Tire Pressure of LT Tires: Who should we listen to?
 

In case anybody asks, I have read every single post of the original "LT Tires Needs Higher Pressure" thread. Upon some digging, calculation, apparently across different models and tire sizes, the ratio between GVWR and OEM tire cold inflation load varies. For example, for the most common 265/65R17 that comes with 4th gen SR5, the OEM cold inflation load is at whopping 2055 lbs, 34% of the gross weight (fixed at 6005lbs, max gvwr for V8 4wd); however, for limited 18 inch rim, 265/60/R18 at the same 32 psi "only" supports 1985 lbs, only 33%. If that difference is tiny enough to not worry about it, check out the current 5th gen TRD Sport and Limited GVWR to OEM tire load: 1794 lbs, only 28.5% of the GVWR. Meanwhile back in 2014, the last gen FJ Cruiser comes with stock BFG KO, demanding 46 psi: that puts the cold inflation load up to 2318 lbs, 41%(!!!) of the GVWR. That means 4 tires combined, these tires support 164% of the GVWR of an FJ, must be designed to jump slopes with full camping gear and a tent and some rock sliders and a fridge.

It's easy to calculate a "safe" pressure from OEM tire pressure and load. As much as setting my E rated 265/65r17 KO2 to 44 psi is not quite unlivable, I do like to find a threshold for the tire pressure similar to the OEM door pressure, means I should not cross that line no matter what in normal tarmac driving. I have read about how underinflated LT tires can generate quite amount of heat, which may be devastating when you run them in harshest environment possible (death valley, Arizona, Gobi desert, etc.) when the sidewalls head up. The detailed explanation can be found at Nitto's Technical Bulletin, just Google Nitto TSB Tire Pressure. Running LT at 28 psi on public highway even for a 4runner is straight up dangerous, you're lucky if you have not run into any problem.

The final question is, who should I listen from a purely "safety" perspective? Is 28.5% GVWR enough of a headroom to not blow in Arizona heat? Because that puts my KO2 only at 36 psi, makes my already rough tires much more enjoyable, as long as I don't jump, hopefully.

Behind that, I understand Toyota engineers also adjust pressure for ride quality, handling, stability, tire wear and some other reasons, but when we put on the already rough but tough LT tires in replace of the original ones, do we accommodate that like these engineers does, and only put in enough load headroom to make these vehicles safe (strictly 25%+ GVWR)? Is that the borderline to not cross not matter what?


Steve


Pressure calculation source: Tire Pressure Calculator

The way I read it is max pressure is for max load, anything less than max load can use less pressure. I run 37psi in my LT Michelins and have for several years, no problem, but I don't off road. I think your 36psi is fine.

End 2007 I got hold of the official european calculation, and went running with it.

Got wiser in time, and now call myself "pigheaded Dutch selfdeared Tirepressure specialist"
Can make a pressure loadcapacity list in wich 90% used of the loadcapacity belonging to the pressure for 99mph. Determined this to give maximum reserve with still acceptable comfort and gripp.

So give tirespecifications, and I will make lists for you.
Give if psi or bar, kg or lbs, and from tire. 1. Maxload or loadindex, 2 kind of tire to determine the reference pressure, 3 speedcode, less important.

Then you " ONLY" have to determine the axleloads acurately succes with that the most tricky part in it all

You simply devide GVWR by 4, and the axleloads are different front and rear.
What you need are the GAWR's or better real axleloads.
Only driver front more heavy, and fully loaded rear more heavy.
.

The simple calculation dividing GVWR by 4(25%) and adding air to meet the weight (+ some) seems pretty solid if you go for HT or C/D loads. But IMO when you go to an E load i personally think its too heavy and the minimal air needed for the GVWR wont inflate the tire enough to help dissipate heat and they will run hard if you fill them properly to reduce that heat.

For me the thing i try not to cross is the max speed of the tire. Highway speeds are what will kill a underinflated tire with heat build up. Luckily my TPMS gives me tire temps so that's a big help.

Currently all I have is my door VIN plate that had my GAWR, rear is higher at 3060lbs. For KO2, that's below KO2's minimum recommended pressure on road (35psi). Furthermore, although at 36 smaller bumps are better damped, but on highway it kills responsiveness. My guess is at that stage I'm relying on the rubber and other sidewall material to maintain control and hence the sluggish feel. It almost feels like a small drift between vehicle itself and the tire.
For reference, 2007 4runner V6 4wd,
GAWR: front 2550, rear 3060 (lbs)
Load index: E, maxload 3195 @ 80 psi
Speed rating S

It is darn heavy, 50.6 lbs per tire, like 25% heavier than my previous tire. Sadly for 265/65R17 that is the only load rating they came with. Why I specifically want KO2? Because I had LTX M/S previously and chunked a piece of tread right off exposing cords, DESPITE I babied it on trail and going as slow as I can in rocky sections. Upon reading KO2 is known to be durable, so that's my sensible choice. Of course it rides way worse than highway tires, but small price to pay.

If you run a chalk test you may find that at 36 you are wearing the outside of the tread.

Then I made you a list for maxload 3197lbs AT 80 psi upto 160kmph/99mph, wich is referencespeed for Q to V speedrated tires. For that speed the maxload is calculated, and for higher speed, I have a better system then the offical used.
Calculated with my extra tight formula, mayby too tight, so certainly gives not to low pressures.
Using that 90% of the calculated loadcapacity for the pressure. This gives max reserve with still acceptable comfort and gripp. And for axleload so 2 tires.
So dont add reserve or devide by 2 yourselfes, all done for you.

For light traveling, 2 persons in front, rear lower load then front so 34 psi all around could do,


The list in the spreadsheet did not go low enaugh when using 1 psi steps, so for lower then 36 psi, I filled in 2psi steps and glued both lists together here.

Psi/axleload
20 psi / 1641 lbs
22 psi / 1784 lbs/lowest in EUR system
24 psi / 1927 lbs
26 psi / 2069 lbs/lowest in US system
28 psi / 2210 lbs
30 psi / 2351 lbs
32 psi / 2491 lbs
34 psi / 2631 lbs/ GAWR Front 2550

36 psi / 2771 lbs
37 psi / 2841 lbs
38 psi / 2910 lbs
39 psi / 2980 lbs
40 psi / 3049 lbs/GAWR Rear 3060
41 psi / 3118 lbs
42 psi / 3188 lbs
43 psi / 3257 lbs
44 psi / 3326 lbs
45 psi / 3395 lbs
46 psi / 3464 lbs
47 psi / 3533 lbs
48 psi / 3601 lbs
49 psi / 3670 lbs
50 psi / 3739 lbs
51 psi / 3807 lbs
52 psi / 3876 lbs
53 psi / 3944 lbs
54 psi / 4012 lbs
55 psi / 4081 lbs
56 psi / 4149 lbs
57 psi / 4217 lbs
58 psi / 4285 lbs
59 psi / 4353 lbs
60 psi / 4421 lbs
61 psi / 4489 lbs
62 psi / 4557 lbs
63 psi / 4625 lbs
64 psi / 4693 lbs
65 psi / 4760 lbs
66 psi / 4828 lbs
67 psi / 4896 lbs
68 psi / 4963 lbs
69 psi / 5031 lbs
70 psi / 5098 lbs
71 psi / 5165 lbs
72 psi / 5233 lbs
73 psi / 5300 lbs
74 psi / 5367 lbs
75 psi / 5435 lbs
76 psi / 5502 lbs
77 psi / 5569 lbs
78 psi / 5636 lbs
79 psi / 5703 lbs
80 psi / 5770 lbs/referencepressure
81 psi / 5837 lbs
82 psi / 5904 lbs
83 psi / 5971 lbs
84 psi / 6038 lbs
85 psi / 6104 lbs
86 psi / 6171 lbs
87 psi / 6238 lbs
88 psi / 6305 lbs
89 psi / 6371 lbs
90 psi / 6438 lbs/ conti gives maxcold +10psi

Wow, thanks a lot! I would definitely keep it around.

Lately adjusted my spreadsheet, so I can make lists with in front of psi other calculation then behind.
For the RV world use that for single and duall load.
But made a mistake so front calculation used parts of rear data.
I saw that when calculating back your 80psi, must be 90% from 2x 3197lbs= 5754lbs and not 5770 lbs.
Repaired it and saw that difference was that small, that I dont need to make a new list.

But can also make list with for instance in front for same sise P-tire, and behind E-load.
Then you see that LT has lower loadcapacity for the same pressure.

My idea is that LT has lesser surface on the ground at the same deflection then P-tire, so lesser lbs to carry. See paint-image I made long ago.

Found the topic about this began in 2012, last answer 2021. I it usefull to react there about this and more?
Or is that topic not actual anymore?

It's partially that and partially LT tires has more structural material, which when flexing at the same extent as P tires, can generate much more heat.

So then part is more heatproduction at same deflection for LT. And part is lesser sufacelength so surface on the ground wich gives lower loadcapacity at same pressure. But smaller surface on the ground gives a bit less heatproduction of the treath, wich then compensates it a little.

Newer material and construction of nowadays tires make them give more surfacelength on ground.
And lesser heatproduction.
Then you could calculate an E-load tire as if a D-load tire so smaller difference in pressure for the load.

Meh, all depends on what you're comfortable with...In summer, I run between 35-45 psi depending how often I'm commuting with said tire and depending on the terrain I plan on rolling on...in winter, I'll run 32-38 depending on the winter conditions. The "Max" PSI is for being loaded or hauling a trailer...what I've experienced and follow the most, no matter the PSI, is run 2-4 PSI less on the rear unless you're towing or you're loaded...on road trips, no matter the season, I'll run over 50 for least rolling resistance...that's just me though and I rotate the tires every 5-10k miles (every or every-other oil change)...my wear is even and true and I have been getting great longevity on the tires because of the rotation intervals...God's speed and 8-10ply tires are amazing and the only tires I run on my 4x4/AWD trucks!

Going back to the original question sans all the scientific information: Who do we listen to? Me? I listened to the tire dealer.

My first set of LT Load Range E BFG All Terrain T/A tires were spooned onto my 2002 Tacoma TRD 4x4, extended cab (I ran load range C BFG’s on my former truck, a 1996 Chevy S-10 4x4 pickup). I ran two sets of those tires on the truck. My dealer told me to keep them at 35psi street pressure. At first I thought I should run them at sticker, but soon found out that there was noticeable wear at the edges by the first rotation and I kept them at 35 on the street.

I’d lower them to 15-20psi for off road use, then air them back up with a 12v compressor. But in time I got lazy and impatient and started running them at off road pressures back home to air up with my shop compressor. It would take nearly 45 minutes for that portable compressor to inflate to street pressure and it would be white hot after that exercise; most of the time I could be home in far less than 45 minutes. I’ve run for up to 75 miles at off road pressure on the highway. Yes, warm to hot to the touch. Yes often quite squirrely in turns and curves. No, I do not recommend it for safety reasons. Yes, I got 80,000+ miles on both sets of tires.

Now, I have an ‘18 SR5 and run BFG All Terrain T/A KO2 Load Range E tires. The dealer put 45 pounds in them. From what I’ve found in print, this is what they should have. I don’t do the off roading that I’ve done in the past, so haven’t yet aired down. Trails where I live now aren’t very rocky. Most of my driving is on maintained dirt, 2-lane pavement, variable Class III and IV on hunting trips; in snow and ice in winter. I’m 26,000 miles into my current set and they still look like new.