. Heck if someone hooked to my boat without ever towing one before, it would probably feel odd to them. Getting my truck back to level may just be a quest for cosmetics:D.

On a side note regarding air bags, I just found out that Torklift recommends running NO MORE than 30 lbs. in air bags if you have Stabilloads installed. Since I do, would 30 lbs. even be worth having in my situation, even if I could custom build a set? I'm thinking not. Timbrens may be my best option.

[Vinsil]

Well in that case I'd be inclined to blame your shocks possibly not able to control your suspension. On top of that, I'd still be leary of spring rates. Yes, the truck could be everything the 89-98 3/4 ton trucks were but it's also a design that is nearing close to 30 years old. Those older trucks did carry weight and campers and you are heavier with the crew cab....you might just be close to taxing the thing. Tires can also contribute to the issues as well. Are you running full/correct pressure and are your tires rated for the weight?

I don't think your trying to do too much with your truck. I think you just need some work/parts to make it comfortable to YOU. Have you had a TC before? What you are experiencing might very well be what it is. Some need a F550 to carry what you are, others do it with a ford ranger. LOL...

Comfort is key, shocks, tires and then maybe some supersprings/timbrens. Should fix you right up.

[jimh406]

You said that you have porpoising without the camper, so I don't think it's the weight distribution.

[TN_Sportsman]

Vinsil wrote:
Could just be simple spring weights. Too light of rates and your shocks can't control it. Sure, you could have possibly heavier rates than a half ton...in the rear. I'd guess your torsion bars and keys up front just might be half ton stuff and they put a heavier spring pack on the rear to control the heavier axle and added payload. IIRC, the quad steer was geared toward the guy that towed a smaller trailer (not a true 3/4 ton) and made it easier to drive. The rear axle is a Dana 60 center section with Dana 44 knuckles/outters and balljoints. This is much heavier than a standard solid rear axle...so spring weights were raised.

This is a guess so I'd look into it. It may have 8 lug axles but it is still a semi floater rear. I'd check, you might the suspenion is just not sprung for the weight. Shocks will help and 52k might have them worn to the point of replacement as well.


Or...another truck works too. I feel your pain and wanting to keep a low mileage truck. I did and had to band aid mine to work....but it was easier than trying it with what your working with...a heavy 1/2 ton. The guys who buy the new Nissan Titan XD will be in the same bought and fall for marketing. I assume we will have them showing up here in the next year or so.....

The 1500 HD is definitely one of the most misunderstood trucks out there, just simply because of the nomenclature. Add the crazy Quadrasteer factor into it, and it becomes even more difficult to understand. Here is what I have found after researching my Frankenstein truck:

The 1500 HD is the same truck as a 3/4 ton 2500 non-HD produced from 2000-2004. Same frame, suspension, leaf springs, ratings, etc. as the older model 2500 3/4 ton GM produced from 1989-99. Similarly the 2500 HD is actually a 1 ton SRW truck, but everybody still calls them "3/4 tons". As for the front end, its definitely not standard 1500 stuff. Front axle rating 4,410 lbs, it has either GK or GL rated torsion bars (GK I believe), bigger disc brakes, tie rods, 8 lug wheels, etc. It also has the 4L80 transmission and 6.0 motor not offered in standard 1500's.

Quadrasteer was not just limited to towing small trailers, that's why they put it in an HD truck. It was actually designed with towing in mind. Now, they did offer it in a 1500 light duty Denali, which in that situation,the truck would be the limiting factor.

The Q-steer rear end in my truck is a semi-floater Dana 60 with a Dana G86 rear axle. Here is a Q&A I found with a Delphi engineer regarding the Q-steer rear end:

Q: Are the CV joints in the rear Dana 60 axle with Quadrasteer, heavy duty?

A: Yes, the quartershaft assembly has a tripot joint which allows the assembly to withstand torque levels similar to HD 2500 applications. The ring gear in the rear axle is a 9 3/4 inch.

Soooo.... I have the same truck as those old 2500's, and they have been hauling heavy a$$ campers around for years without any issues. BUT, most of them were single cabs or extended, not crew cabs. I am wondering if this is actually the culprit for the noticeable squat due to the longer frame and the camper being more rearward on it, and it is merely cosmetic? Especially since I am not really removing much weight off my front axle. Can removing 40 lbs. off the front axle really cause porpoising??

As I said before the shocks are adjustable, and have a "firm" setting. Apparently when this is activated, the electronic switch sends a signal to a solenoid within the shock to send hydraulic fluid through an internal orifice to stiffen the shock up. Now, I'm probably not a good judge of shocks being worn, as I never replace them until I hit a pot-hole and my rear-end continues to bounce:). I know this truck rides a lot rougher than my Tahoe, and when I hit a bump it stands up and recovers quickly, but that's the extent of my shock knowledge.

I absolutely love this truck. I've had 1500's my whole life and this thing is a lot tougher. Yea, I wanted a 2500 HD Duramax, but just not feasible in my situation. I would definitely loose my camper and downsize before giving up my Frankenstein:B.