Rear end bouncing/Equal-i-zer 4-point 10K hitch

[Eric91Z]

So, we finally got our first travel trailer - a Grand Design Imagine 2800BH. Just picked it up last weekend and took it right out for a shake down run. So far, pretty much everything ok. Biggest issue we are having is that it doesn't pull smoothly on the highway. Get a lot of oscillation type bouncing from the rear end.

Now, the roads are not great around where we have towed so far, but I don't think it should be pulling like this. Gets this small oscillation like bouncing from the back end. Doesn't really seem to affect the front end. Front end steering and feel is pretty much same as unloaded, but this back end gets going (not huge up down bouncing, but just constant oscillation).

Just trying to figure out what to try next to get rid of that. Here are numbers:

Tow Vehicle:

- 2016 Chevy Silverado 1500 4x4, crew cab, short box
- Truck weight with full tank of gas, my daughter and me in it: 5960 lbs
- Front tire pressure towing: 40 psi
- Rear tire pressure towing: 41-42 psi


Travel Trailer:

- 2017 Grand Design Imagine 2800BH


Measurements:

- Front: ground to fender lip, unloaded: 36.25"
- Front: ground to fender lip, loaded with WD bars on: 36.5"
- Front: ground to fender lip, loaded, no WD bars: don't have this measurement yet

Hitch setup: Equal-i-zer 4-point 10K

- Hitch head: has 4 washers in it
- L-brackets: mounted with 1 hole left at bottom
- WD bars install with slight up angle towards back - bars not completely level with a-frame


Weights:

- Just truck: 5960

Loaded (CAT scale numbers):

- Front Axle weight: 3320 lbs
- Drive Axle Weight: 3260 lbs
- Trailer weight (loaded for camping): 6080 lbs
- Combined Weight: 12,660

From that, tongue weight is right around 620 lbs. So just over 10% on tongue weight.


So, I have read and gotten opinions, but trying to figure out what to try or look at to get rid of the back end bounce. I have had some say need to increase tongue weight to around 12-14% (730 - 850 lbs). My question is, how do I increase that properly. We only have front pass through storage outside which is where most things are kept. Inside is just mostly items in kitchen area we loaded which is middle area of TT and little to nothing off back end. So not sure how else to re-load trailer for more tongue weight.

And what about adjustments to the hitch setup? Will adjusting the L-brackets for the bars help at all? Maybe drop brackets one hole to take a bit of load off the bars? We are getting zero sway and the other numbers look like we are setup good, so not sure if moving L-brackets will help or hurt. Input appreciated.

And what about tires. I know the stock "P" tires are not ideal for towing, but want to look at upgrading to LT tires as last resort given expenses and only 4600 miles on stock tires. Goodyear says max psi for these tires is 51 psi (Goodyear Wrangler SR-A ****). Would going to 44-45 psi, at least on the rears when towing, help at all?

And if there are good instructions or something out there to help understand the Equal-i-zer hitch setup and affects of changes, please point me towards it. The hitch owner manual doesn't help a whole lot. Would seem to be that if I drop the brackets one hole it will take a bit of WD out which means a little weight off the front and back to the rear axle. But none of that affects tongue weight still, correct? Just which axle it is distributing that weight to?

Any assistance or input appreciated.


Thanks,

[Turtle_n_Peeps]

Throw the old rear shocks away; they are junk from the factory. Yes, I know it's a new truck, but the shocks are still junk from the factory.

Put a new set of Bilsteins shocks on the rear will help a bunch with rebound and that is the problem your having. (At least a lot of it)

You can make all the WD adjustments you want till the cows come home and it won't make any difference with control of the rebound of the spring control.

For some odd reason GM just can't get the rebound valving correct.

[mkirsch]

As you can see, the trailer's tongue weight pulls ~300lbs off your front axle and adds it to your rear axle. The WD bars return most of that weight back to the front axle, the way they are adjusted.

You probably could adjust the bars to get a little more weight transfer and get the front end closer to unloaded height.

[Eric91Z]

Was going to post those numbers, but if not needed...

Here is what I had for measurements:

1. Unloaded - ground to fender lip: 36.25"
2. Loaded, no WD bars: 36.75"
3. Loaded with WD bars: 36.5"

So according to the Equal-i-zer manual, I am about perfect in that regard too as they say come back at least half way between loaded no bars and unloaded which I am right in the middle.

[wgriswold]

gmckenzie wrote:
I've got a similar setup. I'm thinking airbags will help with the bounce, but may try adding a washer as per above.

One thing to note is that your tongue weight is a bit more than the weight added to the truck. I weighed my trailer tongue, not hooked up, just the tongue on the scale, at 1050 (480KGs) but find that all hooked up, it only adds about 800lbs to the truck with some of the tongue weight transferred to the trailer.

So where you show your tongue weight around 620, you may find if you just weigh the tongue, it is 800 or so. But 1K basrs still sounds right for your setup.

You measured tongue weight the proper way, directly on the scale. When hooked up to the truck, including engaging the WD bars, some of the weight on the truck's axles is transferred to the trailer, but the tongue weight remains the same.

When the OP hooked up the trailer without the WD bars weight was removed from the front axle and added to the rear axle. None was transferred to the trailer. Once the WD bars are engaged weight was transferred to the front axle of the truck and back to the trailer axles. The tongue weight remained unchanged.

Your WD bars are adjusted about right. The weight on the front axle is the same, within the error of measurement, as it was originally. I would find some way to increase the tongue weight and then readjust the WD bars.

As long as you are working with the actual weights you can ignore the measurements at the front axle as it is lowered and raised by the WD bars. They are an approximation for the better way of actually measuring the weights on the axle as the WD bars are adjusted.

[Eric91Z]

Ok, so have three weights now. Two were done today, one was from last weekend and think there was water in the fresh water tank that contributes to trailer weight difference. But the TV/TT had the issue both on way to campground (when there was water in there) and on way back home after we had emptied all tanks (except black water had 3-5 gallons in it):

1. Truck only, full tank of gas, just me in it (weighed today):

- Steer Axle: 3360 lbs
- Drive Axle: 2520 lbs
- Gross Weight: 5880 lbs

2. Truck hooked up, no WD bars, me, full tank of gas (weighed today):

- Steer Axle: 3060 lbs
- Drive Axle: 3580 lbs
- Trailer Weight: 5880 lbs
- Gross Weight: 12,520 lbs

3. Truck, hooked up with WD bars, full tank of gas (last week, some water in fresh water tank):

- Steer Axle: 3320 lbs
- Drive Axle: 3260 lbs
- Trailer Weight: 6080 lbs
- Gross Weight: 12,660 lbs


I know, the one problem now is the difference in trailer weight loaded and unloaded. Should have just done one more weight tonight after putting the bars back on before leaving, but two semis behind me in line. I can grab another weight in the morning in same way it is sitting right now since it is all hooked up ready to head out this weekend.

Looks like it is transferring weight, just need that third one to match one from tonight without WD bars for direct comparison. Will run there quick in the morning and get that one...

Have not been on highway yet, but have been on some rougher roads and with only other change being tire pressures being 42 f/46r - compared to 38 f/41 r last weekend, does seem to ride/recovery a bit better going down the road...

[gmckenzie]

I've got a similar setup. I'm thinking airbags will help with the bounce, but may try adding a washer as per above.

One thing to note is that your tongue weight is a bit more than the weight added to the truck. I weighed my trailer tongue, not hooked up, just the tongue on the scale, at 1050 (480KGs) but find that all hooked up, it only adds about 800lbs to the truck with some of the tongue weight transferred to the trailer.

So where you show your tongue weight around 620, you may find if you just weigh the tongue, it is 800 or so. But 1K basrs still sounds right for your setup.

[Eric91Z]

Gotcha on the unloaded vs. loaded with WD bars attached front axle weight. That all makes sense.

Trailer tires are at 65 psi cold as checked yesterday. Bumped truck tires to 42 psi front, 46 psi rear (max is 51 psi). Got the hitch ball height measurement today. Will get the tongue height when trailer level today and get the CAT scale weight when hitched up, but WD bars off when I get trailer tonight, too. Also getting front fender height hooked up, bars off, as those should be rest of numbers I need.

The sheet that came with the trailer from the factory says the UVW of trailer is 6076 lbs and hitch weight it 574 lbs. I have not done a formal tongue weight weigh yet.

[myredracer]

The brochure says the TT tires are LRD. If so, I would run those at max. sidewall 65 psi.

The tongue weight seems rather light at 620 lbs. The factory hitch wt. is 580 lbs and you would expect TW to go up a lot more than 40 lbs. As you mentioned, I would want to be more in the 12-13 percent range. Did you do a pass with the bars engaged and another pass with them dis-engaged. To get TW, you want the bars dis-engaged because the WDH transfers some wt. onto the trailer's axles.

The factory specs say the UVW is 5685 lbs with 7495 lb GVWR and you have calculated the actual TT wt. (GVW) to be 6080 lbs. That indicates you've only added 395 lbs of "stuff" in the TT for 2 adults & 1 child which can't be right. Typically the added wt. on top of the UVW is something like 600 - 1500 lbs. Unless I've missed something, I think maybe you haven't done 3 passes to get all the weights correctly?

Edit: I see you plan to go back to the scale for a 3rd pass with bars disengaged.

[mkirsch]

Most of the weight should be on the rear axle.

When you get the weight with the WD bars off, you will see how much weight is transferred BACK to the front.

Your truck acts like a see-saw when you hitch up. The trailer tongue pushes down behind the rear axle, lifting up on the front axle, removing weight from the front axle and adding it to the rear axle.

Ideally you want the weight of your front axle to be the SAME unhitched, and hitched with the WD bars engaged. You're only 40lbs off, which should be plenty close enough. Given the scale error, it could be anywhere from 20lbs to 60lbs, but even at 60lbs it's still close enough.

[Eric91Z]

Ok, so I know I have more measurements to get still, but did re-weigh the truck today on the same CAT scale I weighed it on with the trailer connected. Numbers are kind of interesting, I think:

1. Truck weight unloaded, hitch head in receiver, full tank of gas, me inside (we didn't load anything inside the truck itself when traveling with the trailer):

a. Front Axle Weight: 3360 lbs.
b. Rear Axle Weight: 2520 lbs.
c. Gross Weight: 5880 lbs.

2. Truck weight with trailer and WD bars on:

a. Front Axle Weight: 3320 lbs.
b. Rear Axle Weight: 3260 lbs.
c. Gross Weight: 12,660 lbs.

So, I know I still need to get a weight with the trailer connected, but WD bars off and plan to do that this afternoon when we get the trailer back out, but just looking at those numbers seems like most of the tongue weight is going on the back axles, not transferring to the front.

[mkirsch]

Ok, I must have misread the ride heights originally. I could swear they both said 36.25"...

Sooooo, ignore my advice from earlier. It's not too much bar tension. Most likely it is not enough.

One universal truth of RVing is, the dealer never sets the WD bars correctly. The reality is, they can't. They don't know what you're going to be putting in the trailer. You need to go through the adjustment process yourself to get it fine tuned to your needs.

[3oaks]

BarneyS wrote:
......................According to his numbers, he is not trying to push the front axle below the stock unloaded ride height. He is .25in above the stock height when the WD bars are tensioned.

This is probably just about right but I would try to get the bars parallel with the A frame so that they ride flat on the L brackets. I think I would lower them one hole and tilt the hitch head back by adding at least one more washer. For the standard sized A frame, Equal-i-zer recommends starting out with 5 washers in the hitch head and he only has 4. When he lowers the L brackets to make the bars level then he needs to tilt the head back some more to keep the same tension on the bars.

What he describes sounds like he could use a bit more tension on the WD bars so I would add two washers and try it out. Can always take one out if it puts too much tension on the bars. The porpoising he describes is a typical result of not enough bar tension.
Barney

Having quite a bit of experience with the Equal-I-zer 4 point hitch, I believe Barney has given you some very good advice and logically so.

[keymastr]

Read the sticky at the top of this section on getting cat scale weight. You must make 3 passes to get all the info you need:
Pass 1, just the truck with the gear and people you normally tow with.
Pass 2, truck and trailer without WD bars attached but with trailer loaded as you will tow.
Pass 3, truck and trailer with WD bars hooked up. Only then will you know what your weights are and how much you are distributing to the front of the truck and back to the trailer.

The trailer also should be level front to back when hooked up on flat ground. Slightly nose down is ok but only slightly. Nose up is not recommended.

[TurnThePage]

Eric91Z wrote:

BarneyS wrote:

According to his numbers, he is not trying to push the front axle below the stock unloaded ride height. He is .25in above the stock height when the WD bars are tensioned.

This is probably just about right but I would try to get the bars parallel with the A frame so that they ride flat on the L brackets. I think I would lower them one hole and tilt the hitch head back by adding at least one more washer. For the standard sized A frame, Equal-i-zer recommends starting out with 5 washers in the hitch head and he only has 4. When he lowers the L brackets to make the bars level then he needs to tilt the head back some more to keep the same tension on the bars.

What he describes sounds like he could use a bit more tension on the WD bars so I would add two washers and try it out. Can always take one out if it puts too much tension on the bars. The porpoising he describes is a typical result of not enough bar tension.
Barney

So I have heard two possible causes: 1. Not enough bar tension and 2. not enough tongue weight...

So first step, drop L Brackets one spot for bars to be parallel with a-frame and one or two washers to head to tilt that a bit and try that?

I agree with Barney, about adding 2 washers. I would also increase tire pressure to max on both vehicles. On top of that, there's a good chance that filling your fresh water tank full might help too. Last but not least, maybe drop your hitch ball height by one notch, which will force the Equal-i-zer to transfer more weight off the rear wheels. Those steps have worked well for me on a couple different tow vehicles utilizing the same hitch you have. You might consider adding a second battery to increase tongue weight, along with the other benefits it provides. JMHO