Just picked up my new to me 2015 F 450. I had four new rear tires installed and immediately left on a 2000 mile road trip towing my 37’ fifth wheel. As soon as I hit 50 mph the truck and trailer started to sway to the point of having to slow down or risk losing control of the vehicle. For the next few hundred miles I had to “learn” how to drive again and was able to manage only 60 mph but when any vehicle large or small would pass it was a white knuckle experience.

I talked to a fellow super duty owner and he said to be sure the rear tire pressure was at 80 psi and front at 90 psi. Now I always heard that when towing you should run the max pressure in your tires. But he explained that 19.5 wheels are for commercial trucks and are over rated for what I was towing. So I lowered the pressure from 110 to 80 psi and wow! What a difference that made. I was able to drive at 70 and at one point had to accelerate to 75 for a brief moment and the truck road like it was on rails with no sway. Now I always cruise at 65 but it is comforting to know that if need be the truck can exceed this with no problem.

When I returned from my trip I did read on this forum of similar experiences from 450 owners having to “run in” the tires for a few thousand miles before they are able to tow. I do have a little sway when 18 wheelers pass but no where near what I was experiencing with 110 psi in the rear tires. I’m hoping that after a couple of thousand more miles the the truck should be even more stable.

 

Thanks for reporting the experience. It is true that those tires take a couple to get broke it.

Much different tire than the LT's.

 

I run 80 in the rear when loaded and 70 empty. I found a load table and went by that. I do run the fronts around max. Hoping that will help get even treadwear since the fronts seem to wear at the edges .

Edit here is the table

 

 

Just curious as to why lowering the PSI would help stability?? I realize they are not LT tires, but logic would still think it would make them a bit more squishy??

 

Great question!
My reflex answer is that 80 psi ain't squishy at all. My f350 has e-rated tires and Max is 80.

I'm guessing here but it seems to make sense.

 

19.5 tire is just heavyduty F or G rated so when running empty or even a moderate pin weight is really nothing for the capacity of the tires. Then having duallies aired all the way up is probably like having the feeling of being on ice. Lower the pressure so the tire has give for better traction and handling would be my guess.

 

Every time we put new 19.5s on the rears of our Freightliner ambulances, it scares the every living mess out of us until they go through several heat cycles and then the tires firm up and we are good. But those first thousand miles are very scary, especially when patient and medic in the back. They nearly get seasick.