Inflation: full of 'hot' air?

Never heard of it but, I would think 18 on the street is too low.

Maybe just a typo but 1862 ÷ by 2 = 931

I always run at max pressure on my cars/jeep. Unless its my truck that calls for 80psi, that I run about 65 or the ride is like a brick. I only run at 80psi when I have my 5th wheel on.

So no, I dont use that formula. Frankly I have never heard of such a thing and I'm not sure its a good idea.

Never heard of it...I run what the door sticker says on my f150 and my wife's Q5. The wrangler says 34 psi...which with LR E tires, makes for a very stiff ride. I played around, and found 28 too be pretty good.

When I was in Formula SAE, we used a pyrometer to set pressure...when the temp was even across the tires surface, that was the pressure we ran for that driver and suspension setup.

I run 26-27psi on my 31x10.5's

JMT said:

I run 26-27psi on my 31x10.5's

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That's what I came here hoping to find out. I have 31 inch Michelins on my stock Sport rims. I knew running the door pressure would wear the centers, but didn't know how low to go. I have experimented and found 25-26 to look right with wear; but was wondering if anyone else had figured it out.

bciocco said:

That's what I came here hoping to find out. I have 31 inch Michelins on my stock Sport rims. I knew running the door pressure would wear the centers, but didn't know how low to go. I have experimented and found 25-26 to look right with wear; but was wondering if anyone else had figured it out.

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Yup, 26 - 28 psi on stock rims is about right for 31x10.50's. The fine tuning depends on tire sidewall construction, load, how "squishy" you like the ride & etc. Aired down I run 8 psi and on the road I run 26 psi in my light, low powered SE. The TJ and the tires seems happy.

Head Lice said:

In theory ..... the 'tire footprint' would be the same area if you were carrying the Maximum load @ the maximum pressure.
I've done this with both Dodge/Cummins trucks. The steering isn't quite as 'quick' .... but, it's more predictable and stable.
There has been negligible difference in mileage numbers or tire heat, and the tires are wearing evenly.

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All other things being equal.

You need to be careful with using calculations for for P-metric or metric passenger tires for flotation tires. T&RA (Tire and Rim Association) has three main tire classifications for passenger and light truck vehicles. P, LT and Flotation. The load/pressure calculations for each are different. The non P tires or metric standards are actually under the umbrella of the ETRTO (European Tire and Rim Technical Organization.) The P-metric calculator (TRA- USA based) and the metric (non-P marked) calculator (ETRTO-European based) produce close results but the ETRTO version usually shows a slightly higher load capacity for the metric tire compared to the P-metric tire of the same size at the same pressure.

But back to the 32X11.50R15 LRC. Below is a load/pressure table for it for 25-50psi.


Although it's feasible that this tire will carry 931 lbs @ 19 psi, there are other things to consider. Handling and stability being a couple of main considerations. Add in passengers, tools, and probably uneven loading and you would probably exceed the load capacity of the tire.

When recommending tire pressures for plus fitments, I always check against the load capacity of the OE tire at its recommended pressure and how that load capacity compares to the GAWR of the vehicle shown on the door placard.

Maybe a little more than you wanted to see but the details are important when it comes to tire loading and pressures.

Airing down for off-roading is another story. Just be sure to air back up before hitting the road again.

IS there a chart like this available for all tire sizes to download somewhere? Looks like good reference information.

I can't send the one I have as it's a T&RA file.
Try this one at tiresafety.com See pages 48-55

www.tiresafety.com/images/tire%20replacement%20manual.pdf

DrDirt said:

I can't send the one I have as it's a T&RA file.
Try this one at tiresafety.com See pages 48-55

www.tiresafety.com/images/tire%20replacement%20manual.pdf

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Thanks! A little lite reading before bed tonight

Not a good idea to use the % of load to determine the % of pressure. If you graph the load/pressure data you will find it's not a linear relationship. It's close, but it's better to use load pressure tables. You can interpolate between two known data points or extrapolate beyond the table end. But I would not extrapolate more than 5psi beyond the end of the table.
Now for the vehicle weight. Was the vehicle loaded when you weighed it? If it's not loaded, add some weight. You are assuming a symmetrical load since you take 50% of the axle weight. In all the recommendations I have made, I take 55% of the axle weight to determine a single tire load. This provides for some non symmetrical loading.
And then what about tire pressure maintenance? Tires will very slowly leak air over a period of time. You may want to add 2-3 psi to allow for some leak down over time. If you check your pressures often, you can reduce or forget this part.
Another consideration is vehicle handling. Is this the pressure you want to drive on-road? There is a component of pneumatic stiffness in the tire that helps handling. I've never recommended lower than 20psi for on-road. You may find that you even like a little more pressure on road to provide a little better handling.
I've attached a copy of load /pressure tables that will soon be available on the bfgoodrichtires.com site. (I finally got the OK to make this happen) Use the tables to get it right.

For those of us that air up with CO2, does CO2 bleed out of the tire faster than air?

Reece said:

I always run at max pressure on my cars/jeep. Unless its my truck that calls for 80psi, that I run about 65 or the ride is like a brick. I only run at 80psi when I have my 5th wheel on.

So no, I dont use that formula. Frankly I have never heard of such a thing and I'm not sure its a good idea.

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Why would you run max tire pressure on a jeep or car? You are possibly exceeding the max PSI recommendation once the tire heats up.

bobthetj03 said:

For those of us that air up with CO2, does CO2 bleed out of the tire faster than air?

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My guess from chemistry is yes, it would leak faster, due to the fact that Carbon is a smaller element (atomic number ^) than Nitrogen, which makes up 78% of our Atmosphere.

"CLAIM #2. "N2 PERMEATES (LEAKS) THROUGH TIRES SLOWER THAN AIR THEREFORE YOUR TIRES WILL MAINTAIN THEIR PRESSURE LONGER AND REQUIRE LESS MAINTENANCE."
Although it is true that nitrogen does permeate through tire rubber slower than oxygen and CO2, there are two things to know. First, the gas permeation difference between oxygen, CO2 and nitrogen through a tire wall is very minute. Second, this difference is made even more insignificant for N2 since oxygen only makes up 17% of air and most of "air" (78%) is nitrogen. Diffusion speed through the walls of your tires has more to do with the quality, the wall thickness, and the age of your tires. More often, tire deflation is due to a leak in the stem core, the stem seal, cracks in the stem, a bad tire to wheel bead seal, cracks in the tire wall, or objects like nails stuck through the tire tread. Also, did you know that your tires may grow during the first 1-2 days as it gets used to being inflated which would reduce the tire pressure. Tire manufacturers recommend checking your tire pressures often no matter what type of gas you';re using to fill your tires. Bottom line: If gas permeation was the only way a tire would lose its "air" there would be very little detectable difference between air (which is already 80% nitrogen), nitrogen, and CO2."

https://powertank.com/nitrogen-truths-myths

Could be biased, but worth a read.