Tire pressures

[BobnLee]

Hi folks I recently go back from a weekend trip. Started to winterize the trailer and noticed 52 lbs of air in all 4 tires. Thinking this a bit odd i checked the mfg. Power King St 225/75R15 the manufacture says psi is 65 but can be lower depending on the load. Anyone know what pressure I should be keeping them at. It is a Cougar 26SAB xlite.

Moderator's Note: This post has been moved from its original section to this new category about tires.

[mapleman3]

Cooler temps? Mine are sitting cold at 40 and were all near 50 in the hot months

[Htfiremedic]

I set mine higher if I load heavy. I set about 10 lower if unloaded.

[CWtheMan]

I set mine higher if I load heavy. I set about 10 lower if unloaded.

The correct pressure is found on the trailer's certification label. Exceptions will be found in the owner's manual.

CW

[hankpage]

Unless you have weighed each axle position ..... play it safe and fill to max cold inflation marked on tire side-wall until you know the actual weight on each axle. Only then can you adjust pressure accordingly. (If needed) JM2¢, Hank

[chris199]

I always fill my tires to 65 (max rating) for trips. Once it got cold I did get a large drop in pressure. Use a TPM to watch pressure and temp while towing....will alarm if mins or max exceeded. So far...so good.

I thought I read here somewhere that lowering the pressure in tires reduces towing integrity and risks tire issues and safety. Obviously..over inflating is a problem.

[Bigsky3625]

I inflate to max. I check pressure before we leave home and before we head back home. I carry a 150 psi compressor all the time in the generator compartment. I also use the TST 507 tpms to keep an eye on pressure and temperature.

[chuck&gail]

Since I actually weigh my TT, in fact I weigh each wheel, I am able to use the advice of the people who designed and built the tires. They publish weight versus pressuire recommendations for tires. I add 5 psi for luck. Note tires on any one axle get the same pressure, that of the highest.

[CWtheMan]

Since I actually weigh my TT, in fact I weigh each wheel, I am able to use the advice of the people who designed and built the tires. They publish weight versus pressuire recommendations for tires. I add 5 psi for luck. Note tires on any one axle get the same pressure, that of the highest.

If you are using ST tires they are all designed to be operated at full sidewall pressures. If you are using LT tires they should be operated at the pressures required to meet the load capacity of the OE tires depicted on the trailer’s certification label, and nothing less.

It is the responsibility of the vehicle manufacturer to set it’s recommended (correct) tire pressure (s). They are found on the vehicle’s certification label. Deviations will be found in the vehicle’s owner’s manual.

If you already know those safety rules you have knowingly chosen to disregard the entire tire industries safety standards and published your own.

Sorry for the strong wording. Maybe your system works for you with meticulous management and the slim load capacity reserves your lucky 5 psi gives you.

The entire tire industry uses the vehicle manufacturers recommended tire pressure (s) to determine when a tire in use has entered into the “run flat” condition. That condition starts when a tire is found with 20% less tire pressure than the recommended amount. That’s 52 psi or less from a 65 psi recommendation.

In the reference below you will find a statement that says NEVER use less tire pressure than what is found on the tire placard/certification label.

http://www.trucktires.com/bridgestone/us_eng/press/zip/WeighForm.pdf

CW

[Bob Landry]

I have read posts on various forums by people who think they have out-engineered the tire manufaturers and like to share exotic formulas to figure tire pressure. According to my tire dealer(YMMV) the best longevity from any tire is going to be had by running at the max recommended pressures. Underinflating will break down the sidewall before anything else and that is where the majority of failures happen. Under inflating = more rubber on the road = drag =equals heat = excessive wear. Makes sense to me, but I'm not an automotive engineer. I've always gotten more that the expected life from tires simply by running them at max recommended pressure.

That said, I check tires on both truck and trailer before every trip and inflate to max pressure(cold). it works for me so far.

[JRTJH]

I agree wtih Bob and CW. Any RV "bouncing down the road" (Most do not have shock absorbers) is going to have tires that "load and unload" with every bounce. Given a moderately loaded RV at a safely loaded weight, once the dynamics of bouncing start to occur at highway speeds, every one of our RV's is going to have loaded/overloaded/underloaded tire status with every revolution of the wheel. Keeping ST tires inflated to maximum recommended inflation pressure will reduce rolling resistance, which reduces heat buildup and will help keep the tires "round" while reducing sidewall flex.

Balancing the tires, keeping them inflated to max pressure, avoiding any side stresses that can be prevented, keeping them clean and protected with a proper tire dressing and storing with covers to prevent UV degredation will enhance tire life, but the most important (I think) is proper inflation.

[SAABDOCTOR]

JRTJH well said:D

[chuck&gail]

If you are using ST tires they are all designed to be operated at full sidewall pressures. If you are using LT tires they should be operated at the pressures required to meet the load capacity of the OE tires depicted on the trailer’s certification label, and nothing less.

It is the responsibility of the vehicle manufacturer to set it’s recommended (correct) tire pressure (s). They are found on the vehicle’s certification label. Deviations will be found in the vehicle’s owner’s manual.

If you already know those safety rules you have knowingly chosen to disregard the entire tire industries safety standards and published your own.

Sorry for the strong wording. Maybe your system works for you with meticulous management and the slim load capacity reserves your lucky 5 psi gives you.

The entire tire industry uses the vehicle manufacturers recommended tire pressure (s) to determine when a tire in use has entered into the “run flat” condition. That condition starts when a tire is found with 20% less tire pressure than the recommended amount. That’s 52 psi or less from a 65 psi recommendation.

In the reference below you will find a statement that says NEVER use less tire pressure than what is found on the tire placard/certification label.

http://www.trucktires.com/bridgestone/us_eng/press/zip/WeighForm.pdf

CW

Thanks for the warning about Bridgestone ST tires. Frankly I did not even know they made them, but if I ever buy some I'll do as they say.

HOWEVER,

I have so far put over 200,000 miles on various non-Chinese ST tires with only a few repairable nail punctures occuring. I use the tables as I said above.

Note Maxxis, one of the most highly recommended 15" tires on this web site, DOES publish weight versus pressure tables for THEIR tires.

Your choice, I'm going to keep doing what has worked for me for more years than I can recall.

[CWtheMan]

[QUOTE=chuck&gail;54440]

Note Maxxis, one of the most highly recommended 15" tires on this web site, DOES publish weight versus pressure tables for THEIR tires.
[QUOTE]

Maxxis provides their load inflation table/chart for proper tire selection. According to their area rep., use by individual trailer owners should be approved by the vehicle manufacturer. That's the answer I got from Mr. Shawn Brennan, their east coast area rep.. He can be reached at 678-407-6772. He is a very knowledgeable and interesting fellow to talk with.

I don't dispute your success with the method you use. It's just not in compliance with industry standards. For most it leads to under inflation, the RV trailer tires number one enemy and destroyer.

CW

[W.E.BGood]

I always fill my tires to 65 (max rating) for trips. Once it got cold I did get a large drop in pressure. Use a TPM to watch pressure and temp while towing....will alarm if mins or max exceeded. So far...so good.

I thought I read here somewhere that lowering the pressure in tires reduces towing integrity and risks tire issues and safety. Obviously..over inflating is a problem.

Chris...what brand/model of TPMS do you use? Thanks, BGood

[zippy]

I have read posts on various forums by people who think they have out-engineered the tire manufaturers and like to share exotic formulas to figure tire pressure. According to my tire dealer(YMMV) the best longevity from any tire is going to be had by running at the max recommended pressures. Underinflating will break down the sidewall before anything else and that is where the majority of failures happen. Under inflating = more rubber on the road = drag =equals heat = excessive wear. Makes sense to me, but I'm not an automotive engineer. I've always gotten more that the expected life from tires simply by running them at max recommended pressure.

That said, I check tires on both truck and trailer before every trip and inflate to max pressure(cold). it works for me so far.

I agree with you. I look on the sidewall of the tire and use the recommended tire psi.

[captbob]

I have seen my tires drop from 65 to 52 in two months of sitting, so I check them anytime I'm off on a long treck.

[smiller]

Just FWIW my unit (a 325SRX) at full gross weight comes in at 20% or so under the max ratings of the stock 235/80-16 tires yet Keystone still recommends that they be run at full pressure (80 psi.) I assume that there's a reason.

[captbob]

Here is an interesting document from Goodyear on their Marathon tires. This document is from 2006. Does anyone know if this has changed.

[Ken / Claudia]

3 years ago I sat thru a RV tire class at Artic Fox even thru I had a truck camper. A tire rep. gave me a Fed. spec. sheet that had the requirements of RV tires and spoke about RV tires for several hours. He said Always inflate RV tires to max psi for the tire. I questioned him about passager vehicles tires psi, being placed to max. always, he said that is a apples to oranges. Due to the differences in tires and use the RV tires should not be run at lower or higher psi than stated max. psi on tire.

[B&T]

I always use max cold pressure on trailer tires and use a TPMS system to keep real-time tabs on tire pressure and temperature. I also always keep the speed at 65 or below when towing since there are no ST tires that are rated for speeds above 65.

[JRTJH]

I always use max cold pressure on trailer tires and use a TPMS system to keep real-time tabs on tire pressure and temperature. I also always keep the speed at 65 or below when towing since there are no ST tires that are rated for speeds above 65.

I don't want to sound like "conflicting data" with this statement and completely agree with you that under what Goodyear calls "normal service" the ST tire is rated at the stamped PSI and 65MPH. However, Goodyear, in a number of pieces of their factory literature states:

Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is
necessary to increase the cold inflation pressures by 10 psi above the recommended pressure for the load.
o Do not exceed the maximum pressure for the wheel.
o If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 mph.
o The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire.

Other tire manufacturers also state the same "exemption" for their ST tires. Not all manufacturers have this "exemption" listed in their literature, but some do.

So, to respond only to your last comment about "NO ST TIRES THAT ARE RATED FOR SPEEDS ABOVE 65" There are some that the manufacturers have conditions for using above that speed.

REF: http://www.goodyear.com/truck/pdf/product_brochures/RV_Brochure_P.pdf

On the reference, go to the last page in the yellow box on the right hand side.

[B&T]

I don't want to sound like "conflicting data" with this statement and completely agree with you that under what Goodyear calls "normal service" the ST tire is rated at the stamped PSI and 65MPH. However, Goodyear, in a number of pieces of their factory literature states:

Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is
necessary to increase the cold inflation pressures by 10 psi above the recommended pressure for the load.
o Do not exceed the maximum pressure for the wheel.
o If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 mph.
o The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire.

Other tire manufacturers also state the same "exemption" for their ST tires. Not all manufacturers have this "exemption" listed in their literature, but some do.

So, to respond only to your last comment about "NO ST TIRES THAT ARE RATED FOR SPEEDS ABOVE 65" There are some that the manufacturers have conditions for using above that speed.

REF: http://www.goodyear.com/truck/pdf/product_brochures/RV_Brochure_P.pdf

On the reference, go to the last page in the yellow box on the right hand side.

Yes, Ive seen that. :)

I found it strange that they used the word "wheel" instead of "rim" in that statement. One could possibly reason that a "wheel" is made up of a combination of the tire and rim and should be rated according to it's lowest rated component.

In the last line:

"The cold inflation pressure must not exceed 10 psi beyond the inflation specified for the maximum load of the tire."

Since I am running mine at "the inflation specified for the maximum load of the tire." -- i can not add 10psi. Very ambiguous statement!

So, in my mind, 65 is still the max speed that my ST tires should be trusted at.

[JRTJH]

B&T,

I agree with you, I usually run about 60 or so and keep my tires at the max rated PSI on the sidewall. I'm just not one to push the envelope by adding a few pounds of air and speeding up. I am just fine tooling along watching the scenery and not feeling like I'm forced to push the limits to get there a couple minutes sooner. I haven't found anything (other than grand kids) that would justify wanting those few extra minutes, and after being with them for a day or so, I am sure you know the outcome of "wanting to get there faster" :jump:

As for that ambiguious statement about exceeding the maximum pressure. You might be interpreting it "ambiguiously"

What it says is that the pressure must not exceed the maximum recommended load PSI rating (plus 10PSI) so, if you're using 13, 14 or 15" load C tires, the max load PSI is 50 so you couldn't exceed 60PSI. however, if you're using 15" load E tires or 16" load E tires, the max load PSI is 65PSI so you couldn't exceed 75PSI. Those maximum increases are based on whether the "wheel" or the "rim" is rated at the increased PSI.

[captbob]

Where do you find the max pressure for the wheel. I have the cast aluminum wheels on my 29res and have been thinking of going to the E rated tires because they are rated at 80psi and I wouldn't have to worry about running them at 75psi being I am fully loaded

[JRTJH]

The maximum load and the maximum pressure should be stamped on the back side of the wheel (closest to the brake drums) if you don't see it there, then it's is INSIDE, on the rim.... If you can find any numbers on the back side of the wheel, most any tire shop can tell you the max pressure. Don't forget to change out the valve stems to the higher pressure as well !!!!!