How to Determine Correct Tire Pressure?

Hey guys,

So I finally got my LT275/70R17 "C rated" Falken Wildpeak AT3w tires installed and (gasp) balanced, and am loving them so far. However, I am now trying to figure out what tire pressure to run in them and am having some difficulty / questions.

I kept seeing people refer to a "chalk test" so I went over to YouTube, watched a few videos, and gave it a go. Problem is, the chalk seems to be wearing off the same whether I use 48 PSI or 38 PSI (especially on the front tires). No matter what, the chalk doesn't seem to ever wear off of the edge of the tire.. I'd say about half of the side tread blocks don't seem to making contact with the ground. So, the chalk test seems pointless. Thoughts?

Then I'm thinking OK, what about math? Well, I don't know much about the way tires are made or any of that, so I really can't speculate how to figure out tire pressures based upon specs. However, for what it's worth (probably nothing)...

The OE tire supports a max 2535 lbs @ 44 PSI, and the new tire supports 2600 lbs @ 50 PSI. So I interpret that as the new tires needing more pressure for the same weight. Got it. However, I don't know if the PSI per weight is a sliding scale or what, so I'm trying to figure all this out. Since the max loads on the tires are basically the same, this shouldn't be too difficult I'd imagine..
[recommended/max] 32psi/44psi (OE) = ??psi/50psi (Aftermarket)... so if the scale is sliding / direct, then I guess 36 PSI would be the correct / new door sticker recommendation? *EDIT: This method does not work because the PSI scale is not direct/sliding.*

After my seemingly useless chalk test, I think I was running 39F/35R COLD on my road trip last week and it all felt pretty good. It did look like the rear tires were flattening a little bit more than the fronts though with our camping gear loaded up, so maybe the rears need to be closer to the fronts when actually using the cargo area / back seats (usually it's just me in the vehicle). For the record, that 39F/35R COLD pressure went up to about 43F/40R once the tires were up to operating temp.

Thoughts?
Thanks!

 

IMO, since the oem tires are usually at 32 psi (which would work for the 265 Wildpeaks I am running now), I would think the 275 size wouldn't be terribly different. I'd try 34-35, but that's just me.

 

Man, i don’t overthink it because it becomes a pain in the ass, like all of that. I tend to find out what other people run and find a happy medium for what gives best ride quality and MPG for commuting. Off roading is another story

 

Haha my brain can certainly be a pain in the ass at times..

Hey @glwood54 , fwiw, I'd run a lb or two more in the P265 Wildpeaks than with the stock tires, based upon the tire specs, but again.. what do I know lol? I only say that because the P265's also have a MAX pressure of 51 vs. the stockers MAX of 44 PSI. The load ranges on all of these is pretty similar, though. So I interpret that as the Wildpeaks needing more air by design.. again, though, noob here.

I'm just at a loss because I'm being given a recommendation of 44 PSI for the fronts, and that just seems to high for me. I'm stubborn. I wouldn't doubt the 44 PSI for an E rated tire, but those have a MAX PSI of 80, which is a lot different than what these P or C rated tires seem to require.

 

FYI, when I got home from Discount Tire, I checked and they had 44 psi (idiots), which I lowered to 35, I believe. I run mine at either 34 or 35 without issue. 32 might be ok, but I have no issue running them a bit more. They don't seem harsh at 35.

 

Yeah I think you're right on with that 34-35 for the P-Rated 265's.
Looking for more opinions on these C-Rated tires...

 

Did Falken just come out with the C rated 275's? I don't remember seeing those when I was looking. I probably would have gone with that size had I known they were available.

 

I don't think they've been around for a super long time. I read that they designed the C Rated 285 for the Jeep Gladiator Rubicon, and I speculate that they decided to make a C rated 275 at the same time.. I imagine the R&D was not as much due to the situation.

All that said, they're SUUPERR heavy so I had a hard time myself deciding between the C Rated 275 and the P Rated 265. Another 10 lbs (per tire) for these 275's on top of the already heavy 265's heh.

 

Aha! Now that you mention the weight, I remember reading that, and it's what probably what steered me away from the C rated tires, not the fact that they weren't available. Given my use of my 4R, I'm more about weight savings...

 

Here: not thinking involved. You can probably adjust to your personal preference, but this is a good starting point.

They were at 44 because that is what is recommended for out trucks on an LT tire at stock size. I did end up running mine (265-KO2's) a little lower (35-36) as well, though.

 

I kept seeing people refer to a "chalk test" so I went over to YouTube, watched a few videos, and gave it a go. Problem is, the chalk seems to be wearing off the same whether I use 48 PSI or 38 PSI (especially on the front tires). No matter what, the chalk doesn't seem to ever wear off of the edge of the tire.. I'd say about half of the side tread blocks don't seem to making contact with the ground. So,the chalk test seems pointless. Thoughts?
If this is the case, then you need to lower you psi, i would try 34 and adjust from that. The chalk test works to show you are getting full contact.

 

I like to drive on a dirt road for a few minutes, then take it to the pavement for a bit. You can see pretty clearly how the tire is running that way.

 

I would get that, but mine are P-rated, not LT. According to the calculator you reference above, the pressure should be the same. So DT doesn't know the difference between a P-rated and LT-rated tire?

 

Whoops, I missed that! Sorry! Then I agree with your assessment.

I like DT, but have little faith in their installers. When I got my KO2's, I noticed that they had installed 2 in load range "C" and 2 in "E." They fixed it after I mentioned it, but I shouldn't have had to point it out.

 

That would scare me. Think I'll go look at my tires...

 

Maybe they gave you load range "C!"

 

Maybe! Perhaps that's why they put in 44 psi!

 

LOL.

So, awesome, thanks for the links. It looks like these load / inflation tables, or "inflation curves" are more or less standardized across all tire brands. I was trying to find the "load inflation chart" for our OE tires and couldn't.. but I suppose that's moot? I feel like the figures must be standardized based upon tire type (P, LT, etc.), or that website that badassguy linked wouldn't be possible. Doing way too much reading over here.. yeah.. looks like they are standard to a degree and are published by the "US Tire and Rim Association" in their annual "year book." It also looks, interestingly, like C rated and E rated tires are both considered LT (duh) and follow the same inflation curve. I honestly assumed that C rated tires were different enough in that their inflation curve would be different, but that is apparently not the case. I suppose a C rated tire simply rides smoother at the expense of ability to hold more air pressure / carry more weight. So now I think of a C rated tire as a softer E rated tire that just can't do as much.

Now I'm trying to wrap my head around this 10% factor that OE tires incorporate for safety, etc. etc... but yeah it's looking like something around 41 PSI should be the ticket. I think I'll run less than that in the rear though unless I'm loaded up.

BTW, my original idea of using a ratio, i.e. "[recommended/max] 32psi/44psi (OE) = ??psi/50psi (Aftermarket)" doesn't work at all because passenger tires max out their carrying load at around 35 PSI, even though the MAX PSI listed for them is usually 44 in our size tires. The 44 is the MAX pressure but it's apparently only there for high speed purposes when a little more pressure could be safer.. however the tire can support no more weight at 44 PSI than it can at 35 PSI.. which is completely different from LT tires that hold max weight at max pressure. I suppose speed is more of a factor with car (passenger) tires than it is for truck (LT) tires where weight is probably of more concern.

 

In my 285/70/17 MT’s i run 45 psi in the front, and 35 psi in the rear. If i happen to add a load, i adjust the psi accordingly. I reached these psi numbers by the chalk method, or the dirt road method.

 

I have 275/70/17 load 3 AT3w’s. 35psi front and rear on road. 18lbs off road

 

I would put 32-34 psi.

 

I run 40 psi year round, and adjust if needed if I’m going to be driving in demanding conditions.

 

I would run it between 32-40psi cold up to your comfort zone. I prefer 35-38psi. Most 38psi. This is pavement not offroad.

 

Load 3?

Off-road varies for me. I usually start around 25 and adjust as needed. I have started lower when I knew I would be in deep sand.

 

I don’t have the wildpeaks anymore but when I did I ran at 38-39 psi on e rated 285/70/17. Now with the nittos in c load same size I am running 35-36 all around and it rides very smooth. The installed originally had 44-45 and it rode like a Walmart buggy

 

So it seems like a lot of guys run a lower than recommended pressure on the road to try to soften the ride with LT tires on these very light trucks. I suppose that's okay as long as they never load it up or go over 80 MPH.

40 PSI (recommended by the engineers) is the answer, for an LT tire on the 5th Generation 4Runner for highway/asphalt use. Adjust from there for comfort, etc. I plan to run a little less than that in the rear when it's empty back there.. but if you do that then don't forget to air up with weight!

BTW, here is the best load and inflation table I could find. Thanks, BFG! I assume the tool that badassguy linked simply uses this table for calculations.

https://www.bfgoodrichtires.com/on/...Size/420bcacc-01bf-42c9-840e-55344685c842.pdf

And this was a pretty solid article so I'll throw it up too:

https://www.tirereview.com/tire-types-and-load-capacity/

 

load c. It’s load 3 when your drinking Tito’s. Lol

 

Lmao!

 

I am running stock size Toyo AT3. I keep them at 32, cold, which after I drive for about 20 minutes, seem to settle at 35/36. I am in Arizona, and the tires tend to warm up rather quickly.