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Old 03-18-2017, 07:37 PM   #1
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Question Tire increase in pressure

I have 275x70 22.5 F @105psi R @ 95psi cold.

what might I expect my tpms to show when hot yest still safe?
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Old 03-18-2017, 07:41 PM   #2
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Quote:
Originally Posted by jimbo2013 View Post
I have 275x70 22.5 F @105psi R @ 95psi cold.

what might I expect my tpms to show when hot yest still safe?
I set mine (same size) at 115 psi and I routinely see 135 psi on a hot day after running 3 or so hours.
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Old 03-18-2017, 08:14 PM   #3
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As long as you have your tires inflated to the proper COLD PSI you should never have a problem with the PSI being too high even on the hottest day. The tires are engineered to handle just about every extreme in high temps you could encounter provided you were not over inflated in the first place.

FWIW, my tire pressure for the front axle run pretty close to gemert's numbers. In general, all my tires gain about 25 - 30 PSI on very hot days.

The only reason you would see unsafe PSI would be if you had something else major happen like a dragging brake heating the rim up which would in turn jack up the PSI but hopefully you would get a heat alarm at that point.
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Old 03-18-2017, 08:28 PM   #4
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SO, What about altitude? Going from sea level to 7000+ feet???
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Old 03-18-2017, 08:29 PM   #5
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How about rear duals? I see my outside tires with higher running pressures than the inside tires. Expected? If so, why?
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Old 03-18-2017, 09:13 PM   #6
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SO, What about altitude? Going from sea level to 7000+ feet???
Again, if you start the day with proper cold tire pressure, no a problem. The same for extreme temp changes during the course of the day.
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Old 03-18-2017, 09:41 PM   #7
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How about rear duals? I see my outside tires with higher running pressures than the inside tires. Expected? If so, why?
One theory is that the inners heat up more because they carry more weight because of the crowns of the road. Another theory is that they can't shed heat as easily. However, they goes directly against what you are seeing so...go figure.

FWIW, I don't see much of a difference between my inners and outers. I can't even tell you if the inners or outers tend to show higher pressure and or temps. The only exception to that is on very hot and sunny days the outer tire facing the sun will show a few degrees warmer and that would tend to support one outer wheel showing higher PSI and temps than the inner on that side.
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Old 03-18-2017, 09:48 PM   #8
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If the air in your tires is too low for the weight on the tire the temps will get very high. Low air pressure is the reason most undamaged tires blow.
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Old 03-19-2017, 09:03 AM   #9
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Don't overthink this. Set the psi correctly when "cold" and trust that the tire engineers allowed correctly for heat expansion and other factors. They have the knowledge and experience to do that correctly so that you don't have to worry. If you travel to a higher altitude, or to a hotter/colder climate, adjust tire pressure the next morning before traveling again, when the tires are once again "cold".

During a days travel, you should expect psi increases of 10-20% simply due to friction heat in the tire. Plus the tires on the sunny side tend to get a bit warmer, whether parked or driving. Crowned roads can cause differences in dual tire pressure, plus the inner and outer dual gain and shed heat at different rates due to differences in air flow, proximity to engine heat (in pushers), etc.

"Cold' means "not driven for several hours". It does not refer to any particular air temperature.
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Old 03-19-2017, 09:20 AM   #10
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Don't overthink this,,,
Could not have described it better.
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Old 03-19-2017, 02:35 PM   #11
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Quote:
Originally Posted by Gary RVRoamer View Post
Don't overthink this. Set the psi correctly when "cold" and trust that the tire engineers allowed correctly for heat expansion and other factors. They have the knowledge and experience to do that correctly so that you don't have to worry. If you travel to a higher altitude, or to a hotter/colder climate, adjust tire pressure the next morning before traveling again, when the tires are once again "cold".

During a days travel, you should expect psi increases of 10-20% simply due to friction heat in the tire. Plus the tires on the sunny side tend to get a bit warmer, whether parked or driving. Crowned roads can cause differences in dual tire pressure, plus the inner and outer dual gain and shed heat at different rates due to differences in air flow, proximity to engine heat (in pushers), etc.

"Cold' means "not driven for several hours". It does not refer to any particular air temperature.

Totally agree with this post. I have a Class A tag and each set runs different cold temp pressures. I set the steer tires to 120psi cold and will see up to 135psi when hot, rears set to 100 psi and will see 120psi when hot. Tag set to 85psi when cold and up to 100psi when hot. I also notice the outside tires will run hotter when sun is on them. Sometimes I needs run higher temps but only a few degrees. All down to cold pressure set up. Temps also change with road temps and you will notice if it rains, temps cool down.
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Old 03-20-2017, 08:54 AM   #12
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makes one wonder why the concern about slightly different cold pressures for each axle. Regardless of what you start with, you will have a large range of operating pressures.
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