New PSI Rating ?

[Mud Pie]

Well, I just put on BFG 265/70/17 K03's, Class C. Anyone know what the PSI should be ? I did an online search and the numbers varied greatly. Some said 34, some said 36, some said 38. One guy said 80 because that's the max rating on the sidewall. I'd bet that if he has any fillings in his teeth, he doesn't anymore.... I searched on here, because you guys know of which you speak, but I couldn't get an answer (my Search-Fu skills are lacking)

My tires are currently at 38, as set from the tire dude NTB. What would be the correct number ? Is 38 right ? I'm going to print a label and stick it on my door jamb because whatever info I glean here will be forgotten in a few months....

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[Sweetums]

Just do 37-38 PSI for the street.

 

[Bandit’s Lair]

About the same here. I think when I did the 4 tire air up I set to 36 and they usually warm up to around 37 on my normal run and 38 when I hit the hiway. That’s for a 37” though so a bit more sidewall. If you can, run em at a few different pressures and see where they are comfy and good on corners for the road. Road conditions are different everywhere so that always plays into comfort levels. I get a little bit of “feedback” in corners if I set them much lower than I have them now.

Side Note: double check the spare too. Tire place that mounted my spare set it to 40 per the TPMS. It was a noticeable difference after my first rotation. Thought I forgot to torque lugs or something.

 

[XraytecH]

My test also came out to 30 cold on Goodyear 35s DuraTracs. Not recommended for tires like Milestar Patagonias, that have a crowning tread.

 

[Freems]

I have 35” 12.50 on 17” 12 ply MT 80 psi rated, for round town and highway trips I run 40 psi. Hauling the 18’ dove tail trailer with a good load I run the rears up around 50 psi. Hauling the jet boat 18’, coolers full, 50 gal fuel tank full, 45 psi rears. Dirt…20 psi to 35 psi depending on speed.

 

[Vtur]

Wheel’s width also affects ideal psi. With the same tires, narrower wheels require lower pressure for an even wear across, but risk running them hot and wears out sooner. Opposite for wider wheels. I’m running 30psi with 37x12.5 tire on 8.5” wide wheels. It has around 40k miles on it and it can probably go another 20k+ miles.

Only way to find out is testing them. I drew a few lines across the treads with a silver sharpie, shoulder to shoulder with 1” spacing. Started with the door psi label, drove around and gradually lowered down couple psi at a time until it wears nearly to the edge.

27-28 psi would uses up the whole shoulder treads, but they ran hotter and slower steering respond, so i chose the happy medium 30 psi.

 

[Zachanadandy]

In reality you can run anything from 23 psi to 50 psi and not see much of a difference in wear. The difference in ride and bump handling on the other hand is night and day. We run 37-39" tires on both Jeeps and never air up beyond 25psi unless towing a heavy trailer. We drove all the way home from moab (1k miles) at 20 psi in the JLUR on nearly new 37s after multiple compressor issues at various service stations trying to air up. Still got nearly 50k miles out of those Yokohama X-MTs so the idea that lower psi is going to damage your tires or cause premature wear is clearly false. Without a tazer or jscan to turn off the idiot light you'll have to get used to it being on, but even on stock size tires it rides better at 30psi cold in my experience.

 

[GuzziMoto]

The chalk test is a good option. You can also watch tire pressure rise as the tires heat up, you should see around a 10% - 15% increase in tire pressure from cold to hot. That tells you the tires are getting to the right temp in use.
A basic way to get a good starting point is math (I know, I hate math too). If you divide the tires max load capacity (2,469 lbs) by its max pressure (50 psi) you get 49 lbs per psi. It takes 50 psi in that tire to support a load of 2,469 lbs, or 49 lbs per psi. Then if your JT is 5,500 lbs (high estimate, but probably better to over-estimate it), divide that by 4 and you get 1,375 lbs per tire. Divide that by 49 (49 lbs per psi) and you get approx 28 psi to support a 1,375 lb load.
Now, I know tire load capacity is not exactly linear, but that should be close enough, especially since we over-estimated the typical weight per tire. But if your JT is heavier, or you carry a lot of gear, you can increase the weight in the calc.

In the end, how it rides and if you are happy with that ride is probably the main factor, that and not overheating your tires (tire pressure is a good reference for tire temp, as the two are linked, pressure and temp). I would run the most pressure you can (within reason) and still be happy with the ride quality.

Also, if you are running pressures much lower than stock you will want to change the TPMS threshold / target pressures.

 

[Wheelin98TJ]

Isn't stock PSI 36-37?

And 265/70/17 is slightly bigger than your stock tire size?

Normally you go down with PSI as you go bigger with tires. Because bigger tires usually can carry a higher load.

You can do the chalk test to see what PSI gives you even wear, but if this # is too low, you'll want to go up for MPG.

 

[Sandman 4x4]

Max psi is just that. Check how much weight each tire is rated in weight to take an educated guess. Let’s say at 80 psi those tires are rated to carry 4,000lbs. That means they’re good for a 16,000 lbs gross weight! That means a 6,000 lbs gross weight vehicle will only need less than HALF the max psi! I would advise to try 35 psi cold, but if the heat raises the psi to 5+ more psi, you might want to add a couple more psi cold to 37 psi.

 

[Reflektr]

I’ll typically see how many psi I’m gaining as the tire heats up and set my cold psi accordingly. For example, if I’m wanting to run 35 psi and I normally gain 3 psi as the tires heat up on my daily commute, I’ll run my tires at 32 psi cold. It’s just enough to keep the dandy-light from coming on too.

A lot of its personal preference as well. On my other truck I was running 10-ply 35’s and you about had to air those bad boys down below 30 to smooth out the ride.

 

[DubyaBee76]

Chalk test worked for me. I run a 37" Patagonia at 24 psi. Why 24? That's where I get a contact patch across approximately 85% of the tire OD surface and still have enough sidewall rigidity to avoid the sloppiness of an under-inflated tire. It's a D rated tire, so running the published air pressure on a Glady made it ride like a covered wagon and the truck doesn't weigh enough to smoosh it down to get a proper contact patch.

 

[Renegade]

My general rule of thumb:
33s, 32 psi
35s, 30 psi
37s, 28 psi
38/39, 26 psi

 

[TARHEELKIDD]

If all else fails, contact the tire manufacturer and give them your vehicle information along with the additional wight if you have added accessories. I did on my last 4 sets of tires on my lifted vehicles with 3 different tire companies. I am currently running 37x13.5x17 Toyo Open Country ATIII. They recommended 26 PSI. The chalk test confirmed that they are spot on.

 

[D_JT]

I have 35” 12.50 on 17” 12 ply MT 80 psi rated, for round town and highway trips I run 40 psi. Hauling the 18’ dove tail trailer with a good load I run the rears up around 50 psi. Hauling the jet boat 18’, coolers full, 50 gal fuel tank full, 45 psi rears. Dirt…20 psi to 35 psi depending on speed.

12 ply tires at 40 PSI on a mid sized truck is bonkers! Considering 37 psi on stock tires is what's recommended, and those are load C. Empty on street you should be at 30. I run 31-33 on my load D 35"s.

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