Great Tire Pressure Calculator Website

[RockShawn]

If you are anything like me, you probably don’t have OEM size tires on your tow rig. Especially if you have a 4x4 or HD truck. Tire vendors like to only go by the OEM door sticker for psi no matter the tire you switched too, but larger tires in the same load range can typically take the vehicle load at lower psi.

For example Load E 265/70/17’s need 60psi for a 2700lb load each, but 35x12.50-17’s only need 44psi for the same 2700lb capability.

You can do the math yourself or use this handy website calculator. Just follow the prompts to enter the OEM info and then what you changed to and it gives you the equivalent psi for the same load.

Tire Pressure Calculator

Easy to use tire pressure calculator. Use our tire pressure calculator to calculate the new tire pressure needed when changing tire sizes.

tiresize.com

This way you don’t feel like you are riding rocks. Happy calculating!

 

[biffdotorg]

what is wrong with the rating molded into the tire? Most agree trailer tires should be run within 5lbs of max to help eliminate odd wear

 

[RockShawn]

what is wrong with the rating molded into the tire? Most agree trailer tires should be run within 5lbs of max to help eliminate odd wear

Nothing wrong with the rating, but you have to take into consideration that the stamp is the MAX load at the MAX psi. And I am talking about Tow vehicle tires, not trailer tires.

So one of my trucks has a GVRW of 5200 front and 6000 rear. That is the max GVRW for the truck, engine, passengers and a load in the bed basically. The original tires were 265/70-17 and had a molded rating on the tire of 3195lb at 80 psi. It is rated to carry nearly 6400lbs per pair but the truck doesn't need that much. The factory sticker on the door says inflation for that tire on that truck is 60psi front and 70psi rear for max GVRW. So the factory is already compensating PSI for GVRW. Meaning they know you don't need 80 psi (max psi) in the tire to carry the proper weight rating of the truck. If you did inflate to Max PSI without the proper loads on it, the tire will perform and wear improperly and ride like rocks.

So my truck tires need to support approximately 2700 each in the front and 3000 each in the rear when loaded. To achieve that the factory put 60psi in the front and 70 psi in the rear on the OEM tires.

Now I changed tire size to 35x12.50 - 17 which have a MAX load of 3640 at 65psi (Big difference) if I inflate to max on these tires the truck is very unstable. (I know cause the tire store fully inflated them at install regardless of me telling them not to)

So even though both tires are Load Range E, they have different PSI requirements for MAX load and they have different MAX load abilities.

To get the proper inflation to support the truck properly (5200lb front and 6000LB rear) you have to adjust the pressure. And unless you like really complicated math equations, the site I referenced will do the math for you.

Rarely do you inflate to MAX psi on a passenger vehicle. The ride is completely uncomfortable, and the tires will wear uneven and most likely have too much sidewall flex, especially in taller tire sizes. As for pick-ups, when unloaded the bed is considerably lighter so realistically you can decrease psi in the rear unless you are loaded (trailer or bed full of concrete etc.) since most people don't have onboard air in their vehicle, they leave the rear alone.

Worth a note too, this is why tire rotation is very important to get the most life out of your tires.

 

[biffdotorg]

Ahh, gotcha, I agree with all of that. Makes sense

 

[RockShawn]

Ahh, gotcha, I agree with all of that. Makes sense

I had planned on posting up that example anyway to try to make it make sense. Please don’t think I was picking on you.

 

[biffdotorg]

I had planned on posting up that example anyway to try to make it make sense. Please don’t think I was picking on you.

Not at all. That was a great explanation. For those of us thinking trailer, our load is very similar each and every time. Those of us that haul lauds in our vehicles, we may change it up. Or as you said, third party tires.

Not like the SXS guys that carry a compressor as they change pressure throughout the day.

 

[RockShawn]

Not at all. That was a great explanation. For those of us thinking trailer, our load is very similar each and every time. Those of us that haul lauds in our vehicles, we may change it up. Or as you said, third party tires.

Not like the SXS guys that carry a compressor as they change pressure throughout the day.

Yeah, most people don’t invest in onboard air. I haul of variety of trailers and loads because I own a granite countertop company. Our loads are almost always changing depending on what we’re doing. So we carry on board air in our tow vehicles. The only place where I’m a little Lacking is implementing a tongue weight scale so we make sure we get that right and balanced. Another project for another time though.

 

[FSH 210 Sport]

I have air bags on my truck, a small receiver tank and taps at the front and rear license plate. The air compressor is a 100% duty cycle. I have a decently long air hose that enables me to air up truck tires or trailer tires. It also comes in handy when I use my dirt bike tire changer that goes into the receiver.

The lowest I run my load range E tires whilst empty in my one ton CC is 65 psi. Fronts always stay at 60 per the B pillar sticker.

All my trailer tires are at max cold pressure. Otherwise they don’t wear correctly.