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Old 11-04-2014, 03:00 PM   #15
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Tire manufacturers don't set tire pressures. Vehicle manufacturers do.

A tire manufacturer may recommend a higher air pressure than the vehicle manufacturer but NEVER a lower one.



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Old 11-04-2014, 03:53 PM   #16
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Quote:
Originally Posted by FastEagle View Post
Tire manufacturers don't set tire pressures. Vehicle manufacturers do.

A tire manufacturer may recommend a higher air pressure than the vehicle manufacturer but NEVER a lower one.



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Tire inflation is a product of weight distribution. The vehicle manufacturer's tire inflation stickers are based on the recommendation of the tire manufacturer for the weight of the vehicle. After all, it is the tire manufacturer who engineered, designed, built and tested the tire. Not the vehicle manufacturer.

If what you are saying were the case, it would be up to the vehicle manufacturer to warranty the tires, not the tire manufacturer. Why? Because the tire manufacturer's lawyers would never agree to warrantying a product that they have lost control of.
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Old 11-04-2014, 05:14 PM   #17
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PSI required depends on the weight it is being asked to carry based on the design. That's why it might say 3500lbs. at 50 psi.
Max psi on sidewall is good for max load. You can certainly operate the tire at max psi with less load and the tire will be "fine", but there are other issues to consider. Particularly ride quality, tread wear, traction and lateral stability. If you had a Ford Explorer with Firestone tires, you understand that the Explorer became unstable with too much psi and would roll over rather than skid in a turn. With too little it would not roll, but the tires eventually failed... and it would roll.
I say this because there is a happy ground where the two work best together.
As with firearms, safety comes from between your ears.
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Old 11-04-2014, 06:12 PM   #18
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Tire inflation is a product of weight distribution. The vehicle manufacturer's tire inflation stickers are based on the recommendation of the tire manufacturer for the weight of the vehicle. After all, it is the tire manufacturer who engineered, designed, built and tested the tire. Not the vehicle manufacturer.

If what you are saying were the case, it would be up to the vehicle manufacturer to warranty the tires, not the tire manufacturer. Why? Because the tire manufacturer's lawyers would never agree to warrantying a product that they have lost control of.
"The pressure your tires require is determined by the vehicle manufacturer in conjunction
with the tire manufacturer and is based on the vehicle’s gross axle load."

"Every vehicle is required by federal regulations to include a tire information placard. This
placard may also be referred to as the tire certification label or federal tire tag. Vehicle
manufacturers are required by federal motor vehicle safety standards (FMVSS) to apply
tires of a suitable size, load range and inflation pressure (as shown on the tire information
placard) that are capable of supporting no less than the gross axle weight rating (GAWR).
Consequently, the vehicle manufacturer’s specified tire inflation pressure is not arbitrary; it is
established by federal safety regulations (ref: Code of Federal Regulations 49, 571.120, and Part 567)."
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Old 11-04-2014, 06:30 PM   #19
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I have taken the weight of each axle on the trailer. I took the heaviest axle and divided by 2 to get what each tire was carrying. (I may go back and get a corner weight for each tire but that is quite difficult because of the tri axle.)

From the tire inflation chart I determined the recommended pressure for the tires on the heaviest axle and I inflate all of the tires on the trailer to the same pressure.

IMO inflating to the max pressure is too heavy as the trailer is rated for 18,000 lbs but I am only carrying a little over 12,000. It will give a harsher ride to the suspension, trailer and contents than I am comfortable with.

I have a TPMS system and drive between 60 - 62. High speed on ST tires is one of the more destructive thing you can do to them I believe.
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Old 11-04-2014, 11:48 PM   #20
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Quote:
Originally Posted by Gordon Dewald View Post
I have taken the weight of each axle on the trailer. I took the heaviest axle and divided by 2 to get what each tire was carrying. (I may go back and get a corner weight for each tire but that is quite difficult because of the tri axle.)

From the tire inflation chart I determined the recommended pressure for the tires on the heaviest axle and I inflate all of the tires on the trailer to the same pressure.

IMO inflating to the max pressure is too heavy as the trailer is rated for 18,000 lbs but I am only carrying a little over 12,000. It will give a harsher ride to the suspension, trailer and contents than I am comfortable with.

I have a TPMS system and drive between 60 - 62. High speed on ST tires is one of the more destructive thing you can do to them I believe.

You’re overlooking a crucial tire design element. ST tires degrade rapidly. It’s the main reason for their short life span estimated to be 3-5 years. In your method of tire inflation you’re sure to have one or two tires overloaded. Lets say those that are slightly overloaded have already degraded 5%. That means you could be adding five more percent of overload to them by not following the trailer manufacturer’s recommended tire pressures.

It’s just not a good risk to fool around with tire pressures on large heavy RV trailers or even lighter ones with very little reserve load capacity in their OE tires.

Every pound of reserve load capacity in the ST tire needs to be used ALL the time.

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Old 11-05-2014, 02:28 AM   #21
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Quote:
Originally Posted by Gordon Dewald View Post
I have taken the weight of each axle on the trailer. I took the heaviest axle and divided by 2 to get what each tire was carrying. (I may go back and get a corner weight for each tire but that is quite difficult because of the tri axle.)

From the tire inflation chart I determined the recommended pressure for the tires on the heaviest axle and I inflate all of the tires on the trailer to the same pressure.

IMO inflating to the max pressure is too heavy as the trailer is rated for 18,000 lbs but I am only carrying a little over 12,000. It will give a harsher ride to the suspension, trailer and contents than I am comfortable with.

I have a TPMS system and drive between 60 - 62. High speed on ST tires is one of the more destructive thing you can do to them I believe.
Then read my post #11 in this topic.
In the spreadsheet there , wich is meanth for ST tires for the moment, you can click the link to other page in the document, where you can also give seperate weighed axle loads as you have done, and then there is assumed to be 5% of axle weightdifference between R/L, but you can set your own percentage.
If you then fill in all and go back with the link at the bottom to the first sheet, you can give tire specifications ( maximum load , maxloadpressure and Speedcode or ST) and it gives a complex looking pressure loadcapacity list filled in with your minimum and maximum determined seperate tire load.
then it gives beween wich pressures your tires are save for the speed you drive ( so 60 to 62m/h) but give the speed you sertainly wont go over for a minute.

Or give the needed data here and I will do it for you and produce a picture of it.
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Old 11-05-2014, 09:15 AM   #22
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Quote:
Originally Posted by FastEagle View Post
"The pressure your tires require is determined by the vehicle manufacturer in conjunction
with the tire manufacturer and is based on the vehicle’s gross axle load."

Pretty sure that was what I said. I just didn't quote CFR.
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Old 11-05-2014, 11:15 AM   #23
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Quote:
Originally Posted by Craig_R View Post
Tire inflation is a product of weight distribution. The vehicle manufacturer's tire inflation stickers are based on the recommendation of the tire manufacturer for the weight of the vehicle. After all, it is the tire manufacturer who engineered, designed, built and tested the tire. Not the vehicle manufacturer.

If what you are saying were the case, it would be up to the vehicle manufacturer to warranty the tires, not the tire manufacturer. Why? Because the tire manufacturer's lawyers would never agree to warrantying a product that they have lost control of.
That marked in red is not a true statement for RV trailers. Tires are fitted to the GAWR (as determined by the vehicle manufacturer). The rest of the weight is supported by the tow vehicle (TV) when being towed or the hitch or built-in supporting devices when parked unhooked from the TV.

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Old 11-05-2014, 11:18 AM   #24
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It’s a topic often disputed in all of the various tire forums. To get to the full picture one has to go all the way back to the basics. Vehicle manufacturers make their needs known to tire manufacturers. Part of the needs is individual tire load capacity. Vehicle manufacturers need load capacity to have some standardization. So load inflation charts were developed from lowest to highest load capacities in 5 psi increments for all load ranged tires (LT, ST and medium & heavy duty truck tires). The load inflation charts are standardized and approved by the Tire & Rim Association (TRA) and made available to all tire retailers. Of course each tire manufacturer will produce their own load inflation charts that mimic the approved TRA charts.

In steps the DOT via the NHTSA. They set minimum standards for vehicle manufacturers to abide when fitting tires to the vehicles they build. In all of that regulation is the fact that NHTSA directs vehicle builders to set minimum acceptable tire pressures and put that recommendation on each and every vehicle certification label. That recommended tire pressure equals a specific load capacity via the use of approved load inflation charts. That load capacity is the minimum acceptable load capacity for any subsequent tires fitted to that vehicle.

Of course those regulations are not binding on the end user. But, tire industry standards are self policing. Never use tires with less load capacity than what the OE tires provide.


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Old 11-05-2014, 06:33 PM   #25
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So, what came first, the chicken or the egg? It was the egg... or was it the chicken.

We are on the same page. We're just coming at it from two different directions.

Check out the definition of the word, "Conjunction" in the context of the sentence it was used in Code of Federal Regulations 49, 571.120, and Part 567.
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Old 11-05-2014, 06:54 PM   #26
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To figure out the tire pressure, load your trailer with everything you normally carry plus a full tank of fresh water. Go to a scale and have the trailer weighed. Divide the total weight by the number of tires on the trailer and that will give you what each tire is carrying. Use one of the above mentioned tire inflation charts to find the minimum PSI for the load each tire is carrying.

Now personal opinion, add at least 10 more pounds of air, as long as it does not exceed the maximum tire pressure listed on the tire. This will give you the best ride for the trailer and a good safety margin for the weight. And as you probably already know, check the tire pressures when the tires are cold, as early in the AM as possible as just the sun heating up the tires can change the pressure.
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Old 11-06-2014, 10:40 PM   #27
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NHTSA writes and enforces tire safety regulations. In this NHTSA brochure on the bottom of page two in bold red letters it describes who is responsible for setting the initial tire pressures for your vehicles.

.78677474,d.aWhttp://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&cad =rja&uact=8&ved=0CCcQFjAB&url=http%3A%2F%2Fwww.nht sa.gov%2Fcars%2Frules%2Ftiresafety%2Fridesonit%2Fi mages%2Fbrochure.pdf&ei=dW1ZVMflLNG0yASM64LQAQ&usg =AFQjCNF0DJFfdPM0Wab-3JTF_r6NyADLrw&sig2=4r9cLRwWKCJgPTOvIVzG1g&bvm=bvw




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Old 11-07-2014, 08:08 PM   #28
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Tire manufacturers have charts with weights and pressures as described above.
Given the size of your trailer the tires will probably have a 50# psi max. Most discussions I have seen about this recommend keeping your tires at their max rating.
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