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Old 02-14-2019, 08:49 PM   #21
Tireman9
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Originally Posted by RayT View Post
concours, do you have a link or other reference source regarding the 70F/20C? I've searched for what temperature the tire pressure ratings are specified at but haven't been able to find anything. I even contacted Goodyear but got a useless answer. I've assumed 60 or 70F but don't like making assumptions.

Here in AZ the Cold/Ambient temp can vary widely based on season and altitude. A cold January morning might be 40F while a "cold" July morning might be closer to 90F. According to Tire Rack the rule of thumb is ~2% change in tire pressure for each 10 deg change in temp. So for my 110 PSI tires I could see an 11 PSI diff between winter and summer. Or if I'm headed into the mountains from the desert, with say a 40F diff in typical "cold" morning temp, the baseline pressure difference is about 9 PSI.

While the over/under inflation may not be too bad if you're within 10-20F of the temperature the manufacturer used to spec the tire pressure rating, it can become significant when you get 30, 40 or even 50F from the temperature used to spec the tire.

As a retired engineer its always bothered men that tire manufacturers don't provide a temperature to go with their PSI specs. I guess the company lawyers just think that extra detail would confuse customers...?

Thanks

Nope. Tire & Rim Association publishes the load & Inflation tables used bu tire companies and DOT which clearly states that the temperature is the "ambient" temperature when tires have not been warmed either by running or from direct exposure to sunlight.



We are not running a High School chem lab test.



Please stop over-thinking tire inflation. The inflation number molded on the tire sidewall is the cold inflation needed to support the stated tire load.



Set your tire pressure when tires have not been warmed. You only need to adjust your pressure when you are planning on traveling that day. I don't bother to adjust my pressure unless it is off by 5 psi. I can do this because I run a +15% pressure over what is needed to support my actual tire load.4
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Old 02-15-2019, 06:52 AM   #22
CWtheMan
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I don't bother to adjust my pressure unless it is off by 5 psi. I can do this because I run a +15% pressure over what is needed to support my actual tire load.4

You'd find that hard to do with just about any OME tires on trailers more than 3 years old. They are most likely already at max from the factory settings.
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Old 02-15-2019, 07:55 AM   #23
concours
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when I have attended training classes at CAT, Detroit and Cummings they all refered to cold temperature as room temp. i.e. the temperature of a service workshop. they stated that spec. for accurate measurement of components. It made perfect sense at the time and still does today
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Old 02-15-2019, 09:19 AM   #24
Tireman9
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You'd find that hard to do with just about any OME tires on trailers more than 3 years old. They are most likely already at max from the factory settings.

Yes I have the option with my Class-C of adjusting inflation based on load.


Trailers, especially multi-axle trailers need to always run the tire pressure on the sidewall, which is also what is probably on the vehicle certification lable.



Trailers can adjust their load to get a 15% reserve on the load capacity. It may not be easy if they carry a lot of "stuff" but that reserve would probably lower the chance of belt separation.
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