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 > Tire Load/Inflation Calculation

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Grit dog

Black Diamond, WA

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Posted: 03/29/22 11:56am Link  |  Print  |  Notify Moderator

JimK-NY wrote:

If you have a TPMS, you might want to try an experiment. Wait for a hot Summer day with the sun beating down on the pavement. Watch what happens to the tire pressures when you start out at the cold pressure corresponding to the maximum load rating. After the tires cool, try the same experiment starting out at the maximum inflation pressure. You will likely see the roughly the same final operating pressure and may even see operating pressures higher for the tires that started out with lower pressure.




Or in summary, temperature and altitude affect tire pressure.
PV=nRT still works.
Not sure what you were trying to say about seeing higher pressure on tire that started out with lower pressure, other than...
Pressure changes about 1psi per 10 deg F and about 1/2 psi (slightly less) for every 1000ft of elevation change.


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dave54

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Posted: 03/29/22 12:27pm Link  |  Print  |  Notify Moderator

JimK-NY wrote:

If you have a TPMS, you might want to try an experiment. Wait for a hot Summer day with the sun beating down on the pavement. Watch what happens to the tire pressures when you start out at the cold pressure corresponding to the maximum load rating. After the tires cool, try the same experiment starting out at the maximum inflation pressure. You will likely see the roughly the same final operating pressure and may even see operating pressures higher for the tires that started out with lower pressure.


Tire manufacturers already know pressure goes up on a hot day and hard drive. They allow for that when setting the max pressure for the tire.


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So many campsites, so little time...
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rfloyd99

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Posted: 03/29/22 12:30pm Link  |  Print  |  Notify Moderator

OP again. I just checked the tread wear - it's even on all four tires,but it looks like there's more wear on the edges (in and out) than in the center.That's how the original tires were also.

Also, I found that I didn't go up in size - orig and new tires are 205/75. New tires are D load range, old were C.

Cummins12V98

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Posted: 03/29/22 12:36pm Link  |  Print  |  Notify Moderator

Mike134 wrote:

Cummins12V98 wrote:

Based on 1,500# and adding 5spi that would be running 45psi at 1,6540# capacity.

CapriRacer has suggested adding 15% to the tire weight and that would put you at 1,725# and use 50psi at 1,760# capacity.

You already inflated the tire load a bit so IMHO either 45 or 50 will be just fine.
You have been running 50 for three years how even is the tread ????????


/\ /\ /\ THIS will tell you the right pressure.

Don't listen to the guy down the block, who talked to his cousin, who knew a guy that read it on the internet.


Using the charts as I mentioned for over a million miles all my tires have worn evenly.


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Cummins12V98

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Posted: 03/29/22 12:37pm Link  |  Print  |  Notify Moderator

rfloyd99 wrote:

Cummins, good question. I've been running 55 psi (I check it often) and have pulled TT maybe 12-15,000 miles on these tires.

I'm headed over to the trailer now and will carefully inspect all four tires. Unless I have some uneven wear issues, it seems that the opinions here are leaning toward 50 or 55 psi being the best choice.

Now, any ideas about that tow vehicle psi?


Sure but I need tire specs and actual weights loaded and unloaded.

Cummins12V98

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Posted: 03/29/22 12:40pm Link  |  Print  |  Notify Moderator

Basic info. On your truck tires add 5psi to the rears and 10 psi to the fronts per what the chart says. Been doing this for many years. 2500 4wd RAM Cummins with 3rd gen take offs Michelins easily 120k and 100k on BFG's.

MFL

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Posted: 03/29/22 12:47pm Link  |  Print  |  Notify Moderator

rfloyd99 wrote:

OP again. I just checked the tread wear - it's even on all four tires,but it looks like there's more wear on the edges (in and out) than in the center.That's how the original tires were also.

Also, I found that I didn't go up in size - orig and new tires are 205/75. New tires are D load range, old were C.


OK...This changes my rec to using full 65 psi in tires for trip, and 60 psi, a very minimum. Doing this, full max 65, should make a noticeable difference in TV mpg, over that many miles of upcoming trip.

Jerry





JimK-NY

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Posted: 03/29/22 01:35pm Link  |  Print  |  Notify Moderator

dave54 wrote:

JimK-NY wrote:

If you have a TPMS, you might want to try an experiment. Wait for a hot Summer day with the sun beating down on the pavement. Watch what happens to the tire pressures when you start out at the cold pressure corresponding to the maximum load rating. After the tires cool, try the same experiment starting out at the maximum inflation pressure. You will likely see the roughly the same final operating pressure and may even see operating pressures higher for the tires that started out with lower pressure.


Tire manufacturers already know pressure goes up on a hot day and hard drive. They allow for that when setting the max pressure for the tire.


I agree, but that is not the issue. The tire that starts out with less pressure is going to flex a lot more. All that flexing is hard on the tire. It will generate heat that will raise the pressure. The pressure could end up even higher than a tire that started out at a higher level of inflation. Again, it is not the pressure that is the issue. It is the flexing and the heat build up. After a highway run with a load on a hot day, go touch your tires. You will quickly feel why heat build up is a concern. If you start out with more pressure the tires will flex less and generate less heat.

Grit dog

Black Diamond, WA

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Posted: 03/29/22 02:10pm Link  |  Print  |  Notify Moderator

MFL wrote:

rfloyd99 wrote:

OP again. I just checked the tread wear - it's even on all four tires,but it looks like there's more wear on the edges (in and out) than in the center.That's how the original tires were also.

Also, I found that I didn't go up in size - orig and new tires are 205/75. New tires are D load range, old were C.


OK...This changes my rec to using full 65 psi in tires for trip, and 60 psi, a very minimum. Doing this, full max 65, should make a noticeable difference in TV mpg, over that many miles of upcoming trip.

Jerry


Yup, 10-4. Air up a bit more from what you're running to get rid of the scrub or underinflation wear. (if it's significant)
And FWIW, even at max pressure, you're not going to balloon those tires with that size trailer and experience wear from overinflection.

JIMNLIN

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Posted: 03/30/22 12:41pm Link  |  Print  |  Notify Moderator

OK please tell me what YOU would do. I h........the "J" has a 6,005# capacity at 125psi.
You've said before you don't run max pressures in your Goodyear heavy trailer tires so its not a surprise your having tire issues from using low psi numbers from a minimum pressure/load chart.
What would I do with a 4500 lb load per tire?
First off I would never over tire a trailers above 15 percent capacity above the gawrs and I also would use the best tire on the market and its sure not a G/H/J Goodyear.
This owner says it best.....

*** ozark mountains
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Posted: 04/27/17 08:01am Link | Quote | Print | Notify Moderator
When it came time for me to replace our tires, I researched many different ways to go. I wound up purchasing 17.5" J rated medium duty truck tires and wheels. When all done and said, it was $5.00 per wheel and tire combo more than just replacing the 16" tires. This tire and wheel combo is good for 6005 pounds each. Using the inflation chart to get the pressure for the load, I inflated to 80 psi which was good for 4500 pounds per tire. With the first tow with these tires to Kansas City, I have made this trip to the speedway several times before, I was down almost 2 mpg both ways. The tires were 20*-25* hotter than the truck, which I have never experienced before. I inflated them to the side wall pressure, 125 psi for max load, before our trip to Florida. Now the tires run 5*-10* cooler than the truck and my fuel mileage is back where it used to be. I have always run max pressure up until I installed these tires, with what I have experienced, I will continue to run what the side wall indicates.***

He now should have a longer lasting tire. Hell even a Goodyear tire might make the grade.


"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers

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