How to determine tire pressures; 255/75-17 C on 7"

[mparker]

I am going from a 265/70 to a 255/75. Just wondering what tire pressure I need to run and what is the lowest I should air down to for sand/beach? I think I run 38 cold and air down to 15 on the beach.

Obviously I can't go by what the manufacture recommends. Vehicle is 4750lbs with a GVWR of 6300lbs on a 7" wheel.

Thanks guys.

::Edit::
More info,
255/75 is the OEM tire on JK Rubicons. It has a 7.5" wheel and weight 4521 and a GVWR 5700. Google says OEM recommended is 37psi.

 

[toddz69]

15 psi sounds great for the beach. I'm curious about your statement on the 255/75 being the tire size for JK Rubicons though - they all ran 285/70/17s as far as I know. My particular vehicle runs the Rubicon takeoffs and weights almost exactly what yours does. I generally run 29-31 psi on the road.

Todd Z.

 

[mparker]

Well, what I can tell you is according to the TRA load and inflation tables the rating of the tire load limit at 40psi for the two sizes mentioned is:

LT265/70R17 is 2,075lbs
LT255/75R17 is 2,055lbs

So if you were running 38psi the difference of psi in terms of load is ineligible between the two sizes.

As for what psi to run aired down, someone else may be able to advise.

StackPath

Interesting that the smaller tire (265/70) has a slightly higher capacity.

I am switching from a Nitto Terra Grappler 265/70 LT rated to a 255/75 C rated

 

[mparker]

15 psi sounds great for the beach. I'm curious about your statement on the 255/75 being the tire size for JK Rubicons though - they all ran 285/70/17s as far as I know. My particular vehicle runs the Rubicon takeoffs and weights almost exactly what yours does. I generally run 29-31 psi on the road.

Todd Z.

Correct me if I am wrong, I am not a Jeep guy. In my googleing JK used the 255/75 the JL went to the 285/70

As far as running lower pressures, I just want to be certain I won't slip a bead being on a skinny tire and a narrow wheel.

Although Toyo specs say 6.5 - 7.0 - 8.5. Ive never seen a range listed like that and is seems odd to ONLY specify 3 wheel widths... I dunno.. BUT my 7" is right in the middle, so I am happy with that.

 

[MontySquareo]

Try running factory psi. If the tires feel soft, or get hot (you can't comfortably put your hand on the tire after a drive) then your pressure is too low. If they feel rock hard or the edge of the tread doesn't touch the ground then you've got too much pressure.
I run my tires a little too full (1/4 inch at the edge of the tread doesn't touch the ground) but they ride ok and give decent gas mileage. The middle of my tires will wear a tiny bit faster than the edge but I can drop pressure and wear the edges more in the future. This is how I do it, as long as your tires stay round they'll be alright

 

[1stDeuce]

A narrow tire is better on a skinny wheel than a wide wheel... Your setup is what I would consider appropriate, not too far either direction. 15psi is where I would start for beach or other off road travel. If the surface is harder, you could even try 20psi. If the vehicle is struggling, let more out. All you have to do to keep from debeading a tire is to drive like a reasonable human, not a TV commercial. I've never pushed a bead off, even running dunes at 4.5psi on my Jeep on 285's with 8" wheels and no beadlocks. Tires don't just fall off, you have to do stuff to push them off, like high speed sharp turns, donuts, etc.

Sand is different in different places and weather conditions. If the sand is super dry and deep, you will have to go lower to feel like you're at the appropriate pressure. As you do, you just need to limit how fast you steer and how rough you are with your driving.

"As slow as possible and as fast as necessary" is my philosophy for low pressure operation. If you want to banzai, keep the pressures a bit higher.

There is no perfect or easy answer, you have to make adjustments and make your own choices through experience with your vehicle, driving style, terrain, etc. You're in the ballpark, go play ball!!

 

[Trestle]

The most accurate way is to ask the manufacturer, but the tire manufacturer not the vehicle manufacturer. Take the vehicle to a scale twice. Once when your normally daily driver mode, the second time when fully loaded. Contact the tire manufacturer and give them half the axle weights. (sometimes you can find it in a chart on their website, it is size, load rating, specific) Weigh front normal, then front loaded, then rear normal, then rear loaded. They will tell you what pressure to run it at for street pressure. I.E.: if your front axle weight comes in at 2000 pounds, then ask them the correct pressure for 1000 pounds for that tire, then follow their advice.

Aired down you can usually do half of the street pressures fairly safely if you keep speeds below 35mph and lower. You can experiment down from there based upon tire deflection. People often forget to remind that lower pressure requires that you don't go fast. Ambient temps play a big part in that equation too.