Put 255/85/16s on stock OR wheels and suspension

This is all the same stuff I've heard before. What I'm asking for is experience-based (i.e. science-based) evidence that this test actually produces an optimal tire pressure. I'm aware that you can define optimal in more than one way.

I just got curious about this again and did a quick search and found this from a tire manufacturer.

https://www.intercotire.com/using_chalk_method_determining_psi

"A Word of Caution: The proper air pressure for the original equipment tires has been determined by the vehicles manufacturer, but when larger tires are installed the air pressure recommended by the factor for the original equipment tires may not apply to a larger size tire. Two things come into play concerning the load carrying capacity of tires. These two things are; the volume of air and air pressure. The larger tire has the greater volume of air. When attempting to determine an air pressure number by using the “chalk” method you may find that the tread foot print is nice and flat at a very low pressure. When this is the case the air pressure you come up with may very well be too low for highway service. Even though the “chalk” test gave you a full tread contact patch, at a low pressure the tire may not be stable at highway speeds. The large volume of air can support the load, but the low pressure causes the tire to become unstable. If air pressure is too low for highway service the tire will run hot from over flexing and will cause fast tread wear due to the “squirming”. This overheating can also cause a tire to fail."

 

Yes this is true. An easy way to avoid this issue is you overinflated on purpose to about 10% over the recommended tire pressure.

Drive for several Miles, due to heat and you will wear at this pressure. Then find a flat area to avoid turning. Chalk the entire tire patch drive hop out and check it. Slowly reduce tire pressure until you reach the contact patch that is even across the tires.

Doing this will avoid under inflating (because the contact patch will still wear across the entire tire if it is under inflated) so you will be too high then slowly get to where the edges of the tire is making contact, at your cruising temp and pressure.

You can also look at the chalk on the tire. Or on the ground. Tire is easier for me, avoid turning if possible to get a better result

Edit: I ran my stock tires everywhere, quite surprised at how they worked honestly for 30k I was not easy on em. Ran 12 psi offroad no issues. Chalked them this way and had even wear to 30k before I replaced. Tires still have 7/32" left, roughly 50% and all 4 are the exact same. I ran a different pressure than the manufacturer reccomendation due to front skid and sliders. I was 35 front 33 rear at warmed up. Your results may vary. That being said I've heard of the 255 crowd getting close to the same psi reccomend from the factory based on wear and comfort so you might not have to mess with the E's much.

 

I should point out that much of intuition about this subject comes from my background in bicycles. I use a lot of different sized tires on my 3 bicycles for various conditions. The rule of thumb is to put less air pressure in a bigger tire. The theory is that you need less air pressure because the contact patch is larger. Force equals pressure times area. Since the force is a constant for the same rider (unless you eat too many cliff bars), the tire pressure needs to go down as contact area gets larger. I don't have any other support for this theory, except for ample personal experience running different sized tires.

 

You’re making the assumption that optimal tire air pressure equates to the pressure at which this chalk test passes. If I were worried about how some chalk looked on my tire, I would wholeheartedly agree with you.

 

Yeah absolutely. It is the same reason why you air down offroad. Your contact patch becomes longer resulting in better traction. Vs an on road tire with a smaller contact patch at a higher PSI to reduce friction between the tire and the ground.

Great for road bikes, terrible for say a dirt jumper.

 

I think what you are getting at here is that there is more than one way to define optimal tire pressure. Is optimal tire pressure that one that gives the best traction? The best cushion? The best wear resistance? The best rolling resistance? The optimal balance of all of the above?

I change the tire pressure in my bicycle tires dependent on the conditions: higher pressures for dry roads, lower pressure for wet dirt, etc. It's all really subjective and trial-and-error though; more art than science.

 

BTW, I have never noticed lower air pressure giving me noticeably more traction, but I have definitely noticed it increasing rolling resistance (bad) and cushion (good). It's the main trade-off that I have experienced between low and high pressure. Tire wear is harder to measure, so I can't comment. YMMV.

 

So for offroad the best wear is traded off for better cushion if your doing pre runner stuff like tearing ass down a Forrest roads or a desert.

Lower tire pressure for rocks or anything other than a maintained fire road to help grab traction. Albeit rocks, wet, mud, snow ect.

The wear is strictly for road ( to a point )

I too change my tire pressure with conditions. My wife has a road favored bike and I got maxxis tires that work ok for roads when i maintain 70 psi. 50 psi for maintained trails. 30 for mud, rain, or aggressive trails to bot eat shit as much.

 

Food for thought.

https://ecomodder.com/forum/showthread.php/mythbusters-tests-tyre-tire-pressure-17151.html

I'm surprised that over-inflation improved fuel economy that much. This is an often debated topic in the bicycle community. The rule of thumb is that higher air pressure reduces rolling resistance up to a point. That point depends on the road conditions beyond which it can increase rolling resistance due to bouncing up and down on the road.

If higher air pressure increases fuel economy that much, why aren't the car manufacturers (and/or the government) encouraging it more? MPG is king these days. There must be a bigger draw back than tire wear as myth busters gives. Safety perhaps, but what's the risk? Tires exploding? Cars bouncing off the road? Lack of traction? Personally I just don't like my teeth being rattled out, but I could put up with some of that if I was getting paid in MPG.

EDIT: Before someone pokes at me for buying a truck and then worrying about MPG, keep in mind that higher MPG equates to higher effective power, i.e. the truck goes faster. I think this is often ignored on this forum. It sure isn't ignored in the bicycle community.

 

Worn out tires quicker. Shitty ride. Not always safe

Edit: plus the amount you save by mpg offset by the amount of mileage out of a tire. Also probably takes more resources to make tires than it offsets with MPG

 

Here is another method.

https://www.tacomaworld.com/threads/air-pressure-in-10-ply-tires.666417/#post-23368540

Using the table in the Toyo PDF I see 35 psi for a LT255/85R16 gives a 1920 lb load limit which is what the author of the post suggests (I did not verify that recommendation). I assume all LT255/85R16 tires are about the same because they all use the same reporting standards.

 

I run 33psi in my LT 265/75 16 Toyo AT3s

 

This PLEASE.

Id love to run 255/85's once my OEM wranglers are toast. I would also like to put on at least 1", but up to 1.5" spacers. I'm up 1.5" in front (5100), stock billy rears.

Anyone running 33 skinnybois on spacers?

 

I am guessing that if you run a spacer, that will increase your chances of needing a CMC as it will put your tires where a 285 would be. They fit juuuuuust right without the offset.

 

This! Stock wheels and offset makes it easy. Tires fit just inside the wheel well and you don't need to worry about throwing rocks/gravel up.

 

Thanks for the reply! This is exactly what I was afraid off. I am torn. I would love to widen my track some, but also absolutely love how these trucks look on 255/85’s. Oh well, sounds like I’ll be cmc’n at some point

 

start with the 255s then see if you still want to CMC

 

I really like the 255s, but I may eventually go to 285s, mostly for the tire selection. Not many choices in 255. Love the ST Maxx, but I want to go to STT Pros.

 

If you won't be stuffing wheel wells at full lock, run the spacers and don't worry about it.

 

I think they will rub without flexing with spacers. I rubbed over bumps when turning before lift. Moved out an inch, it would have been bad rubbing during turns on flat ground. Nice thing about spacers is that you can put them on the front and see. Can be removed easily, but I think it will be bad. 1"+ spacers will be worse than 285s on stock rims.