I'm in the same boat here, and was 100% convinced I needed to get out of my passenger rated tires. But a few on this board w/ way more towing experience than I have stated over and over again that the OEM tires will handle the load that my truck can take.

So I'm stuck - do I run Defender LTX passenger tires? According to the load charts, 35 pounds is where you get the most load - the higher PSI gives me no more load carrying but I suppose it helps keep the tire cooler. So towing I'd probably air them up to 40.

Or - the same tire in a Load E running at 40 pounds daily and 45 towing.

I'm confident w/ the 40 pounds on the Load E as a fellow forum member posted his door placards with factory installed Load C tires. I have the same GAWR for both axles, and the same tire size from the factory. So for me, this is the holy grail of 'what is proper' if I'm upgrading the tire.

https://www.f150forum.com/f118/lt-ti...2/#post5660233

Load C, Load E - same chart same row so I'm assuming the same pressure.

 

The OEM pays people a lot of money to figure this stuff out. The tire size picked by the OEM is more than capable to handle loads the vehicle is designed for. All tires of a given size and load range can carry the same load.

If you put an LT tire on, the inflation pressure for your load will be the same regardless of load rating, C-E. LT tire are slightly more durable than a P tire.

Tire manufacturers make different quality tires, depending on the customer.

Inflation should be set according to load. For example: if I am loaded heavy I inflate to the max pressure indicated for the tire load. Running with the bed empty I use a lower pressure for a better ride.

over-inflation just wears out the tire faster and give a ****ty ride.

 

when you switch from stock tires, you need to at least run the minimum pressures for the load you are hauling... when you look at the charts, you'll only need ~<2000 pds of capacity per tire because even that would exceed rear gross axle weight anyways. running too much pressure can make tires run cooler and make it feel like you are running a stiffer tire as well as improve gas mileage; however, it does so at the cost of decreased traction and decreased/uneven tread wear.

you likely know this, but i just want to make sure because the way you phrased it makes me question it... you do not increase your truck's load capacity by airing up the tires more regardless of what a tire chart says about that tire's load carrying capacity

 

I think what is missing is when you look at load ratings that doesn’t include sidewall flex. This is where the LT tires make a difference if you are talking about towing, you really need the stiffer sidewall when cornering with a trailer attached. There is a video on youtube and they take a truck and run over a steel rod with A, C and E rated tires, it is interesting to watch.

 

The sidewall height is the key, not necessarily weight.- on my 2002 sport trac, it had P235/70/16's and was a bear when buses and tractor-trailers passed.. switched to LT265/70/16 and issue went away 100%.. My f-150 came with 265/60/16 P tires in it, and was way better than sport trac with stock tires, but still was buffeted. Put on some LT265/65/18's on it and issue is gone 100%... With your 20" tires, I would imagine their short sidewall would be fine for towing. I would air them up to the max recommended pressure if you had issues. if you weight your rear wheels when loaded, you can lookup pressure spec online at the tire mfgr's site.

 

I'd check out the LT285x55x20 BFG's...D rated and only a tad bit larger then the stock tires. Stock tires on some Toyota Tundra's and should ride good and have extra sidewall stability for towing.

 

I'm not sure if this was to me or not - Ford's door placard pic means that the 39psi for the Load 'C' tire is good to go for the 3800 pounds of that rear axle. Airing up to 45 in the rears would simply be because I could. And to be honest, driving around at the door placard pressures with just my butt in the seat, you start to get used to the way it feels. Load the truck at that psi and it'll feel different - airing up the 5 pounds in the back might give a little of that original feel back. Lets face it, we're all used to driving in unloaded trucks at the trucks loaded psi.

 

In fact for the LT275/65R18 40 psi is good for 2130 pounds. So 2130 * 2 = 4260 - or 460 pounds more then the 3800 pound axle can take.

 

I put Michelin Defender LTXs in Load Range E on my truck. Love them. The Cooper AT3s I had before were fine, but when hauling the truck felt "squishy" if that makes sense. It feels much more planted now.

 

The laws of thermodynamics contradict this...