Tire pressure when it's cold

Rule of thumb is 1 PSI for every 10 degrees. It's bang on but not linear.
Every manufacturer says a cold tire is one that has sat for at least 4 hours or driven less than 1 mile.
I hope you're using the same gauge to compare.

 

IIRC, 70 degrees is the start point for inflating tires. That comes from the maintenance council.
Thus why it cracks me up when Speedco etc ask if I want my tires checked when I pull in the building, right after running 300 miles at highway speeds with 39,000 on my drives...........Useless.

Martin

 

Air up your tires when they're cold before you start to the cold pressure you're using. Doesn't matter whether its 70, 90 or -10. That's your starting point for the days ambient conditions. Going from warm weather to a much colder morning will guarantee you need to get out there and air 'em up.

 

Like leftlane says check 'em cold at 70°. If it gets colder outside no matter since 99% of you truckers over-inflate your tires anyway. Some to get better fuel mileage, some because they don't realize the max pressure on the sidewall is for max load and not legal load, and some just because it feels good.
Check tire mfr's load/inflation tables to see what you really need.

 

So... you set your pressure at 110psi in 70 degrees in Miami. Drive to North Dakota where it's -10 degrees. My own observation is your tire pressure decreases about 3lbs for every 10 degrees worth of temperature decrease. That's an 80 degree difference, and about 24 pounds less pressure in your tires. You're now running at 86 pounds... which is severely underinflated. That puts you at risk for a blow-out, and nearly at the point that DOT will write you up for running on an under-inflated tire.

I believe that settles it. You'd be well advised to put some air in those tires when the temperature drops.

 

A solo driver would take a 10 hour break between Miami and North Dakota. That means a proper pre-trip inspection after the 10 hour break and correcting air pressure if needed. You folks sometimes tend to over-analyze and over-complicate the simple. Check and adjust daily if necessary. Correct air pressure is load/weight dependant are you sure 86psi is underinflated in every scenario?

 

The premise put forward was you only air your tires at 70 degrees. Not at 10 hours. That being said... you're right; regardless of the ambient temperature at the end of the 10-hour break, you'd be inflating your tires to the cold pressure at that time.

I'll check the DOT inspection procedure, and post back on that tomorrow. I believe they consider anything below 80 pounds on a class 8 truck to be underinflated. But yeah, you'd have to check the tech data on your tires. OTOH, that's only if you run your tires at that sort of a really low pressure, IMO.