Airbags and bounce

[tomhole]

I was playing around with the airbags today on the truck. I pumped them up to 50 psi with no load on the truck then stood on the back bumper and bounced up and down. Felt like an old '69 Lincoln I was looking at buyin 15 years ago. It bounced like it had no shocks. Released the air back to 5 psi and it was a nice, tight suspension again.

This leads me to conclude that airbags are not good at preventing bounce in a system. I guess it makes sense once you consider that they are just airbags. Squeeze them and they expand.

So, anyone looking to prevent bounce while towing or hauling, I would recommend new shocks, not airbags. The airbags are good for raising the rear end while carrying a heavy load, but my conclusion is that's all they do.

Tom

[Tankerhank]

Makes since, like bouncing on a bouncy ball that kids have.

I have the Hellwig springs my truck doesn't bounce any more or any less, but when I put a load on the truck it doesn't sag either.

[campertom]

That matches my own experience. I added air bags (Air Lift 5000) and saw no improvement on the bounce when loaded (towing a 9000lb trailer). Unloaded, the kids in the back seat would be launched in the air if I hit a speed bump too fast. Every time we hit a rough road, the kids would ask if I had the air bags filled, and request that I let the air out. With a load, adding air to the bag didn't make any noticeable difference in the bounce. Then, two weekends ago, I added a set of Rancho 9000XL adjustable shocks to the rear. Set to max, the bounce under load was gone (no matter what the air bag pressure). Set to mid range, the bounce was back, no matter what the air pressure. Without a load though, the new shocks did not help with the kid launching when going over speed bumps.

I did notice that, when I had the truck overloaded once, there was a roughness to the ride that I could smooth out by adding air to the bags. On that occasion, adding air to the bags traded roughness for bounce. I didn't have the shocks then, so I can't say if the combination of air lifts and shocks would have made for a comfortable ride - I expect that it would have. Of course, a better solution would have been to not overload the truck.

[TundraBay]

Originally Posted by tomhole

I was playing around with the airbags today on the truck. I pumped them up to 50 psi with no load on the truck then stood on the back bumper and bounced up and down. Felt like an old '69 Lincoln I was looking at buyin 15 years ago. It bounced like it had no shocks. Released the air back to 5 psi and it was a nice, tight suspension again.

This leads me to conclude that airbags are not good at preventing bounce in a system. I guess it makes sense once you consider that they are just airbags. Squeeze them and they expand.

So, anyone looking to prevent bounce while towing or hauling, I would recommend new shocks, not airbags. The airbags are good for raising the rear end while carrying a heavy load, but my conclusion is that's all they do.

Tom

Tom, I can't help but ask if you have the TRD off road suspension, because the problem you're having sounds to me like not enough damping on the return, which is more of a problem with the non-TRD shocks.

My "bed bounce" is much better with about 10-15 PSI than 5 PSI which is the loaded advised amount. I think it's a combination of shocks, springs, and air bags which need to be addressed. I'm not sure that just adding more air (which cranks your a$$ end so high in the sky that your shocks have trouble damping the return) is going to help, but as I mention, it's a combination of factors!

[tomhole]

Non TRD suspension. The experiement was designed to compare the suspension response with minimum air in the bags (which was tight and well damped), to the respomse with 50 psi in the bags (which was bouncy, poorly damped). Certainly the fact that the bags lifted the rear end by an inch would effect the shock's performance, but the bouncy bags probably contributed more to the adverse change in system response than a shock extended by 1".

[SE2000]

With 50 psi, you have unloaded the spring for the most part. so you are riding on bags which have no dampening ability at all. Leaf springs do because of friction. That is why some people insert teflon between the leafs.
If you end up with a smooth ride you will have to find another way of threatening the kids to behave besides going over speed bumps

[Corban_White]

The issue is when you air up the bags you have greatly increased the spring rate. The shocks will respond the same regardless of where in the stroke they are (barring hitting one end or the other). The higher spring rate overcomes the damping rate of the shocks. Shock's damping and spring rate need to be matched in order to work in harmony. As shown by campertom, increasing the damping of the shocks to correspond with the increased spring rate will not result in bounce.

[fivecodys]

Very Interesting thread Tom.
I just experienced this last weekend.
We were on J59 going up to Columbia, CA.
The road is horrible. Lots of dips and rises.

I felt at times as thought the rear end of the truck was actually leaving the road.
The bouce was almost unbearable.

I have about 1200 lbs of pin weight from the 5th wheel.
P rated tires at 44 psi and Airlift Bags with 38 pounds of pressure.

If I am understanding this right, I took out all of the shocks ability to handle the bounce by adding too much pressure in the bags.

I'll try next time with only 10 lbs of pressure and see if that helps.

LT tires are on the list but not for a while.

Bill

[Art64]

That's the reason why I replaced my shocks with Rancho adjustables. Works great with airbags cause it provides more damping on rebound to counteract the airbag's kick ups. I've tried Bilstein HD's. Not good for airbag set up. Nice and soft on the compression, but not much rebound control. I've learned my lesson on driving with airbags when the bed is unloaded. Dips and speed bump-like road conditions will launch the rear airborne.

[tomhole]

On my last trip, I set the bags at 5 psi vs. the 35 psi I normally run. The result was interesting. When I hit a dip, the result with 5 psi was a larger suspension displacement followed by an immediate damping with no overshoot. This was ok, but I would prefer a tighter system with less amplitude on the initial displacement. But damping was ok.

With 35 psi in the bags, the initial displacement was greatly reduced, but the damping was greatly reduced as well. Instead of one large displacement, I was now getting several smaller, but diminishing, displacements.

Best towing was with 15 psi in the air bags.

One thing to keep in mind is that my WDH introduces a level of complexity that would not be seen by someone towing without a WDH. Airing the bags unloads the WDH which removes some of the damping that the WDH offers. But that just makes it look more like a simple load rather than a dynamic load.

So, I have myriad options available to adjust. Based on my assumption that the air bags are merely a spring, I think a set of Rancho adjustable shocks would be the next best step. A set of LT tires would be good as well. I know these P rated tires bounce a lot even at max pressure.

Tom

[bilztrd]

I use the Firestone bags. I run them at 7 around town empty. I use 25 with the toyhauler attached and the bed loaded with @350 lbs of stuff. The ride is good and controlable.

[fivecodys]

Originally Posted by Art64

That's the reason why I replaced my shocks with Rancho adjustables. Works great with airbags cause it provides more damping on rebound to counteract the airbag's kick ups. I've tried Bilstein HD's. Not good for airbag set up. Nice and soft on the compression, but not much rebound control. I've learned my lesson on driving with airbags when the bed is unloaded. Dips and speed bump-like road conditions will launch the rear airborne.

Can you give me a part # for the Rancho's and point me towards a dealer?

Thanks,

Bill

[harper223]

I thought about getting airbags for my Tundra, but since I have the TRD package- I backed off a little and looked at some other options. After some reflection, I was noticing that with the new Hensley attached to the truck and weight being evenly distributed, there was still some sag in the rear of the truck. I have never had a problem with bounce, but the sagging was bothering me a little. I also knew I wanted to increase what could be placed in the bed of the truck without it sagging, even before I bought the new hitch. So I decided on a new set of helper springs from Hellwig. I just ordered them today, and I really think that will take care of sagging for good.

I always tell people who are buying Tundras to get the TRD package if they can. I know they are running scarce where I live. In fact, I have not seen a truck like mine on the lot since I bought it back in fall/08 (2wd crewmax limited TRD).

But I agree with the OP, bounce goes away with a change in shocks. I think I have the Bilstein on mine.

[SE2000]

There is several factors that make up the suspension. What may work for one might not work for another. Another thing to consider is some of the assumptions made by the experiments may be off

[Tankerhank]

I have Hellwigs on my '07 and they do the trick with style. I have them set to allow between 1" and 2" of drop when I hook the 5'er up to level off the truck, after that they just give a nice ride.