Hi All,

So I just got done swapping out to Bilstein 5100's and had some Goodyear Duratrac 275/65R20's put on. Truck looks sharp and I like the ground clearance. The truck is sitting the way I want it now with a slight rake and it doesn't wallow anymore through the turns. But the question I have is this: What is the stock pressure on an LT tire equipped ford F-150? I'm really looking for the pressures used on the 7-lug heavy duty owners since I know they're stock with load range "E" tires.

On my door jam, I have 35psi for the stock P-metric tires, but I noticed my spare tire which is an 18" LT load range "D" tire had a stock pressure of 56psi. So for the time being, I've aired all my LT tires to 56psi all around since my new tires are load range "E". So for you owners that have stock LT tires, does the jam say 56 psi for your tires all the way around? I know the raptor guys have a stock pressure of 40, but that truck was designed for fun, not hauling or trailering.

Also, for those that are curious. My truck has gone from Stock, to Daystar leveling, to Bilstein 5100 leveling (full height). For those who are curious, I highly recommend the 5100's. With the daystar leveling system (basically just a spacer), I noticed that my truck wallowed more through the turns when going up steeper curbs and drive ways versus stock. When I switched to the 5100's from the daystars, I noticed that the truck no longer wallowed. I would put the ride similar to a european luxury car. It is firmer, but it doesn't bob and weave like it did with the daystars. I wish I went this route to begin with. So running with 56psi in my tires and the new 5100's, I have to say that it really isn't all that rough. It's more taught, but it still absorbs the expansion joints and pot holes nicely.

Thanks for all the help in advance.

*EDIT* Here's the pic for those wanting to see it. Weather isn't exactly perfect for pic taking.
High Shot


Low Shot


Shock Shot

 

No pics? C'mon, you can do it.

Check this link out: https://www.google.com/url?sa=t&rct=...47008514,d.eWU

The prevailing info that I'm finding is that everyone wants to tell us NOT to run an LT tire over 80 PSI but adjust the inflation rate based on the load being carried. There is so much confusing information out here that my head is spinning right now.

I'm gonna venture a guess that if you run around 50 psi for daily driving then you'll be fine and enjoy good tire wear and some degree of comfort.

 

This is correct.

Most of us running SuperDuties run 55-65 in the front (depending on the engine), and 55 in the rears, when unloaded.

Running on 80 PSI makes the tire hard as a rock, and you'll still have a good 1/4 inch of tread on the outer rib of the rears when the center rib is down to the wear bars.

A quick-and-dirty method to figure out what PSI to run is to run a line of chalk across the tread, and move the truck for 3-5 tire revs. You're looking for even scrubbing-off of the chalk all the way across the tire. If it's scrubbed of in the center and remaining on the edges, your tire pressure is too high. If it's scrubbed off on the edges and remains in the middle, your pressure is too low.

-blaine

 

Remember that required inflation pressure is a factor of the amount of surface area you want in contact with the pavement. The only thing that load range has to do with inflation is it sets the maximum limit. That's it.

My Excursion weighs 7,350 lbs and requires 45 PSI front, 55 PSI rear on Load Range E tires. There's even a sticker in the door that tells me I can air them down to 38 PSI in the front if the truck will be lightly loaded. The only reason I can't install LR C tires(in the stock size) is that they don't permit the required pressure for the rear, and the maximum load is correspondingly lower.

If your LR E tires are the same size than your stock tires you shouldn't change the pressure at all. Asking the HD users what theirs recommend is useless because they are inflating for axle capacity that you don't have. Your rear axle isn't rated for 4,800 lbs, and neither are your rear wheels, but the HD trucks are, which requires them to have tire pressures to support that. Off the top of my head you should still want ~35 PSI in each.

 

Actually, the law is only concerned with the weight rating on the tire at a given air pressure. Not all P-metric tires have the same weight rating at a given pressure... same for LR-E tires.

The only right way to do it is the chalk trick. You should do this on nice flat even ground - a parking lot being a good option. Once you figure out the pressures you won't need to change the front very often - but the back will vary based on load. You should perform this test for whatever "common" scenarios you may have - daily driving, towing a travel trailer, etc. - and come up with good numbers for those scenarios. You can then extrapolate other values as necessary.

 

I can see a superduty being loaded at point that could overload a LR e tire. I don't think an F-150 has enough available GVW to do this.

 

It's virtually impossible to load a Super Duty to be over tire weight but under GVWR. It would take ~3,800 lbs on the rear axle to achieve that for an SRW truck, and I've never seen one that has that much payload capacity.

Can you reference this? I've never seen a tire that varies from the norm. For example, can you find me a P265/75R16 LRE that isn't rated at 3,415 lbs @ 80 PSI?

I can't.

 

I was referring more to the P-metric tires, which have a lot more variation. The LR-E tires are all usually identical.

This wasn't always true - when I had my 05 Super Duty, the General tires had a higher rating that the BFG A/Ts that I installed. Both were load range E - but the Generals (crap tires) had a higher load index.

 

Were the sizes identical? I know it will vary by size, and lots of people replace stock tires with larger ones. Typically a larger tire with the same load range will have a higher capacity due to the increased surface area for the pressure to act on.

 

OK, for inquiring mines I've gone ahead and posted pics of my truck . Now I spent a good deal more time last night trying to find the information that I needed and I ran across this from Toyo (you'd have to click the load inflation table. Toyo Tires Load Inflation Index. Knowing from tirerack that the stock Pirellis have a load rating of 2409 lbs at 35 psi (all p-metric tires with a standard load are rated at max capacity from 35 psi to their maximum air pressure). So using the Toyo reference table, I see that my load capacity is achieved at 45psi for a load range "E" tire at the size I now have, 50psi gets me to 2600 lbs and 60psi gets me to 3000lbs. I decided to shoot the difference and inflate to 55psi, since my spare LT tire from ford came at 56psi. I can't help but feel that ford undersized the 20" tires if they recommend 56psi for a similar overall sized load range "D" tire for the spare (according to Toyo, this gets the tire to 2600lbs load capacity so I guess my "E" tire is a little stronger). My only question though, would this inflation table be universally applicable to all tire brands of similar size and load range? I would feel better if this came from goodyear since that's the brand of tire I bought, but hopefully this would make a good universal guide.

As for why I asked for the 7-lug user's input, I was thinking that they would probably have 2 air ratings for that rear axle. My 2nd vehicle ever owned (1989 ford F-250 with a 460 v-8) had 2 pressures to run at the rear axle for empty and loaded. So I was wondering what their sticker says. I know my rear axle weight is roughly 4400lbs, I'm very well aware of my VIN sticker's specs .

And thanks for the chalk line idea. I'll try that out to ensure I'm getting even wear. I may deflate to 50psi if I'm not getting even wear.

Hopefully this will help our fellow ford enthusiasts if/when they swap from p-metric to LT-metric tires.

 

Interesting. Ive got the same truck (and color) except I have the 18in rims and bought 275/70 wrangler duratracs 3 weeks ago. Mine are at 45lbs.

 

Just curious, why buy E rated tires for an F150? Was that the only option for the size you wanted?

 

Generally speaking, yes. All LT tires in this size are E rated and there are no p-metric tires that I'm aware of in this size. There's several more factors as well. But I wanted a 35" tire after leveling and living with it for a while. After digging in, I found out that most of those tires are 34.5" tires, and I found out that the stock 20" size for a super duty are 275/65R20 and are only 0.4" smaller. So the tires in the 275/65R20 size are immensely cheaper than any other tires similar in size. I'm figuring it's due to production volume.

Another reason for the LT tire is that I wanted an all-condition tire. Living in the pacific northwest and driving the passes, it's far easier to find an all season tire that is mountain-snowflake branded (meaning no snow chains required) when going over the passes compared to P-metric tires. The other size I considered was 275/60R20, but the only tire that fit this profile is the Goodyear Silent Armors and the reviews for that tire aren't as great as they were for the Duratrac. There are also other branded tires in the LT size. But for pure load hauling, the 275/60R20 p-metric tires had a load range in the 2600 range for the most part, but they weren't quite large enough to fill-out the wheel well the way I wanted.

Another reason is that I wanted more "cushion" as well. Even though the rear axle is only rated to 4050, when you go around a turn you are shifting the load to the outside set of tires. I've hauled rock and dirt quite a few times with my truck and I'm pretty sure I may have over-loaded it a time or two, even though there was suspension travel left (not riding on the bump stops). I don't carry a set of wheel scales, but I try not to exceed my payload. When they're dumping dirt into your bed, they give you an estimate on weight per yard, but sometimes that estimate can be really far off. I'd rather have more cushion than not enough, especially when loads shift.

 

Can't comment on the tire pressure, however truck looks great with the leveling kit and those tires Off topic: Do you find yourself using the bed-side step often?

 

Thanks, and yes I do use those steps very often. Usually when I'm securing items close to the back of the cab, it's nice being able to reach out to the middle of the bed, especially when securing a tarp or grabbing a strap. I'm 6'0" and the tall bed sides of these trucks make it a challenge to get to items that may have slid closer to the middle. Having raised my truck a little has made it more of a challenge. I'm glad my wife talked me into the 6.5 bed since the 5.5 bed doesn't come with these steps (and she likes to remind me of that fact whenever she sees me loading something up or securing something with me on the step).