Air Pressure on 31" A/T

[Josie'sLandCruiser]

Hi all,

Simple "rule of thumb" on airing down tires for better floatation and traction: for off-road use half (roughly) the tire pressure from what is run on the street & highway.

So, if the tire is at 30 PSI on the street, air-down to 15 PSI on the trail.

Obviously, there are many variables that can affect this. But you won't loose a bead seat at 15 PSI.

Regards,

Alan

 

[gaijin]

Had a feeling I went off track somewhere. The new tires are LT245/75r17

Your recommended tire pressures for the new tires are:

Front: 35psi yields a 1,770 pound Load Limit which is higher than required 1,483 pounds, but is the minimum pressure recommended for on-road use of these tires.

Rear: 37psi yields a Load Limit of 1,840 pounds - pretty close to our target of 1,844 pounds.

 

[Spook50]

Now that sounds closer to what they should be!

Thanks man.

 

[gaijin]

Now that sounds closer to what they should be!

Thanks man.

You're welcome.

I'll be in my bunk ...

 

[Spook50]

I'll be in my bunk ...

Nice

 

[carbon60]

Wow, I went searching for tire pressure information and came across this thread. Now I have a headache.

I have a 1996 FZJ80, it's stock tires are P275/70R16:

Click for large view - Uploaded with Skitch

I now have Goodyear Wrangler Duratracs in LT285/75R16 126/123P on it. And some added weight, of course. Full specs:

Click for large view - Uploaded with Skitch

What should my highway pressure be?

Thanks for any help!

A.

 

[gaijin]

Wow, I went searching for tire pressure information and came across this thread. Now I have a headache.

I have a 1996 FZJ80, it's stock tires are P275/70R16:

Click for large view - Uploaded with Skitch

I now have Goodyear Wrangler Duratracs in LT285/75R16 126/123P on it. And some added weight, of course. Full specs:

Click for large view - Uploaded with Skitch

What should my highway pressure be?

Thanks for any help!

A.

That's an easy one I've answered before.

On road tire pressure should be 38psi Front and Rear.

That will give you a Load Limit of 2,255 pounds / tire - well within the 94% safety margin for your Rear GAWR (GAWR should not exceed 94% of the tire Load Limit - 2,255 x 2 = 4,510, 3,970 / 4,510 = 88%) and is the equivalent "LT" tire pressure as Toyota recommend for the OEM "P" tires.

Toyota recommended "P" Load Limit is 2,480 pounds @ 32psi - "LT" equivalent is 10% less, 2,255 pounds @ 38psi (2,255 x 1.1 = 2,481).

Hope your headache is gone

 

[carbon60]

Sweet, thanks so much! I'm off to fill my tires right now.

A.

 

[markthemenace]

You're welcome.

I'll be in my bunk ...

Kind sir, could I trouble to you share your wisdom with me as well?
Mine is a 1987 HJ60 Landcruiser. Its currently running 235-75-15s and I've been thinking of getting 30 inch General AT2 on them, or maybe just stick with 235-75-15 but this time in LT form.

General even has a skinnier option, 225-75-15, but I think it would be too small for my Cruiser.

One thing though, on Tire Rack's website, when I choose the 235-75-15 LT Grabber AT2s, a warning comes up that I should expect a harsh ride.

Any thoughts on this?

 

[gaijin]

Kind sir, could I trouble to you share your wisdom with me as well?
Mine is a 1987 HJ60 Landcruiser. Its currently running 235-75-15s and I've been thinking of getting 30 inch General AT2 on them, or maybe just stick with 235-75-15 but this time in LT form.

General even has a skinnier option, 225-75-15, but I think it would be too small for my Cruiser.

One thing though, on Tire Rack's website, when I choose the 235-75-15 LT Grabber AT2s, a warning comes up that I should expect a harsh ride.

Any thoughts on this?

I'm away from my reference material right now, but give me a couple of days and let me see what I can put together.

 

[markthemenace]

Thank you sir, no hurry at all!

 

[gaijin]

Thank you sir, no hurry at all!

Hey Mark - I did not forget about you!

Here's what I found:

With an LT tire, the larger GAWR of your vehicle (in this case 3,220 pounds for the Rear) should not exceed about 94% of the Load Limit of the tires being used.

The General Grabber AT2's size LT235/75R15 are a Load Range C tire with a maximum Load Limit of 1,985lbs@50psi. When inflated to 41psi, they have a Load Limit of 1,709lbs which meets the Load Limit criterion. So if you go with these tires, I'd recommend 41psi Front and Rear.

The General Grabber AT2's size 225/75R15 are NOT an LT tire and do not have sufficient Load Limit to safely use on your vehicle. A non-LT tire's Load Limit must be 10% higher than an LT tire. In your case, this means it must have a Load Limit of 1,880lbs, but the tire is only rated for a Max Load of 1,874lbs @ 44psi. It's pretty close, but I would not recommend it as you would be right at the limit (or a little below).

At 41psi, in my opinion the Load Range C LT235/75R15 tires should not be a harsh ride.

Sorry it took so long, but if you have any further questions, just post 'em up!

 

[markthemenace]

Thanks a lot man! Just the info I need!

 

[Sdandrew75]

I'm using the Load Limit/Tire Pressure tables and guidelines published by the Tire and Rim Association, Inc.

Using these tables one can determine the factory recommended Load Limit for the stock tires at stock pressure. From there, it is easy to calculate the pressure required to have the same Load Limit for a tire of a different size. There is even an easy calculation for substituting a LT tire for a P tire.

For example, my 2013 LC200 has a recommended tire pressure F/R of 33/33 psi.

The stock tires are P285/60R18 114V. The Load Limit @ 33psi for those tires is 2,520 pounds. Since these are P-Metric tires used on an SUV, the Load Limit was increased by 10%. The "raw" Load Limit is therefore 2,520/1.1 = 2,291 pounds.

The larger of 1/2 the GAWR (Front or Rear) can be no more than 94% of this "raw" Load Limit. My Rear GAWR is 4,300 pounds, so 4,300/2 = 2,150 pounds which is 93.8% of the "raw" Load Limit.

OK so far?

So if you want to substitute a different size P-Metric tire, you must find the Load Limit/Pressure that results in 2,520 pounds.

Since LT tires do not have to have their Load Limits increased by 10%, if you want to substitute an LT tire, you must find the Load Limit/Pressure that results in 2,291 pounds.

In my case, this resulted in going from a P285/60R18 114V tire @33 psi (Factory recommended size and pressure) to a LT285/70R17E 121R tire @ 40 psi.

So ... if I have the information I requested in my previous post, I can look up the values on the Tables and give the recommended tire pressure for the new tire.

Clear as (IH8)mud, right?

Hey, not sure if still on this, but I have LT285/60R-18 BFGOODRICH ALL-TERRAIN T/A KO2 D with recommended 33/33psi on a 2016 LC200. I’m taking it off to eastern Sierra/ Mona he meadows, mostly hard pack sand and some washboard. I’m thinking 22-25psi?

 

[FLATU8ER]

Lots'a tire experts and math experts.
Go by what is stamped on the tire.
Think about FORD and their Bronco II, door jamb said one thing, and tire said another.
How much did that cost FORD, and how many lives were lost?

 

[gaijin]

Hey, not sure if still on this, but I have LT285/60R-18 BFGOODRICH ALL-TERRAIN T/A KO2 D with recommended 33/33psi on a 2016 LC200. I’m taking it off to eastern Sierra/ Mona he meadows, mostly hard pack sand and some washboard. I’m thinking 22-25psi?

First of all - and perhaps most important - is the Recommended Cold Tire Inflation Pressure (RCTIP) for those LT285/60R18 BFG KO2 tires on your 2016 LC200 is 46psi Front/Rear.

NOTE: At 33psi, which it appears you are currently operating, you are not only dangerously underinflated for your vehicle, but also below the absolute minumim pressure recommended for those tires on any vehicle.

As to the second part of your question, my general rule of thumb for slow speed (<25mph) operation offroad, one half the RCTIP is a good starting point. In your case, since your onroad pressure is 46psi, I would recommend starting at 23psi offroad and adjust from there as desired. Don't forget to increase pressure back to 46psi before driving above 25mph or for extended periods onroad.

Get your onroad pressures up to 46psi where they belong!

HTH