Hey everyone, new to the forums but looking for some help.

Got a new 2016 F150 and added a 4" coil over lift with KMC Rockstar Wheels and BFGoodrich All-Terrain T/A KO2 Radial Tire -LT325/65R18/E 127/124R

The truck sticker says to inflate to 38 PSI, and the tires say max pressure 65 PSI. I've been searching for days and can't figure out what the appropriate pressure is, it seems there are many different theories.

Any advice?

Pics here in New Truck thread https://www.ford-trucks.com/forums/1...l#post15875954

 

This isn't a theoretical question, the math has already been done, you're not looking in the right place yet. The only time you should be concerned with max pressures is if you're going to be approaching the tire's maximum load, which you will be coming nowhere close.

If your truck is like mine, you have a 3,450 lb front and 3,850 rear GAWR. The official load inflation table is attached, and for this size doesn't go below 35 PSI. At 35 PSI these tires are rated for 2,335 lbs EACH, or 4,670lbs per axle. That's close to 1,000 lbs over the maximum capacity for your axles unless you have the HD payload package.

I would set them at 35 PSI since the tires aren't rated for any less, but it's gonna ride like a brick no matter what you do. You have WAY too much tire for the truck IMHO. I've attached the load inflation table for your reference.

ON edit: The truck looks good!

 

For that size a tire I'd probably start at 50-55 in front , 45 in back......then test your tires footprint to fine tune psi......you could run em at 65 but it'll ride harder and may cause premature wear if it causes center of tire tread to bulge up.....ideally you want just enough psi to give you a nice even contact patch all along the tread as it touches the ground

 

[QUOTE=Tom;15876075] You have WAY too much tire for the truck IMHO.

it's perfect IMHO

 

Weight rating, not appearance. I think they look fantastic!

 

Those pressure tables are for Toyo, I can't seem to find the same for BF Goodrich for AT KO2 . Any ideas? Or just use the closest tire from Toyo?

 

The publication is from Toyo, but the data is from the Tire and Rim Association, which is an industry trade group that establishes standards. A tire's ability to handle a load is a function of surface area and pressure. Because sizes are industry standard, so is surface area, and thus required pressure. You can apply that table to any tire manufactured by anyone, as long as it's DOT approved.

 

Tom, you are awesome. Thank you both very much!

 

The best way is the old-school chalk test. Mark a line across the face of the tire, edge to edge. Drive a few revolutions straight forward. If the line has faded evenly, then you have the right pressure. If the chalk is heavier on the outside than the inside, too much pressure... if heavier on the inside, too little.

 

I just mounted a set of BFG's on my truck this summer. The shop aired them to 35 PSI. My door jamb also says to inflate to 38 PSI. I asked the shop manager about this. He stated that BFG rates to the tires to run empty at 35 but 38 will not hurt them in any way shape or form if that's what makes me feel better.

So, I run them at 38 because I'm a little bit OC that's what the door jamb says.

 

Tom - Rep's to you for all that. However, the document says to ensure that the tire is suitable to fit on the rim width, and I don't see a table in it of tire size vs rim width. Is there one available? I've been going by Tire Rack's info, but wondered if there is an industry table.

I ask because I know many people are not aware of the issue. Getting the right tire pressure to carry the load with the wrong width wheel is going to cause wear problems. And, if carried to an extreme, like an FJ Cruiser my brother bought with oversized tires, it can be a serious safety issue. So tire's and wheels need to be matched.

 

Thanks Gary, and that's a great point. I've never found an industry table for that, but I'm sure one exists somewhere. A couple years ago I was looking for more information and had a tough time finding any. The TRA wants you to pay for just about all of their publications, and the Toyo chart is the only one I was able to find. If you find a good table please post it up, in the meantime I'd be comfortable using info from TireRack.

 

Thanks, Tom.

As clarification for others, my bother bought an FJ Cruiser with new tire's on it, but much bigger than original. He initially liked it, but then brought it down for me to look at as it didn't drive quite right. I drove it but hadn't gone a quarter mile before started asking questions about tire pressure as it was following every crack in the road. Turns out he'd tried pressures below the TIP recommended pressure, right on the pressure, and above it. Nothing would make it drive correctly.

So we took it back to my shop. The first thing I do is to look at the pattern the concrete from the driveway leaves on the tires, as my driveway is very white and chalks a bit. In this case the pattern was narrow and in the center of the tire only - with the pressure at about what was recommended. That usually means too wide of a tire for the rim, causing the tire's sidewalks to be pulled in and the tread to bulge in the center. A bit of checking with Tire Rack proved that guess to be correct - the tires were to be used on a 1" to 2" wider rim.

Then, on further inspection we found that the sidewalls bulged so much that they were actually rubbing steering components in certain conditions. It is one thing to have the tread rub, but having the sidewall rub is a no-no. So, he "discussed" things with the dealer that sold him the vehicle, and after pointing out the safety issue finally got +1 sized tires on it. Now it drives like a new vehicle. And, it is safe.

I say all of that to point out that the tire inflation table specifically says to make sure the tire is to be used on that width rim. If the tire is too wide for the rim the only way to get a flat wear pattern on it is to run it dangerously low on pressure. Don't do it. Match the tire's to the rims.

 

Not a while lot more to add to what's been said above, but I'll throw my two cents in anyway.
I've had Load Range E tires on a half ton before, and what I found was that the ride was about the same all through the lower inflation range down to minimum pressure. Because the tires were so stiff, I think it was the sidewalls were transmitting most of the shocks, not the pressure.
Anyway, once I figured that out, I ran them around 55PSI, which was giving them the ability to handler higher loads, but as good of a ride as I could make it.

Some trial and error may be in your future.

 

BF Goodrich had this on their website- see under "Rim Width Range"