OK, I know I have covered this before, but I still get some folks who either missed my posts or think what they remember from high school is good enough. This became obvious again last week when I was informed that I was trying to “remove chemical principles.”
I had said that cold inflation pressure meant when the tire had not been in direct sunlight or driven on in the previous 2 to 3 hours. However, the reader knew that ”Pressures are always and only set off Standard Pressure and Temperature. Which is 20C and something like 800 mm/hg.”
What my statements are based on
For those who are new to my posts on RVtravel.com or as found in my blog RVTireSafety.net, you should know that I base my technical statements on my 50+ years of designing, working on, testing and evaluating tires. I also refer to published tire industry standards and guidelines, such as found in the 192-page “The Tire & Rim Association” aka “TRA” yearbook, or the European or Japanese equivalent of the U.S. TRA. I also rely on the “Tire Maintenance Council Radial Tire Condition Analysis Guide” that has more than 140 pages covering various tire conditions with pictures.
Those publications are developed and used by more than two dozen tire and tire-related product manufacturers. Also, the U.S. Department of Transportation references the TRA as a source for information on load and inflation for their testing and performance requirements.
Cold inflation pressures according to TRA
As stated on the first page of each section, including Passenger, Light Truck, Truck-Bus, Off-The-Road, Agriculture, Industrial, ST and Cycle sections of TRA:
“COLD INFLATION PRESSURES: The inflation pressures shown in this section are those taken with the tires at the prevailing atmospheric temperatures and do not include any inflation pressure build-up due to vehicle operation.”
Some tire companies publish a copy of the Load and Inflation tables, but a review of that information will reveal the same information for Load Capacity and Inflation for tires sold in the USA, Canada and a few other countries. This is the pressure number you see published in tire company “Load & Inflation” charts.
The pressure you see on the Certification Label / sticker aka tire placard that vehicle manufacturers apply to cars, trucks and RVs is identical to what is found in the published industrial standards books.
What “cold” does and does not mean relating to tires
To repeat, for those that think they know more about tire loads and inflation than all Tire Design Engineers, the word “cold” on the tire sidewall does not mean the tire needs to be refrigerated. It also does not mean that inflation pressure needs to be “adjusted” by calculating the difference between some theoretical laboratory standard and the current air temperature.
“Cold” for tires simply means at ambient air temperature and not warmed by either being driven on or being in sunlight for the previous two to three hours.
I hope this clarifies what we mean by “COLD INFLATION”. But if history is any predictor of future internet posts, I will not be surprised to see someone posting a table for “Pressure & Temperature adjustments” within the next few weeks.
For those interested, you can order your own copy of TRA for $160 from its website publication list so you can then check the statements I make versus tire industry standards.
Roger Marble
*****
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If you have tire questions, check out Roger’s Blog as well as his posts on RVtravel.com. There are hundreds of posts covering everything to do with tires.
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Roger, thanks for continuing to provide expert valid tire info. I took both of your classes last August in Redmond and thoroughly enjoyed them.
I always have to chuckle a little when keyboard experts think you are wrong! 😁
I think I sat behind you for both classes last year Mikal.
Yes they were both enjoyable and educational as well.
Thanks for all your informative articles Roger!!
And for all of your replies to all of the columns presented in the newsletters as well Mikal !!
One other thing to consider when checking the pressures. If one or two tires have been sitting in the sun, they will show a higher pressure than ones in the shade. It may only be a few PSI.
Common sense prevails.
No generation before has had the entirety of human knowledge available at their fingertips yet stupidity still thrives….(sigh).
The thing to remember is that the tire can’t read a thermometer, nor can it read a barometer. It only knows how much air is inside relative to how much is outside.
Thank you for the reminder of when one should take tire pressures and adjust as needed according to the weight the tires/axle are/is carrying and the tire manufacturer’s inflation table. Have a great week and safe travels!
I set my tire pressure in the spring when the temps are >70 F , and in the fall when the temps are around 35 F. If I don’t increase the pressure when around 35 F my TPMS will go off from low pressure.