Braking News- Max Speed on ST type tires

[Tireman9]

Originally Posted by herk7769

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.

[Herk7769]

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).

[Tireman9]

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.

[OldCoot]

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.

[BarryD0706]

Thanks very much Roger!

I also agree with Lou and OC's conclusions.

[Witch Doctor]

Originally Posted by herk7769

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.

[Herk7769]

Originally Posted by gljurczyk

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.

[Tireman9]

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.

[Ford Idaho]

Originally Posted by Tireman9

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?

[Witch Doctor]

Originally Posted by Ford Idaho

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.

[Ford Idaho]

Originally Posted by gljurczyk

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.

I have no idea who made the rims that are on my Coachmen.
I was hopping for more info BEFORE I pull a wheel.
There is much information, I consider it then proceed with all due caution.

[Herk7769]

My rim information is on the inside "flat" part of the rim.
Can't see it without pulling the wheel off the camper.
However my spare is accessible and I will get a photo of the stamping.

Maybe Tireman9 can help with the other codes, but like most rims I have seen, this one only has the load info.

Herk

[Ford Idaho]

I have alloy wheels on the trailer but the spare is painted steel... bet they saves 3 bucks a unit that way....

[DDC]

Originally Posted by Ford Idaho

I have alloy wheels on the trailer but the spare is painted steel... bet they saves 3 bucks a unit that way....

Do you really think it is that much?

[Witch Doctor]

Originally Posted by herk7769

My rim information is on the inside "flat" part of the rim.
Can't see it without pulling the wheel off the camper.
However my spare is accessible and I will get a photo of the stamping.

Maybe Tireman9 can help with the other codes, but like most rims I have seen, this one only has the load info.

Herk

Herk I do not doubt what you said but that looks like steel rim and not an aluminum rim. Maybe I'm wrong but I know the HTW aluminum rims do not have stamping on them. They are the rims on the trailer wheels not the steel spare that is supplied by FR's vendors. Most wheels from FR are Aluminum on the axles. As I said blanket statements do not help. On my unit the CP is 60 PSI for the rim max, makes no difference to what the inflation chart show. I need to stay at the pressure. Your trailer might have all steel rims I do not know. But my spear is steel and my rims are HTW supplied by Lionhead with the Trail Express tires when new "C" rated aluminum rims and max pressure was 50 PSI. I think the load rating then was 1850 per wheel with 4000 lb axles. But hell I have been wrong before. The last weight I did I'm still under the 4000 per axle. Just move up to D rated because of the tire construction only. You can not compare apples to oranges.

[BarryD0706]

Maybe an analogy with towing limits will help.

Your truck comes towing nothing. If you want to tow with it, it's not sufficient to look at just GCWR, you have to look at GAWR too (for instance).

Your trailer comes with a tire inflation sticker on the outside. The manufacturer would never put rims on the RV which could not handle that inflation pressure. If you want to change tires or inflation (for other reasons), it's not sufficient to just look at load/inflation charts; you have to determine your rim limits as well.

No one has stated that consulting inflation tables is sufficient (that I have seen). The Goodyear Bulletin that is the major source of information here very specifically states that you have to consider rim limits.

No one has stated that they know for sure what is stamped on rims (or where). If you can find the information on your rim, great! If you can't, you need to determine the limit by other means.

[OldCoot]

Originally Posted by BarryD0706

Maybe an analogy with towing limits will help.

Your truck comes towing nothing. If you want to tow with it, it's not sufficient to look at just GCWR, you have to look at GAWR too (for instance).

Your trailer comes with a tire inflation sticker on the outside. The manufacturer would never put rims on the RV which could not handle that inflation pressure. If you want to change tires or inflation (for other reasons), it's not sufficient to just look at load/inflation charts; you have to determine your rim limits as well.

No one has stated that consulting inflation tables is sufficient (that I have seen). The Goodyear Bulletin that is the major source of information here very specifically states that you have to consider rim limits.

No one has stated that they know for sure what is stamped on rims (or where). If you can find the information on your rim, great! If you can't, you need to determine the limit by other means.

Tire inflation charts on the trailer are useless if you have upgraded to a higher load rated tire. The rims need to be checked for a load rating &/or max pressure rating which can be done usually by removing the tire or by the wheel mfg'rs specifications sheets. The wheels will determine the max pressure allowed if they are LOWER than the tire charts.

[BarryD0706]

Originally Posted by OldCoot

Tire inflation charts on the trailer are useless if you have upgraded to a higher load rated tire. The rims need to be checked for a load rating &/or max pressure rating which can be done usually by removing the tire or by the wheel mfg'rs specifications sheets. The wheels will determine the max pressure allowed if they are LOWER than the tire charts.

Exactly!

[Airdale]

Here is a little info on how it works for rim/wheel fitments.

First is Identification. Tire manufacturers are required by regulations to provide a list to be made available to the public of approved rim sizes for every tire they build for highway service. That particular size is the width and diameter of the rim. Other markings such as load capacity and air pressure ratings are not required - by regulation - to be on the rims/wheels.

Vehicle manufacturers are responsible for providing approved rim/tire fitments for their vehicles.

Vehicles that are altered must follow industry standards for such procedures. When a retailer is performing the alteration they become responsible for proper fitments including insuring the tires and rims provide adequate load capacities and air pressures to support the capacities of the Original Equipment (OE) tires/rims.

When individual owners alter their own equipment it will behoove them find the proper procedures to follow with their replacements.

Rims must have reference marks that identify their manufacturer. An eMail or phone call to the rim manufacturer that provides the rims proper identification will be all that is needed to acquire their load and pressures ratings.

With RV trailers it's imperative to provide load capacity reserves above the GAWR. 12% - 15% are good numbers.

Airdale

[Herk7769]

Originally Posted by gljurczyk

Herk I do not doubt what you said but that looks like steel rim and not an aluminum rim.

I have 4 steel rims and a steel spare as OEM.