Why do brand-new tires lose air pressure?
Air molecules are very small. And rubber, though it looks very solid, is, at the microscopic level, a sort of tangled, fishnet-like mass of long, stringy molecules.

Over time, air molecules can make their way through the maze of molecular chains and escape to the outside world. Basically, they go right through the sidewalls.

Truck tires can lose up to 2 psi per month of inflation pressure as a result of air molecules diffusing through sidewalls.

Can’t you make tires that seal better?
Air molecules are just too tiny. Besides, if the surfaces of the bead and wheel are not clean, if the wheel is corroded, or if the mounting lubricant doesn’t coat the bead and wheel properly, it’s possible for air molecules to sneak through there as well.

There’s no way to make a tire absolutely airtight.

Air can also escape where the bead and wheel meet, especially if dirt or corrosion is present, or if the components weren’t properly lubricated.

Are these big losses?
A truck tire can lose 2 psi per month, even when brand-new and properly mounted. That’s 24 psi a year, which would take any tire way below the run flat level. It’s another reason we place so much emphasis on regular inflation pressure maintenance.

How much air loss is acceptable?
Maybe none. That’s what suggested the topic of this article. Everybody has seen load and inflation tables. If you know your tire’s load rating and the actual maximum load it will encounter, you can find an inflation pressure on the chart.

But do you know what that pressure is?

What do you mean?
The pressure you read on the chart is the minimum recommended pressure for that tire at the specified load.

So, what happens if you lose a little air, either through diffusion, or a slow leak? That’s right, underinflation.

But we can’t stop all air losses.
No, but this is an additional reason why frequent air pressure checks and adjustment are necessary.

How often should inflation pressure be checked?
If you go by pre-trip inspection guidelines, it should be every day. And that means with a good quality, calibrated air gauge, not a tire billy or boot tip.

But few if any truckers gauge their tires every day. Nevertheless, most would find many of their tire problems would vanish if they checked their inflation once a week.

What kinds of problems?
Underinflated tires wear out faster, are more prone to irregular wear, suffer reduced retreadability and are easily damaged by road hazards. And, they can provide sloppy road feel and severely reduced wet traction. Plus, underinflation cuts fuel economy.

Can’t letting out a little air provide a more comfortable ride?
That’s doubtful. With today’s suspensions and shock absorber systems, it’s not likely reduced air pressure could make a significant difference in ride.

Besides, it’s certainly not worth the loss of tire life, fuel economy and traction that come with it.

If inflation table pressures are minimums, can we go higher?
You can. Let’s say your steer axle is running at exactly 12,000 pounds. According to the table, if you’re using 295/75R22.5 radials, you need at least G rated tires.

If you chose to use H rated tires instead, you could still set inflation to 110 psi, which would be correct for 6,175 pounds, 175 pounds per axle end more than your load.

So that inflation pressure is all we need?
Not exactly. Notice that if the inflation falls to 100 psi, just 10 psi lower, the tires are only rated for 5,780 pounds. Lose 10 psi and your tires are 220 pounds overloaded.

Five months of no air pressure checks could easily put you there.

What if we went up to 115 psi?
You could. In fact, inflation pressures up to 120 psi are suitable for this tire (at its full load capacity). The advantage of going to 115 psi however, is that you could lose a little inflation due to leakage, and still have enough capacity for the load.

How much higher can we go above recommended pressures?
Too high a pressure is not good. It can make tires very stiff. They have less give, and become more susceptible to impact breaks, the kind of thing that happens when you hit the edge of a chuckhole at high speed.

Experience shows that higher inflation pressures (not more than 10-15 psi above table specifications) can provide a bit of a cushion against losses, improve fuel economy slightly and result in increased resistance to irregular wear.

We like to standardize on specific inflation pressures for our tires.
That’s an excellent idea. If you standardize, one of the things you can do is try slight variations on some of your vehicles to determine if inflation pressure increases will produce any of the beneficial effects we mentioned.

Once you deside the correct pressure for your tires, communicate it to your drivers and maintenance personnel. Make sure everyone who maintains tires knows the correct inflation pressure.

Nothing will go as far toward prolonging tire life, increasing retreadability, conserving fuel and maximizing traction as maintaining the correct inflation pressure in all tires at all times. The more often you check and adjust it, the better you’ll maintain it.