...to match the load capacity of a P-metric tire.*

*A Standard Load tire (SL), usually P-metric (or metric, euro-metric -- a nearly identical twin). This is the tire found on nearly every new car, SUV, and Light Truck. On the sidewall it looks like P265/70/17 (or 265/70/17) as opposed to LT265/70/17.

How much more pressure?

• 10-15lbs, if an LT is switched for a P-metric tire with the same dimensions.
• LT load range (C,D,E) doesn't affect this.
• Tire size does.

This continues to come up and is often a source of confusion.

Not surprising though, considering that both of the following statements are true:

LTs carry less load than P-metric.
LTs carry more load than P-metric.

Throw Load Range into the discussion and things get nice and tangled. Describing the relationships in words doesn't paint a clear picture so I thought I'd try to make some -- pictures, that is.

The charts are based on tire size 265/70/17 and, in the 2nd chart, how it relates to the 5th gen 4Runner because that proved easiest, but the application to other generations is obvious and not too dissimilar. The curves should be reasonably accurate and more than good enough to illustrate the point. P-metric tires get load capacity de-rated 9% when used on an SUV and the curves reflect that. The tables used for reference come from this.




Hopefully it's easy to see how an LT can carry both less and more load than P-metric. It's all about air pressure and, for this tire size, it takes about 12psi added to the LT to match the load capacity of the P-metric tire. Hopefully it's also clear how pretty much the only distinction that matters is between P and LT. Load Range doesn't meaningfully affect the choice of air pressure for LT -- unless very high pressures are desired -- since the the longer load E curve is overlapped by the shorter D and C curves.There may, however, be implications for speed capability in the selection of load range. See Baldwin here.





Extending the line for LT down past where it ends (because load tables stop there) in this chart might seem to imply that making a pressure adjustment when switching to LT isn't important since it appears there would still be load reserve at 32psi even if no additional pressure was added, but that doesn't mean there's no benefit to adding more pressure (leaving it at 32 would be the equivalent of around 20psi in the stock tire). For one thing, the curve bends more as it goes down the chart towards zero psi, so calculating it as a straight line overestimates load capacity. Secondly, having plenty of load reserve is desirable since tires change over time -- and they don't get stronger. Lower pressures result in more heat which speeds the process. The cumulative effects of dynamic loading, speed, heat, age, hard use -- not to mention the inevitably lower speed rating in an LT -- are all good reasons the load reserve established by the factory tire at recommended pressure should be given due consideration. If nothing else, the level where the tpms triggers should be a good clue to that. Most of this is covered in the doc already linked. There is also the option to Ask a tire engineer - Toyota 4Runner Forum - Largest 4Runner Forum. The horizontal lines on the P-metric tires represent the ability to add pressure for special conditions (like high speed) but the extra psi assigns no additional load capacity. The language in load tables indicates that extra pressure for LTs at high speed is recommended, as well, and at lower speed thresholds than P-metric. The capability of a tire in both load and speed necessarily overlap each other.




Tire size makes a difference. More air equals more load capacity, whether it's a bigger tire or more pressure in a given tire. The grey curve extends the full distance, so it would be Load E

Reserve

Where did the charts originate? Copy this over to the 5G side please. I'm sure it will help some of those guys. Good stuff.

I'm under the impression that would be against forum rules.

Good catch. I'll edit the intro to include the source of the numbers.

Good work JB.

Whohooo 1E - charts, graphs, statistics, fax & figgers.

good charts. The only thing is not clear to me is a maximum pressure when tires still keep enough traction to make a stable ride and especially stable turns let say on rain. Becasue as I see it if I pump tires up at let say 50 psi I might like bumpy ride and it's going to be safe from load capacity point of view but I'm sure that I'll reduce traction at least by half. And I'm going to regret it if I have to make sharp turn on wet pavement. Or hit an icy path on the road.
But I guess that nobody knows it for sure.

Someone's on a tire research mission! This is good info, a gap in my auto knowledge apparently! Nice to fill it in some, I can make sure I'm at 22 PSI or greater when towing my boat now after some quick mental math... :P

Should be 5000lb 4 Runner / 4 tires = 1250 / tire, adding 200 per rear tire for a 400 lb tongue weight (obviously conservative by ignoring fronts) = about 1450 lbs / tire --> ~22 PSI?

Anyway, cool to see some numbers, take away seems to be there's plenty of room for error before things get bad... unless you have a Firestone Exploder and love to run 12 PSI ahahaha...

ok i see what you are saying, and your theory is correct, lb for lb yes a p rated tire will carry a greater load, but in reality you can run a E rated tire at 25psi and it will hold the weight of a 4runner just fine, you CAN NOT do the same thing with a P rated tire, it simply wont work... if you do not believe me try it.

you are trying to do a lb for lb comparison but your only control is tire size and, you have too many variables to make your statements concrete.

so i can carry a load of 15,000lbs @80psi with my tires, my 4runner lets say weighs 1/3 that @5000lbs(thats with a average daily load roughly). now for my tires to support that load i should only need 1/3 of their max psi correct? yes so i really should only need 26.4psi per tire to hold the weight properly, and i can assure you that at even 25psi in my tires there is no abnormal squatting or increase in rolling resistance, or increased consumption of fuel. now lets try the same thing with your passenger rated tire your max load is 11332lbs @ 35psi. so 5000lbs of the 11332 is roughly 44% so we will run our P rated tires at 44% of 35psi which is 15.4psi... does anyone see a problem yet? you need to run your P rated tires are a high percentage wise psi than you do an E rated tire, no way no how will a p rated tire cary more load then an e rated tire per psi, even in a ratio comparison such as this...

and if you are gonna try and tell me that the side walls will break down faster with an E rated tire run at a lower psi than recommended im not gonna buy it, besides even if it did, i still only have a 5000lb truck, not a 10,000lb truck so im not worried in the least that i might have lost 20% of my tires load carrying capacity

i get your theory, and it works in theory but in reality its never gonna work out, physics and natural "laws" and science and math say otherwise, so does the real world and everyday usage.

now what i will agree on is that a P rated tire will have a much softer ride at 35psi then a E rated tire will at 80psi, but just as i have shown above there is no need to run the E rated tire at 80psi in our rigs unless you are looking to the up-most possible mpg say like on a road trip where 98% of your driving will be hwy driving. other than that you can run your E rated tire at a much lower psi, say like 35psi and have at least as nice if not nicer ride than the P tire, all the while having a tire that has deeper treat, and a thicker carcass to help hold up to road hazards like potholes or glass or curbs ect. and with a P rated tire there is as not much leeway in your psi adjustments as there is in a E rated tire, you cant just drop 10lbs and call it good cause you want a softer ride or you cant increase psi cause you want better mileage or you want to carry a heavy load like you can with the E rated tire. nor will the tire hold up off road to rock and sticks or other dangers like an E rated tire will, not to mention the shallower tread.

get it done

Now I'm still very very confused on this topic and keep obsessing about it... When you look at the specs, our OEM tire vs a new C rated Duratrac, the 265-70-17 Duratracs hold more weight at a lower psi... Not sure why I should be running them at 42-47 psi given this information. Seems to me I need to be at a lower psi. Tires don't necessarily carry that amount of plys (ie 6 or 10 for c or e) technically, but more about total weight handling.

I just got these last week and tried 42 and felt like I was allll over the road. Then I tried 38, 35, and now down to 30 and it feels perfect at 30 which also corresponds with the math for Duratracs based on the weight of my 4th Gen.

Trust me I'm not saying I'm right because I'm nobody and frankly ignorant on this stuff. I'm just trying to get the best wear and keep my family safe. And it feels safest at 30 psi, because I felt all over the road at higher pressures. Also felt cold to the touch after a 30 min drive last night - so doesn't seem to be creating excess heat either.

Gonna post a couple screen shots and pics here. One of my alignment (which is arguably out on caster because I have a frozen LCA bolt they couldn't break) and then two of the specs between what I think is the OEM tire vs the Duratracs.

Thanks for any thoughts and/or replies!

*I was driving on Toyo Open Country AT2's in P 265/70/17 with 30 psi for the last 3 years with the old alignment and everything felt great (for the record. So it's likely not the alignment causing the all over the road feeling - especially since it t feels perfect with the Duratracs at 30 psi).

The basic message of this thread is that an LT tire of the same dimensions and psi as a Standard Load tire, will carry less load (About 15 to 20% less in an SUV application).

That's it.

Afterward, determining "proper" pressure is all about whichever reference point you choose. You can reference the load inflation tables. You can reference the load reserve of the stock tire at door sticker pressure, just to name two.

Your tire stat examples don't work because they reference max pressure which is distorted in the case of the Standard Load tire because the increases in load capacity that come with additional pressure cease at 35psi even if the tire is inflated higher to its maximum (51lbs). Ignoring the size difference, in effect, the pics compare 35psi to 50psi.

At 30psi in your Duratracs, you still have about 13% load reserve at GVW. Hopefully, that makes you more comfortable. On the other hand, the stock tire has 37% GVW load reserve at the recommended 32psi and a survey of various vehicles and their stock tire fitments reveals that seldom does the GVW load reserve go below 20%. You can decide if that means anything. And then there's speed rating.

It's up to you how you weigh the various factors and which reference point(s) you choose.

Great post! This helps a lot. Thank you.

Either way I'll definitely try to heed your advice and bump it up for more reserve. Hopefully I can find a happy point where I don't get the wandering on the road.

Thanks again - very helpful.

THANK YOU for bringing this particular tire up for debate. Will all the respect for JB and the effort he put into the research, this topic still remains a mystery. Here's why.

I too am having a hard time finding the sweet spot for these tires. Started at 38PSI and they felt horrible. Kept going down and I was still not satisfied. The rear was having a party dancing all over the place. The party actually ended with the aftermarket suspension I just installed. However, I still can't explain the following pictures I took after washing the truck and driving for a couple of miles.

32 PSI rear tire
outer view
inner view

You can clearly see that even at stock pressure, the rear tires don't fully make contact with the ground. There's at least half an inch of unused rubber on each side, which hurts traction and stability.

34 PSI front tire
outer view
inner view
inner view

The front tires look better in terms of usage, due to the front weight bias.

So no one cares to venture a guess as to why those pics of the rear tires look so bad at stock pressure? We've given up on the topic?