Hi I have a 2019 4x4 Crew 6.5' box 157" wb with a 3.5L ecoboost and I love the power but hate the stability while towing. After reading reviews and forums for dozens of hours about so many people with 2015+ F150s having the same problem I was very frustrated that no one was able to solve it. I had read about several people who have tried different add ons with limited success. Some guys added Timbrens, some Sumos, some added air bags, some super springs, some tried a Propride, some (including me) tried RAS. They all help but only a small amount. I have towed my TT with a 2008 Silverado 2500 and a 2018 Silverado 1500 and neither had the stability issues. After looking closely at the Silverado 1500 the rear leafs look much heavier on that truck. And finally after one guy on a forum said, "you never hear the HDPP guys complaining about stability" it really seems like the new F150 is sprung to light. I've read several people say their new HDPP has more stability than their older model F150. I have also seen a pile of people say their new aluminum body is horrible compared to their older steel body. The RAS raised the rear of the truck 1" empty and towing and solved the axle wrap but didn't do much for the sway. So I am planning to change the rear springs to match a HDPP pack and upgrade the shocks as well. Here are my questions:

1. Does the HDPP just have a 3rd identical spring added that the max tow has or is it an entirely different pack?
2. Does anyone know the spring rates for the max tow and HDPP front and back?
3. Would Bilstein 5100 in the rear be as good or better than factory HDPP shocks?
4. Can I stiffen the rear suspension w/o stiffening the front? My thoughts here are when towing the travel trailer the front lifts slightly so I shouldn't need any more spring rate there.
5. My max tow has a block/spacer in the rear suspension. Does the HDPP come with this too? If I add that extra leaf can I take the block out? I don't want to raise the front and I don't want anymore rake than stock.
6. Does anyone have the part numbers for the front and rear springs & shocks for the HDPP?

 

You didn't list the specs of your current trailer or the WDH you're using, but if you take a look at this thread, I have most of the modifications made to my truck to help it's towing ability listed there.

https://www.f150forum.com/f82/upgrad...477722/index2/

For my current setup I consider my truck solved. In all but very high winds and the occasional T-storm, I hardly know my trailer is back there. And with your longer wheelbase, you're definitely starting off with a better base than most of us have.

 

If you want max rigidity side to side then skip the springs. Have a fab shop install a panhard bar and install LT tires. You can then use airbags as needed to up spring rate if needed. Putting on heavy springs isn't directly addressing the issue.

 

LT tires make a huge difference.

I towed a 2018 Heartland M-185SO (https://www.rvtrader.com/listing/201...185-5010169589) with 23ft OAL at 3800lb dry, with two passengers, food, water and luggage in a 2016 Nissan Frontier shortbed crew cab doing 70-80mph down the highway with 100% stability. Never swayed an inch, with the butt of the truck pretty low to the ground no less.

LT tires man. LT tires. LT265/75-16 Wildpeaks @ 48PSI. Towed like a dream. Alternatively, increase your tire pressures slightly on P rated tires, but when I was on P rateds, that side to side shimmy in the rear was very prevalent.

 

I think the issue would be solved better with trailing arms but I’m not sure that’s an option? The way the *** end darts abruptly sideways it feels like it has rear wheel steering. The rear axle needs to be firmed up so it stays in place. Needs to stay perpendicular to the longitudinal axis of the truck.

 

Kind of what a panhard bar does.

 

sorry I’m not too familiar with those bars. I just looked on wiki and it showed a single support rod running parallel to the axel but angling up to the frame. This looks to me like it wouldn’t limit the axle twisting away from perpendicular.

 

Trailing arms are normally used in conjunction with a panhard bar. Trailing arms locate the axle front to back but they don't stop the axle from moving side to side. That's what the panhard bar does. Most of the sway is not caused by the axle self steering left or right as your thinking but moving side to side with the leaf spring flexing like a tire sidewall. In extreme cases it gets worse and worse on each cycle like a chine walking boat until it eventually exceeds the tires coefficient of friction and your truck and trailer become a bolo.

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I agree with Mike and slow3v. If a panhard bar isn't something you'd want, consider upgrading to a Helwig sway bar. And definitely LT tires. I am running these and my truck tows like a dream:

https://www.truckcamperadventure.com...-at3-xlt-tire/

Added bonus, they're made in the USA.

 

Correct. It's purpose in life is to hold the axle from motion side to side relative to direction of travel. It has no impact on either spring or roll rate. If body roll were the issue then the correct fix would be either stiffer springs or anti-roll bar (sway bar). An anti roll bar would be a better addition if the complaint was excess body roll or if wanting to accommodate larger and higher loads. Trailer stability is best enhanced by limiting sideways motion, which is why the best fixes are LT tires with stiffer side walls and/or panhard bar.

EDIT: The roll rate comment was not in reference to things like roll centers. Whole different and far more technical discussion.