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Old 03-15-2020, 03:56 PM   #1
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Tire pressures, what to expect

Just took out first trip since installing a TPMS. When we pulled out of the driveway the readings were from 108 to 110. As I traveled down the road Max speed 60 mph overcast day with the temps in the mid 50's the pressures elevated to 122 to 125 psi. Is this the norm? At what level is there reason for concern? Would the pressure get even higher on warmer days? Nice to know the readings but it be even nicer if I new what to expect.
Thanks.
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Old 03-15-2020, 04:36 PM   #2
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I found the same issue with our Carlisle tires. I changed tires and added the TPMS at the same time. Never knew the temps and pressure went up like that while driving.
After checking with the dealer as well as a relative in the tire business, the answer was "this is normal". Both recommended keeping an eye on the pressure and temps primarily looking for any inconsistencies among the tires being monitored. They assured me that the tire manufacturers allow for the increase in pressure and heat in their engineering. I can even notice which side the sun is shining on by several degrees
I once noticed one trailer tire about 15 degrees hotter than the others. Turned out the brake on that wheel had seized slightly creating the added heat. Having the TPMS saved our vacation that summer!
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Old 03-15-2020, 04:40 PM   #3
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If tires are set properly to cold pressure rating (technically at 68į F with 1 psi added or subtracted for each 10į above or below). That’s the overly anal method, but in the real word check and set when “cold” meaning not driven on in past 3 hours. Either way rise in temperature in use should still keep you within design limits of the tires.

Now that being said, your actual tires will decide how safe this is. Stock tires (like Trailer King, or Power King) might pose a concern as they have a dubious reputation, whereas aftermarket tires (like Goodyear, Carlisle or Sailun) might give you more peace of mind.
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Old 03-15-2020, 04:53 PM   #4
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I believe the manual says set tire pressures when cold. Could be 0F or +70F. YMMV
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Old 03-15-2020, 05:08 PM   #5
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I set my air pressures 5 psi below max when the ambient temperature first thing in the morning at daylight is 15 C (~60F). That is the typical temp for us in the mornings when we set off towing. I am comfortable with the 5 psi below max since a 10 F temp rise brings them up to max. This way I do not have to keep adjusting the air pressure the entire season.
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Old 03-15-2020, 05:08 PM   #6
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"Cold pressure" is before traveling. Best to check in the morning before traveling. You do not have to check precisely at 68 degrees.
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Old 03-15-2020, 06:42 PM   #7
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I have always been told that you inflate to max psi before travel and20% increase in pressure is safe.
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Old 03-15-2020, 09:14 PM   #8
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Quote:
Originally Posted by slow View Post
I set my air pressures 5 psi below max when the ambient temperature first thing in the morning at daylight is 15 C (~60F). That is the typical temp for us in the mornings when we set off towing. I am comfortable with the 5 psi below max since a 10 F temp rise brings them up to max. This way I do not have to keep adjusting the air pressure the entire season.
If the max you speak of is the recommendation on the vehicle certification label, you're starting the day off 5 PSI under inflated.
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Old 03-16-2020, 02:34 AM   #9
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"If the max you speak of is the recommendation on the vehicle certification label, you're starting the day off 5 PSI under inflated. "
Slow, what Cal said is on the money, although he doesn't need me to back his statement. That pressure is on that tire for a reason, and done by people in the know.
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Old 03-16-2020, 02:45 AM   #10
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I should have also stated that my tire capacity is 50% over my FW GVWR. So no concern with being 5 psi low at 60 F. Others that do not have this level of reserve capacity need to be more proactive in adjusting to temperature changes.
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Old 03-16-2020, 10:05 AM   #11
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Quote:
Originally Posted by tech740 View Post
I have always been told that you inflate to max psi before travel and20% increase in pressure is safe.
That's what I was looking for, thanks.
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Old 03-16-2020, 10:24 AM   #12
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For the tire experts?
You replace tires with a load, or 2, range higher so in theory you can lower the max psi which to me increases sidewall flex thereby increasing temperatures, so why not inflate to max psi for either load range? I've always ran max psi regardless of load rating with no noticable difference in ride in the truck with higher or lower psi, no one is riding back for the ride to bother anyway.
As to more jarring on the RV with higher psi doing harm, how would you know if it was tire inflation, our wonderful highways or high quality built RVs, things fall apart while parked.
I will continue to inflate the tires to max psi as I have for the past 40+ years towing trailers, but it might be good info for others with no experience.
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Old 03-16-2020, 11:07 AM   #13
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Quote:
Originally Posted by travelin texans View Post
For the tire experts?
You replace tires with a load, or 2, range higher so in theory you can lower the max psi which to me increases sidewall flex thereby increasing temperatures, so why not inflate to max psi for either load range? I've always ran max psi regardless of load rating with no noticable difference in ride in the truck with higher or lower psi, no one is riding back for the ride to bother anyway. As to more jarring on the RV doing harm, how would you know if it was tire inflation, just our wonderful highways or high quality built RVs, things fall apart while parked.
I will continue to inflate to the tires max psi as I have for the past 40+ years towing trailers, but it might be good info for others with no experience.
Thanks for the input. I've only been doing this for about 8 years now but have always ran max PSI and no tire failure or unusual wear yet. Maybe I've been plain ole lucky.
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Old 03-16-2020, 12:05 PM   #14
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Originally Posted by slow View Post
I should have also stated that my tire capacity is 50% over my FW GVWR. So no concern with being 5 psi low at 60 F. Others that do not have this level of reserve capacity need to be more proactive in adjusting to temperature changes.
Because we donít know your trailerís actual Original Equipment tire sizes, Iím just going to do a hypothetical.

Your OE tires were probably ST225/75R15 LRD. So Iím going to use the figures for that tire in this hypothetical. To get tire with 50% reserve load capacity for your trailer you would have to use 16Ē tires. The first best fit to gain that 50 % would be the ST235/80R16.

The recommended inflation pressures for your OE tires are displayed on the vehicle certification label and are minimum inflation pressures for that fitment. So letís say the recommended inflation pressures for the OE tires are 65 PSI. That would provide 2540# of load capacity per tire. Looking at a chart for the above mentioned 16Ē tires reveals they could have a recommended inflation pressure of 50 PSI to satisfy the requirement of providing a load capacity equal to or greater than what the OE tires provided.

For the 16Ē tires to provide 50% load capacity reserves they would have to be inflated to 75 PSI, 5 PSI below their maximum allowed PSI.
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Old 03-16-2020, 12:39 PM   #15
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Quote:
Originally Posted by travelin texans View Post
You replace tires with a load, or 2, range higher so in theory you can lower the max psi which to me increases sidewall flex thereby increasing temperatures, so why not inflate to max psi for either load range? I've always ran max psi regardless of load rating with no noticable difference in ride in the truck with higher or lower psi, no one is riding back for the ride to bother anyway.
As to more jarring on the RV with higher psi doing harm, how would you know if it was tire inflation, our wonderful highways or high quality built RVs, things fall apart while parked.
I will continue to inflate the tires to max psi as I have for the past 40+ years towing trailers, but it might be good info for others with no experience.
Tire inflations for Original Equipment RV trailer tires has almost always been set at the tires maximum allowed PSI displayed on the tire sidewall. The most common reason for that procedure is it's the only way to insure the OE tires are inflated to a value that will support the maximum load capacity of the vehicle manufacturer's GAWR axles. (An OE tire is not over inflated as long as its cold inflation pressure does not exceed its sidewall PSI).

The following standard is why all TV trailer tires are required to only provide a load capacity equal to or greater than the trailer's certified GAWR (s).

The sum of the maximum load capacities for the Vehicle Certified GAWR axles, when added to the trailer manufacturer's recommended tongue weight for that trailer, must not be less than GVWR. Therefore, all tire fitments for RV trailer axles MUST provide a load capacity that will support the maximum load rating of the vehicle certified axles.

When replacing tires such as an ST225/75R15 LRC with a ST225/75R15 LRE it is not necessary to change the recommended inflation pressures. Both tires will provide an identical load capacity at 50 PSI. The LRD/E allows for increased inflation pressures resulting in increased load capacity. Wheel/valve stem PSI values for the OE equipment must be confirmed as sufficient for the increased inflation pressures. Optional inflation pressures for increased load capacity are allowed all the way to sidewall max. Again, it must be done safely.
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Old 03-16-2020, 01:44 PM   #16
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Tire pressures, what to expect

Quote:
Originally Posted by CWtheMan View Post
Because we donít know your trailerís actual Original Equipment tire sizes, Iím just going to do a hypothetical.

Your OE tires were probably ST225/75R15 LRD. So Iím going to use the figures for that tire in this hypothetical. To get tire with 50% reserve load capacity for your trailer you would have to use 16Ē tires. The first best fit to gain that 50 % would be the ST235/80R16.

The recommended inflation pressures for your OE tires are displayed on the vehicle certification label and are minimum inflation pressures for that fitment. So letís say the recommended inflation pressures for the OE tires are 65 PSI. That would provide 2540# of load capacity per tire. Looking at a chart for the above mentioned 16Ē tires reveals they could have a recommended inflation pressure of 50 PSI to satisfy the requirement of providing a load capacity equal to or greater than what the OE tires provided.

For the 16Ē tires to provide 50% load capacity reserves they would have to be inflated to 75 PSI, 5 PSI below their maximum allowed PSI.

I am running the ST235/80R16 E.
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Old 03-16-2020, 03:28 PM   #17
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I posted this two years ago:


"Just for comparisons, I am out on the road driving south from KY to the gulf shores of MS. With the same Sendel wheel and the Sailuns, run 125 +/- 1 psi between the 4 tires at 70mph (110psi cold inflation). Temp is right around 100F with it being 90+ ambient. All 4 tires run very consistent with each other."
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Old 03-16-2020, 04:11 PM   #18
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I am running the ST235/80R16 E.
Well, inflated to 75 PSI and going down the road at 65 MPH they ought to feel just like solid rubber.
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Old 03-22-2020, 08:11 AM   #19
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I onxe determined that if pressure is calculated for the weight with some reserve for 99mph, that then if ambiŽnt temp is 65degrF , and driving 50 to 55mph, pressure rises about 10% .

Now your pressure rises 14/15 psi on 108/110 psi.
Is about 13 to 13.6% rising of pressure.
Now ambiŽnt temp was 50 degr F and speed 60 mph , so higher speed gives more temp rising in tire, so more pressure rising expected, and colder ambiŽnt temp so relatively more deflection of tire.

Taking this all into account, your 13/13,6% rising seems to be normal.
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Old 03-22-2020, 08:28 AM   #20
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Originally Posted by NH_Bulldog View Post
If tires are set properly to cold pressure rating (technically at 68į F with 1 psi added or subtracted for each 10į above or below). Thatís the overly anal method, but in the real word check and set when ďcoldĒ meaning not driven on in past 3 hours. Either way rise in temperature in use should still keep you within design limits of the tires.

Now that being said, your actual tires will decide how safe this is. Stock tires (like Trailer King, or Power King) might pose a concern as they have a dubious reputation, whereas aftermarket tires (like Goodyear, Carlisle or Sailun) might give you more peace of mind.

Sorry but setting tire pressure is done at Ambient Temperature. No adjustment or calculation to some theoretical High School Chem lab experiment.
No idea what you think the "design limits" are for tires. The MINIMUM pressure at ambient temperature is the pressure in the charts for your Actual measured load on the heavy end of each axle.
I recommend adding 10% so you are not chasing your tail whenever the air temperature changes a few degrees.


I would expect "normal" operating temperature to increase above ambient by 10F to 50F depending on ambient as cooler air will transfer heat faster to the wheel and then to the air. With a +50F that would suggest a pressure increase of 10% to 20% as "normal" variation comes from air flow and heat transfer variations. You also have variation of +/- a couple % for pressure reading from TPMS.


Please stop overthinking this. I have covered this is detail ini my blog.
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