Tire Load/Inflation Calculation

[rfloyd99]

Exactly three years ago I bought new tires for my Jayco 23' (27'OAL). I had previously had the trailer professionally weighed at an Escapee's weigh station where they weigh the load on each tire. Unfortunately, that information is in Colorado, and I'm in Florida. But I remember that the total weight was 5500 lbs. We were fully loaded for a three month trip, and that is within the GVWR of 5995 lbs.

The tires (Goodyear Endurance ST205/75R14) are rated for for a load of 2040 lbs (per tire). I knew I didn't have that much wt, so I ran them at 55 psi, thinking I would do some research when I had more time to figure out recommended psi.

Well, three years and many thousand miles later, I finally looked it up. The chart on Goodyear's site shows a psi of 40 for a load of 1500 lbs. 25% of 5500 is 1375, which calls for a psi of 30-35. I increased the wt estimate by 10%, since there may be more weight on an individual tire. That's where I got the 40 psi estimate.

A psi of 35-40 just seems low to me. We are about to leave on a trip of 2,500 miles, and I would like to get this right.

Anyone have expertise in this?

Thanks!

[dedmiston]

Things finally got weird and personal.

I deleted the snottiest reply and I'll close the thread.

Why is it that tire threads turn people into psychos?

[JIMNLIN]

OK please tell me what YOU would do. I have about 4,500# on my GY "H" tires and the tires are not ho...
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
Senior Member
Joined: 10/22/2011
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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.

[Grit_dog]

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.

[JimK-NY]

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.

[MFL]

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

[Cummins12V98]

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.

[Cummins12V98]

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]

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.

[rfloyd99]

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.

[dave54]

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.

[Grit_dog]

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.

[dedmiston]

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.

I don't use my TPMS much because it's not a very good unit, but the data is fascinating when it's actually working. It's surprising to me that the PSI is so much higher on the sunny side of the rig than the shady side.

[Grit_dog]

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?

Your truck, your trailer, with the info you've given, 50-55psi is perfect for the trailer. The slight change from 205-C to 215-D tires is not a cause to change much, if anything.
Rear wheels of the truck, I'd be in the 45psi range, possibly a bit higher if it's feeling squishy, to add stiffness and better handling to the @ss end of the truck.
Front tires, you're presumably not adding much weight, if any, from running bobtail. Possibly even a shade lighter unless you're going ham on the wdh weight transfer. Fronts I'd also be at about 45psi, possibly a bit higher as well, unless they feel "too" stiff.

This is presuming you're running P/XL typical 1/2 ton tires still. Wouldn't change much if running D or E tires, maybe a shade lower than P/XL if they feel too hard, due to thicker tire carcass having better lateral stability and less flex, comparatively.

[JimK-NY]

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.