Tire PSI

So a little while back I put on 4 new tires. The tire shop filled the tires up with air because they don't do nitrogen. I had nitrogen on my old tires. So I rode around about 6 mo or so and just took it to the dealer for the nitrogen. After a few days all my tires look kind of low so checked the pressure according to the side of the tire. The tires did not say psi hot or cold like I am used to. All pressures read 32 and the tire says inflate to 42. Did they just screw it up or does the pressure have to be lower for some reason?? I feel they just screwed it up and now either take it back or find some where else that does nitrogen.

 

I think Costco does nitrogen. Are your new tires P-rated? If so, the sticker on the driver’s door jamb will tell you how much air to put in them - 33-35psi if I recall correctly.

 

Its an XSP-X, sticker in door jamb is null an void for tires and air pressure.

 

The pressure on the side of the tire is max pressure. Air expands as it heats up. Do not fill your tires to 42 lbs. They will blow out. If you’re using a passenger tire, 32 lbs is right where it should be.

 

But nitrogen does not expand.

 

There is no reason to fill your tires to the tires max pressure rating. You would literally be driving a tire that is at its threshold. One good bump could easily blow the tire.

 

Yea I get what your saying but the pressure should be at least within 2-4 psi not 12.

 

Not true. It’s based off weight of the vehicle. It has nothing to do with what you think the pressure should be. LT tires are rated up to 80 psi. But every half ton truck runs them at 35-40 psi because that’s what is called for based on the weight of the truck.

 

False. 42 psi is actually on the lower end of what P-rated tires are usually good for. Most are 50 psi+ but most cars say to fill them to 32. Stick with the numbers in the door jamb of your truck. I believe mine is 30 in front and 33 in the rear or something like that.

 

I never inflate my tires to the max indicated on the sidewall. I always go by the owners manual states.

Are you sure nitrogen does not expand? Can you provide a reference for that statement as I think it does expand.

The "benefit" of Nitrogen in tires is that Nitrogen has larger molecules as compared to compressed "air" so they seep out of your tire more slowly.

But then our atmosphere is about 78% Nitrogen, so a 100% nitrogen fill in a tire is only moving the nitrogen % from 78% to 100%. So technically you tire will hold pressure longer with 100% nitrogen vs "regular air". But practically IMO it is a big nothing sandwich.

 

https://www.tundras.com/threads/how-to-determine-your-new-air-pressure-with-lt-tires.56860/
Read this thread until you understand the content. By then, you’ll realize the pressure listed on the tire itself is completely irrelevant to how much pressure you should run.

 

First off tires have their own cold max pressure on the tire. Door jamb don't mean squat except for factory tires and ratings for a soft ride. Tires should be checked cold. Nothing wrong with inflating to max cold temp. They WILL NOT blow up because of this. I usually run just a couple of pounds under max cold pressure. This delivers a more harsh ride, but better fuel mileage. You can lower a bit more if roads are wet or icy for better traction, simply up to each individual and their preference. Under inflation is what causes friction/heat and blows tires.

 

Here are the numbers in the door jamb. Like i mentioned earlier this is an XSP-X, came with 20 in wheels and nitrogen from the dealer along with this new sticker.

 

Like I said the door jamb data don't mean squat.

 

Amontons’s law: "If a gas's temperature increases, then so does its pressure if the mass and volume of the gas are held constant."
Mass and volume do not change if it's contained, such as in a tire, so it will increase in pressure.

 

There are posts here about people spending money to get a more comfortable seat..ie more comfortable ride. And then this post to accept a more harsh ride to save a few pennies.

Too funny.

 

You all can do what you want but running a car tire with 34 psi is asking to peel a tire off during evasive maneuvers. I run my LT tires at 45-50 and would never run anything less than a 118 rating. I have LT 121 E tires on my GX @ 48psi cause she fat.

 

I bought a truck and like a truck, had I wanted a Lexus, yep would have bought one.

 

@Ol' Salty Dawg
For anybody to really answer we need to know

What tires you bought (brand, model, load rating, size)

Once you go away from stock the numbers on the door don't mean much. Some confusion happened here when you said your tires say 42psi, most tires have a max psi listed on the sidewall. That seems awfully low for a max psi and now that we see your door sticker it makes more sense.

Your car door doesn't know what tires you run. Your tires don't know what truck they're mounted to. Best psi is really case by case. Personally I don't think nitrogen is worth messing with. Regular air is fine and makes adjustment so much easier.

 

Fwiw air is mostly nitrogen folks. Pretty close to 80%.

 

78% as I posted above.

 

Splitting hairs...summer time and hwy cruising, I'll do between 55-60 for less rolling resistance and negligible increase in MPG - my brain likes efficiency but my other brain knows its negligible...when towing anything 60-65 psi...winter time, 40psi with 600 lbs of sand in bed.. steroidal traction is the name of the game...long story short, depends on your drive/driving....