Safety & Compliance

What Exactly Constitutes an Underinflated Truck Tire?

July 2013, - WebXclusive

by Jim Park, Equipment Editor - Also by this author

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"Underinflated" isn't always this obvious. Enforcement officials are looking for a usable definition. (Photo by Evan Lockridge)
"Underinflated" isn't always this obvious. Enforcement officials are looking for a usable definition. (Photo by Evan Lockridge)

We've all heard the claims that running tires underinflated hurts fuel economy (1 to 1.5% for every 10% under, they say), increases tire wear and wrecks casings.

So what is underinflated?

By definition, it's any pressure less than the minimum recommended for the tire load. For example, a steer tire with a load of 6,000 pounds would be underinflated at 105 psi (see below). A drive tire loaded to 4,520 pounds would be underinflated at 75 psi. It all depends on the load on the tire and the minimum inflation pressure for the load. 


Why should we worry about defining underinflation? Because of the Federal Motor Carrier Safety Administration's CSA (Compliance, Safety, Accountability) enforcement program.

The Commercial Vehicle Safety Alliance is currently exploring how to define underinflation for enforcement purposes. CVSA has already settled on a definition of a "flat" tire: 50% of the max cold inflation pressure stamped on the sidewall of the tire, e.g., 60 psi in a tire stamped for its max load at 120 psi inflation pressure. That's clean and simple; now CVSA wants a similarly clean and simple definition of under-inflated.

That won't be as easy.

Peggy Fisher, president of Tire Stamp, led a discussion at this year's annual meeting of ATA's Technology and Maintenance Council on the subject and failed to resolve the question. Difficulty arises because of an almost outdated DOT requirement that evaluations of hot or in-service tires be temperature-compensated.

"DOT inspectors won't usually check tire pressure unless they suspect a problem, like the tire looks soft," Fisher said. "The problem is they have nothing to go by except what's stamped on the tire. To determine the proper inflation pressure of a tire, they need to know the temperature of the tire and the load on the tire. All that comes into play in determining the proper inflation pressure of a tire." 

Back in the days of tube tires, it was established that inspectors would subtract 15 psi from the gauged pressure of the tire to compensate for temperature. For example, a hot tire gauged at 85 psi would be considered cold-inflated to 70 psi. If that seems low, consider that according to the Goodyear's and Bridgestone's Load & Inflation tables, a 70-pound tire can still carry a load of 3,875 pounds. Michelin allows up to 4,500 pounds at 70 psi. Even at 3,875 pounds per tire, that would still allow 31,000 pounds over a tandem axle group. Is that tire actually underinflated with a light load?

There was also a CVSA official in the room at TMC. Kerri Wirachowsky of CVSA's vehicle committee, said the definition has to be simple or officers won't get it right.

"I don't think a lot of trucks get citations for underinflation, but they are getting written up on the inspection reports and that's just as impactful as far as CSA is concerned," she said. "As an officer checking tire pressure at roadside, I might not be at a scale; I don't know the load or the temperature of the tire. There's no way I can tell the variation between hot and cold. If you're going to make a reg change, get rid of the minus-15 and go to the lowest common denominator." 

TMC and CVSA are still working on this, and a solution doesn't seem close at this point. But maybe this information can help you in a DataQ challenge. Is that 70-psi tire really underinflated?


Load & Inflation Table examples

Michelin 275/80R22.5

Steer 5,980 @ 105 psi; 6,175 @ 110 psi

Drive/trailer 4,770 lb single @ 75 psi

Bridgestone 295/75R22.5

Steer 5980 @ 105 psi; 6175 @ 110 psi

Drive/trailer 4540 lb single @ 80 psi


Goodyear 295/75R22.5

Steer 5,980 @ 105 psi; 6175@110

Drive 4,690 @ 75 psi

Read more about tire inflation in the July issue of HDT.


  1. 1. Jamie Serfass [ July 10, 2013 @ 11:52AM ]

    Actually the load inflation tables are labeled for single and dual configuration not steer or drive/trailer.

    Considering 34K for a set of tandems divide by 8 tires and the max legal load most tires will see is 4,250 lbs each. You can run 11R24.5 tires at 70 psi and be properly inflated for the max load in a dual application.
    Dual apps are actually rated with higher psi than single to account for one of the pair running on an elevated section compared to the other such as an edge of a roadway where one would bear more weight than the other.

    Most tires are running over-inflated. Some are over-inflated so there is 'extra' in case some leaks out. Some are over inflated because of that number on tyhe sidewall. Some are over-inflated for better mpg. Running rock-hard tires is bad for the tire, truck, driver comfort and highway. A properly inflated tire is the first part of a suspension system as it absorbs all of the initial road bumps.

  2. 2. Alfonso Carmenate [ June 23, 2015 @ 07:45AM ]

    You are doing great. THANKS A LOT!!!!!

  3. 3. george [ November 06, 2015 @ 01:57PM ]

    I heard friend of my in Ohio or Kentucky the dot give him a tiket of 100 dollar for each tire under 110 he didn't do nothing about it. that is not fear the officers didn't found nothing on him try to get him for that what he can do is this case ? Thanks

  4. 4. george [ November 06, 2015 @ 02:06PM ]

    I know safety is first but this was not about safety I went Ohio two week ago for keep my tires with 110 psi it blow up 4 tires in good condition. that could created an accident if I lose control of my truck me or Innocent people cold die. with 100 psi will be good enough to handle a load safe matters I been driving like that I never got a problem someone can help me with this situation thanks .

  5. 5. Jeff [ April 09, 2016 @ 09:59AM ]

    I routinely, as standard practice, inflate my tires according to Michelin's load inflation tables (I run Michelin exclusively), considering the maximum legal load on the tire in question. While my steering tires are kept near the sidewall maximum as a result, both my drive and trailers are well below that same value. I further utilize a simple "per tire" pressure monitor to make routine visual checks of pressure easy to perform.

    It concerns me mightily the enforcement community thinks they can come up with a "one size fits all" solution to the issue of proper inflation when the people who design, manufacture and sell the tires obviously feel a lengthy discussion of load, altitude (ambient air pressure) and temperature (both tire and ambient) factor into a correct determination regarding this nonetheless critical component of tire service and tire life. Without, at a bare minimum, a manufacturer's load inflation tables at hand, along with an accurate weight for the axle group in which the tire resides, I don't see any way a fair rendering of opinion on the inflation of any single tire in a roadside inspection can be given.

    Given the enormous consequences of any sort of negative finding in a roadside inspection (fines, CSA points, driver and carrier records, etc.), I think it behooves CVSA and other enforcement entities to think long and hard about the viability of any standard other than their existing 50% of sidewall maximum, as values of as low as 66% of sidewall maximum are permissible (and desirable, actually) on a legally loaded dual tire, according to Michelin.

  6. 6. Jim Park [ May 02, 2016 @ 08:20AM ]

    Jeff, CVSA has backed off on trying to determine underinflation by tire pressure and load on the tire. In a regulator guidance issued last year, they say the underinflation is to be determined by 50% of the tire's maximum inflation pressure, usually 110 or 120 psi. A violation could be written if the truck and tire can be weighed and it's proven that the load on the tire exceeds the rating for the pressure -- but only if the officer has L&I tables for the tire and it can be weighed. The most likely violation in this case would be a steer tire, often inflated to just 100 psi when it may in fact need 105 or more, or when the axle is loaded heavy. As in the case of a 13,200-lb axle with load range G tires at 100 psi.

    And George, I'd say your friend is either pulling your leg on the $100 fine for having tires at less than 110 psi or they were way less than 110, like maybe 50 or 55 psi. That would be a violation.

  7. 7. chet cline [ May 11, 2016 @ 07:10PM ]

    Thanks for writing this excellent article. The CVSA is wrong on this issue. The correct pressure depends upon the tire size and the load. Michelin shows pressures down to two bar, 29 psi. We at AIR CTI recommend pressures down to that pressure, for light loads, and we always improve tire life by at least 30%.


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