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Old 10-25-2013, 11:34 AM   #21
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Originally Posted by herk7769 View Post
The max is "up to" 10 PSI over the "pressure required for the actual tire load" taken from the charts.
If the tire is already at its max load at its max sidewall pressure, no further increase in pressure is allowed and speed rating is then 65 MPH.

Where did the statement "max is "up to" 10 PSI over the "pressure required for the actual tire load" taken from the charts" come from?

Your statement "If the tire is already at its max load at its max sidewall pressure, no further increase in pressure is allowed and speed rating is then 65 MPH" is not true for GY Marathon tires per the GY Tech bulletin.

The point of my doing this thread was to try and clear up the question of the max cold inflation pressure.

1. The pressure molded on the sidewall that is associated with the max load is often incorrectly called the "max pressure". This pressure is just the cold inflation pressure associated with the max load which is molded on the sidewall.

2. The normal max speed for ST type tires is 65mph unless:
A. You have a published document from the RV MFG stating the specific tires applied by the RV MFG are rated for a different max speed. This might include alternate load and inflation numbers. This would ONLY apply to the exact Brand, size, line and Load Range of tires supplied by the RV MFG.

or
B. You have a published document such as the example Goodyear Tech Bulletin with alternate specifications.

3. In the case of Goodyear Marathon tires, Goodyear is allowing a max speed of up to 75 mph only if the original inflation is increased by 10psi. The original inflation would be the inflation on the RV Tire Placard.

4. I contacted GY engineers and was told I could get clarification from TRA Engineers. The TRA Engineer confirmed that it was allowed to increase the tire inflation to 10psi above the inflation molded on the tire sidewall. (see#1 above)

5. None of the above inflation increases allow an increase in load capacity beyond what is published in the Load Infl tables for the original inflation.

Example:
If you have a GY Marathon ST225/75R15 LR-D it is rated for 2540# @ 65psi and a max speed of 65 mph. If you increase the cold inflation to 75psi the tire would now be rated for 2540# @ 75psi and a max speed of 75 mph.
The example currently only is OK for Goodyear Marathon ST tires as I have not seen a published document from any other tire manufacturer.
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Old 10-25-2013, 03:57 PM   #22
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Well, after stewing on Roger's (Tireman9) post, I re-read the tech bulletin several times and find that his interpretation regarding exceeding the cold side wall pressure by 10 PSI (but not the load capable) is the correct one.

But the "Do not exceed the maximum pressure for the wheel" raises even more questions than it answers. The rims are not "pressure rated" (on any rim I have seen advertised). They are "load rated" in pounds; not PSI.

It states on my 15x6 inch rims that the maximum load is 2150 pounds.

Using the tech sheet, then it follows that with D (65 PSI) rated tires, the maximum load that can be supported by the wheel is 2150 pounds even though my tire (ST225/75R/15 D) can be inflated to 65 PSI (or 15 PSI above the pressure required for the actual load of 2150. (We will leave out the fact that my AXLES are only rated for 4000 pounds (or 2000 pounds per tire).

Using E rated tires inflated to 80 PSI would be even more ridiculously over hard. So basically, I am glad I went with D rated tires (though I actually considered E rated ones).
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Old 10-25-2013, 05:14 PM   #23
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Never said I agreed with the TRA "options" or GY Tech Bullitin. If asked I would have written it differently but they didn't ask me. My objective was to try and provide some clarity to a situation I felt was not as clear as it could have been.

Yes, there are other items that the owner must consider i.e. wheel, valve, axle, spring limits are obvious ones. If you want to operate outside the normal limits for speed, then you have to be very careful to do a lot of checking and research to be sure you haven't missed an important item.

Some wheels do have max pressure ratings on them but not all. many do not even have a max load rating on them. I would say it is the owner's responsibility to get, in writing, a statement from the wheel manufacturer and not just the dealer, that the wheels he has are approved for xx psi and yyyy pounds load with a radial tire. If the wheel mfg will not provide such documentation then the RV owner will need to find different wheels. Same goes for any component that would be affected by the increase in load or inflation if making a change from the system provided originally.
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Old 10-25-2013, 05:19 PM   #24
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Bottom line is hold to cold pressure and 65mph and don't worry about it. IMO those that tow on ST tires over 65 are not the sharpest tacks in the pack.
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Old 10-25-2013, 06:02 PM   #25
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Thanks very much Roger!

I also agree with Lou and OC's conclusions.
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Old 10-25-2013, 06:26 PM   #26
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Originally Posted by herk7769 View Post
Well, after stewing on Roger's (Tireman9) post, I re-read the tech bulletin several times and find that his interpretation regarding exceeding the cold side wall pressure by 10 PSI (but not the load capable) is the correct one.

But the "Do not exceed the maximum pressure for the wheel" raises even more questions than it answers. The rims are not "pressure rated" (on any rim I have seen advertised). They are "load rated" in pounds; not PSI.

It states on my 15x6 inch rims that the maximum load is 2150 pounds.

Using the tech sheet, then it follows that with D (65 PSI) rated tires, the maximum load that can be supported by the wheel is 2150 pounds even though my tire (ST225/75R/15 D) can be inflated to 65 PSI (or 15 PSI above the pressure required for the actual load of 2150. (We will leave out the fact that my AXLES are only rated for 4000 pounds (or 2000 pounds per tire).

Using E rated tires inflated to 80 PSI would be even more ridiculously over hard. So basically, I am glad I went with D rated tires (though I actually considered E rated ones).
Herk if I looked up my rims, they will show in their tech bulletin the load rating and max PSI, the site from them is Series 06, aluminum trailer wheels by HWT, Inc.. It plainly states load and psi for each rim they produce by this manufacturer.
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Old 10-25-2013, 07:06 PM   #27
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Herk if I looked up my rims, they will show in their tech bulletin the load rating and max PSI, the site from them is Series 06, aluminum trailer wheels by HWT, Inc.. It plainly states load and psi for each rim they produce by this manufacturer.
I did say most, but obviously not all.

I was on several rim web sites and those aluminum wheels are almost unique in that they do list both.
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Old 10-26-2013, 10:56 AM   #28
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My experience is that many cast aluminum wheels do have max load and pressure information molded on the back side of the wheel while only a small portion of steel wheels have load or inflation information stamped onto the wheel.
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Old 10-26-2013, 11:13 AM   #29
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My experience is that many cast aluminum wheels do have max load and pressure information molded on the back side of the wheel while only a small portion of steel wheels have load or inflation information stamped onto the wheel.

So if I pulled one of the alloy wheels this info is on a spoke or the wall?
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Old 10-26-2013, 02:06 PM   #30
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So if I pulled one of the alloy wheels this info is on a spoke or the wall?
mine do not have it stamped on them, I found our by the web site that sells them. Lionhead who supplies most of the rims and tires is listed on the web site. I pulled the wheel it is not stamped on them, I asked OC about it and he said that it is probably on the inside and he is probably right at least for my rims. I got the web site off the hub cap of the rim itself. I know that this is what they use on the 8289WS line by Rockwell. May be on others I can not say. There are just too many variables involved between manufacturers of rims. If you do not know who made your rims, then I would call FR and they can tell you. All this stuff is just pur injection. In other words if you read the spec from the manufacturer the inflation charts mean nothing at all, unless your rim can hold it. What I learned is that you first get the speck of the rim then you pick your tire for it. Unless you want to change the rims too.
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