My 315 ridge grapplers, don't fully contact pavement even at 35 psi, not enough weight on the truck. Going up to 45-50 is even narrower contact patch. I keep them 30-35, better ride and even wear.

So Can we airdown a fully loaded 4runner (Near 6300Lbs) with E load tire to 20 PSI in offroads ? what will happen if we do not obey that formula ?

As far as I understand tire minimum tire pressure is needed to keep your tires from overheating and blowing up as a result. Severely underinflated tires might also slide from wheels.

So I'd say if you are not going fast - 20psi would be fine, a lot of people air down offroad. But when you're back on highway it will be not safe to keep tires inflated under minimum pressure for your load.

Hmm.

It appears that a C rated tire would be pretty useless off road since you cant lower it down below 35psi and maintain the ability to carry load. Let alone in order to carry load normally you would need at least 40+psi for just a 5gen with a bit of weight.

So it appears you are stuck with going P rated for not so heavy better MPG tire or E rated so you don't over load and can air down enough.

I wish i knew this before i got my C rated Duratracs for my 5gen. Never even heard of a D rating suggested for a 4R, heck Goodyear doesn't even list the C rated tires anywhere.

I dropped pressure for my C rated tires offroad to 20 psi with no problem. Danger to lower tire pressure is that tire will overheat on high speed or won't hold up on high speed sharp turns. As far as I know if you driving offroad at pedestrian speed (or lower) you can lower pressure as much as you want providing that tires won't slip from wheel.

Yeah... no.

I was running 15psi on my Ridge Grapplers on the beach this past weekend with the cargo area full of coolers and gear, pulling our trailer (1800lbs loaded) which was aired down to 20psi. I've routinely gone down to 18-20 psi while offroad with gear in the back, sometimes pulling the trailer.

This is all good to hear, though not exactly what the numbers imply. But very logical since the real concern/danger is if there was a failure at speed due to heat build up or instability.

I probably wouldn't run below 20psi off roading since even at 35psi my Duratracs seem compliant/soft.

A little off topic but I just got installed Toyo AT3 P285 70 17. I wanted the LT but that's another story and I don't off road anyway.

They put 41 pounds air in each tire, with a max of 44. I lowered it to 36 and rides great. Toyo says I should use 26 pounds. To me, that sounds a little light. I haven't chalked.

With all this, is 36 lbs ok and can I run 20 lbs when I go off road since they recommended 26 for every day driving?

Thank you so much

I cannot believe Toyo is saying 26.

There are two reasons why lowering the pressure is an offroad ritual for low range offroading:
1/ comfort in choppy terrain
2/ traction in slippery terrain

In addition, airing down plus AWD or 4H is needed for sand (not desert sand, but dunes, beach).

If the tires are compliant, like P metric tires at 32 psi or said LTC, then what you get by airing down offroad is increased chance of sidewall issues. However, in really challenging terrain for traction, airing down will still be needed especially on an SR5 or Limited that don't have a real locker or very aggressive traction control.

Obviously, exactly how much one needs to air down should be done reflexively not just following someone's rules blindly.

If I feel I need more traction, I would air down my LTE to 20 or P metric to 28. Sand is different, but how much depends on the sand.

However, if I intend to keep good pace/4H then I only air down my LTE to 28. I don't air them down for normal dirt roads but that requires a stiff suspension for a comfier ride (opposite effect to street).

The issues with airing down and then driving at speeds too high for low range offroad are pretty significant:

--tire squishes on a bump, in a ditch and if you hit hard enough you can get a pinch flat or damage the wheel even if on proper suspension that can take the hits
--even if you don't get niceties like that, you are killing the sidewall which impacts how the shocks work (now out of position when you need them the most).

So airing down has its reasons but should be done more reflexively than just following a ritual.

Finally, tires and suspension should be chosen together. A stiffer, offroad suspension or a well-adjustable suspension will work better with LTE tires while a soft suspension will work better with lighter SL tires.

On my Outback, I had KO2s on stock suspension and while it worked well on smooth dirt or when going slow it was utterly pathetic on washboard or just any dirt road at street pressures. That's an exaggerated version of what can be experienced on a 4R but same principle. The reverse way of getting the same effect would be running a stiff suspension with some light weight street tires.

The easiest scenario for knowing the "best" pressure is door sticker pressure on stock size/type tires. In that light, the number from Toyo makes perfect sense for the tire you're running. 26psi closely approximates the load capacity of stock tires at door sticker pressure.

As others have said, yes you can… I’ve aired down my stock metric tires (265/60/18 Dunlop AT25s) from the stock pressure of 29psi to 15psi on soft sand at the beach and 18psi on rocky trails…just have to keep your speed to something suitable for those pressures and it’s not a problem.

Exactly right…the normal pressures you would run are just for paved roads where you’ll drive full speed. So you need an appropriate volume of air shoved into those tires to keep them from overheating. If you are running a higher load, you’ll need more air. I’ve aired down my KO2 LT D load tires from my street pressures of 35 psi all the way down to 9psi on soft sand…again, no problem as long as you’re driving at the right speed. The footprint on the KO2s at those pressures are close to what my stock tires were at 15psi more or less, but I didn’t drive more than 30km/h at those pressures.

26psi would be too low for LT tires for the road, but P metric tires at those pressures are fine…probably close to what your stock metric tires were running if I had to guess.

The tire pressure calculator that others have posted (Tire Pressure Calculator) seems to be pretty spot on. That’s how I first got to 35psi for my new tires. After driving around for an hour, including some high speeds, the pressures bump up to around 38.5-39 psi, which is perfectly within the “4 psi rule”.

I love all the great information I get to read on here and think about, my wife already doesn’t understand how I can think about my 4Runner so much and then I run across this thread. Now to find the perfect pressure for my new p-metric 285 Wildpeaks……

Very interesting. So I used the tire pressure calculator on tiresize.com and it says I should be running my P285’s at 26 psi to get the same load rating as the stock P265 at the factory recommended 32 psi. I get it as far as load rating goes, but will they wear evenly and handle well at 26 psi? Seems a little low……

So, just installed Falken Wildpeak LT265/70/17 in E rating. Also bought new TRD Pro wheels!

Went thru the calculation in the Tire Pressure Calculator linked here: Tire Pressure Calculator

The OEM P rated tires were 32 psi. The new tire pressure is coming in at 44 psi. I have them at 40 psi for now, but will ride around on these tires for a bit and see how they feel. May bump them up to 44 soon. We'll see how it goes.

BTW-Have TRD Off Road wheels and tires (3800 miles) for sale. ;)